Development and characterization of luminescent oxygen sensing coatings

DEVELOPMENT AND CHARACTERIZATION OF LUMINESCENT OXYGEN
SENSING COATINGS

By

JOANNE M. BEDLEK-ANSLOW

A DISSERTATION PRESENTED TO THE GRADI IATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DE-GREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA

2000

Copyright 2000

by

Joanne M. Bedlek-Anslow

For Jody

The little girl with curly brown hair who thought b's Cere d's id p's wecre q's.

ACKNOWLEDGMENTS

As I approach the completion of nearly 21 years of education, it becomes

challenging to properly thank the numerous people that have helped me along the way.

Foremost, my parents deserve my sincerest love and appreciation for always being there

for me with constant and unconditional love, encouragement, and praise throughout the

ups and downs of my life. As a young child, they encouraged my interests and helped me

to realize that any dream is possible. One of their greatest lessons was that life is about

decisions and choices. I am solely responsible for my happiness and must always be my

greatest ally. The significance of this advice continues to grow with each passing year.

Only recently, have I begun to realize the extent of their sacrifices and support of my

successes. Their examples as parents, companions and genuine people are constant

reminders of the person I am trying to become.

I must also thank my sister, Jeanne, for her love and faith and exquisite example

as a woman of compassion and conviction. My appreciation also extends to my small but

boisterous family for their love and support: Uncle Jim and Aunt Pat, Aunt Pam and

Uncle Ken, Alyssa and Chris, Arianna, Kevin and Roxann, Shay and Angie, Godmother

Helen, Russ and Dee, Matt and "little" Grandma. Unfortunately, my grandfather did not

live to see me finish my doctorate, yet I am positive he is rejoicing in my successes.

I am also fortunate to be the beneficiary of a large extended family of people who

if not through ties of blood but rather ties of friendship have blessed me with guidance,

love, and praise for longer than I can remember. This nucleus of people includes my dear

friends: Shannon and Joel Gruenke, Liz and Mark Tinch. Kerr% and Scot Corkey, Jackie

and Brian Brown, Sara Wadford. Dr. Mike and Andrea Robertson, Heather and John Me

Cabe. Dr. Marijean and Wayne Levering. Dr. Mary Frances and Joel Barthel, Ellen and

Brian Rasmussen. Louis Nicoulin, Regina Tonnesen. Janis and Dick Sil\erman. Diane

and Russ Mueller, Irene Mueller. Anna and Wes SchwLabedessen. Baba and Dzidzio

Iwanciew, and Klaus and Traudel Kummer. There %w as also an entire army of angels

praying for me night and day as I wrote: Sr. Kathleen Leonard, Sr. Claire Hanson. Sr.

Genevieve Therese. Sr. Dorothy Marie. Sr. Helene and all of the Sisters-of-Providcnce

and Salesian Nuns. I was also %cry fortunate for the friendships of some remarkable

people during my stay in Gainesville: Dr. Barbara Tsuie. Dr. Karen and Peter Torraca.

Dr. Keith Walters. Marilyn Peyton. and Dr. Gretchen Potts.

Credit must also be gien to m\ undergraduate tadv isor. Professor Mars K. Bo\d.

She has been an outstanding mentor and friend through the years. She is the one

responsible for my beginnings in chemical research and the one who first encouraged me

to pursue a Ph.D. in chemistry. Also a remarkable graduate student, Dr. Maria Valentino,

enhanced my years at Loyola. It was under her tutelage that I developed Im skills and

self-confidence in my "art." She was patient and kind and a model for the type of

graduate student I wished to become.

My formative research years led me to the laboratory of Dr. Kirk Schan/e. I must

thank Kirk for the many lessons he has made possible to foster my growth as a person

and as a scientist. I am truly grateful for the amazing multi-disciplinary project with

which he has matched me. and his belief in its and my successful outcome. He has given

me opportunities along with encouragement to present my research and publish my

findings. The members of the Schanze research group, past and present, have also aided

me in fulfilling my potential not only as a scientist but also as an integrated person. I

must give particular praise to Dr. Yibing Shen for taking me under his wing and

instructing me in the initial techniques for my project. He continued to be a source of

encouragement and collaboration as I finished my research. Since my project was multi-

disciplinary, thanks must also be given to our collaborators, Professor Bruce Carroll and

Dr. J. Paul Hubner, for their work on this project. I learned an amazing amount of

engineering, imaging techniques, and computer programming from Paul. He, like Maria,

was exceptionally patient and helpful. Of course my other committee members deserve a

thank you for their advice and help through these last four-and-a-half years: Dr. William

Dolbier, Dr. Lisa Mc Elwee-White, and Dr. James Boncella.

On a more personal note, a special acknowledgment of thanks and gratitude must

be given to my husband, Paul. He deserves the Golden Test Tube Award for enduring

my Ph.D. quest and the trials and tribulations graduate school inevitably imposed on our

life together. I cannot even begin to express my appreciation for his selflessness, love,

compassion, encouragement and constant reminders to take care of myself: eating,

sleeping, exercising, laughing. He will always be my true love and best friend.

Last but certainly not least, a most grateful Thank You is given up to God. When

I lost faith in Her, She never lost faith in me. It is only through her compassionate love

that I found the strength and perseverance within myself to continue on with my studies.

Her love and jubilation in my life are clearly evident in the number of truly gifted and

outstanding people I have been fortunate to know and love. I am blessed beyond

measure!

TABLE OF CONTENTS

A C K N O W LED G M ENT S ...... ..... ..................................................................................... iv

LIST OF TABLES ....................................................................................................... x

LIST O F FIG U R ES.... ............ .... .............................................. ....... ..................... ....... xv

A B ST R A C T .............. ............. ............... ................................................................... xxiv

CHAPTERS

I IN T R O D U C T IO N ........... ......... ............. .............................................................. 1

B background ...................................................................................... ..................................
Lum inescence Q uenching .................. ....................................................... ............... 2
Bimolecular Stern-Volmer Quenching .............. ......................2
Modeling Non-linear Stem-Volmer Response. ..................................... 3
Luminophores and Polymers.................................. ..........
R u(II) ct-Dni m ine C om plexes ..................................................................................... 7
Pt(llII)/Pd(II) Porphyrnn M acrocycle ......................................................................... 9
S ilic o n e ................................... ........................... .... .... .... ............ .. ............ ........ I I
Plasticizer% ...................... ... .... ..... .... .. .. .............. 12
M modified Polym ers ......... ......... ............ .............. .............................................. 12
W ind-T unnel A application ............. ....... ........................ ........................................... 15
T em perature Effects .................................................................................................. 18
Isotherm al C alibration ... .... .... .. .. .... ... ... ... .. .. ........................... 19
In -,itu C alib ratio n .................. .............................. ............................................... 19
K -fit C alib ration ....................................................................................................... 20
Temperature-corrected Pressure Calibration ........... .. ........ ................. ... 1
Physical Manifestations of the Temperature Effect .............. ...............................21
A advances in PSP D design .............. ............................... .......................................... 23
M monitoring M ethods...................................... ................. ..... ............... ..... ... ... .. 24
L um inescence Intensity .......... .................................... ........................................... 24
P used L ifetim e ............................ ......................... ................................................. 25
Phase-shift .................................................................................................................... 25
Scope of This W ork .................... .................................... .... ... ..................... 26

vii

2 DUAL-LUMINOPHORE OXYGEN SENSING COATINGS .................................... 27

Introduction ................................................................................................................... 27
Results ...................................................................................................................... 32
Dual-luminophore Coatings ...................................................................................... 32
Temperature Dependence and Thermal-stability ........................................... ........... 36
Temporal-stability .................... ............................. ................................................ 46
Photostability....................................................................................................... 53
Scanning and Transmission Electron M icroscopy........................................ ............ 59
Fluorescence M icroscopy ........................................................................................ 70
Image Testing...... ....................... ....................................................................... .... 85
Discussion ............................................................................................................... 94
PtTFPP ...................................................................................................................... 94
DOCIpgsp and DOCI-Ssisp............................................................................... 95
PtDOCIppsp/VPDMS and PtDOCI-Spsp/VPDMS Coatings................................... 97
Experimental ........................................................................................................... 98
Preparation of DOCI Highly Cross-linked Polymer Microspheres (DOCIpgsp)..... 98
Preparation of DOCI Sulfonated Polymer Microspheres (DOCI-Ssg.sp) .................99
Oligomers ................................................................................................................ 102
Luminophores.................................................................................................... 103
Preparation of Coatings... ............................ ....................... .... ............... .......... 103
Instrumentation..................................... ............................................................... 104

3 MICROSCOPIC ANALYSIS OF LUMINESCENT OXYGEN SENSOR THIN
FILM S ............................................................................................................................. 109

Introduction ................................................................................................................. 109
Results ..................... .................................................................................................. 112
Fluorescence Microscopy of Increased Concentrations of PtTFPP in SPDMS...... 112
Fluorescence Microscopy of Increased Mole Ratios of Cross-linker in
PtTFPP/SPDM S ....................................................................................................... 123
Fluorescence Microscopy of Ru(II) a-diimine Complexes in SPDMS................. 132
Fluorescence Microscopy of [Ru(dpp)3]C12 in SPDMS and PDMS with Fumed SiO2
...................................................................................... ..................................... 150
Discussion ................................................................................................................... 163
Analysis of PtTFPP Films ....................................................................................... 163
Analysis of Ru (II) a-diimine Films ................................................................... 164
Experimental ......................................................................................................... 168
Oligomers ................................................................................................................ 168
Luminophores............................................................................................... 168
Preparation of Coatings........................................................................................... 174
Instrumentation........................... ....................................................................... 175
Fluorescence M icroscope Image Analysis.............................................................. 175

4 CONCLUSIONS.............................................................. ...................................... 178

viii

PV-WAVE MACRO AND SUBROUTINES............................................................ ..182

LIST OF REFERENCES ............................................................................................... 192

BIOGRAPHICAL SKETCH ....................................................................................... 204

ix

LIST OF TABLES

Table Page

1-1: Photochemical Characteristics of the Ru(II) a-diimine Complexes in Water.............. 8

1-2: Platinum and Palladium Porphyrin Based Optical Oxygen Sensors.......................... 11

2-1: Percent change in PtTFPP emission area at seven pressures over a 40 K range for
PtDOCIpgsp/VPDMS coating on primed glass............................................. 39

2-2: Percent change in PtTFPP emission area at seven pressures over a 40 K range for
PtDOCI-Sspsp/VPDMS coating on primed glass............................................... 39

2-3: SV analysis of PtTFPP emission quenching in PtDOCIpjsp/VPDMS coating on
primed glass for a cyclic temperature run................................................... 40

2-4: SV analysis of PtTFPP emission quenching in PtDOCI-Sslsp/VPDMS coating on
primed glass for a cyclic temperature run................................................... 40

2-5: Percent change in DOCIpgsp emission area at seven pressures over a cyclic
temperature run of 40 K for PtDOCIpjtsp/VPDMS coating on primed glass.....44

2-6: Percent change in DOCI-Ssglsp emission area at seven pressures over a cyclic
temperature run of 40 K for PtDOCI-Ssgsp/VPDMS coating on primed glass. 45

2-7: SV Analysis of PtTFPP emission quenching in PtDOCIppsp/VPDMS coating on
bare glass. ....................................................................................................... 47

2-8: SV Analysis of PtTFPP emission quenching in PtDOCI-Sspsp/VPDMS coating on
bare glass. ............................................................... ..................................... 47

2-9: SV Analysis of PtTFPP emission quenching in VPDMS polymer on bare glass. ....... 48

2-10: SV Analysis of PtTFPP emission quenching in PtDOCIpgsp/VPDMS coating on
prim ed glass................................................................................................... 48

2-11: SV Analysis of PtTFPP emission quenching in PtDOCI-Sstsp/VPDMS coating on
prim ed glass................................................................................................... 48

2-12. SV Analysis of PtTFPP emission quenching in VPDMS polymer on primed glass.. 49

2-13: Analysis of the area under the emission curve for DOClpp.sp in
PtDOCIpp.sp/VPDMS coating on bare and primed glass................................. 50

2-14: Analysis of the area under the emission cure for DOCI-Sspsp in PtDOCI-
Sslpsp/VPDMS coating on bare and primed glass.................. ....................51

2-15: Analysis of the area under the emission curve for DOCIppsp in VPDMS poly mer
on bare and prim ed glass .................................................................................. 51

2-16: Analysis of the area under the emission curve for DOCI-Sspsp in VPDMS
polymer on bare and primed glass..... ............................. ... ... .. ..... 52

2-17: Percent photodegradation of the relative emission intensity for DOCIppsp in
PtDOCIppsp/VPDMS coaling on hare and primed glass ................................ 5

2-18: Percent photodcgradation of the relative emission intensity for DOCI-Ssp.sp in
PtDOCI-Sspsp/VPDMS coaling on primed glass .............................................. 59

2-19: Number of microsphere objects for 1f'e regiions of the ID)CIppspVPIDMS ilm.....72

2-20: Number of microsphere objects for five regions of the D)(CI-Spsp/VPIDMS film.. 72

2-21: Average and standard deviation of the microsphere objects' lengths for each region
of the DOCIp sp/VPDM S film ........................................................................ 73

2-22: Average and standard deviation of the microsphere objects' lengths for each region
of the DOCI-Ssl sp/VPDMN S film. ............................ ...................... ............ 73

2-23: Microscopic SV analysis of fi'e regions for Ptl)()Clpisp/VAPDMS thin fiilm using
the 10X and 40X objectives. ............................... .......................................... 81

2-24: Microscopic SV analysis of five regions for PtI))OC-SspIVspPDMS thin film
using the 10X and 40X objectives. ... ....... .. ....... 81

2-25: Macroscopic SV response data for PtDOCIppsp/VPDMS and PtDOCI-
Sspsp/V PD M S film on glass. .......................................................................... 83

2-26: Corresponding pressure values and statistical distributions for the uncorrected
ratioed intensity images of the PiDOCIlppp/VP)DMS coating on an alumLinum
plate at seven pressures hetw een 2 14.8 p i. ................................ ............ 88

2-27: Corresponding pressure values and statistical distributions for the corrected ratioed
intensity images of PtDOCIppsp/VPDMS coating onn an aluminum plate at
seven pressures between 2 14.8 psi ......................................... .......... ............ .. 89

2-28: Corresponding pressure values and statistical distributions for the corrected ratioed
intensity images of PtDOCI-Ss.sp/VPDMS coating on an aluminum plate at
seven pressures between 2 14.8 psi.......................................... ............ .... 91

3-1: Macroscopic SV response data for increased concentrations (mM) of PtTFPP
dispersed in SPDM S binder on glass. ............................................................... 114

3-2: PtTFPP emission intensity area (X = 630 670 nm) values for increased
concentrations (mM) of PtTFPP dispersed in SPDMS binder on glass .............. 114

3-3: Maximum fluorescence intensity values for 10X microscopic regions of increased
concentrations (mM) of PtTFPP dispersed in SPDMS binder on glass at 0.4
p si........................................................................................................................ 1 16

3-4: Percent standard deviation (a, %) in intensities at seven pressures for microscopic
regions of increased concentrations (mM) of PtTFPP dispersed in SPDMS
binder on glass using the 10X objective.............................................................. 117

3-5: Maximum Ksv values for 10X microscopic regions of increased concentrations
(mM) of PtTFPP dispersed in SPDMS binder on glass.................................. 119

3-6a: Microscopic SV analysis of five 10X regions for increased concentrations (mM) of
PtTFPP dispersed in SPDMS binder on glass .................................................. 121

3-6b: Microscopic SV analysis of five 10X regions for increased concentrations (mM) of
PtTFPP dispersed in SPDMS binder on glass................................................... 121

3-7a: Microscopic SV analysis of five 40X regions for increased concentrations (mM) of
PtTFPP dispersed in SPDMS binder on glass................................................... 122

3-7b: Microscopic SV analysis of five 40X regions for increased concentrations (mM) of
PtTFPP dispersed in SPDMS binder on glass................................................... 122

3-8: Macroscopic SV response data for PtTFPP/SPDMS on glass at five different mole
ratios of cross-linker......................................................................................... 124

3-9: PtTFPP emission intensity area (X = 630 670 nm) values for increased mole ratios
of cross-linker in PtTFPP/SPDMS on glass ........................................................ 124

3-10: Maximum fluorescence intensity values for 10X microscopic regions of
PtTFPP/SPDMS on glass at five different mole ratios of cross-linker at 0.4
psi............................................................................................................ ..... 126

3-11: Percent standard deviation (a, %) in intensities at seven pressures for microscopic
regions for PtTFPP/SPDMS on glass at five different mole ratios of cross-
linker........................................................................................................... 127

3-12: Maximum Ksv values for IOX microscopic regions for PtTFPP/SPDMS on glass at
five different mole ratios of cross-linker................................ .......................... 129

3-13a: Microscopic SV analysis of five 10X regions for PtTFPP/SPDMS on glass at five
different m ole ratios of cross-linker. ........ ....................................................... 130

3-13b: Microscopic SV analysis of five 10X regions for PtTFPP/SPDMS on glass at five
different mole ratios of cross-linker ....... ......................................................... 131

3-14a: Microscopic SV analysis of five 40X regions for PtTFPP/SPDMS on glass at fie
different m ole ratios of cross-linker......... .................................................... 131

3-14b: Microscopic SV analysis of five 40X regions for PtTFPP/SPDMS on glass at five
different mole ratios of cross-linker .................................................................. 132

3-15: Macroscopic SV response data for Ru( Il ao-diimine complexes dispersed in
SPD M S hinder on glass. ................................................................................ 134

3-16: Ru II) a-diimine complex emission intensity area (X = 6X) 640 nm) \ values at 0.1
psi for Rut l) a-diimine complexes dispersed in SPDMS hinder on glass ........ 135

3-17: Ru( II) a-diimine complex molar concentration (mM) for Ru 11l) c-diiminc
complexes dispersed in SPDMS hinder on glass.......................................... 135

3-18: Maximum fluorescence intensity values for 10X microscopic regions of Ru( I) a-
diimine complexes dispersed in SPDMS hinder on glass at 0.4 psi .................. 139

3-19: Percent standard deviation ( '; ) in intensities aX seen pressures for microscopic
regions of Rut iI) u-diimine complexes dispersed in SPDMS hinder on glass .. 140

3-20. Maximum Ksv values for 10X microscopic regions of Ru(IIl a-diimine complexes
dispersed in SPDM S hinder on glass. ............................................................. 143

3-21a: Microscopic SV analysis of five IOX regions for Ru(Ill a-diimine complexes
dispersed in SPDM S hinder on glass ........................................................... 144

3-21b: Microscopic SV analysis of five IOX regions for Rut ll) a-diimine complexes
dispersed in SPDM S hinder on glass ............................................................ 144

3-21c: Microscopic SV analysis of five 10 X regions for Ru( II) a-diimine complexes
dispersed in SPDM S hinder on glass. ................................................................. 145

K R"
3-22a: Discrete "' (x,y) values for three regions outlined in 10X microscopic Ksv(x,y)
image maps of Ru(II) a-diimine complexes dispersed in SPDMS hinder on
g lass ..................................................................................................................... 14 6

Ktavg
3-22b: Discrete sv (x,y) values for three regions outlined in 10X microscopic Ksv(x,y)
image maps of Ru(II) a-diimine complexes dispersed in SPDMS binder on
g lass ..................................................................................................................... 14 7

3-23a: Microscopic SV analysis of five 40X regions for Ru(II) a-diimine complexes
dispersed in SPDM S binder on glass. ............................................................... 149

3-23b: Microscopic SV analysis of five 40X regions for Ru(II) a-diimine complexes
dispersed in SPDM S binder on glass. ............................................................... 149

3-23c: Microscopic SV analysis of five 40X regions for Ru(II) a-diimine complexes
dispersed in SPDM S binder on glass. ............................................................... 150

3-24: Macroscopic SV response data for [Ru(dpp)3]Cl2 dispersed in SPDMS or PDMS
binder on glass with increased weight percent of fumed silica gel ................. 152

3-25: Maximum fluorescence intensity values for 10X microscopic regions of
[Ru(dpp)3]Cl2 dispersed in SPDMS or PDMS binder on glass with increased
weight percent of fumed silica gel..................................................................... 155

3-26: Percent standard deviation (o, %) in intensities at seven pressures for microscopic
regions of [Ru(dpp)3]C12 dispersed in SPDMS or PDMS binder on glass with
increased weight percent of fumed silica gel................................................... 156

3-27: Maximum Ksv values for 10X microscopic regions of [Ru(dpp)3]C12 dispersed in
SPDMS or PDMS binder on glass with increased weight percent of fumed
silica gel......................................................................................................... 158

3-28a: Microscopic SV analysis of five 10X regions for [Ru(dpp)3]Cl2 dispersed in
SPDMS binder on glass with increased weight percent of fumed silica gel..... 159

3-28b: Microscopic SV analysis of five 10X regions for [Ru(dpp)3]C12 dispersed in
PDMS binder on glass with increased weight percent of fumed silica gel ...... 160

3-29: Discrete K (x,y) values for three regions outlined in 10X microscopic Ksv(x,y)
image maps of [Ru(dpp)3]Cl2 dispersed in PDMS or SPDMS binder on glass
with increased weight percent of fumed silica gel........................................... 161

3-30a: Microscopic SV analysis of five 40X regions for [Ru(dpp)3]Cl2 dispersed in
SPDMS binder on glass with increased weight percent of fumed silica gel..... 162

3-30b: Microscopic SV analysis of five 40X regions of [Ru(dpp)3]Cl2 dispersed in
PDMS binder on glass with increased weight percent of fumed silica gel. ...... 162

LIST OF FIGL'RES

Figure Page

1-1: Stern-Volmer plots of 1JI versus pO2 for the follow ing optical oxygen sensors:
[Ru(phen)h]* in silicone rubber, GE RTV 118 (A), and [Ruthpy)3]2j in
silicone rubber. G E RTV 118 ( )....... ......... ..................................................... 4

1-2 Structures of the major Ru(T ) a-diimine luniinophores uLsed in optical oxXgen
sensors. ([Rut hp )~1', [Ru( phen)jhl*, and [ Ru dpp)]J2*) .................................. 8

1-3: Structures of the major platinum and palladium porphi rings used in optical o\\ gen
sensors. ( M = PtUl ) or Pd II)) .................................................................. .......... 9

1-4: Repeat unit of (fuor/c soprop)y/butyll acrylic poll mer................................................ 13

1-5: Repeat unit of pol) (styrene-co-pentat'luorostyrene) copolymer ................................... 14

1-6. Repeat units of pol (aminotthionylphospha/ene)-h-poly(tetrah droturan) block
copolym er. ........................................ .............................. .. ....... ................ 15

1-7: Pressure Sensitive Paint measurement system for testing of air pressure profiles on
an airplane m odel in a \ ind-tunnel...... .......................................................... 16

1-8: Gray-scale pressure distribution map for a nitrogen jet protruding from a PSP
coating ........................................................................................................ ..... 17

2-1: Scheme for preparation of DOCI highly cross-linked polymer microsphcres
(DOCIp.sp). A) 5 vol DVB relative to total volume. AIBN 2 wl. r;
relative to monomer, A 70 C for 24 h.. EtOH wash. dry in vacuoi at 50 C for
12 h. B) 1 mL MeOFH, ,onicate I h., soak in dark for 7 d., IMOH and CH2Cl:
wash. dry in vacuo at 30" C for 12 h........................................................ ... 2

2-2: Scheme for preparation of DOCI sulfonated polymer microspheres (DOCI-SsJpp).
A) 45 vol % DVB relative to total volume, DI H0O:porogen = 25:1 v/v,
porogen:monomcr = 1:1.4 v/v, porogen = 1:1 l-dodecanool:toluene, sodium
laurylsulfate 0.3 mol 'r relative to monomer, A 260 700 C 7 h. at 250 rpm.
DI H20 and acetone wash. THF Soxhlet extraction, dry in wvacu 480 C 12 h.
B) 40 mL CH.Cl2, 00 C, 0.5 mL CISOIH in 40 mL CHJCI dropwisc, warm to

250 C, stir 24 h. 250 C, CH2C12 wash, air dry. C) 150 mL DI H20, 50 mL
NaOH (150 mM), stir 100 min. 250 C, 3x100 mL DI H20 wash, 100 mL
acetone wash, dry in vacuo 53 C 40 h. D) 4 mL MeOH, 2 mL DI H20,
sonicate for 20 min., MeOH and acetone wash............................. ............ .. 30

2-3: Scheme for preparation of dual-luminophore oxygen sensing coatings.
PtDOCIpgpsp/VPDMS and PtDOCI-Ssgsp/VPDMS ........................................ 31

2-4: Emission intensity spectra for PtTFPP and DOCIpgsp dispersed in VPDMS
polymer on primed glass. .................................................. .......................... 33

2-5: Emission intensity spectra for PtTFPP and DOCI-Ssjsp dispersed in VPDMS
polym er on primed glass. .................................................. .......................... 35

2-6: SV plot PtDOCIpgsp/VPDMS coating on primed glass for temperatures between
273 313 K. AREF: area between 630 670 nm at 14.7 psi and 313 K. ........... 38

2-7: SV plot PtDOCI-Ssgsp/VPDMS coating on primed glass for temperatures between
273 313 K. AREF: area between 630 670 nm at 14.7 psi and 313 K............ 38

2-8: Emission intensity spectra for DOCIppsp in PtDOCIpgsp/VPDMS coating on
primed glass at 0.1 psi for five temperatures between 273 313 K..................41

2-9: Emission intensity spectra for DOCI-Sspsp in PtDOCI-Sspsp/VPDMS coating on
primed glass at 0.1 psi for five temperatures between 273 313 K.................. 42

2-10: Temperature dependence of emission for DOCIppsp in PtDOCIppsp/VPDMS
coating on primed glass for a series of pressures between 0.1 14.7 psi. AREF:
area between 530 570 nm at 273 K and 0.1 psi ............................................. 43

2-11: Temperature dependence of emission for DOCI-Ssgsp in PtDOCI-Ssgsp/VPDMS
coating on primed glass for a series of pressures between 0.1 14.7 psi. AREF:
area between 530 570 nm at 273 K and 0.1 psi ............................................. 43

2-12: Photostability of PtTFPP emission in PtDOCIppsp/VPDMS coating on bare and
primed glass at 5 and 14.7 psi and RT. AREF: area between 630 670 nm at
240 m in.......................................................................................................... 54

2-13: Photostability of PtTFPP emission in PtDOCI-Ssgsp/VPDMS coating on bare and
primed glass at 5 and 14.7 psi and RT. AREF: area between 630 670 nm at
240 m in.......................................................................................................... 54

2-14: Photostability of PtTFPP emission in VPDMS polymer coating on bare and primed
glass at 5 and 14.7 psi and RT. AREF: area between 630 670 nm at 240 min. 55

2-15: Photostability of DOClppsp relative emission intensity in PtDOClppsp/VPDMS
coating on bare and primed glass at 5 and 14.7 psi and RT. AREF: area
between 530- 570 nm at 240 m in ................................................................ .... 56

2-16: Photostability of DOCI-Sstasp relative emission intensity in PtDOCI-
Sspsp/VPDMS coating on bare and primed glass at 5 and 14.7 psi and RT.
AREF: area betu een 530- 570 nm at 240 min ................................ ................. 57

2-17: Photostability of DOCIppsp relative emission intensity in VPDMS polymer
coating on bare and primed glass at 5 and 14.7 psi and RT. AHF: area
between 530 570 nm at 240 min. ............ .... ....... ........................................ 57

2-18: Photostability of DOCI-Ssp.sp relative emission intensity in VPDMS polymer
coating on bare and primed glass at 5 and 14.7 psi and RT. ArEF: area
between 530 570 nm at 240 m in. .................... .......................................... 58

2-19: Scanning electron micrograph of precipitation Imicrospheres (ppsp)(5 vol ; of
DVB55; acetonitrile). The scale bar consists of 11 w white vertical lines and is
5 pm long from the first line to the last line............................... ................... 60

2-20: Scanning electron micrograph of fractured precipitation microspheres (ppsp)(5 \ol
r' of DVB55; acetonitrile). The scale bar consists of I1 white vertical lines
and is 1.5 pm long from the first line to the last line. .........................................61

2-21: Scanning electron micrograph of precipitation microspheres (5 vol c; of DVB55:
acetonitrile) with 7.27 wt. "; adsorbed DOCI (DOCIppsp). The scale bar
consists of 11 white vertical lines and is 2.31 pm long from the first line to the
last line. .......... ........... ......... .................................................................. ........... 62

2-22: Scanning electron micrograph of fractured precipitation microspheres (5 ,ol of
DVB55; acetonitrile) with 7.27 wt. q DOCI (DOCIppsp). The scale bar
consists of 11 white vertical lines and is 750 nm long from the first line to the
last line. ...................................................................................................... .... 62

2-23: Scanning electron micrograph of negatively charged. sulfonated, suspension
microspheres (Sspp')(45 vol r, of DVB55: I-dodecanol:toluene = 1:1). The
scale bar consists of 11 white vertical lines and is 10 pm long from the first
line to the last line ................. ................. ........................................ ........... 63

2-24: Scanning electron micrograph of fractured negatively charged, siulfonated.
suspension microspheres (Sspp') (45 1vol 'r of DVB55; 1-dodecanol:toluene =
1:1). The scale bar consists of 11 white vertical lines and is 750 nm long from
the firsl line to the last line. .................................................................... ......... .. 64

2-25: Scanning electron micrograph of fractured negatively charged, sulfonated,
suspension microspheres (45 vol % of DVB55; I-dodecanol:tolucne = 1:1)

xvii

with 3.83 wt. % adsorbed DOCI (DOCI-Sslsp). The scale bar consists of 11
white vertical lines and is 2.73 ptm long from the first line to the last line......... 65

2-26: Scanning electron micrograph of the surface of a thin film (~ 10 plm) of SPDMS
containing DOCIppsp (7.27 wt. % DOCI)(5 vol % of DVB55; acetonitrile).
The scale bar consists of 11 white vertical lines and is 5.02 p.m long from the
first line to the last line.................................................................................. .... 66

2-27: Scanning electron micrograph of the interior morphology of a thin film (- 10 plm)
of VPDMS containing DOCIppsp (7.27 wt. % DOCI)(5 vol % of DVB55;
acetonitrile). The scale bar consists of 11 white vertical lines and is 33.3 p.m
long from the first line to the last line. ................................................. .......... 67

2-28: Scanning electron micrograph of the interior morphology of a thin film (~ 10 p.m)
of VPDMS containing DOCIppsp (7.27 wt. % DOCI)(5 vol % of DVB55;
acetonitrile) (27X magnification of Figure 2-27). The scale bar consists of 11
white vertical lines and is 1.20 p.m long from the first line to the last line......... 67

2-29: Transmission electron micrographs of a < 100 nm slice of [Ru(dpp)3]Cl2 dispersed
in SPDMS polymer. (A) X4500 magnification of polymer, white scale bar is
3.0 p.m long and (B) X70000 magnification of polymer, white scale bar is 0.4
m long. ......................................................................................................... 69

2-30: Fluorescence microscope image of A) DOCIpp.sp/VPDMS film and B) DOCI-
Sslsp/VPDMS film obtained with a CCD camera through a 40X and 60X
objective, respectively. White scale bar is 26.5 pm and 17.8 pgm long,
respectively.................................................................................................... 7 1

2-31: Histogram of the microsphere objects' major axis lengths for A)
DOCIppsp/VPDMS film and B) DOCI-Ssgpsp/VPDMS film. Vertical bars
equal a 0.5 lpm length increment................................................. ................ 73

2-32: Fluorescence images of PtDOCIpplsp/VPDMS film obtained with a CCD camera
through a 40X objective. White scale bars are 37.9 pm long. A) PtTFPP
emission (ca. 630 nm), B) DOCIpplsp emission (ca. 525 nm), C) PtTFPP and
DOCIpplsp emissions (> 475 nm). ............................................... ........ .... 76

2-33: Line scan analysis of the emission intensity of a fluorescence microscope image of
PtDOCIpp.sp/VPDMS film obtained with a CCD camera through a 40X
objective with a 525 nm 50 nm, bandpass filter (DOCI emission response).
A) Fluorescence microscope image of DOCIppLsp emission and B) Emission
line scans for three 30 p.m lines through microsphere clusters in image A...... 77

2-34: Line scan analysis of the emission intensity of a fluorescence microscope image of
PtDOCIppsp/VPDMS film obtained with a CCD camera through a 40X
objective with a 630 nm 60 nm, bandpass filter (PtTFPP emission response).

xviii

A) Fluorescence microscope image of PtTFPP emission and B) Emission line
scans for three 30 pm lines through microsphere clusters in image A............... 78

2-35: False-colored quantitative microscopic fluorescence intensity (0.5psi. O1X) and
Kss(x.y) image maps for PtDOCIppsp/VPDMS thin film. White scale bars
are 61.5 pm long. A) False-colored quantitative microscopic fluorescence
intensity image. Ima, = 11081 a.u.. yellow color and B) Quantitative
microscopic Ksv(x,y) image map for the identical region. K = 0.87() psi'
yellow color ....................................................................................................... 80

2-36: False-colored quantitative microscopic fluorescence intensity (0.5psi, 10X) and
Ks,(x,y) image maps for PtDOCI-Ssp.spVPDMS thin film. White scale bars
are 61.5 pm long. A) False-colored quantitlati\e microscopic fluorescence
intensity image. I, = 16562 a.u.. yellow color and B) Quantitati\e
microscopic Ks (x.y) image map for the identical region. K = .88() psi 1,
yellow color............... ...... ............ .... ................................................... ...... 80

2-37: Macroscopic SV plot of PtDOClpp.sp/VPDMS thin film on glass. AKe-: area
between 630 670 nm at 14.7 psi and 298 K ..................................................... 82

2-38: Macroscopic SV plot of PtDOCI-Sspsp/VPDMS thin film on glass. ARE-: area
between 630 670 nm at 14.7 psi and 298 K ................................................... 83

2-39: Fluorescence microscopy images of 250 pm thick [Ru(dpp)hCI:/SPDMS strips
embedded in formvar resin obtained with a CCD camera through a 60X
objective. White scale bars are 24.5 pm long. ...................................... 85

2-40: Stern-Volmer plot and ratioed emission plots \Lrsus pressure and temperature for
PtDOCIppsp/VPDMS coating analyzed and imaged in a static calibration cell.
A) SV plot. emission integrated over an approximate area of 630 670 nm,
excitation at 460 nm. B) Ratioed emission plot versus pressure, emission
integrated over an approximate area of 530 570 nm. excitation at 460) nm.
C) Ratioed emission plot versus temperature, emission integrated over an
approximate area of 630 670 nm. excitation at 460 nm. and D) Ratioed
emission plot versus temperature, emission integrated over an approximate
area of 530 570 nm. excitation at 460 nm .................................................... 86

2-41: Luminescence ratioed intensity images at seven pressures from 2 14.8 psi for
PtDOCIppsp/VPDMS coating on an aluminum plate assuming a constant
temperature distribution over the plate. Emission collected at 650 nm peak
and excitation at 460 nm. Intensity scale bars appear to the right of each
im age for 0 18.0 psi ........................................................................................ 87

2-42: Corrected luminescence ratioed intensity images at seven pressures from 2 14.8
psi for PtDOCIppsp/VPDMS coating on an aluminum plate. Emission

collected at 650 nm peak and excitation at 460 nm. Intensity scale bars appear
to the right of each image for 0 18.0 psi..................................... ............ .. 89

2-43: Stern-Volmer plot and ratioed emission plots versus pressure and temperature for
PtDOCI-Ssglsp/VPDMS coating analyzed and imaged in a static calibration
cell. A) SV plot, emission integrated over an approximate area of 630 670
nm, excitation at 460 nm, B) Ratioed emission plot versus pressure, emission
integrated over an approximate area of 530 570 nm, excitation at 460 nm,
C) Ratioed emission plot versus temperature, emission integrated over an
approximate area of 630 670 nm, excitation at 460 nm, and D) Ratioed
emission plot versus temperature, emission integrated over an approximate
area of 530 570 nm, excitation at 460 nm.................................. ............. 90

2-44: Corrected luminescence ratioed intensity images at seven pressures from 2 14.8
psi for PtDOCI-Sgsp/VPDMS coating on an aluminum plate. Emission
collected at 650 nm peak and excitation at 460 nm. Intensity scale bars appear
to the right of each image for 0 18.0 psi..................................... ............ .. 91

2-45: Calibration cell intensity images of the PtDOCIpgsp/VPDMS and PtDOCI-
Ssgsp/VPDMS coatings on an aluminum plate imaged at 650 nm and 550 nm.
Excitation at 460 nm. A) PtDOCIptsp/VPDMS at 650 nm, B)
PtDOCIpgsp/VPDMS at 550 nm, C) PtDOCI-Ssglsp/VPDMS at 650 nm, D)
PtDOCI-Ssgsp/VPDMS at 550 nm......................................................................93

2-46: Inverted Fluorescence Microscope set-up for imaging of luminescent oxygen
sensing thin film s. .......................................................................................... 105

3-1: Scheme for preparation of PtTFPP/SPDMS luminescent thin films........................ 112

3-2: Macroscopic SV plots for increased concentrations (mM) of PtTFPP dispersed in
SPDMS binder on glass. AREF: area between 630 670 nm at 14.7 psi.......... 113

3-3: Qualitative microscopic fluorescence images (10X, 0.5 psi) for increased
concentrations (mM) of PtTFPP dispersed in SPDMS binder on glass. White
scale bars are 153 glm long. A) 2 mM, B) 3 mM, C) 5 mM, D) 10 mM, E) 17
mM PtTFPP in 500 mg SPDMS polymer binder.............................................. 115

3-4: Quantitative microscopic fluorescence intensity images (10X, 0.4 psi) for increased
concentrations (mM) of PtTFPP dispersed in SPDMS binder on glass. White
scale bars are 92 im long. Intensity color scale bars are shown to the right of
all images. A) 2 mM, B) 3 mM, C) 5 mM, D) 10 mM, E) 17 mM PtTFPP in
500 mg SPDM S polymer binder......................................................................... 116

3-5: Intensity distribution curves for intensities obtained with a 10X objective at seven
pressures for A) 2 mM PtTFPP dispersed in SPDMS binder on glass and B)
17 mM PtTFPP dispersed in SPDMS binder on glass....................................... 118

3-6: Quantitative microscopic Ksv(x.y) image map, for increased concentrations (mM)
of PtTFPP dispersed in SPDMS binder on glass. White scale bars are 92 pm
long. Ksv color scale bars are shown to the right of all images. A) 2 mM. B)
3 mM. C) 5 mM. D) 10 mM. E) 17 mM PtTFPP in 500 mg SPDMS polymer
binder........................................................................................................................ 120

3-7: Macroscopic SV plots for PtTFPP/SPDMS on glass at five different mole ratios of
cross-linker. AREF: area between 630 670 nm at 14.7 psi............................. 123

3-8: Qualitative microscopic fluorescence images (10X, 0.5 psi) for PtTFPP/SPDMS at
five different mole ratios of cross-linker on glass. White scale bars are 153
pm long. A) 1:4, B) 1:5, C) 1:7, D) 1:9, E) 1:19 mole ratio of oligomer:cross-
linker ....................................................................................................... .... 125

3-9: Quantitative microscopic fluorescence intensity images (10X, 0.4 psi) for
PITFPP/SPDMS on glass at five different mole ratios of cross-linker. White
scale bars are 92 pm long. Intensity color scale bars are shown to the right of
all images. A) 1:4, B) 1:5, C) 1:7, D) 1:9, E) 1:19 mole ratio oligomer:cross-
lin ker.................................................................................................................... 126

3-10: Intensity distribution curves for intensities obtained with a 10X objective at se\en
pressures for A) 1:4 mole ratio of oligomer:cross-linker in PtTFPP/SPDMS
on glass and B) 1:19 mole ratio of oligomer:cross-linker in PtTFPP/SPDMS
on glass .................................................................................................... ... ......... 128

3-11: Quantitative microscopic Kso(x,y) image maps for PtTFPP/SPDMS on glass at
five different mole ratio, of cross-linker. White scale hars are 92 pm long.
Ksv color scale bars are .show n to the right of all images A) 1:4, B) 1:5, C)
1:7, D) 1:9, E) 1:19 mole ratio oligomer cross-linker....................................... 29

3-12: Ru( II) a-diim ine com plexes .................................................................................. 133

3-13: Macroscopic SV plots of Ru(ll) a-diimine complexes dispersed in SPDMS binder
on glass. AREF.: area between 600 640 ni at 14.7 pi ..................................... 133

3-14: Qualitative microscopic fluorescence images (O0X, 0.5 psi) for Ru(II) a-diimine
complexes dispersed in SPDMS binder on glass. White scale bars are 153 pmr
long. A) [Ru(dpp),]CI:. B) [Ru(dpp)i( PF,,:, C) [Ru(dpp)3](BPh4)2, D)
[Ru(dpp)3](B(Ph(CF h))4)2, E) [Ru(dbdtap)](PF,):, F) [Ru(dpp)3](B(PhFs)4)2. 136

3-15: Qualitative microscopic fluorescence (A-C) and bright-field (D-F) images (10X,
14.7 psi) for Ru(Il) a-diimine complexes dispersed in SPDMS hinder on
glass. White scale bars are 153 pm long. A and D) [Ru(dpp)i]Cl2, B and E)
[Ru(dpp)3](B(Ph(CFh)2)4)2, and C and F) [Ru(dpp).](B(PhFs)4)2...................... 137

3-16: Quantitative microscopic fluorescence intensity images (IOX, 0.4 psi) for Ru(II) a-
diimine complexes dispersed in SPDMS binder on glass. White scale bars are

xxi

92 Lim long. Intensity color scale bars are shown to the right of all images.
A) [Ru(dpp)3]Cl2, B) [Ru(dpp)3](PF6)2, C) [Ru(dpp)3](BPh4)2, D)
[Ru(dpp)3](B(Ph(CF3)2)4)2, E) [Ru(dbdtap)3](PF6)2, F) [Ru(dpp)3](B(PhFs)4)2. 139

3-17: Intensity distribution curves for intensities obtained with a 10X objective at seven
pressures for Ru(II) a-diimine complexes dispersed in SPDMS binder on
glass. A) [Ru(dpp)3]C12, B) [Ru(dpp)3](PF6)2, C) [Ru(dpp)3](BPh4)2, D)
[Ru(dpp)3](B(Ph(CF3)2)4)2, E) [Ru(dbdtap)3](PF6)2, F) [Ru(dpp)3](B(PhF5)4)2. 142

3-18: Quantitative microscopic Ksv(x,y) image maps of Ru(II) a-diimine complexes
dispersed in SPDMS binder on glass. White scale bars are 92 gtm long. Ksv
color scale bars are shown to the right of all images. A) [Ru(dpp)3]C12, B)
[Ru(dpp)3](PF6)2, C) [Ru(dpp)3](BPh4)2, D) [Ru(dpp)3](B(Ph(CF3)2)4)2, E)
[Ru(dbdtap)3](PF6)2, F) [Ru(dpp)3](B(PhF5)4)2................................................... 143

3-19: Analysis of discrete regions (white boxes) in quantitative microscopic Ksv(x,y)
image maps of Ru(II) a-diimine complexes dispersed in SPDMS binder on
glass. White scale bars are 92 gpm long. Ksv color scale bars are shown to the
right of all images. A) [Ru(dpp)3]C12, B) [Ru(dpp)3](PF6)2, C)
[Ru(dpp)3](BPh4)2, D) [Ru(dpp)3](B(Ph(CF3)2)4)2, E) [Ru(dbdtap)3](PF6)2, F)
[R u(dpp)3](B (PhF5)4)2. .................................................................................... 146

3-20: Macroscopic and microscopic SV plots of Ru(II) a-diimine complexes dispersed
in SPDMS binder on glass. AREF: area between 600 640 nm at 14.7 psi....... 148

3-21: Macroscopic SV plots of [Ru(dpp)3]C12 dispersed in SPDMS or PDMS binder with
increased weight percent of fumed silica gel on glass. AREF: area between
600 640 nm at 14.7 psi................................................................................ 151

3-22: Qualitative microscopic fluorescence images (10X, 0.5 psi) for [Ru(dpp)3]Cl2
dispersed in SPDMS or PDMS binder on glass with increased weight percent
of fumed silica gel. White scale bars are 153 gim long. A) 0 wt. % in
SPDMS, B) 1 wt. % in SPMDS, C) 10 wt. % in SPDMS, D) 0 wt. % in
PDMS, E) 1 wt. % in PDMS, F) 10 wt. % in PDMS.......................................... 153

3-23: Quantitative microscopic fluorescence intensity images (10X, 0.4 psi) for
[Ru(dpp)3]Cl2 dispersed in SPDMS or PDMS binder with increased weight
percent of fumed silica gel on glass. White scale bars are 92 lim long.
Intensity color scale bars are shown to the right of all images. A) 0 wt. % in
SPDMS, B) 1 wt. % in SPDMS, C) 10 wt. % in SPDMS, D) 0 wt. % in
PDMS, E) 1 wt. % in PDMS, F) 10 wt. % in PDMS........................................ 155

3-24: Intensity distribution curves for intensities obtained with a 10X objective at six
pressures for [Ru(dpp)3]C12 dispersed in PDMS or SPDMS binder on glass
with increased weight percent of fumed silica gel. A) 1 wt. % in PDMS, B)
10 w t. % in SPD M S. ........................................................................................... 157

xxii

3-25: Quantitative microscopic Ks,(x,y) image maps for [Ru(dpp)3]Cl2 dispersed in
SPDMS or PDMS binder with increased weight percent of fumed silica gel
on glass. White scale bars are 92 p.m long. Ksv color scale bars are shown to
the right of all images. A) 0 wt. Q in SPDMS, B) 1 wt. g in SPDMS, C) 10
wt. t in SPDMS. D) 0 wt. I( in PDMS. E) 1 wt. '; in PDMS. F) 10 wt. C; in
PD M S. ..... ...................................................... ................................................ 158

3-26: Analysis of discrete regions (white boxes) in quantitative microscopic Ks\ (.y)
image maps of [Rucdpp)3]Cl2 dispersed in PDMS or SPDMS binder on glass
with increased weight percent of fumed silica gel. White scale bars are 92
pim long. Ksv color scale bars are show n to the right of all images. A) I wt.
in PDM S. B) 10 wt. in SPDM S............................................... ........ 160

3-27: Macroscopic and microscopic SV plots of [Ru(dpp)3ClI dispersed in PDMS or
SPDMS binder on glass with weight percent of fumed silica gel. ArHF: area
between 600 640 nm at 14.7 psi A) I wt. C in PDMS and B) 10 wt. ; in
S P D M S ...................................................................................................... ....... 16 1

a

xxiii

Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

DEVELOPMENT AND CHARACTERIZATION OF LUMINESCENT OXYGEN
SENSING COATINGS

By

Joanne M. Bedlek-Anslow

December 2000

Chairman: Kirk S. Schanze
Major Department: Chemistry

Traditional aerodynamic model systems monitor surface pressure at discrete

points along a model surface. Models must be designed sufficiently large to

accommodate placement of small electronic pressure transducers along the model surface

and placement of the corresponding wiring through the model's hull. This process is

time-consuming, expensive, and detection is limited to the point of sensor placement.

Conversely, CCD (charge-coupled device) camera technology surveys the entire model's

surface pressure by monitoring oxygen concentration induced intensity variations of a

luminescent pressure-sensitive coating. However unfavorable intensity variations

originating from surface temperature fluctuations can disrupt accurate pressure

determination.

The research presented in this dissertation focuses on the development of several

dual-luminophore coatings. These systems simultaneously determine surface pressure

(oxygen concentration) and surface temperature. Therefore correction of the

xxiv

temperature-induced intensity fluctuations of the pressure sensing luminophore is

accomplished by determining the run-time temperature field across the model surface.

Spectral resolution, compatibility with polymer binder and surface primer, and chemical

inertness with respect to one another indicate successful integration of the to

luminophores into one binder matrix. These systems are primarily evaluated using

fluorescence spectroscopy to ascertain variations in luminescent intensity with respect to

the degree of oxygen quenching. Experiments utilizing continuous illumination

monitored photodegradation and luminescence quenching studies conducted at various

temperatures evaluated the temperature-dependence of the pressure and temperature

components and binder matrix. Studies conducted in a calibration cell determined

application readiness.

Non-linear luminescent response to oxygen concentration prompted development

of a new fluorescence microscopy technique The technique interrogates se eral regions

of a coating's surface analyzing its microscopic luminescent pressure-sensitive response.

It is believed that deviations from linearity are due to heterogeneity of the polymer matrix

or the luminophore distribution. Successful quantitative measurement of the degree of

oxygen quenching at the pixel level with micrometer spatial resolution is presented for

several mono- and dual-luminophore sensing coatings utilizing various luminophores in a

polymer binder. Characterization. evaluation, and discussion of the systems' attributes

provide insight for the enhanced design of future luminescent oxygen sensing coatings.

XXV

CHAPTER 1
INTRODUCTION

Background

The quest to quantitatively measure oxygen concentration in the gas phase,

dissolved in the liquid phase or in solid gas permeable polymers with reproducible,

accurate and precise results, has garnered considerable research interest throughout the

past four decades. The beginnings of oxygen measurement are rooted in electrochemical

sensors such as the amperometric Clark cell or the galvanic Mancy cell.2 These cells

are robust and reliable measurement tools, when properly used; however, reliable

measurements are often prohibited by electrical interference, and reproducibility is

hindered by consumption of the oxygen analyte during analysis. The systems also suffer

from a bulky instrument size, which is difficult to miniaturize. Therefore the focus of

oxygen detection shifted from these traditional invasive measurement methods to the

development of noninvasive optical oxygen sensors.

As a detection system, optical sensors are advantageous, since they are robust,

cost-effective, disposable, and easily scaled to suit their desired application. Optical

sensors have been employed in numerous detection systems for such analytes as H,3-6

CO2,7,8 vapors of explosives,9 and biochemical compounds. 10-12 However, the

analysis of oxygen concentration in blood and biological systems,13,14 combustion

analysis, 15 and pressure-sensitive paint (PSP) development16-20 has been at the

forefront of optical sensor research. In particular. development in the area of pressure-

sensitive paints (PSP) has grown considerably in the last fifteen years

PSP's fundamentally consist of a luminescent molecular probe (a luminophore)

dispersed or dissolved in an oxygen permeable polymer binder. The beginnings of this

technology are seen as early as 1980, when Peterson and Fitzgerald demonstrated the

quenching of a luminophore's photoluminescence emission by oxygen.21 The)

employed Fluorescein Yellow dye as the luminophore, and adsorbed it onto a silica gel

chromatography plate. This initial experiment of flow visualization demonstrated the

possibility of oxygen concentration measurement across a surface as a determination of

overall surface pressure.

Luminescence Quenching

The composite mixture of luminophore in polymer hinder described above is

typically applied as an aerosol to substrate material such as aluminum, steel, polymer, or

composite as a film of thickness less than 50 p.m. Under 'V or blue light illumination (X

< 450 nm), the sensor coating emits light (photoluminescence) in the green, orange or red

region of the visible spectrum (X L 500 nm).21-23

Bimolecular Stern-Volmer Quenching

The photoluminescence intensity of the sensor film is inversely proportional to

the partial pressure of O2 (pO2) in the gas phase that is in equilibrium with the surface of

the coated substrate. Moreover, since under normal conditions and assuming Henry's

Law holds, pO is then proportional to the total air pressure (i.e., pO2 = cP ai). The

following processes thus define the kinetic scheme for the Stern-Volmer (SV)

himolecular quenching of the luminophore's photoluminescence intensity by oxygen:

L + hv -4 *L photon absorption (1-1)

*L L + hv luminescence, kr (1-2)

*L -* L + A non-radiative decay, knr (1-3)

*L + Q -4 L + *Q dynamic quenching, kq (1-4)

The term L is the luminophore, and Q is the quencher molecule, 02. Therefore, by

reference to the SV calibration in equation (1-5) it is possible to quantitatively relate the

photoluminescence intensity to Pair,18

I(X em, Pair = 0) / I(XPem, Pair) = 1 + KsvPair (1-5)

Ksv = kqTo = kq(kr + knr)-1 (1-6)

where I is the photoluminescence intensity at emission wavelength ,Pem, and Ksv is the

SV coefficient. Therefore the photoluminescence intensity is inversely proportional to

Pair.

In many applications it is impractical to use Pair = 0 as a reference condition, and

consequently the SV equation is re-cast as equation (1-7),

I(XPem, Pair = 1 atm)/ I(X em, Pair) = A + BPair (1-7)

where the reference condition is taken as Pair = 1 atm,24 and the non-zero coefficients A

and B are a function of temperature and reference conditions (B/A = Ksv).

Modeling Non-linear Stern-Volmer Response

Some luminescent 02 sensor films feature linear SV calibrations in accord with

equations (1-5) or (1-7); however, many sensors exhibit non-linear calibrations that are

curved downward such as those displayed in Figure 1-1.25-27

3,m
4 .

0 200 400 600 800
Oxygen pressure Torr i

Figure 1-1: Stern-Volmer plots of I/, versus p02 for the following optical oxygen
sensors: [Ru(phen)3]2 in silicone rubber, GE RTV 118 (A), and [Ru(hpyh)]2 in silicone
rubber, GE RTV 118 ().

Although a number of studies have attempted to identify the basis for this non-

ideal SV response, the fundamental processes) responsible are still not \\ell

understood.25,28 Several mathematical models have been developed to fit the non-linear

SV correlations. These mathematical models are formulated based on the physical

hypothesis that the sensor film is inhomogeneous. possibly due to nano-or nmeso-scale

irregularities in the polymer morphology or the environment surrounding the luminescent

sensor molecules Several models have received considerable attention.

The two quenching site model in (1-8),25.29,30 explains the complex quIenching

behavior exhibited by a microheterogeneous system. The two-site equation is

I I
--o- (1-8)
I f +, f0z
+
1+K~Pp I+KSvPo

where fj is the fraction of each of the two sites contributing to the unquenched intensity,

and the Ksv values are the quenching constants for the two sites. The model works well

5

for quantitatively fitting intensity quenching data; however, it should be cautioned that

while it is able to fit more complex systems, the fitting parameters should be judiciously

chosen to avoid mechanistic misinterpretations.25,31 In other words, the fact that the

response of a specific sensor can be modeled by equation (1-8) does not necessarily mean

that the sensor has two specific quenchable sites.

The Gaussian or log-Gaussian distributions represent another set of models which

give predictive values for the non-linear response exhibited by SV plots.26,29,32,33 The

log-Gaussian distribution in the natural luminescent lifetime of the luminophore (To) and

the quenching rate constant (kq') generates theoretical model parameter values which are

physically plausible and consistent at all partial pressures of oxygen, p02. The log-

Gaussian distribution in to and kq' with respect to x is

1exp(pix)exp(- x2)ix
Io. ---- (1-9)
I {exp(p,x)exp(- x2 )[ 1+ exp({ p1 + p2 x)] }dx

where

px = ln(To,i/T,mdl) (1-10)

P2X = ln(kq,i/kq,md) (1-1)

0 = KsV,mdl pO2 = tO,mdl kq,mdl pO2 (112),

and where pi is a measure of the breadth of the distribution with respect to To,i, and TOmdl

is the natural lifetime associated with the modal number of sites; P2 is a measure of the

breadth of the distribution with respect to kq,i, and kq,mdl is the quenching rate constant by

oxygen of the modal number of sites; P2 can be of the same sign or opposite to pi. The

model is capable of providing physical rationale for disparate response features in typical

optical oxygen sensors: however, it fails to explain physical phenomena associated with

bi-phasic material.33

Finally, first-, second-, and third- order polynomials applied to non-linear SV

response data20 tend to fit the data sets in a limited pressure region. but they fail when

predicting extended pressure regions or an extrapolation of the data set.24 Therefore the

dual sorption model has been applied to the SV relationship (1-5) producing the intensity-

pressure relationship in (1-13),24

I_ P D(P/P )
S=A+B-+C D(P/Ptf (1-13)
I Pf I+ D P/P )

where the non-zero coefficients A, B, C, and D are a function of temperature and

reference conditions The model Vworks well with cases where pressure ranges are large

or extrapolated regions are needed; however, due to the non-lincarity of such data. it

requires an iterative technique for determining the calibration coefficients. Theerefore, for

high pressures and limited pressure regions. a first- or second-order polynomial is

recommended.24

Luminophores and Polymers

The luminescent molecular probe dispersed in a PSP is generally a luminescent

transition metal complex (TMC). TMC's are more advantageous than fluorescent

organic luminophores because of their long excited state lifetimes (Ti) and high

luminescence quantum yields (QL).34 Most often, these metal complexes are either

Ru(II) a-diimine31,35 complexes or Pt(II)/Pd(II) porphyrin macrocycles. 16,36-38 The

oxygen permeable polymer binder most commonly used is silicone; however, other

polymers such as cellulose acetate (CA),39 polymethylmethacrylate (PMMA),40

polyvinylchloride (PVC),41 polystyrene (PS),42 and sol-gels43,44 all with or without

plasticizers have also been employed.

Ru(II) a-Diimine Complexes

The Ru(II) a-diimine complexes have been investigated extensively as oxygen-

quenchable species both in the liquid45,46 and solid phases:47 tris(2,2'-

bipyridyl)ruthenium(II), [Ru(bpy)3]2+; tris(1,10-phenanthroline)ruthenium(II),

[Ru(phen)3]2+; and tris(4,7-diphenyl-1,10-phenanthroline)-ruthenium(II), [Ru(dpp)3]2+

Their extensive use is due to several factors: (1) their ability to be excited in the visible

region; (2) their long emission lifetimes (To), which are generally hundreds of

nanoseconds to tens of microseconds, allow the excited state to be easily quenched by

oxygen; (3) they exhibit high luminescence quantum yields (0L); (4) large Stokes shifts

in the emission spectra minimize excitation source interference; and (5) they possess

excellent photostability.25,48,49 Several examples of Ru(II) a-diimine complexes are

shown in Figure 1-2.50

) [RI
N ND bip
N
N [R

N
N

/- 4,7
N N N

u(bpy)3]2
,yridyl

u(phen)3]2
0-phenanthroline

i(dpp)h
-diphenyl-1,10-phenanthroline

Figure 1-2: Structures of the major Ru(II) a-diimine luminlophores used in optical
oxygen sensors. ([Ru(hpyh)l', [Ru(phenh)]', and [Ru(dpp)Il").

As a result of the desirable properties shown in Table 1-1.50 the ldeign of Ru(II) X-

diimine complexes has been extensively investigated 25,3 1.34

Table 1-1: Photochemical Characteristics of the Ru(II) o-diimine Complexes in Water.

Luminophore To, Is Xx, nm E, Xn,. nm OL
(absorption) 104 dm3 (emission)
mol'"cm'

[Ru(bpy)h] 0.60
[Ru(phen)h]* 0.92
[Ru(dpp)3J2 5.34'
a in methanol. b in

(423),. 452
447.421
460
2-butanone, in

1.46 613.627 0.042
1.83. 1.90 605.625 0.080h
2.95 613, 627 -0.30L
water/ethanol, sh = shoulder

Pt(II)/Pd(II) Porphyrin Macrocycles

Pt(II)/Pd(II) porphyrin macrocycles have received considerable recent research

interest because of their ability to be more sensitive to oxygen quenching than the Ru(II)

a-diimine complexes.36,37,51 Several examples of Pt(II)/Pd(II) porphyrin macrocycles

are shown in Figure 1-3.50

N- N N

N" N

Tetraphenyl porphyrin (TPP) Octaethyl porphyrin (OEP)

NN

Porphyrin

Octaethyl porphyrin ketone
(OEPK)

Figure 1-3: Structures of the major platinum and palladium porphyrins used in optical
oxygen sensors. (M = Pt(II) or Pd(II)).

Their high oxygen sensitivity results from long excited state lifetimes, generally

tens to hundreds of microseconds, due in part to nt-n* transitions centered on the

porphyrin ring. 16 A strong spin-orbit coupling exists resulting from significant

interaction between the Pt(II) or Pd(II) metal d-orbitals and the anti-bonding 7t* orbitals

of the porphyrin ring which induces intersystem crossing to the triplet state.52,53 This

effect significantly decreases the triplet lifetime and increases the phosphorescence N field:

therefore, surrounding oxygen molecules effectively quench the luminophores'

photoluminescence.

In addition to their enhanced ability to be quenched by oxygen. Pt(II)/Pd(II)

complexes also possess the same desired excitation and emission characteristics as the

Ru(II) a-diimine complexes: (1) they are easily excited in the visible region: (2) they

possess high luminescence quantum yields (OL); and (3) they exhibit large Stokes shifts

and excellent photostability. 16,50 A listing of several optical sensor characteristics for

Pt(l)/Pd(II) porphyrins disbursed in polymer hinders are displayed in Table 1-2.50

Table 1-2: Platinum and Palladium Porphyrin Based Optical Oxygen Sensors.
Luminophore To, ms Xmax, nm (L Medium
(emission)

Pd-CPP
Pd-CPP
Pd-CPP
Pd-CPP
Pt-OEPK
Pt-OEPK
Pt-OEPK
Pd-OEPK

0.40
0.80
1.06
0.91
0.061
0.061
0.058
0.46

667
667
667
667
760
759
759
790

0.2
0.2
0.2
0.2
0.1
0.12
0.12
0.01

Water
Silicone rubber RTV 118(GE)
PS
PMMA
PS
PS
PS
PS

Pt-OEPK 0.064 759 0.12 PVC
Pd-OEPK 0.44 790 0.01 PVC
Pd-TPP 690 Arachidic acid L-B film
Pd-TSPP 1.0 702, 763 Water
Pd-TSPP 0.5 698,685 Water
Pd-CPP 0.53 667 Water
Pt-TDCPP 0.082 650 0.16 Silicone Rubber RTV 118(GE)
Pt-TFMPP 0.030 646 0.08
Pt-Br8TMP 0.023 721 0.02
Pd-OEP 0.99 670 0.2 PS
Pt-OEP 0.091 644 0.5 PS
Pt-OEP 0.091 644 0.5 PS

CPP: cc

)proporphyrin; OEPK: octaethyl porphyrin ketone; TPP: tetraphenylporphyrin;
TSPP: tetrakis(4-sulfonatophenyl)porphyrin; TDCPP: meso-tetra(2,6-
dichlorophenyl)porphyrin; TFMPP: meso-tetra(3,5-
bis(trifluoromethyl)phenyl)porphyrin; Br8TMP: meso-tetramesityl-P-
octabromoporphyrin; OEP: octaethyl porphyrin

Silicone

Silicone is the most widely used polymer binder matrix employed in optical

oxygen sensors due to its high permeability (62 x 10-9 (cm3 cm)/(cm2 s cm Hg) at 28' C)

and solubility (0.31 ml-g-~ at 280 C) to oxygen associated with a low glass transition

temperature, Tg, (- 1270 C), high chemical and mechanical durability, and benign

physiological effects beneficial to in vivo measurement applications.54,55 However,

silicone as a binder matrix is incredibly hydrophobic in nature due to its extended

I

I

nonpolar Si-O-Si backbone which forms during polymerization.25 Adequate

homogeneous distribution of the hydrophilic Ru(II) a-diimine complexes in the polymer

binder then becomes a challenge in avoiding aggregation or microcrystallization effects

which lead to inefficient oxygen quenching.31 Therefore, several researchers have

investigated the addition of Rut II) a-diimine adsorbed silica gel to the polymer binder.

The addition of silica gel aids luminescence oxygen quenching by lessening the negative

quenching effects due to formation of metal complex aggregates and

microcrystallites.25,56

Plasticizers

Other polymers such as cellulose acetate (CA),39 polymethylmcthacrylate

(PMMA),40 polyvinylchloride (PVC),41 polystyrene (PS),42 and sol-gels43,44 hae

been employed as oxygen permeable polymer hinders. These polymers are not as

permeable to oxygen as the elastomeric silicone polymer hinders and slow and inaccurate

oxygen concentration measurements result. When a plasticizer such as tetrabutyl borate

or dodecyl sulfate is incorporated into the given polymer, it lowers the Tg and improves

the parent polymer's permeability to oxygen.8,37 However, a plasticizer can leach from

the polymer binder and adversely affect the polymer's ability to adsorb oxygen.27

Modified Polymers

One way to avoid incorporating additives such as silica gel or plastici/crs into the

polymer binder is to design synthetically modified polymers. These polymers are

designed to possess similar oxygen permeability as the silicone polymers yet not suffer

from the same inaccurate sensing affects arising from inadequate luminophore

distribution or impurity leaching. Several alternative polymer binders have been

developed recently.

Puklin et al. have developed a fluoroacrylic copolymer (FIB),

(fluoro/isopropyl/butyl)acrylic polymer displayed in Figure 1-4.57 When Pt(II)

tetra(pentafluorophenyl)porphyrin (PtTFPP) is distributed through the polymer, the

coating displays a Ster-Volmer dynamic range of 0.9 [defined as (Ivac Iatm)/Ivac)],

where I is luminescence intensity and the subscripts vac and atm refer to vacuum and

atmospheric pressure, respectively. Other attributes include a response time of less than

1 s to an increase in pressure from near vacuum to 1 atm, good photostability, and low

temperature dependence (~ 0.6 %-C-1).

CH3
-CH- CH -CH-
I2 2m L 2" n
=0 0
O O
0 0
CH2(CF2)2CH3 CH(CF3)2

Figure 1-4: Repeat unit of (fluoro/isopropyl/butyl)acrylic polymer.

Amao et al. have developed a different fluorocopolymer [copoly(styrene/PFS)],

poly(styrene-co-pentafluorostyrene) illustrated in Figure 1-5.51 When Pt(II)

octaethylporphyrin (PtOEP) is distributed through the polymer, the coating displays a

Io/IIoo = 18.0 response as compared to Io/IIoo = 4.5 for a simple polystyrene coating,

where Io and Iloo represent the detected phosphorescence intensity from a coating exposed

to 100 % argon and 100 % oxygen, respectively. The photoluminescence response times

are 5.66 s for polymer exposure to argon then oxygen and 30.0 s for polN mer exposure to

oxygen then argon.

n

Figure 1-5: Repeat unit of poly(st) rene-co-pentafluorostyrene) copol rmer.

The preceding research groups are working from the basis that fluoropolmer

coatings possess an increased permeability to ox\gen-5 and a higher stability) to wards

photo-oxidation compared to polymers lacking highly electronegative groups. The C-F

bonds possess a large bonding energy (116 kcal-mol ") and short bond lengths (I.3.81 A)

which enhance the bonds' stability tow yards photo-oxidation and increases their affinity

towards oxygen sorption when incorporated into a polymer binder backbone.59

Ruffolo et al. have developed another type of block copol% mer

poly(aminothionylphosphavene)-b-poly(tetrahydrofuran) (PATP,-PTHF,) displayed in

Figure 1-6.60 When [Ru(dpp)3]Cl2 is distributed through the block copolymer, the

coating displays good quenching sensitivity and linear Stern-Volmer response compared

to earlier poly(butylaminothionylphospha7ene) (PBATPy) and PBATP/PTHF, blends.

NHCH NHCH 0
N=P-N=P-N-=S--O
I I I JYL 0 T
NHCH3 NHCH3 NHCH3

PMATPy-PTHFx

Figure 1-6: Repeat units of poly(aminothionylphosphazene)-b-poly(tetrahydrofuran)
block copolymer.

This particular design idea stems from the often-impractical necessity for silicone

coating polymers to cross-link prior to formation of a solid stable coating. The cross-

linking is not a controlled physical process and can change in degree and directionality

from coating to coating leading to irreproducible SV response.25,50,61 This lack of

cross-linking continuity can be one source of problems associated with poor luminophore

distribution. Therefore the (PATPy-PTHFx) design benefits from production of a

dimensionally stable coating without the need for cross-linking. Moreover, such a design

leads to a better understanding of the polymer coating's structure-function relationship.60

It will be interesting to see how future polymer designs will compare to the above

modified polymers, to one another, and to the more traditional elastomeric silicone binder

systems; what current morphological questions will be answered; and how will knowing

such answers lead to the development of other luminophore/polymer binder systems.

Wind-Tunnel Application

In a typical application of aerodynamic engineering, a sensor coating is composed

of a luminophore dispersed in a polymer binder which is dissolved in a volatile thinning

solvent and sprayed onto an aerodynamic model. The coating forms upon evaporation of

the volatile solvent. The model is installed in a wind-tunnel, and the photoluminescence

from the sensor coating at XPem is imaged with a camera (digital or film-based) that is

fitted with appropriate filters that pass light of wavelength X~em. By using appropriate

computer algorithms, it is possible to apply the Ster-Volmer calibration (1-5) to convert

the photoluminescence intensity map generated by the camera into a full-field map of air

pressure (Pair) over the surface of the model displayed in Figure 1-7.27

Blue filter Red filter Computer

'I I ~
Light Camera
source

Air flow

Figure 1-7: Pressure Sensitive Paint measurement system for testing of air pressure
profiles on an airplane model in a wind-tunnel.

Pressure maps obtained from the set-up in Figure 1-7 would show luminescence

characteristics similar to Figure 1-8. Figure 1-8 displays an intensity pressure map for a

nitrogen jet protruding out of the plane of a PSP coating.62 The direction of the tunnel

air-flow travels from behind the nitrogen injection jet forward (bottom to top of image).

A pressure field of high and low pressures develop. The oval shape preceding the

nitrogen jet indicates an area of high pressure or high oxygen concentration, and the cone

shape directly preceding the nitrogen jet indicates an area of low pressure or low oxygen

concentration due to air-flow disruption. Colors would then be assigned to the gradients

of gray in the image to enhance and discriminate among the pressure changes by making

them more discernable to the viewer's eye.

Injector

0 5 10 15 20 25
Air Pressure (psi)

Figure 1-8: Gray-scale pressure distribution map for a nitrogen jet protruding from a PSP
coating.

As demonstrated, PSP technology has revolutionized traditional wind-tunnel

testing which monitors discrete surface pressure measurements at localized pressure taps

across a test model. The transducers are connected to multitudes of electronic wiring and

hardware, and the assembly of such a model takes 9 12 months to design and construct.

As compared to the complexity of the transducer system, PSP coatings are easily applied

to a model surface and ready to use within a few hours. The noninvasive approach

offered is essential to prototype aerodynamic model testing; therefore, luminescence

imaging has generated significant research interest in the aerodynamic engineering

community. 16,27

Temperature Effects

Under ideal conditions, the photoluminescence intensity of a sensor coating

would respond only to changes in pO2; other environmental parameters such as

temperature (T) would not interfere with the measurement. Unfortunately, it is well

known that at constant air pressure, the photoluminescence intensity of most oxygen

sensor coatings varies inversely with T as does the Stern-Volmer coefficient (Ksv).63.64

For many sensor coatings. Ksv varies linearly with T over a narrow range of temperatures

demonstrated by equation (1-14).

Ksv(T) = Ksv f + bT (1-14)

Because of the temperature dependence of Ks\, when a sensor coating is applied

under non-isothermal conditions (most often the case in a wind-tunnel), the global map of

Pair that is created will be in error. On the other hand. ,ince Ksv is a well-behaced

function of temperature as in equation (1-14), if one knows the temperature distribution

over the surface of the aerodynamic model, it is possible to apply computer algorithms to

correct for the temperature dependence of Kw and obtain an accurate global surface

pressure distribution.63-65

Several data reduction methods have been developed, which convert the

processed wind tunnel image into false-color image representations of the quantitative

pressure distribution across the model surface. The intensity-ratios obtained at each pixel

are converted into pressures using a modified Henry's law relation, which accounts for

the non-ideal porous nature of the polymer binder in equation (1-15),64

P/Pef = CI + C2(lr~iTrcf/Irun(Trun)) + C3(lrTref)/Irun(Trun))2 (1-15)

where CI, C2, and C3 are the reduction method coefficients, and Iref(Tref)/Irun(Trun) is the

intensity-ratio obtained at each pixel.

Isothermal Calibration

An isothermal calibration assumes that the wind-tunnel surface is spatially and

temporally isothermal during the run of the flow.66 An initial static calibration is taken

at a reference temperature over a given pressure range, and a least-squares fit is employed

to obtain the resulting calibration curve. The pressure values obtained from pressure taps

fashioned along the model surface are compared to the intensity-ratio images obtained.

As is expected, the method does not account for the temperature drop that occurs across

the model during airflow that results in a prediction of pressure values lower than

measured. Therefore, it is best that this method only be used for qualitative evaluations

of coatings.64

In-situ Calibration

An in-situ calibration accounts for the change in surface temperature across a

model surface during wind-tunnel operation. 19 For this reduction method, a limited

number of pressure taps are placed across the surface of the model. These taps should be

placed in the regions of highest and lowest pressures as well as several intermediate

regions for the best results. However, a priori knowledge of the pressure distribution is

difficult to know and a disadvantage for this reduction method.

The intensity of the paint around the taps is evaluated and used in conjunction

with the pressure values obtained at the taps to develop a calibration curve. A least-

squares fit is applied to equation (1-15), and the pressure tap and intensity values are used

to determine the values for CI, C2, and C3. The pressure values across the model surface

are then obtained through interpolation of the data.

K-fit Calibration

The K-fit calibration is a hybrid of the isothermal and in-situ calibration methods.

It was found that equation (1-15) will coalesce if Tn, = Trf; therefore, equation (1-15)

can be re-cast as equation (1-16),

P/Pref = C' + C'2(lrliTi)/Irun(Ti)) + C'3(lrL.fT)/Iln(TI))2 (1-16)

where Ti is an arbitrary number, and the coefficients C'1, C'2, and C'3 do not vary with

temperature. A scaling process, function K in equation (1-17), is applied to rescale the

reference image (I,.Ti,)), so it then emulates a reference image taken at T2.

K = Ir,,{Ti)/Ire, T2) = f(T,,T2) (1-17)

Equation (1-16) is recast as (1-18),

P/Pref= C'I + C'2(KIreT2)/Irun(Ti)) + C' ,(KlreT2)/Irun(Ti))2 (1-18)

where Ti, T2, and K are constant over the model surface. If Ti = T1un and T2 = Trf, then a

least-squares fit of equation (1-18) will result in K.64 This reduction method is superior

to the isothermal method but less accurate than the in-situ method, since this model

under-predicts the pressure values in the low-pressure region. A possible explanation for

this is that it may not be physically reasonable to assume that there exists a separation in

the pressure-dependent (C'I, C'2, and C'3) and the temperature-dependent (K)

relationships of the coating. Therefore, the K value in equation (1-17) may be pressure-

sensitive, and the equation should be recast as equation (1-19).64

K = f(Ti,T2,P) (1-19)

Temperature-corrected Pressure Calibration

This method accounts for the change in surface temperature across the model

surface between the reference image and the wind-tunnel images. It utilizes a pixel-by-

pixel correction method by employing the image information of a temperature-sensitive

coating to correct for the temperature-dependence of a pressure-sensitive coating. By

knowing the intensity-ratio and temperature values at each pixel, a pressure value can be

determined by equation (1-20).64

Iref/Ica = f(P,T) (1-20)

The pressure values at each pixel are calculated through a linear interpolation between

isothermal calibration curves generated from in-situ taps and the temperature-sensitive

coating's temperature values. The advantages of this method allow for knowledge of the

slightest temperature gradient across the surface with no need for pressure taps to

calculate the final pressure values. However, there can be problems associated with

photodegradation of the coating materials; an inconsistent use of substrate material for

calibration samples and wind tunnel fixtures accounts for inaccurate comparisons of

pressure-sensitivities in calibration curve generations; and the temperature values

obtained from the temperature-sensitive coating may not be the exact values experienced

by the pressure-sensitive coating.64

Physical Manifestations of the Temperature Effect

The temperature effects experienced by the pressure-sensing coatings are due to

the two major components of the PSP: the luminophore and the polymer binder. First, it

is known that in degassed solution experiments that the temperature dependence of a

luminophore is dependent on the non-radiative decay pathways, since the radiative decay

rates are only weakly temperature dependent.63 Luminophores such as the RulII) a-

diimine complexes experience temperature dependence of non-radiative decay processes

because of the coupling of the excited state with vibrational levels of the metal ground

state and the solvent or polymer matrix. More specifically, for the Rut II) a-diimine

complexes, temperature dependent excited state decay arises due to increased coupling of

the emissive MLCT (metal-to-ligand charge-transfer) state to a nearby dd manifold.

Temperature dependent quenching can arise due to the temperature-dependence

of the diffusivity and solubility of the quencher molecule (02) in the polymer matrix.

The permeability ( P, ) of oxygen in the binder is a product of the solubility (S, ), and

diffusivity ( D, ). The rate constant for quenching (kq) is proportional to Do, and the

concentration of oxygen [021 in the polymer is affected by So, However, since it is

known that the solubility of diatomic gases in polymers is only weakly dependent on

temperature, temperature dependent quenching then arises primarily due to the

temperature dependence of Do .55 Gas diffusivity in polymers depends on the polymer

total free volume, which increases with increased temperatures. Polymer segments

undergo thermal expansion creating free sites accessible to oxygen molecules.67

According to Schanze et al.. kq[O2] = Aqexp(-E,/RT), where Aq and Eq are the frequency

factor and activation energy for oxygen quenching. respectively. Since kq is proportional

to Do it can be assumed that the Eq is related to the activation energy of diffusion (Ea).

Therefore, by the relations outlined above, PSP coatings should be developed which have

the lowest possible activation energy for oxygen diffusion.

Advances in PSP Design

A convenient method for obtaining the necessary information regarding the

temperature distribution over the aerodynamic model is to incorporate into the sensor

coating a second "temperature sensitive" luminophore that has the following

properties:65 (1) it is sufficiently excited at the same wavelength as the oxygen sensing

luminophore; (2) photoluminescence occurs in a different region of the visible spectrum

(X em) than the photoluminescence of the oxygen sensing luminophore (i.e., XTem # ,em);

(3) photoluminescence intensity is independent of pressure; (4) the luminophore is

photostable or deteriorates at a rate similar to that of the oxygen sensing luminophore;

and (5) photoluminescence intensity varies strongly and monotonically with temperature.

With such a dual-luminophore sensor system, one would be able to obtain a global map

of the temperature of the surface of an aerodynamic model by imaging the

photoluminescence from the temperature-sensitive luminophore with a camera fitted with

filters that pass light only at wavelength XTem. The resulting temperature map could then

be used in an algorithm to correct for the temperature-dependence of the

photoluminescence intensity from the pressure-sensitive luminophore.

The Gouterman research group has worked extensively in developing

luminophores and polymer binders which correct for temperature-dependence. They

reported in 1998 the incorporation of a second luminophore to a polymer binder: a

pressure-insensitive but temperature-sensitive inorganic phosphor to correct for the

temperature-dependence of the PSP coating. However this coating experienced some

problems with competitive absorption of the excitation light by PtTFPP, absorption of the

emission light from the phosphor (BaMg2A16027:Eu2+) by PtTFPP, and a heterogeneous

24

distribution of the phosphor particles. Expanding on earlier work with platinum

porphyrins, the Gouterman group investigated the use of silicon octaethylporphine

(SiOEP) as a new pressure-insensitive, temperature-sensitive luminophore. The silicon

porphine complex suffers from an increase in fluorescence intensity as the temperature

rises due to repopulation of the singlet excited state via the triplet state; moreover, the rise

in fluorescence can cause confusion in calibration runs at vacuum. Fortunately, the

temperature-dependence is only at vacuum conditions not a standard wind-tunnel

condition.65

Gouterman's group has also researched the development of a polymer possessing

a low activation energy to oxygen diffusion. A temperature sensitivity of- 0.6 o-"C1

for PtTFPP dispersed in the fluoroacrylic polymer FIB (Figure 1-4) has been reported.

This number is significantly better than a temperature sensitivity of- 1.7 "'; -C reported

for PtOEP in the silicone polymer binder Genesee GP-197.57

Monitoring Methods

There exist three monitoring methods for the analysis of PSP coatings:

luminescence intensity method, pulsed lifetime method, and phase-shift method.

Luminescence Intensity

The luminescence intensity method measures the emission intensity produced by

the luminophore(s) in the sensor coating. It is the most widely used method, since the

equipment is relatively inexpensive to assemble and small enough to be portable. The

pressure profile experienced by the coating is then determined from a calibration curve.

However, an accurate analysis by the method is directly affected by changes in the

excitation source intensity, variations in efficiency of the system equipment to collect the

emission signalss, and the photostability of sensing coatings. Fortunately, collecting a

reference signal and limiting the exposure time of the sensor coatings can help alleviate

the effects of these problems.

Pulsed Lifetime

The pulsed lifetime method utilizes an excitation source with a pulse termination

time that is shorter than the lifetime of the emission lifetime(s) being evaluated. This

method is employed less frequently due to the problem of reducing the complex decay

curves obtained by the traditional least-squares method; however, the simpler technique

of rapid lifetime determination (RLD) is being employed to reduce the complex decays to

a single parameter.68 The RLD technique allows for direct integration of various regions

under the integration curve resulting in reduction to a single parameter.

Phase-shift

The phase-shift method employs a sinusoidally modulated excitation source

combined with phase-sensitive detection.23 The modulated emission is delayed in phase

by an angle 4, relative to the excitation demonstrated by equation (1-21),

= arctan(ot) (1-21)

where o= 2nf (1-22),

and f is the linear modulation frequency. The phase shifts are easy to measure, since the

phase shift varies monotonically with oxygen concentration.69 The equipment required

for this method is relatively inexpensive. This method like the RLD method does not

provide an a priori knowledge of the complexity of the decay(s) measured; however, the

frequency can be varied for optimization of accuracy at a known concentration of

oxygen.27

Scope of This Work

Initial research has focused on development of a "temperature-sensitive"

luminophore, which is temperature-sensitive and pressure-insensitive. This system

configuration corrects for the temperature dependency of the pressure component by

determining the run-time temperature field. Dual-luminophore sensor coatings were

developed where the temperature sensing luminophore, encapsulated in polystyrene

microspheres, and the pressure sensing luminophore are conjointly distributed through a

polydimethylsiloxane polymer binder. Extensive studies were conducted to e ialuate the

photo, thermal-, and temporal-stability of the luminophore/binder coatings, and

fluorescence microscopy, SEM and TEM analytical techniques were employed to

evaluate the molecular distribution of the luminophores in the coatings. Finally the

coatings were subjected to static calibration cell imaging to evaluate their overall

application performance.

Fluorescence microscopy has also been employed to analyze the variable non-

linear Stern-Volmer response exhibited by several Ru(II) o-diimine based coatings and

the linear Stern-Volmer response exhibited by several Pt(II)

tetra(pentafluorophenyl)porphyrin based coatings. It is believed that deviations from

linearity are due to heterogeneity of the polymer matrix or the luminophore distribution.

By quantitatively measuring the oxygen quenching efficiency at the pixel level with

micrometer spatial resolution, we have been able to provide experimental evidence to

explain the linear and non-linear SV responses exhibited by such coatings.

CHAPTER 2
DUAL-LUMINOPHORE OXYGEN SENSING COATINGS

Introduction

As outlined in Chapter One, ideal oxygen sensing conditions produce

photoluminescence intensity which responds only to changes in pO2; however, other

environmental parameters such as temperature (T) interfere with this measurement. For

many sensors, the Ksv value varies linearly with temperature over a narrow range of

temperatures as indicated by equation (2-1).

Ksv(T) = Ksvref + bT (2-1)

When a sensor coating is evaluated under non-isothermal conditions (most often

the case in a wind-tunnel), the global map of Pair that is created will be in error, because

of the temperature dependence of Ksv. Since Ksv is a well-behaved function of

temperature as in (2-1), if one knows the temperature distribution over the surface of the

aerodynamic model, it is then possible to apply computer algorithms to correct for the

temperature-dependence of Ksv and obtain an accurate global surface pressure

distribution.63-65

A convenient method for obtaining the necessary information regarding the

temperature distribution over the aerodynamic model is to incorporate into the sensor

coating a second "temperature-sensitive" luminophore that exhibits similar properties65

to those outlined in Chapter One under PSP Advances. Therefore a dual-luminophore

sensor system would provide a global temperature map for the surface of an aerodynamic

model by imaging the photoluminescence from the temperature-sensitive luminophore.

27

The global temperature map would then be used to correct for the temperature-

dependence of the photoluminescence intensity imaged from the pressure-sensitive

luminophore, and a corrected global surface pressure distribution would result.

When incorporated separately (i.e., one at a time, but not together) into a polymer

binder, many photoluminescent probe molecules display desirable emission

characteristics for oxygen or temperature sensing. However, when two or more probe

molecules are mixed into the same binder, they typically do not display the desired

oxygen and/or temperature sensing photoluminescence properties. This non-ideal

behavior arises from both physical and chemical molecular interactions, and often yields

unpredictable results with respect to the overall photoluminescence properties of the

sensor coating.65 One solution to this problem is to design nanometer to micrometer

sized "molecular cages" or "compartments" that separate the luminophores in the

polymer binder at the molecular level yet provide a coating that is spatially homogenous

on the millimeter scale (i.e., camera spatial resolution). In this manner, it is possible to

produce a sensor coaling system incorporating two or more photoluminescent probe

molecules which display separate and well-defined photoluminescence intensity

variations due to temperature and oxygen sensing.

Recent work by Gouterman et al. has yielded two types of dual-luminophore

sensor coatings. In one coating, they have incorporated a second luminophore: a

pressure-insensitive but temperature-sensitive inorganic phosphor to correct for the

temperature-dependence of the PSP coating.70 Expanding on their earlier work with

platinum porphyrins. the Gouterman group has also investigated the use of silicon

octaethylporphine (SiOEP) as a new pressure-insensitive, temperature-sensitive

luminophore.65

In the work presented in this chapter, two dual-luminophore coatings were

developed and characterized. These coatings contain a temperature-sensitive

luminophore adsorbed onto polystyrene microspheres and an oxygen-sensitive

luminophore. The dyed-microspheres and the oxygen sensing luminophore were

distributed in a gas-permeable polymer binder. Detailed schemes for the preparation of

the dyed-microspheres and resulting dual-luminophore coatings are outlined in Figures 2-

1, 2-2, and 2-3.

+ ^

ppsp
B
pplsp + DOCI DOCIplsp

Figure 2-1: Scheme for preparation of DOCI highly cross-linked polymer microspheres
(DOCIppsp). A) 5 vol % DVB relative to total volume, AIBN 2 wt. % relative to
monomer, A 700 C for 24 h., EtOH wash, dry in vacuo at 500 C for 12 h. B) 1 mL
MeOH, sonicate 1 h., soak in dark for 7 d., MeOH and CH2C12 wash, dry in vacuo at 300
Cfor 12h.

K-

+

.SO3-Na+

C

SsPsp"

Sspsp- + DOCI

Ssp.sp

S DOCI-Sspsp

Figure 2-2: Scheme for preparation of DOCI sulfonated polymer microspheres (DOCI-
Sspsp). A) 45 vol % DVB relative to total volume. DI H20:porogen = 25:1 v/v,
porogen:monomer = 1:1.4 v/v, porogen = 1:1 l-dodecanol:toluene. sodium laurylsulfate
0.3 mol % relative to monomer, A 260 70 C 7 h. at 250 rpm, DI H20 and acetone wash,
THF Soxhlet extraction, dry in vaciu 480 C 12 h. B) 40 mL CH2C12, 0 C, 0.5 mL
CISO3H in 40 mL CH3CI dropwise, warm to 250 C, stir 24 h. 250 C, CH2CI2 wash, air
dry. C) 150 mL DI H20, 50 mL NaOH (150 mM), stir 100 min. 250 C, 3x100 mL DI
H20 wash, 100 mL acetone wash, dry in vacuo 530 C 40 h. D) 4 mL MeOH, 2 mL DI
H20, sonicate for 20 min.. MeOH and acetone wash.

SO3H

A

PtTFPP
3 3.5 % Pt divinyltetramethyl disiloxane catalyst
methylhydrosiloxanes-dimethylsiloxane copolymer
CH3 H CH3 CH3
1 3 1 1 3 I 3
H3C-Si-O- -Si-O -Si-O+ Si-CH3
ICH CH3 OI n CH
OH3 OH3 OH3 OH3
I

DOCIppsp or DOCI-Sspsp and vinyl
polydimethylsiloxane
Mix 20 min.
CH3 CH3 CH3
I rI + 1
CH2=CH-Si-O--Si-O-n Si-CH=CH2
CH3 CH3 CH3

air-brush application

PtTFPP

Polymer Binder

,O DOCI-Ssusp or DOClpusp

S0 Primer
P_ Primer

4--

Substrate

PtTFPP

Figure 2-3: Scheme for preparation of dual-luminophore oxygen sensing coatings.
PtDOCIpgsp/VPDMS and PtDOCI-Sslsp/VPDMS.

Extensive studies were conducted to evaluate the photo, thermal-, and temporal-

stability of the dual-luminophore coatings, and SEM, TEM, and fluorescence

microscopic analytical techniques were employed to evaluate the size and distribution of

the luminophores in the coatings. Finally the coatings were subjected to static calibration

imaging to evaluate their overall application performance. The results and discussion of

this work are presented in the following chapter.

Results

Dual-luminophore Coatings

Two dual-luminophore coatings were developed incorporating an oxygen sensing

luminophore and a temperature sensing luminophore adsorbed onto a polystyrene

microsphere dispersed in a polydimethylsiloxane (PDMS) polymer binder.

PtDOCIppsp/VPDMS Coating

The first coating consists of Pt(II) me.so-tetrakis(pentafluorophenyl)porplhine

(PtTFPP) as the oxygen sensing luminophore and DOCI-adsorbed microspheres

produced via precipitation polymerization (DOCIpp.sp)(3,3'-diethyloxacarbocyanine

iodide = DOCI) as the temperature sensing luminophore dispersed in a vinyl

polydimethylsiloxanes (VPDMS) polymer hinder. The preparation of the coating is

schematically represented in Figure 2-3.

A typical emission spectrum of the coating is shown in Figure 2-4.

1.4e+5 -2.033 psi
4.519 psi
i 1.2e+5 --6.124 psi
S- 8.015 psi
1.0e+5 10.103 psi
--- 14.639 psi
S8.0e+4

o 6.0e+4

S4.0e+4 'i
2.0e+4

0.0
500 550 600 650 700 750 800
Wavelength (nm)

Figure 2-4: Emission intensity spectra for PtTFPP and DOCIppsp dispersed in VPDMS
polymer on primed glass.

Two emission bands are detected when the coating is excited with 450 nm light.

The PtTFPP emission consists of two bands: an intense band, T(0,0), centered at 645 nm

and a weaker band, T(0,1), centered at 710 nm. The emission bands are due to

phosphorescence from the 3TI(1,71*) state of the porphyrin macrocycle.16 Back bonding

between the dxz and dyz orbitals of the Pt with the empty eg(it*) orbitals of the porphyrin

produce a strong spin-orbit coupling. This leads to singlet-triplet mixing which increases

the radiative decay rate from 3T1(.TC,*) -- ISo. The increase in phosphorescence

facilitates efficient oxygen quenching.71 Therefore, a decrease in emission intensity is

observed as the oxygen concentration above the coating sample is increased.

The DOCIpgsp temperature-sensing luminophore exhibits two weak emission

bands centered at 510 nm and 550 nm, respectively. This is fluorescence from the n-rC*

transitions centered along the conjugated chromophore backbone. The fluorescence is

split at 540 nm due to absorption by PtTFPP.

The PtTFPP porphyrin is a d8 phosphorescent hypso porphyrin possessing

absorption features blue-shifted relative to normal porphyrins. PtTFPP exhibits several

absorption bands. The first band is an intense near-UV band termed the Soret band at

395 nm, 'So -- 'S2(,t*). The second two bands appear in the visible region between

505 to 540 nm and are referred to as the Q bands. The first Q hand. Q(0,0), represents

the excitation from the lowest vibrational level of the ground-state singlet to the lowest

vibrational level of the first singlet excited state, and the second Q band. Q(1,0), has one

quantum of vibration in the first singlet excited state. 'So -- SIt(17,*). For square planar

metalloporphyrins, such as PtTFPP, the Q bands are due to degenerate excited states with

x and y polarization.72

For a d8 metalloporphyrin, the filled d, orbital. dx or dyz, are located between the

occupied alu(;), au,(n) orbital and the empty degenerate LUMO e,(t*) of the porphyrin

ring. The metal dn electrons can then interact with the empty eg(n*) orbitals inducing a

mixing between the empty eg(nl*) orbital and the filled e,(dni) orbital. Stabilization of the

filled eg(dn7) orbital raises the energy of the eg(7l*) orbital and results in a blue-shift of the

absorption bands.52,73

The fluorescence emission of the DOCIpplp is centered at 510 nm due to n-n*

transitions, and the Q bands of the PtTFPP overlap well with the DOCI fluorescence.

Therefore, the PtTFPP luminophore can absorb some of the DOClplpsp emission, and the

DOCI emission band experiences an emission bleach around 535 nm. The effect is

clearly seen in Figure 2-4.

35

PtDOCI-Ssjsp/VPDMS Coating

The second coating is a modification of the first. The formulation still contains

Pt(II) meso-tetrakis(pentafluorophenyl)porphine (PtTFPP) as the oxygen sensing

luminophore; however the DOCI-adsorbed microspheres were produced via a suspension

polymerization, sulfonated, and negatively charged prior to dye adsorption. The

luminophores are dispersed in a vinyl polydimethylsiloxanes (VPDMS) polymer binder.

A typical emission spectrum of the coating is displayed in Figure 2-5.

le+5
2.023 psi
S........ 4.056 psi
8e+4 --- 6.024 psi
.-.- 8.192 psi
10.501psi
6e+4 -- 14.615 psi

.2 4e+4

W 2e+4

500 550 600 650 700 750 800
Wavelength (nm)

Figure 2-5: Emission intensity spectra for PtTFPP and DOCI-Sslsp dispersed in
VPDMS polymer on primed glass.

Under 450 nm excitation light, the coating exhibits two emission bands that are

similar to the previous coating. The Imax of PtTFPP is only slightly less intense than in

Figure 2-4. However, the intensity of the DOCI-Sspsp is less than half intense as the

previous DOCIppsp emission in Figure 2-4. Adding twice as much dyed-microspheres

(DOCI-Sspsp) to the coating formulation did not significantly increase the emission

intensity either. The impact of the different microsphere preparation methods to the

overall performance of the PtDOCIppsp/VPDMS and PtDOCI-SsLsp/VPDMS coatings

will become clearer when the quantity and distribution of the PtTFPP, DOCIpLsp, and

DOCI-Ssgsp luminophores in relation to imaging of the coatings with CCD camera

technology is discussed later in the chapter.

Temperature Dependence and Thermal-stability

The temperature dependence and thermal-stability of the PtDOCIppsp/VPDMS

and PtDOCI-SslspN/PDMS coatings were assessed over a 40 K temperature range from

273 313 K. The temperature dependence of the PtTFPP pressure probe's

photoluminescence response to oxygen quenching for the emission region 630 670 nm

was established, and the stability of the probe's emission response to cyclic variations of

temperature from 273 313 -- 273 K was evaluated. The temperature dependence and

thermal-stability of the photoluminescence between 530 570 nm for the DOCIplsp and

DOCI-Sspsp temperature probes were evaluated in the same manner as the

photoluminescence of the pressure probe.

Specimens were prepared by air-brushing four layers of each coating onto

borosilicate microscope slides primed with a TiO2/SPDMS (SPDMS = silanol

polydimethylsiloxanes with methyltriacetoxysilane cross-linker) coating and storing the

specimens in the dark at room temperature and 33 'r relative humidity until analysis.

Exact details of the coating preparations can be found in the Experimental section. The

specimens were evaluated 24 h. after coating application using the pressure cell

attachment on the fluorimeter. The samples were illuminated with 450 nm light, and the

emission was evaluated at predetermined wavelength areas. This procedure was followed

to maintain consistency in coating characterization. The samples evaluated using the

fluorimeter were also evaluated using a calibration cell with CCD detection (as described

in the Experimental section). The calibration cell set-up monitors photoluminescence

utilizing a series of bandpass filters with an optical bandwidth of 40 nm FWHM.

Therefore in keeping with consistency, emission values obtained utilizing the fluorimeter

were calculated for areas rather than discrete wavelengths.

PtTFPP

The temperature dependence of PtTFPP photoluminescence was analyzed. The

luminescence intensity decreases moderately with increasing temperature at all pressures

from 0.1 14.7 psi. This is a typical behavior for many pressure probes. 16,57 Stern-

Volmer (SV) analysis of the solid coatings were conducted utilizing equation (2-2),

I(XPem, Pair = 1 atm)/ I(XPem, Pair) = A + BPair (2-2)

and (B/A) = Ksv. The pressure probe's response to oxygen quenching at different

temperatures yields linear SV plots with excellent correlation and high Ksv values. The

coatings are strongly pressure sensitive, as the total light intensity decreases by nearly a

factor of 10 when the pressure above the film increases from 0.1 14.7 psi. A SV plot

for each temperature is displayed in Figures 2-6 and 2-7 for the two coatings on primed

glass. The temperature dependence of the coatings' emission is evidenced by the "fan-

out" of the regression lines at higher pressure. Comparison of Figures 2-6 and 2-7

reveals that the pressure probe in the PtDOCI-Ssgsp/VPDMS coating is more

temperature-dependent than the PtDOCIpgsp/VPDMS coating.

0 2 4 6 8 10 12 14 16
Air Pressure (pi)

Figure 2-6: SV plot PtDOCIppsp/VPDMS coating on primed glass for temperatures
between 273 313 K. AREF: area between 630 670 nm at 14.7 psi and 313 K.

0 2 4 6 8 10
Air Pressure (psi)

12 14 16

Figure 2-7: SV plot PtDOCI-Sspsp/VPDMS coating on primed glass for temperatures
between 273 313 K. AREF: area between 630 670 nm at 14.7 psi and 313 K.

For the SV analysis, the data for the percent decrease in PtTFPP emission area at

each pressure as a function of oxygen concentration for a change in temperature are listed

in Tables 2-1 and 2-2 for the two coatings on primed glass. At all pressures, the

corresponding percent change in emission is consistent and provides evidence for a well-

behaved oxygen sensing coating. These numbers are consistent with ones obtained by

Puklin et al. for PtTFPP dispersed in fluoroacrylic polymer (FIB) and

poly(methylmethacrylate) (PMMA) polymers.57

Table 2-1: Percent change in PtTFPP emission area at seven pressures over a 40 K range
for PtDOCIpp.sp/VPDMS coating on primed glass.
Pressure (psi) AA %-K-'
273 313 K
0.1 -1.05
2 -0.78
4 -0.55
6 -0.77
8 -0.57
10 -0.77
14.7 -0.80

Table 2-2: Percent change in PtTFPP emission area at seven pressures over a 40 K range
for PtDOCI-Ssgsp/VPDMS coating on primed glass.
Pressure (psi) AA %-K-1
273 313 K
0.1 -1.30
2 -0.73
4 -0.78
6 -0.78
8 -0.76
10 -0.87
14.7 -0.88

The thermal-stability of the pressure probe's photoluminescence was evaluated by

subjecting the samples to various pressures between 0.1 14.7 psi at specific

temperatures during a cyclic run from 273 -> 313 -- 273 -- 313 -- 273 K. Analysis of

the pressure probe's response to oxygen at each temperature reveals a consistent SV

response at all temperatures, and no indication of hysteresis or change in the coatings

morphology. The SV data at each temperature evaluated for the PtDOCIppsp/VPDMS

and PtDOCI-Sspsp/VPDMS coatings are presented in Tables 2-3 and 2-4, respectively.

Table 2-3: SV analysis of PtTFPP emission quenching in PtDOCIppsp/VPDMS coating
on primed glass for a cyclic temperature run.
Temperature Run Intercept" Slope (psi')b r Ksv (psi-1)
273 K 1 0.064 0.067 0.990 1.05
293 K 1 0.051 0.067 0.995 1.31

313 K 1 0.030 0.065 0.998 2.17
293 K 2 0.048 0.066 0.995 1.38
273 K 2 0.063 0.067 0.991 1.06
293 K 3 0.047 0.067 0.996 1.43
313 K 3 0.031 0.065 0.938 2.10
293 K 4 0.056 0.067 0.994 1.20
273 K 4 0.051 0.067 0.995 1.31
intercept = A in equation (2-2), b slope = B in equation (2-2), c Ksv = B,

/A

Table 2-4: SV analysis of PtTFPP emission quenching in PtDOCI-Ss.sp/VPDMS
coating on primed glass for a cyclic temperature run.

Temperature
273 K
293 K
313 K

Run
1
1
1

Intercept"
0.047
0.024
0.029

Slope (psi' )b
0.067
0.067
0.067

R2
0.995
0.999
0.999

Ksv (psi')c
1.43
2.79
2.31

293 K 2 0.025 0.068 0.999 2.72
273 K 2 0.027 0.068 0.999 2.52
293 K 3 0.016 0.068 0.999 4.25

313 K
293 K
273 K
a intercept = A in

3
4
4
equation

0.025
0.070
0.026
(2-2), b

0.067 0.999
0.062 0.986
0.068 0.998
slope = B in equation (2-2),

2.68
0.88
2.62
SKsv = B/A

As can be seen in Tables 2-3 and 2-4, Ksv increases with temperature. This is not

surprising, since the diffusion of oxygen in a polymer is a thermally activated

phenomenon.55 Raising the temperature increases the diffusion rate of oxygen thereby

enhancing the efficiency of luminescence quenching.67 Even though small changes in

--

the intercept value can greatly affect the calculated Ksv value. The Ksv values in Tables

2-3 and 2-4 do not differ significantly and indicate that the coating is stable with respect

to repeated thermal cycling over the 273 313 K range.

DOCIppsp and DOCI-Sspsp

The temperature dependence of the photoluminescence from the DOCIpjisp and

DOCI-Ssgsp temperature probes was evaluated. The luminescence intensity of either

temperature probes did not vary significantly with change in pressure at a constant

temperature; however, it did decrease with increasing temperature.

The emission spectra for both coatings at 0.1 psi and five temperatures between

273 313 K are displayed in Figures 2-8 and 2-9 for the PtDOCIpglsp/PDMS and

PtDOCI-Ssgsp/VPDMS coatings on primed glass, respectively.

50000
273 K
-- -283 K
S40000 293 K /
303 K
..... 313K 33\
30000 .

0 20000 -

10000 -

500 550 600
Wavelength (nm)

Figure 2-8: Emission intensity spectra for DOCIpgsp in PtDOCIpjisp/VPDMS coating
on primed glass at 0.1 psi for five temperatures between 273 313 K.

14000

2 -- 293 K

4000 .

Wa elengh (nmi

Figure 2-9: Emission intensity spectra for DOCI-Sspsp in PtDOCI-Sspsp VPDMS
coating on primed glass at 0.1 psi for five temperatures between 273 313 K.

Analysis of the response of the temperature probes' emission at specific

temperatures from 273 313 K are displayed in Figures 2-10 and 2-11 for the

PtDOCIppsp, VPDMS and PtDOCI-Sspsp V'PDS coatings. respecti\elv. The origins of

the probes' temperature dependence and pressure independence will be discussed later in

the chapter.

1.05

1.00

0.95

0.90

S0.85

0.80

0.75 -0- 0.1 psi
-- 4 psi
0.70 --- 8 psi
-.>-0- 14.7 psi
0.65
270 280 290 300 310 320
Temperature (K)

Figure 2-10: Temperature dependence of emission for DOCIpgsp in
PtDOCIpptsp/VPDMS coating on primed glass for a series of pressures between 0.1 -
14.7 psi. AREF: area between 530 570 nm at 273 K and 0.1 psi.

1.05

1.00

0.95

S0.90

0.85

0.80 0.1 psi
-- 2 psi
0.75 1-- 8 psi
-0- 14 psi
0.70
270 280 290 300 310 320
Temperature (K)

Figure 2-11: Temperature dependence of emission for DOCI-Sslsp in PtDOCI-
Ssgsp/VPDMS coating on primed glass for a series of pressures between 0.1 14.7 psi.
AREF: area between 530 570 nm at 273 K and 0.1 psi.

The temperature dependence was nearly linear over the temperature range 273 -

310 K with a slope of the linear correlation of approximately 0.80 %-K-~ for Figure 2-10

and 0.54 %-K-1 for Figure 2-11. For the PtDOCIplsp/VPDMS coating, 0.80 %-K-1

correlates well with the percent change in emission area as a function of temperature for

each pressure displayed for Run 1 of Table 2-5. The temperature dependence at assorted

pressures varied between 0.69 to 0.80 %-K' for the temperature range 273 --- 313 K.

For the PtDOCI-SspspIVPDMS coating, the 0.54 %-K'' value agrees with the percent

change in emission area as a function of temperature for each pressure displayed for Run

1 of Table 2-6. The temperature dependence varied between 0.33 to 0.66 '-K'.

Compared to DOClppsp emission variation in Table 2-5, DOCI-Sspsp exhibit less

temperature dependence at each pressure with greater breadth in the distribution of

percent change from pressure to pressure. These are both undesirable features and

provide evidence for DOCIppsp as the better temperature-sensitive probe.

Table 2-5: Percent change in DOCIplpsp emission area at seven pressures over a cyclic
temperature run of 40 K for PtDOCIppsp/VPDMS coating on primed glass.
Pressure (psi) AA % %-' %-K AA' %-K-' AA %-K'
273 313 K 313 273 K 273 313 K 313 273 K
Run 1 Run 2 Run 3 Run 4
0.1 0.74 0.60 0.75 0.63
2 -0.69 0.60 0.73 0.54
4 0.78 0.64 0.80 0.62
6 0.76 0.60 0.70 0.59
8 0.75 0.64 0.73 0.56
10 0.79 0.55 0.70 0.57
14.7 -0.80 0.62 -0.63 0.52

Table 2-6: Percent change in DOCI-Ssgsp emission area at seven pressures over a cyclic
temperature run of 40 K for PtDOCI-Ssisp/VPDMS coating on primed glass.
Pressure (psi) AA %-K-1 AA %-K'1 AA %-K-' AA %-K1
273 313 K 313 273 K 273 313 K 313 273 K
Run 1 Run 2 Run 3 Run 4
0.1 0.63 0.60 0.47 0.52
2 0.44 0.44 0.40 0.47
4 -0.48 0.41 -0.43 0.51
6 0.33 0.25 0.40 0.55
8 -0.41 0.49 -0.62 0.61
10 0.34 0.40 0.44 0.45
14.7 0.40 0.53 0.61 0.48

The data for the thermal-stability of the temperature probes' emission obtained by

subjecting the samples to cyclic temperature changes from 273 -- 313 -- 273 -- 313 --

273 K is outlined in Tables 2-5 and 2-6. Three trends from these tables should be noted.

(1) The DOCIpgsp exhibit greater temperature dependence when the coating is heated

then when it is cooled. (2) The DOCI-Ssg.sp display a consistent temperature-

dependence when the coating is heated or cooled. (3) Both probes' emission intensity

response is appreciable with changes in temperature yet reproducible and thermally stable

throughout the cyclic run of temperatures. This last characteristic will allow for

correction of the photoluminescence temperature dependence exhibited by the PtTFPP

pressure probe.63-65

Emission Intensity

Throughout the thermal cycling experiments, the stability of not only the probes'

responses to oxygen pressure and temperature changes were monitored but the stability of

the probes' overall intensity was monitored as well. The magnitude of the emission

intensity data for both the pressure and temperature probes did not change during the

thermal cycling. This is an indication that the photoluminescence of both coatings is not

only responsive to repeated pressure and temperature changes but the magnitude of the

probes' luminescence intensity is stable as well.

Temporal-stability

The stability of photoluminescence emission intensity over time was analyzed for

the PtDOCIppp/VPDMS and PtDOCI-Sspsp/VPDMS coatings. To better understand

possible influences one luminophore might impart on the other over time, the individual

luminophorcs in VPDMS polymer were separately analyzed. The coatings, dual- and

mono-luminophore, were applied to plain and primed (TiO2/SPDMS) borosilicate

microscope slides and stored in the dark at room temperature and 33 % relative humidity.

For each spectroscopic analysis, the specimen slides were scored and a fresh piece

broken-off for evaluation of the photoluminescence properties. The specimen was

excited with 450 nm light, and emission was monitored from 475 800 nm. Particular

emphasis vwa placed on evaluating the areas under the emission curve between 530 570

nm for the temperature probes and 630 670 nm for the pressure probe at seven distinct

pressures in the range of 0.1 and 14.7 psi. All spectroscopic evaluations were conducted

at room temper.lture.

PtTFPP

The area of emission for the PtTFPP pressure probe (X = 630 670 nm) in the

PtDOCIppsp/VPDMS, PtDOCI-Ssgsp/VPDMS and PtTFPP/VPDMS coatings was

evaluated for its response to oxygen pressure. The coatings were analyzed at weekly

intervals for the first month after application and then at monthly intervals for a total

period of four or eight months. Stern-Volmer (SV) analysis of the pressure probe's

response to quenching at seven different pressures was performed for each analysis, and

the data are displayed in Tables 2-7, 2-8, and 2-9 for the coatings on bare glass and Table

2-10, 2-11, and 2-12 for the coatings on primer.

Table 2-7: SV Analysis of PtTFPP emission quenching in PtDOCIpgsp/VPDMS coating
on bare glass.

Time Intervala Interceptb Slope (psi')
24 h 0.046 0.065
1 wk 0.031 0.066
2 wk 0.020 0.066

r2
0.994
0.998
0.999

Ksv (psi-1)d
1.43
2.16
3.23

3 wk 0.030 0.068 0.998 2.28
4 wk 0.011 0.067 0.999 5.96
4 mo 0.015 0.069 0.985 4.56
8 mo 0.045 0.068 0.986 1.51

a fresh sample used for each SV measurement,
slope = B in equation (2-2),

intercept = A in equation (2-2), c
d Ksv = B/A

Table 2-8: SV Analysis of PtTFPP emission quenching in PtDOCI-Ssgsp/VPDMS

coating

Time Intervala
24 h

1 wk
2 wk
3 wk

4 wk
2 mo
4 mo

Intercept
0.048
0.023
0.031
0.055
0.018
0.047
0.018

on bare glass.
Slope (psi-)c
0.067

0.068
0.066
0.067
0.068
0.063
0.065

a fresh sample used for each SV measurement,
slope = B in equation (2-2),

0.995

0.999
0.999
0.992
0.995
0.992
0.998

Ksv (psi-')
1.40

2.96
2.13
1.22
3.78
1.34
3.61

intercept = A in equation (2-2),
d Ksv = B/A

r

Table 2-9: SV Analysis of PtTFPP emission quenching in VPDMS polymer on bare
glass.

Time Interval'
24 h
1 wk
2 wk
3 wk
4 wk
2 mo

4 mo
8 mo

Intercept"
0.100
0.054
0.110
0.047
0.083
0.135
0.111
0.072

Slope (psi')c
0.067
0.068
0.061
0.067
0.063
0.065
0.068
0.064

rz
0.969
0.986
0.995
0.995
0.981
0.965
0.946
0.979

Ksv (psi-')'
0.670
1.26
0.555
1.43
0.759
0.481
0.613
0.889

a fresh sIplle used for each SV measurement. intercept = A in equation (2-2), c
slope = B in equation (2-2), d Ksv = B/A

Table 2-10: SV Analysis

of PtTFPP emission quenching in

PtDOCIppsp/VPDMS

Time Intervala
24 h
1 wk
2 wk
3 wk
5 wk
4 mo

coating on primed glass.
Intercept" Slope (psi1)C
0.005 0.068
0.011 0.067
0.013 0.068
0.016 0.065
0.017 0.067
0.042 0.066

8 mo 0.018 0.065 0.996 3.70
a fresh saliple used for each SV measurement, b intercept = A in equation (2-2),
slope = B in equation (2-2), d Ksv = B/A

Table 2-11: SV Analysis of PtTFPP emission quenching in PtDOCI-Sspsp/VPDMS

Time Interval"
24 h
1 wk
2 wk
3 wk

4 wk
2 mo
3 mo
4 mo

a fresh sample used

coating on primed glass.
Intercept" Slope (psi')c
0.020 0.067
0.024 0.068
0.017 0.067
0.047 0.068
0.030 0.067
0.042 0.066
0.061 0.066
0.045 0.066

for each SV measurement. b
slope = B in equation (2-2),

2

r2
0.999
0.999
0.999
0.993
0.998
0.999
0.996
0.998

Ks, (psi")d
3.35
2.83
3.94
1.45
2.23
1.57
1.08
1.47

intercept = A in equation (2-2), c
d Ksv = B/A

rZ
0.999
0.999
0.999
0.997
0.999
0.999

Ksv (psi")d
14.4
5.96
5.14
4.09
4.01
1.56

~

--

I

Table 2-12: SV Analysis of PtTFPP emission quenching in VPDMS polymer on primed
glass.
Time Intervala Interceptb Slope (psi-')e r2 Ksv (psi-l)d
24 h 0.025 0.067 0.999 2.68
1 wk 0.033 0.067 0.999 2.03
2 wk 0.028 0.067 0.999 2.39
4 wk 0.019 0.067 0.999 3.53
8 mo 0.028 0.066 0.998 2.36
a fresh sample used for each SV measurement, intercept = A in equation (2-2),
slope = B in equation (2-2), d Ksv = B/A

Over a four- or eight-month period, the coatings retained an excellent response to

variation in Pa,i as evidenced by the high Ksv values in Tables 2-7 to 2-12. At all time

intervals, SV evaluation results in steep linear plots with minimal fluctuations in the

intercept values a small intercept value indicates excellent coating sensitivity to oxygen

concentration. The small variations in intercept however translate into large overall

variations in Ksv values. The most noticeable variation in Ksv is for the

PtDOCIpgsp/VPDMS coating on primed glass 24 h. after application. The Ksv value of

14.4 psi' is 3.5 times larger than the average Ksv value, 4.08 psi-', for subsequent time

intervals. The increased Ksv value is possibly due to photolysis of the coating and not

necessarily a consequence of oxygen pressure.

Complt ison of the intercept and Ksv values from Tables 2-7, 2-8, 2-10, and 2-11

to those in Tablcs 2-9 and 2-12, makes it is clear that the sensitivity of PtTFPP emission

to oxygen pressure is more sensitive in the dual-luminophore coatings than in the mono-

luminophore coating. Enhancement of PtTFPP's emission sensitivity in the dual-

luminophore coatings is a beneficial finding which counters negative effects seen in other

dual-luminophore coatings.70

DOClppsp and DOCI-Sspsp

Anals is of the area of the photoluminescence spectrum for the DOCIppsp and

DOCI-Ssgsp (X = 530 570 nm) temperature probes resulted in fairly consistent

emission intensity that was unaffected by oxygen pressure. The emission intensity areas

for each pressure were averaged (this is assuming that the emission intensity does not

fluctuate gre.lly with variation in Pair), and the coefficient of variation (CV %) (the

standard devi.ation of average emission intensity area divided by the average emission

intensity arei) '.\;s determined for each time interval analysis. The CV % statistically

describes the dlce-rcc of variance in the emission intensity areas of seven spectral emission

scans for prc,,utres between 0.1 14.7 psi. Since the temperature probe is ideally

pressure insclnitive, a low CV is expected. The CV % data at different time intervals

for the tempcililure probes are presented in Tables 2-13 and 2-14 for the

PtDOCIpgsp/VI'DMS and PtDOCI-Sspsp/VPDMS coatings on bare and primed glass.

Table 2-13: Analysis of the area under the emission curve for DOClppsp in
PtDOCIppsp/VPDMS coating on bare and primed glass.
Time lterval" CV % for glass Time Interval' CV % for primer"
24 h 3.26 24 hr 1.23
1 wk 6.14 1 wk 4.87
2 wk 5.06 2 wk 3.64
3 wk 7.25 3 wk 2.98
4 wk 3.76 2 mo 4.92
4 mo 2.97 4 mo 4.45
8 mo 1.41 8 mo 6.47
a fresh sample used for each SV measurement, b CV % for seven emission scans of the
sample obtained at pressures between 0.1 14.7 psi.

Table 2-14: Analysis of the area under the emission curve for DOCI-Ssgsp in PtDOCI-
Ssgsp/VPDMS coating on bare and primed glass.
Time Intervala CV % for glass Time Intervala CV % for primerb
24 h 3.75 24 h 2.94
I wk 3.29 1 wk 3.33
2 wk 4.06 2 wk 5.95
3 wk 5.82 3 wk 9.24
4 wk 3.31 4 wk 4.82
2 mo 9.15 2 mo 2.99
4 mo 3.65 3 mo 6.81
8 mo 7.74 4 mo 1.26
a fresh sample used for each SV measurement, bCV % for seven emission scans of the
sample obtained at pressures between 0.1 14.7 psi.

The DOCIppsp and DOCI-Ssgsp temperature probes were also analyzed

separately in the VPDMS polymer binder. This was done to prove that the emission of

the dyed-microspheres is not quenched by oxygen, regardless if the microspheres were

dispersed in VPDMS with or without the PtTFPP oxygen sensing probe. The CV % data

for dyed-microspheres in VPDMS on bare and primed glass are presented in Tables 2-15

and 2-16.

Table 2-15: Analysis of the area under the emission curve for DOCIppsp in VPDMS
polymer on bare and primed glass.
Time Intervala CV % for glass Time Intervala CV % for primerb
24 h 8.36 24 h 6.82
1 wk 11.5 1 wk 6.92
2 wk 12.7 2 wk 3.96
3 wk 11.8 3 wk 6.95
4 wk 9.04 5 wk 7.01
4 mo 4.48 4 mo 4.32
8 mo 7.04 8 mo 9.29
a fresh sample used for each SV measurement, b CV % for seven emission scans of the
sample obtained at pressures between 0.1 14.7 psi.

Table 2-16: Analysis of the area under the emission curve for DOCI-Ssisp in VPDMS
polymer on bare and primed glass.
Time Intervala CV % for glass Time Interval' CV % for primer
24 h 10.2 24 h 10.2
1 wk 8.78 1 wk 16.1
3 Ak 11.8 2 wk 13.3
4 wk 12.3 3 wk 15.3
2 ino 16.9 4 wk 8.95
4 mo 6.78 2 mo 4.57
8 mo 6.21 4 mo 17.1
8 mo 7.16
a fresh samlpk used for each SV measurement. CV % for seven emission scans of the
sample obtained at pressures between 0.1 14.7 psi.

Inspection of Tables 2-13 to 2-16 reveals that the data are similar. The variance

in the emission response for the dyed-microspheres is characteristic to the spheres and is

not influenced by dual-luminophore interactions.

Emission Intlnisity

Throughout the temporal-stability experiments, the magnitude of emission

intensity for the pressure and temperature probes' responses to oxygen pressure was

monitored. The -lmission intensity data for both probe types decreased by an order of

magnitude betv cen their respective first to last and final interval emission scans. This

effect was consilent for the coatings on glass but not for the coatings on primer. Only

the emission inicnsity of the PtTFPP, DOClppsp. and PtDOCIppsp in VPMDS on primer

decreased by an order of magnitude between their first to last and final interval emission

scans. The en io i intensity of the DOCI-Sslisp and PtDOCI-Sslsp in VPDMS on

primer were st.ible throughout the interval emission scans. The decrease in emission

intensity is not detrimental to the coatings, since the decrease in emission intensity did

not hinder the SV response of the pressure probe. Nor did it increase the small variance

in emission int: insity exhibited by the temperature probes to variation in Pair.

Photostability

The stability of the photoluminescence intensity to continuous illumination for a

period of four hours was examined for the PtDOCIppsp/VPDMS and PtDOCI-

Ssgsp/PDMS coatings. To better understand possible influences one luminophore

might impart on the other over time, the individual luminophores were also analyzed

separately. The coatings, dual- and mono-luminophore, were air-brushed onto plain and

primed (TiO2/SPDMS) borosilicate microscope slides. After application, the coatings

were stored in the dark at room temperature and 33 % relative humidity. The coating

samples were illuminated with 450 nm light with a 50-W arc-bulb, and emission was

monitored from 475 800 nm. A fresh specimen piece was broken-off the respective

prepared slide for each photostability experiment. Illumination was initiated at time

equals zero and an emission scan was obtained every 30 min. These experiments were

carried out in the fluorimeter. Particular emphasis was placed on evaluating the area

under the emission curve between 530 570 nm for the temperature probes and 630 630

nm for the pressure probe at two pressures, 5 and 14.7 psi, and room temperature.

PtTFPP

The phot abilityiy of the photoluminescence of the PtTFPP pressure probe (X =

630 670 nm) in PtDOCIpgsp/VPDMS and PtDOCI-Ssgsp coatings was evaluated at 5

and 14.7 psi. Analysis of the relative PtTFPP emission intensity versus time is displayed

in Figure 2-12 for the PtDOCIplsp/PDMS coating on bare and primed glass, in Figure

2-13 for the PtDOCI-Ssgsp/PDMS coating on bare and primed glass, and in Figure 2-

14 for PtTFPP in VPDMS polymer coating on bare and primed glass as a comparison.

1.2
-- 5 psi on glass
-0- 5 psi on primer
14.7 psi on clhis
I1I V 14.7 psi on primer
i ; v

10

0.9

0 30 60 90 120 Ic i 210 240
I ime (minutes)

Figure 2-12: Photostability of PtTFPP emission in PtDOCIppsp'VPDIMS coating on bare
and primed glass at 5 and 14,7 psi and RT. ArI : area between 630 670 nm at 240
min.

15 -
--0- p'"' gl.eh
1.4 5 psi on primer
-W 14 7 psi on glass
13 14.7 psi on primer

3 12i

0 8 ----r'~ '--r-- --_-
< I

0 30 60 90 120 1 '1 I l 210 240
lime (minutes)

Figure 2-13: Photosiability of PtTFPP emission in PtDOCI-Sspsp'VPDMS coating on
bare and primed glass at 5 and 14.7 psi and RT. A, HF: area between 630 670 nm at
240 min.

1.2

1.1

1.0

0.9

0.8
-*- 5 psi on glass
0.7 5 psi on primer
--- 14.7 psi on glass
O 14.7 psi on primer
0.6 -I I
0 30 60 90 120 150 180 210 240
Time (minutes)

Figure 2-14: Photostability of PtTFPP emission in VPDMS polymer coating on bare and
primed glass at 5 and 14.7 psi and RT. AREF: area between 630 670 nm at 240 min.

The photostability of the photoluminescence of the PtTFPP pressure probe in the

PtDOCIpgsp/VPDMS and PtDOCI-Ssgsp/VPDMS coatings exhibits minimal random

fluctuations in intensity ratio over the four-hour period. These results are within a

standard deviation of error for each scan point and similar to photostability experiments

conducted by Lee and Okura for PtTFPP in polystyrene.74 The PtDOCI-SsgspNPDMS

coating on primed glass at 14.7 psi experiences a decline in photoluminescence emission

intensity over the first 60 90 minutes of illumination. This "photolysis period", only

exhibited for one pressure condition of the photostability experiments, is not uncommon,

and has been observed by other groups not only for the PtTFPP luminophore but for other

Pt(II) porphyrin macrocycles. 16,74

The photostability of the photoluminescence of the PtTFPP pressure probe in

VPDMS polymer without incorporation of the dyed-microspheres behaves similarly to

the PtDOCIpgsp/PDMS coating. Therefore, the PtTFPP ratioed emission intensity

exhibits minor fluctuations over the time period that are not dependent on chemical or

physical interactions with the temperature probes.

DOCIpplsp and DOCI-Sspsp

The photostability of the photoluminescence of the DOCIpp.sp and DOCI-Sspsp

temperature probes (X = 530 570 nm) in PtDOCIppsp/VPDMS and PtDOCI-Sspsp

coatings were evaluated at 5 and 14.7 psi. Analysis of the relative DOCIppsp emission

intensity versus time is displayed in Figure 2-15 for the PtDOClppsp VPDMS coating on

bare and primed glass. The relative DOCI-Ssisp emission intensity versus time is

depicted in Figure 2-16 for the PtDOCI-Sspsp/VPDMS coating on bare and primed glass,

and the relative emission intensities of the DOCIppsp and DOCI-Sspsp temperature

probes, dispersed separately in VPDMS polymer coating without incorporation of the

PtTFPP pressure probe, versus time are illustrated in Figures 2-17 and 2-18, respectively,

as a comparison.

1.8
17" -*- 5 psi on glass
-- 5 psi on primer
1.6 14.7 psi on glass
1.5 0 14.7 psi on primer

1.3
I .4
< 1.2

1.0
0.9
0.8
0 31i 60 1() 120 150 i si1 210 24n1
Time (minutes)

Figure 2-15: Photostability of DOClppsp relative emission intensity in
PtDOCIppsp'VPDMS coating on bare and primed glass at 5 and 14.7 psi and RT. AREF:
area between 530 570 nm at 240 min.

1.3

1.2
.? 1.1

1.1

0.9
-*- 5 psi on glass
0.8 -- 5 psi on primer
--- 14.7 psi on glass
O 14.7 psi on primer
0.7
0 30 60 90 120 150 180 210 240
Time (minutes)

Figure 2-16: Photostability of DOCI-Sspsp relative emission intensity in PtDOCI-
Sspsp/VPDMS coating on bare and primed glass at 5 and 14.7 psi and RT. AREF: area
between 530 570 nm at 240 min.

0 30 60 90 120 150 180 210 240
Time (minutes)

Figure 2-17: Photostability of DOCIpgsp relative emission intensity in VPDMS polymer
coating on bare and primed glass at 5 and 14.7 psi and RT. AREF: area between 530 -
570 nm at 240 min.

142

S1.0

0.8
--0 5 psi on glass
0.6 5 psi on primer
--- 14.7 psi on LJ.1.i
0 14.7 psi on primer
0.4
0 ( 0 60 90 120 150 ImS 210 240
Time (minutes)

Figure 2-18: Photostability of DOCI-Sspsp relative emission intensity in VPDMS
polymer coating on bare and primed glass at 5 and 14.7 psi and RT. ARFF: area between
530 570 nm at 240 min.

The photoluminescencc of the temperature probes in PtDOClppsp. VPDMS and

PtDOCI-Sspsp coatings is less photostable than that of the PtTFPP pressure probe in the

same coatings. The DOClppsp temperature probe in the PtDOClppsp VPDMS coating

on bare and primed glass exhibits a decrease in relative emission intensity over the 240

min. time period at both pressures. The results for the percent photodegradation are listed

in Table 2-17.

Table 2-17: Percent photodegradation of the relative emission intensity for DOCIppsp in
PtDOClppsp/VPDMS coating on bare and primed glass.
Pressure (psi) Glass Primer
5 0.119 %-min" 0.77 no-min'
14.7 0.094 o-min- 0.179 o-mini1

The DOCI-Sspsp temperature probe in the PtDOCI-Sspsp coating on bare glass

experiences minor fluctuations in relative emission intensity over the four-hour time

period. However, the relative emission intensity decreases over the 240 min. time period

for the coating on primed glass. The results for the percent photodegradation of the

coating on primed glass are listed in Table 2-18.

Table 2-18: Percent photodegradation of the relative emission intensity for DOCI-Ssjlsp
in PtDOCI-Ssgsp/VPDMS coating on primed glass.
Pressure (psi) Primer
5 0.028 %-min-
14.7 0.079 %-min-

DOCIpgsp and DOCI-Ssjisp, dispersed separately in VPDMS polymer without

PtTFPP incorporation, display relative emission intensity plots versus time which are

scattered from point to point, however, the scatter from point to point is within the one

standard deviation error bars. Therefore the emission intensity for the temperature probes

in the VPDMS polymer coating is stable over the four-hour illumination period and

unaffected by chemical or physical interactions with the PtTFPP luminophore.

Scanning and Transmission Electron Microscopy

Scanning electron microscopy (SEM)

SEM was used to image the two types of microspheres used in this work. Images

were obtained on the undyed samples as well as on the dyed samples that were used in

the coating preparations. The method used to prepare the SEM specimens is discussed in

the Experimental section.

DOCIppsp. The poly(divinylbenzene) microspheres were prepared by

precipitation polymerization. A typical image of the microspheres prior to DOCI (3,3'-

diethyloxacarbocyanine iodide) adsorption is illustrated in Figure 2-19. All images

display the microspheres as aggregates of large and small particles.

Figure 2-19: Scanning electron micrograph of precipitation microspheres (ppsp)(5 vol '-
of DVB55; acetonitrile). The scale bar consists of 11 white vertical lines and is 5 Pim
long from the first line to the last line.

The larger particles are 3 to 5 jim in size while the smaller particles are as tiny as

0.5 Jpm. The polymer particles possess a nonspherical shape and no evidence of pore

formation. It appears that in some instances the particles are fused together. This fusion

is most likely a consequence of an earlier stage in their growth.75

Placing carbon tape on an aluminum stud and pressing it against the above-

prepared sample fractured the polymer particles. The fractured microspheres were

transferred to the carbon tape and sputter-coated with 15 nm of gold As a result of

fracturing the polymer particles, a closer look of their interior morphology \% as obtained

and imaged in Figure 2-20.

Figure 2-20: Scanning electron micrograph of fractured precipitation microspheres
(ptsp)(5 vol % of DVB55; acetonitrile). The scale bar consists of 11 white vertical lines
and is 1.5 jpm long from the first line to the last line.

Magnification of the microspheres depicts the fusion of the smaller particles to the

larger particles as seen in the upper half and left side of the figure. The sphere in the

center of the figure exhibits jagged incisions due to the crushing process. Closer analysis

of the exterior and interior morphologies reveals a cauliflower-like surface. This effect is

most likely due to pore formation at the sub-micron level.75

When 3,3'-diethyloxacarbocyanine iodide (DOCI) was adsorbed onto the

microspheres, the particles possess a more spherical swollen shape with no evidence of

pore formation. Figure 2-21 displays a typical cluster of swollen 7.27 wt. % DOCI

adsorbed microspheres (DOCIpjtsp).

Figure 2-21: Scanning electron micrograph of precipitation microspheres (5 vol I' of
DVB55; acetonitrile) with 7.27 wt. % adsorbed DOCI (DOCIppsp). The scale har
consists of 11 white vertical lines and is 2.31 p.m long from the first line to the last line.

Again, the particles were fractured to display the interior morphology imaged in

Figure 2-22. Magnification of the polymer particles reveals that the interior and exterior

morphologies are tightly polymeriied spheres creating .mall pores.

Figure 2-22: Scanning electron micrograph of fractured precipitation microspheres (5 vol
c of DVB55; acetonitrile) with 7.27 wt. % DOCI (DOCIppsp). The scale bar consists of
11 white vertical lines and is 750 nm long from the first line to the last line.

DOCI-Sspp. The poly(divinylbenzene) microspheres were also prepared via

suspension polymerization, sulfonated, and negatively charged. A typical image of the

microspheres prior to dye adsorption is displayed in Figure 2-23.

Figure 2-23: Scanning electron micrograph of negatively charged, sulfonated, suspension
microspheres (Ssgp-)(45 vol % of DVB55; l-dodecanol:toluene = 1:1). The scale bar
consists of 11 white vertical lines and is 10 gm long from the first line to the last line.

Polymerization produced a variety of microsphere sizes. The majority are 3 gm

and smaller; although, some are as large as 8 to 10 plm. The microspheres exhibit a

porous structure due to the use of a porogen 1-dodecanol nonsolvent.76 The larger 8 to

10 [im polymer particles possess larger pores but are also more agglomerated and less

spherical than the smaller microspheres. St6ver reported similar character in porosity,

shape, and size distribution of poly(divinylbenzene) microspheres polymerized with

increased percentages of porogen nonsolvent.76

The interior morphology was revealed upon fracturing the microspheres. Figure

2-24 illustrates how the porous nature of the exterior surface is channeled throughout the

interior morphology.

Figure 2-24: Scanning electron micrograph of fractured negatively charged, sulfonated.
suspension microspheres (Ssppp) (45 vol % ofDVB55; l-dodecanol:toluene = 1:1). The
scale bar consists of 11 white vertical lines and is 750 nm long from the first line to the
last line.

DOCI was adsorbed onto the charged, sulfonated, suspension microspheres

(Ssppp) replacing the Na' counter ion. Figure 2-25 reveals that some of the mIicrospheres

are spherical while others are fractured from the preparation procedure. The most

noticeable feature of these spheres is the appearance of a "sticky film" connecting and

covering the spheres.

Figure 2-25: Scanning electron micrograph of fractured negatively charged, sulfonated,
suspension microspheres (45 vol % of DVB55; 1-dodecanol:toluene = 1:1) with 3.83 wt.
% adsorbed DOCI (DOCI-Ssgsp). The scale bar consists of 11 white vertical lines and is
2.73 gm long from the first line to the last line.

The film forms an incomplete coating across the spheres in the left side of the figure and

a bridge connecting a larger particle and its nearest neighbors in the image right of center.

The film appears to be less than 1 gm thick, and its origins are unknown. However, its

existence was reproducible in additional SEM preparations.

SPDMS and VPDMS incorporating DOCIppsp or DOCI-Ssisp. Clusters of

microspheres penetrating the surface of the coating are observed when a thin film of

SPDMS (silanol polydimethylsiloxanes and methyltriacetoxysilane cross-linker)

containing DOCIpglsp (7.27 wt. % DOCI) (prepared by air-brush; approximately 10 jim

thick) was imaged by SEM. The randomness and irregularity of the microspheres'

distribution and size can be clearly seen in Figure 2-26. This image compliments

findings presented later in the chapter which utilize fluorescence microscopy to describe

the distribution of the microspheres in the polymer binder, Figure 2-30.

Figure 2-26: Scanning electron micrograph of the surface of a thin film (- 10 pm) of
SPDMS containing DOCIpgsp (7.27 wt. % DOCI)(5 vol of DVB55; acetonitrile). The
scale bar consists of 11 white vertical lines and is 5.02 pm long from the first line to the
last line.

A thin film of VPDMS (vinyl polydimethylsiloxanes) containing DOCIpsp (7.27

wt. % DOCI) was more difficult to image than the DOCIppsp in SPDMS polymer binder.

The surface of DOCIppsp in the VPDMS film did not produce characteristic clusters of

microspheres. Only random indentations and crevices are found which are due to either

the morphology of the polymer cure, dust particles or embedded microspheres. However

upon fracturing the sample and imaging the interior film morphology, clusters of

microspheres are found and imaged in Figure 2-27.

Cluster of
microspheres

Film
Surface

Film
Interior
Glass
Substrate

Figure 2-27: Scanning electron micrograph of the interior morphology of a thin film (-
10 gm) of VPDMS containing DOCIplsp (7.27 wt. % DOCI)(5 vol % of DVB55;
acetonitrile). The scale bar consists of 11 white vertical lines and is 33.3 gm long from
the first line to the last line.

Magnification of the microsphere cluster is displayed in Figure 2-28. This image

further confirms scanning electron microscopy and fluorescence microscopy results

which indicate that the microspheres are not homogeneously distributed within the

polymer film.

Figure 2-28: Scanning electron micrograph of the interior morphology of a thin film (-
10 im) of VPDMS containing DOCIpp.sp (7.27 wt. % DOCI)(5 vol % of DVB55;
acetonitrile) (27X magnification of Figure 2-27). The scale bar consists of 11 white
vertical lines and is 1.20 im long from the first line to the last line.

DOCI-Ssp dispersed in VPDMS polymer could not be imaged with SEM. The

surface of the DOCI-SsLsp/VPDMS film did not reveal a globular texture as seen with

the DOCIppsp in SPDMS polymer (Figure 2-26). Fracturing of the DOCI-

Ssgsp/VPDMS sample did not reveal microspherical clusters of distinct microsphere

regions either. Two factors could be affecting the imaging. (1) It is possible that due to

the elastic nature of the VPDMS. the fractured specimen polymer binder close' over the

exposed interior region masking the microspheres.77 (2) The DOCI-Sspsp are smaller

than the DOCIpptsp and more difficult to image, since, as will be seen in the fluorescence

microscopy data, the DOCI-Ssl.sp are more evenly distributed and less clustered than the

DOCIppsp in the VPDMS polymer binder.

One solution to the problem of imaging is cooling the sample to 77 K, fractioning.

and using a cryostat-stage for the SEM imaging thereby precluding any negative effects

exhibited by the polymer's tendency to resume its shape at room temperature. This

option was not available at the time of the imaging. Regardless, it still does not guarantee

that the microsphere particles will be revealed and successfully imaged.

Transmission electron microscopy

Due to the elastomeric nature of the polydimethylsiloxane (PDMS) polymer

binders utilized in PSP/TSP coatings, the coatings exhibit rather poor mechanical

properties and were therefore difficult to microtome and analyze.77 However, after a

three month storage period at 50 % relative humidity, tris-(4,7-diphenyl-1,10-

phenanthroline)ruthenium (II) dichloride ([Ru(dpp)3]Cl2) dispersed SPDMS polymer was

sufficiently cured making it possible to microtome slices that were less than a 100 nm

thick. Visual and physical inspection of the SPDMS coating showed that cured SPDMS

was not as soft and pliable and easier to cleanly microtome than cured VPDMS polymer.

TEM images of the microtomed [Ru(dpp)3]C12 thin film are shown in Figure 2-29.

Due to the spraying application of the film, the SPDMS polymer is visualized as droplets.

Dark gray areas are indicative of increased electron density either from a single heavy

atom, Ru, or a high concentration of a low atomic weight atom, C, Si, O. The dark black

areas are the formvar resin used in sample preparation. The [Ru(dpp)3]C12 complex was

not discernable as discrete microcrystals, possibly due to the fact that its concentration

was low (i.e. 0.2 wt. % relative to polymer weight, 500 mg).

Figure 2-29: Transmission electron micrographs of a < 100 nm slice of [Ru(dpp)3]Cl2
dispersed in SPDMS polymer. (A) X4500 magnification of polymer, white scale bar is
3.0 ptm long and (B) X70000 magnification of polymer, white scale bar is 0.4 (pm long.

Energy dispersive spectroscopy (EDS)

Energy dispersive spectroscopy coupled with TEM was utilized to determine the

elemental composition of the darker droplet areas in Figure 2-29. The [Ru(dpp)3]Cl2

complex could not be identified, since its concentration at any one point was less than I

wt. % (the limit of detection for this method). However the atoms along the exterior of

the droplets (the darker areas of Figure 2-29 B) were identified as Si. The abundance of

silicon atoms along the exterior surface of the droplets is 3.29 times greater than the

abundance of interior droplet Si concentration. The ratio of Si was calculated by

determining the electron count from Si in the sample and Cu from the copper mesh disk

on which the polymer slice was attached. Ratio of Si = Edge/Interior =

(722/794)/(253/914) = 3.29.

Fluorescence Microscopy

Fluorescence microscopy techniques were employed to better understand the size

and distribution of [Ru(dpp)3]Cl2, PtTFPP, DOCIppsp, and DOCI-Ssgsp in the VPDMS

and SPDMS polymer binders. First, DOCIppsp and DOCI-Sspsp are analyzed for size

(length of particle major axis) and distribution (number of particles per region analyzed).

Second, the PtDOCIppsp/VPDMS and PtDOCI-Sspp/VPDMS film coatings are

analyzed for determination of the relative position of PtTFPP to the dyed-microspheres.

Third, the spatial distribution of the PtTFPP probe's luminescence response to oxygen

quenching in the PtDOCIpplsp/VPDMS and PtDOCI-Ssglsp/VPDMS films are evaluated.

Fourth, the evaluation of [Ru(dpp)3]Cl2 distribution in SPDMS binder.

Size and distribution of DOCIppsp and DOCI-Sspsp

The DOCIpp.sp (0.6 wt. %, relative to polymer weight, 500 mg) and DOCI-Sslsp

(0.2 wt. %, relative to polymer weight, 500 mg) were distributed separately in VPDMS

polymer binder. Two layers of each coating were air-brushed onto clean borosilicate

microscope slides. The DOCI-Sspsp/VPDMS film was approximately 5 pm thick, and

the DOCIppsp/VPDMS film was approximately 10 plm thick, as measured by

profilometry. The slides were analyzed using the inverted fluorescence microscope. A

detailed explanation for the system set-up is found in the Experimental section. For this

experiment, an IR filter, oc 50 % neutral density filter, and a 425 nm 40 nm, bandpass

filter were used in front of the 100-W mercury-bulb excitation source. The

DOCIpplsp/VPDMS film was imaged with the 40X objective and the DOCI-

SspspNPDMS film was imaged with the 40X objective set at 60X magnification by the

microscope's 1.5X magnification knob. The emission light was filtered through a 475

nm long-pass filter, and the side of the slide that was coated with the polymer film faced

the objective. Five regions of each coating were analyzed at an exposure time of 150

msec for the DOCIpglsp/PDMS film and 200 msec for the DOCI-SsgspNPDMS film.

Fluorescence microscope images of the DOCIpgspNPDMS and DOCI-

Ssgsp/PDMS films are displayed in Figure 2-30. Image A is 218 im x 173 im (1300 x

1030 pixels; calibration 0.168 gm-pixel-'). Image B is 146 pm x 115 [im (1300 x 1030

pixels; calibration 0.112 [lm-pixel-1). The images are representative of each film. Within

each image the white clusters and solo particles are defined by the DOCI fluorescence

emission detected from the microspheres.

Figure 2-30: Fluorescence microscope image of A) DOCIpgsp/VPDMS film and B)
DOCI-SsgspNPDMS film obtained with a CCD camera through a 40X and 60X
objective, respectively. White scale bar is 26.5 im and 17.8 pm long, respectively.

Five regions were imaged for each film. White clusters were considered one

microsphere object rather than counting the individual microsphere components. The

number of objects in each region for the DOCIpgsp/VPDMS and DOCI-Sslsp/VPDMS

films is given in Tables 2-19 and 2-20, respectively.

Table 2-19: Number of microsphere objects for five regions of the DOCIppsp/VPDMS
film.
Region Number of DOCIppsp Objects
1 94
2 56
3 61
4 75
5 62
Average 69.6 13.7

Table 2-20: Number of microsphere objects for five regions of the DOCI-Sslsp/VPDMS
film.
Region Number of DOCI-Sspp Objects
1 81
2 66
3 72
4 90
5 84
Average 78.6 8.57

For all of the microsphere objects counted, the objects' major axis lengths were

determined using a statistical imaging program. Sigma Scan Pro (SPSS Inc.). The

average and the standard deviation for the microsphere objects' lengths for each region

analyzed are given in Tables 2-21 and 2-22.

73

Table 2-21: Average and standard deviation of the microsphere objects' lengths for each
region of the DOCIpgsp/VPDMS film.
Region Objects' Average Length (gm)
1 6.04 5.97
2 2.46 + 1.31
3 3.93 + 3.20
4 4.24 + 4.20
5 2.10 0.46

Table 2-22: Average and standard deviation of the microsphere objects' lengths for each
region of the DOCI-Ssgsp/VPDMS film.
Region Objects' Average Length (pjm)
1 1.55 + 0.51
2 1.52 + 0.56
3 1.19 0.26
4 1.22 + 0.32
5 1.44 + 0.48

The lengths of the objects' major axes from the five regions analyzed for each

film are represented by histograms in Figure 2-31. The number of objects for a given

size range are plotted versus the length of the objects (0.5 gim bin increments).

SIllIllllllllIllllillhIlllHnlll nnlnnn l n nl nP y
0 3 6 9 12 15 18 21 24 27 30
Length of Major Axis (pnm)

140
120
g 100
90
0 80
60
Z 40
20

0 3 6 9 12 15 18 21 24 27
Length of Major Axis (rm)

Figure 2-31: Histogram of the microsphere objects' major axis lengths for A)
DOCIppsp/VPDMS film and B) DOCI-Ssgsp/VPDMS film. Vertical bars equal a 0.5
Lm length increment.

For the DOCIpgspNPDMS film, the microsphere object lengths' are in the range

of 0.5 to 30 im with a substantial number of objects between 2 7 pmr in length. For the

DOCI-SsLtsp/VPDMS film, the microsphere object lengths' are in the range of < 0.5 to

7.5 plm with a substantial number of objects between 0.5 2.5 lam in length. Considering

that the number of objects per region for each film is similar, the large number of objects

(- 140) for the DOCI-SsgspVPDMS film proves that the microspheres are smaller and

less aggregated than the microspheres of the DOCIppspNPDMS film. The measured

object lengths correlate well with the lengths determined from the SEM images. Figures

2-19 and 2-23.

The number and corresponding lengths of DOCIppsp particles in Tables 2-19 and

2-21 and the objective depth of focus (DOF) were used to predict the density distribution

of microspheres in the VPDMS polymer binder for any given region. In this analysis, the

DOF is 4 pam at 40X. (The DOF is defined as the length along the optical axis of the

microscope by which, for a constant level of the image, the focusing position of the

objective can be varied without disturbing the sharpness of the image at the center of the

field.)78 Since the numbers of objects for each region are within a standard deviation of

one another as were the respective object lengths, then it can be derived that a certain

number of microspheres of average length are distributed throughout the coating for a

known region of predetermined size. This is not to say that the microspheres are evenly

distributed throughout the coating; rather, for any region analyzed, an average number of

spheres with average length are found. For example, the DOCIppspNVPDMS film

average is (69.6 objects)/(4 pm x 218 pmr x 173 im) = 4.61x10-4 objects-pm"3.

For the DOCI-Ssgsp/VPDMS film, the 60X objective DOF is not known, but a

rough estimate using the fine focus adjustment of the microscope yields a 2 ptm

measurement for the DOF. By evaluating the microspheres' quantity and length data in

Tables 2-20 and 2-22, the numbers of objects for each region were within a standard

deviation of one another as were the respective object lengths. Therefore, a certain

number of microspheres of average length are distributed throughout the film for a

known region of thickness and size. For example, the DOCI-SslspNPDMS film

average is (78.6 objects)/(2 gm x 146 gm x 115 pm) = 2.34x10-3 objects-gm-3. Although

the DOCI-Ssgsp may not be evenly distributed throughout an analyzed region, an

average number of microspheres with average lengths are found in any region.

Relative distribution of PtTFPP, DOCIppsp, and DOCI-Sspsp

The position of the PtTFPP probe relative to the microspheres in the

PtDOCIppsp/VPDMS and PtDOCI-Ssgsp/PDMS films was determined using the

fluorescence microscope. Two layers of each formulation coating were air-brushed onto

clean borosilicate microscope slides, and the luminescence of the two luminophores

(PtTFPP and DOCIpgsp or DOCI-Ssgsp) was detected. Three images from each coating

were obtained using the 40X objective, IR filter, oc 50 % neutral density filter, and a 425

nm 40 nm, bandpass filter in front of the excitation source. Three emission filters were

used interchangeably: a 475 nm longpass filter for imaging PtTFPP and DOCIpgsp or

DOCI-Ssglsp luminescence; a 525 nm 50 nm, bandpass filter for imaging DOCIpgsp or

DOCI-Ssgsp luminescence; and a 630 nm 60 nm, bandpass filter for imaging the PtTFPP

luminescence.

	Title Page
	Dedication
	Acknowledgement
	Table of Contents
	List of Tables
	List of Figures
	Abstract
	Introduction
	Dual-luminophore oxygen sensing...
	Microscopic analysis of luminescent...
	Conclusions
	PV-wave macro and subroutines
	List of references
	Biographical sketch

MILLISECOND	CLASS.METHOD	MESSAGE
0	sobekcm_page_globals.constructor
0	sobekcm_page_globals.constructor	Application State validated or built
0	sobekcm_database.verify_item_lookup_object
0	sobekcm_page_globals.constructor	Navigation Object created from URI query string
0	sobekcm_database.verify_item_lookup_object
0	sobekcm_page_globals.display_item	Retrieving item or group information
0	sobekcm_page_globals.get_entire_collection_hierarchy	Retrieving hierarchy information
0	sobekcm_assistant.get_entire_collection_hierarchy
0	cached_data_manager.retrieve_item_aggregation
0	cached_data_manager.retrieve_item_aggregation	Found item aggregation on local cache
0	item_aggregation_builder.get_item_aggregation	Found 'all' item aggregation in cache
0	system.web.ui.page.page_load (ufdc.page_load)
0	sobekcm_page_globals.constructor.on_page_load
0	html_echo_mainwriter.add_style_references	Adding style references to HTML
0	html_echo_mainwriter.add_text_to_page	Reading the text from the file and echoing back to the output stream
67	html_echo_mainwriter.add_text_to_page	Finished reading and writing the file