Group Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Title: 3.2.3 - Droplet impact of viscous Newtonian and non-Newtonian liquids
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 Material Information
Title: 3.2.3 - Droplet impact of viscous Newtonian and non-Newtonian liquids Particle Bubble and Drop Dynamics
Series Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Physical Description: Conference Papers
Creator: Bolleddula, D.A.
Berchielli, A.
Aliseda, A.
Publisher: International Conference on Multiphase Flow (ICMF)
Publication Date: June 4, 2010
 Subjects
Subject: droplet spreading
colloidal dispersion
non-Newtonian fluid
 Notes
Abstract: Droplet impact has been studied for over a hundred years dating back to the pioneering work of Worthington (1876). In fact, much of his ingenuity contributed to modern day high speed photography. Over the past 40 years significant contributions in theoretical, numerical, and experimental work have been made. Droplet impact is a problem of fundamental importance due to the wealth of applications involved, namely, spray coating, spray painting, delivery of agricultural chemicals, spray cooling, ink-jet printing, soil erosion due to rain drop impact, and turbine wear. Here we highlight one specific application, pharmaceutical tablet spray coating. Although most studies have focused their efforts on low viscosity Newtonian fluids, many industrial applications such as spray coating utilize more viscous and complex rheology liquids. Determining dominant effects and quantifying their behavior for colloidal suspensions and polymer solutions remains a challenge and thus has eluded much effort. In the last decade, it has been shown that introducing polymers to Newtonian solutions inhibits the rebounding of a drop upon impact, Bergeron et al. (2000). Furthermore Bartolo et al. (2007) concluded that the normal stress component of the elongational viscosity was responsible for the rebounding inhibition of polymer based non-Newtonian solutions. We aim to uncover the drop impact dynamics of highly viscous Newtonian and complex rheology liquids used in pharmaceutical coating processes. The generation and impact of drops of mm and m size drops of coating liquids and glycerol/water mixtures on tablet surfaces is systematically studied over a range of We O(1 􀀀 10), Oh O(10􀀀1 􀀀 1), and Re O(1 􀀀 10). We extend the range of Oh to values above 1, not readily available to previous studies of droplet impacts.
General Note: The International Conference on Multiphase Flow (ICMF) first was held in Tsukuba, Japan in 1991 and the second ICMF took place in Kyoto, Japan in 1995. During this conference, it was decided to establish an International Governing Board which oversees the major aspects of the conference and makes decisions about future conference locations. Due to the great importance of the field, it was furthermore decided to hold the conference every three years successively in Asia including Australia, Europe including Africa, Russia and the Near East and America. Hence, ICMF 1998 was held in Lyon, France, ICMF 2001 in New Orleans, USA, ICMF 2004 in Yokohama, Japan, and ICMF 2007 in Leipzig, Germany. ICMF-2010 is devoted to all aspects of Multiphase Flow. Researchers from all over the world gathered in order to introduce their recent advances in the field and thereby promote the exchange of new ideas, results and techniques. The conference is a key event in Multiphase Flow and supports the advancement of science in this very important field. The major research topics relevant for the conference are as follows: Bio-Fluid Dynamics; Boiling; Bubbly Flows; Cavitation; Colloidal and Suspension Dynamics; Collision, Agglomeration and Breakup; Computational Techniques for Multiphase Flows; Droplet Flows; Environmental and Geophysical Flows; Experimental Methods for Multiphase Flows; Fluidized and Circulating Fluidized Beds; Fluid Structure Interactions; Granular Media; Industrial Applications; Instabilities; Interfacial Flows; Micro and Nano-Scale Multiphase Flows; Microgravity in Two-Phase Flow; Multiphase Flows with Heat and Mass Transfer; Non-Newtonian Multiphase Flows; Particle-Laden Flows; Particle, Bubble and Drop Dynamics; Reactive Multiphase Flows
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Bibliographic ID: UF00102023
Volume ID: VID00077
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: 323-Bolleddula-ICMF2010.pdf

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7th International Conference on Multiphase Flow,
ICMF 2010, Tampa, FL, May 30 -June 4, 2010


Droplet impact of viscous Newtonian and non-Newtonian liquids


D.A. BolleddulaT A. Berchiellit and A. Aliseda*

Department of Mechanical Engineering, University of Washington, Seattle, WA 98105, USA
t Pharmaceutical Development, Pfizer, Inc., Global Research and Development, Groton Laboratories,
Eastern Point Road MS 8156-35, Groton, CT 06340, United States
dabolla@uw.edu, Alfred.Berchielli@pfizer.com, and aaliseda@uw.edu
Keywords: Droplet spreading, Colloidal dispersion, non-Newtonian fluid




Abstract

Droplet impact has been studied for over a hundred years dating back to the pioneering work of Worthington (1876).
In fact, much of his ingenuity contributed to modem day high speed photography. Over the past 40 years igi iik.ilm
contributions in theoretical, numerical, and experimental work have been made. Droplet impact is a problem of
fundamental importance due to the wealth of applications involved, namely, spray coating, spray painting, delivery of
agricultural chemicals, spray cooling, ink-jet printing, soil erosion due to rain drop impact, and turbine wear. Here
we highlight one specific application, pharmaceutical tablet spray coating. Although most studies have focused their
efforts on low viscosity Newtonian fluids, many industrial applications such as spray coating utilize more viscous and
complex rheology liquids. Determining dominant effects and quantifying their behavior for colloidal suspensions
and polymer solutions remains a challenge and thus has eluded much effort. In the last decade, it has been shown
that introducing polymers to Newtonian solutions inhibits the rebounding of a drop upon impact, Bergeron et al.
(2000). Furthermore Bartolo et al. (2007) concluded that the normal stress component of the elongational viscosity
was responsible for the rebounding inhibition of polymer based non-Newtonian solutions. We aim to uncover the
drop impact dynamics of highly viscous Newtonian and complex rheology liquids used in pharmaceutical coating
processes. The generation and impact of drops of mm and pm size drops of coating liquids and glycerol/water
mixtures on tablet surfaces is systematically studied over a range of We 0(1 10), Oh ~ 0(10 1 1), and
Re ~ 0(1 10). We extend the range of Oh to values above 1, not readily available to previous studies of droplet
impacts.


Introduction

The impact of liquid drops on solid surfaces is a well
studied problem with two general reviews to date Rein
(1993) and Yarin (2006). The outcome evinced can take
one of three forms as seen in Fig. 1 and can be com-
monly discriminated through a ratio of forces. Dimen-
sional analysis provides a list of relevant parameters use-
ful in discriminating drop impact outcomes,


pDU2
We P2Re

Oh (
(paD)1/2


pDU


We1/2
Re


LSG CSL
(LG


where p, p, and a denote the liquid density, viscos-
ity, surface tension, respectively, and D and U are the


initial drop diameter and impact velocity, respectively.
We, Re, and Oh are the Weber, Reynolds, and Ohne-
sorge numbers, respectively. Young's equation which
describes the balance of forces at the liquid/gas/solid in-
terface introduces the role of the contact angle or wet-
tability of a solid/liquid pair. Gravity related effects are
described through the Bond number Bo pgD2 / or
by the Froude number Fr U2/(gD) = We/Bo.
Usually, gravity effects are considered negligible in drop
impact, yet this assumption is typically unsubstantiated.
Most studies have focused their efforts on low vis-
cosity liquids (p< lOcP) which are relevant to the inkjet,
aerospace, and agricultural applications. The pharma-
ceutical industry uses highly viscous solutions to coat
tablets in final oral dosage form. The coating liq-
uids used in the pharmaceutical industry contain large
amounts of insoluble solids (up to 2 by weight) and
can be characterized, to first approximation, as colloidal












0







O o
oo


spread ing


Figure 1: Impact of a drop on a solid surface: spreading,
bouncing, and splashing


dispersions. This class of liquids has received little at-
tention in relation to droplet impact and is the focus of
our efforts herein.
These complex liquids, where the rheology is dom-
inated by large concentrations of colloids, are unlike
previously studied polymer solutions and their behav-
ior upon impact is significantly different. Bergeron et al.
(2000) demonstrated by adding small concentrations of
polymers to Newtonian solutions, rebounding can be
completely inhibited. The suppression was explained
further by Bartolo et al. (2007) who derived that the
normal stress difference associated with the elongational
viscosity was responsible.
Another feature that has received Niii lii.,ii .II I ii,'n I,
is the role of surfactants which introduced the concept of
dynamic surface tension. Surfactant solutions were in-
vestigated in a series of works relevant to spray coating
operations since the liquid/gas interface undergoes rapid
adjustments over a short time scale. The importance of
these types of solutions comes with the ability of re-
ducing surface tension and thereby enhancing spreading.
The accumulation of surface active materials along the
drop surface provides a dynamic nature to the fluid inter-
face and points toward the concept dynamic surface ten-
sion. Dynamic surface tension is a quantity commonly
measured over a range of surfactant concentrations and
typically decreases until a new lower equilibrium sur-
face tension is reached. Surfactant solutions were stud-
ied in the work of Pasandideh-Fard et al. (1996) where
they explored the effect of equilibrium contact angle re-
duction. Surprisingly, they concluded that dynamic sur-
face tension did not influence drop impact. However,
Mourougou-Candoni et al. (1997) concluded that droplet
retraction was drastically influenced by the adsorption
kinetics of the surfactants which limited the return to the
equilibrium surface tension, a. In a subsequent publi-
cation, Mourougou-Candoni et al. (1999) observed two
types of retraction: a fast destabilizing and an exponen-


7th International Conference on Multiphase Flow,
ICMF 2010, Tampa, FL, May 30 -June 4, 2010


tially decaying slow retraction. The works of Basaran's
group also studied the effects of surfactants, and (d, and
reasoned that the decreases in surface tension thereby
enhances spreading, yet in opposition is the non-uniform
distribution of surfactants along the fluid interface giving
rise to Marangoni stresses inhibiting spreading, Zhang
and Basaran (1997).
The impact and spreading of a neutrally buoyant sus-
pension was investigated in Nicolas (2005). The study
was conducted over a range of particle volume fractions
and deduced that the particles are unevenly distributed
throughout the drop with preference towards outer por-
tion of the drop forming an annular structure. Further-
more, for large Re, splashing was observed and ex-
plained by the additive role of particles. We hypothesize
that the addition of particles reduces the liquid surface
energy allowing the particles to break through.
The spreading of shear thinning liquids on hy-
drophillic surfaces was explored in the work of Rafai
et al. (2004). They found that Tanner's law, D(t) ~
1/10 is rather robust and only required logarithmic cor-
rections. Drop sizes were 0(mm) and spread to sizes
of centrimetric size. Here we investigate a regime of
droplet impact where viscous and capillary forces dom-
inate, utilizing both Newtonian and complex rheology
liquids used in the pharmaceutical industry. The role of
colloidal particles in resistance to spreading will also be
explored.
Our study is aimed at understanding and modelling
the dynamics of drop impact on a surface under an ex-
tended range of parameters (Oh ~ 0(1 10)) that in-
clude highly viscous fluids used in the pharmaceutical
industry. We also aim at clarifying the role of colloidal
particles (through complex rheology of the dispersion)
in the dynamics of impact. Our previous efforts have fo-
cused mostly on the mm size drop impacts ejected from
a syringe on surfaces of varying wettability. We focused
on a higher range of We and Oh easily accessible for
larger (mm) drop impacts. Furthermore, the early behav-
ior of the impacts where inertia dominates spreading was
recorded. Herein, we focus on the later stages of spread-
ing, specifically utilizing smaller size drops (pm) such
as those created in typical atomization conditions. We
will explore the creation of highly viscous (p>10cP) im-
pacting hydrophilic surfaces to explore the regime where
capillary and viscous forces dominate. The generation
of micron size drops will be surveyed over a small range
of velocities. We explore deviations in the impact behav-
ior between Newtonian fluids and non-Newtonian col-
loidal dispersions with equal shear viscosity values.
The experimental setup and experimental parameter
range are described, followed by the results. Finally, dis-
cussion of the results and conclusions are presented.











Droplet impact experiments

We focus our attention on colloidal dispersions rele-
vant to coating processes in the pharmaceutical industry.
These coating liquids are aqueous suspensions and are
commonly defined by their solid content by weight. It is
noteworthy that the ratios studied here are realistic pro-
portions for industrial scale coating operations. We will
study three commercially available coating liquids from
Colorcon, Inc. The three coating liquids are OpadryTMII
White differentiated by contents of partially-hydrolyzed
polyvinyl alcohol (PVA), polyethylene glycol(PEG),
hydroxypropyl methylcellulose (HPMC). The powders
also consist of Lactose/TiO2/Triacetin. The coatings are
identified from here on by ID's # 4 and 5. Coatings
#4 and 5 and differ by the addition of PEG. The rheol-
ogy of these fluids is dominated by the high concentra-
tion of colloids, not by polymers in solution, differenti-
ating these liquids from previous drop impact studies. A
summary of these coatings and their physical properties
are shown in Table 1. Coatings are prepared by slowly
adding solid content to water over a magnetic stir plate.
Care is taken to avoid aggregation of colloidal particles
and obtain uniformity. The resulting liquid forms an
aqueous suspension of colloidal particles that are fully
wetted by the dispersion medium. We will also study
glycerol/water solutions with equal values of shear vis-
cosity.
Experimental Setup
Fig. 2 is a schematic of our experimental apparatus. A
high speed camera Phantom V12, Vision Research Inc.,
is used to visualize the impact of a drop from a solid sur-
face. The im.igiii k.i ii l provides a spatial resolution of
17 pm/pixel and 2 pm/pixel for the mm and pm sized
droplets, respectively. A long distance microscopic lens
provided by Infinity USA Inc. is utilized in the micron
sized drop impacts. The impact is backlit by an Ed-
munds fiber optic light source. Single mm size drops are
ejected by a syringe pump through a stainless steel nee-
dle (22g) and fall under their own weight with a diame-
ter, D ~ 2.5mm. The vertical and horizontal diameters
are measured and an equivalent diameter is calculated
by Deq (D~D~)1/ The averaged impact velocities
are measured by the distance travelled by the drop five
frames prior to impact. The uncertainty in this measure-
ment is 0.13 m/s and 0.09 m/s for mm and pm sized
impacts, respectively. The height of release is adjusted
to obtain different velocities. The use of a piezoelec-
tric sleeve bonded to a capillary tube of diameter 120/pm
provides drops of size 0(100pm). The piezo nozzle and
voltage generator are provided by MicroFab, Inc. A typ-
ical waveform to eject droplets is shown in Fig. 3. In
a typical experiment, mm and micron drop impacts are
recorded at 7600 fps and 63063 fps, respectively.


7th International Conference on Multiphase Flow,
ICMF 2010, Tampa, FL, May 30 -June 4, 2010


In order to resolve the very short term dynamics at
impact for micron sized droplets, a higher temporal res-
olution (0 (ps)) would be necessary. We concentrate on
the later stages of the impact where capillarity driven
spreading is resisted by viscosity. Here we investigate
the parameter space defined in We 0(1 10) and
Oh = (10 1 1) achieved with D ~ 0(100/m) size
drops. By working with such highly viscous fluids we
are able to realize higher Oh ~ 0(1) numbers thereby
extending the range of previous studies. All quantitative
data is collected with image processing software devel-
oped by NASA, Spotlight Klimek and Wright (2006).

50





0






50
0 10 20 30 40 50 60 70
t, pfs

Figure 3: Typical waveform used to eject droplets from
nozzle. Frequencies vary but range from 10-
100 Hz. Voltages are typically 40-60 V.

Rheology
Characterization of the coating suspensions was car-
ried out through shear viscosity measurements. We used
a Brookefield II Cone+plate viscometer and a Anton
Paar MCR301 Rheometer with a double gap rheometer
configuration. Figure 4 shows a typical viscosity mea-
surement over a range of shear rates of 10 3-103s 1 for
#5.
The shear viscosity maintains a very slight shear thin-
ning profile for all coating suspensions used in this study
and thus the implementation of the shear viscosity at
1000 s-1 is a conservative estimation. The shear rates
upon impact can range from 1-1000 s-1, thus employ-
ing the lowest viscosity serves as a first order approxi-
mation and is used herein. The viscosity can be fit excel-
lently to the form p = mn" 1 for > 1. Furthermore,
the viscosity at 1000 s-1 versus increasing solid content
obeys an exponentially increasing function as observed
in Figure 5. Assessing if any non-Newtonian feature is
present over the range of shear rates indicative of im-
pact regimes is challenged by the coatings composition
containing colloids of varying size, shape, and ability to







7th International Conference on Multiphase Flow,
ICMF 2010, Tampa, FL, May 30 -June 4, 2010




SD,U jetting driver


tdt syringe pump JB

or






light


Figure 2: Schematic of experimental apparatus. Data extracted is spreading diameter d(t) and centerline height h(t)


O 3%


18%


102 104


10-2 100
1/s


0 3%
+ 5%
* 10%
A 12%
15%
18%


i = 0.322 6774


10
% solids


15 20


Figure 4: Shear viscosity of Opadry suspension # 5


aggregate. It is proposed that using the shear viscosity
is an appropriate first characterization of these coating
solutions. However we anticipate further characteriza-
tion is necessary to gain quantitative understanding of
the influence of colloidal particles in spreading. To date
we are aware of only one quantitative study on the im-
pact of a suspension of density matched particles Nico-
las (2005).
The surface tension is measured with a du Nuoy Ring
method and maintains a values between 40-50 mN/m.
Table 1 shows a summary of the fluid properties used to
define dimensionless parameters.
Micron droplet ejection
Although it was demonstrated that gravity has only
a minor effect in droplet impacts, it was only validated
for low viscosity liquids, with Oh ~ 10 2 Dong et al.
(2007). We anticipate that gravity will also be negligible
here, at least for pm size drops where Bo < 1. How-
ever, when mm size drops are employed then Bo ~ 1.
Many authors justify neglect of gravity by introducing


Figure 5: Shear viscosity of Opadry suspension # 5
taken at 1000 s-1 versus solid content.



the Froude number expressed as Fr U2/Dg >1 for
both mm and pm size drops. This is not an accurate
parameter to characterize the effect of gravity. The Fr
characterizes the propagation of gravity surface waves
against the convective fluid motion, whereas the key
effect of gravity is to modify the overall shape of the
droplet through the balance between potential, kinetic
and surface energy.
Here we utilize viscosities of O(102cP) thus obtain-
ing Oh ~ 1. Drop-on-demand technology has generally
been motivated by the ink-jet industry, yet the need for
developing polymer based electronics such as polymer
LED's has provided a need to generate micron size drops
of more complex rheology liquids, Son and Kim (2009).
Here we demonstrate that by applying a suitable wave-
form and frequency we are able to generate 50 100 pm
diameter drops with glycerol/water mixtures and coating
#5, 10% solids both having p ~ 100cP. A sample se-







7th International Conference on Multiphase Flow,
ICMF 2010, Tampa, FL, May 30 -June 4, 2010


Table 1: Summary of fluid properties and wettability
Fluid p, mPa s @1000 s p, kg/m3 n, N/m T, "C 6 on mica
"nl nn^n ^rI


4, 135, Upadry ll White, HPMC/PEGt
5, 10%, OpadryT II White, HPMC
75% Glycerol/H20
85% Glycerol/H20


1U4U U.U4/U/
1020 0.04822
1195 0.063a
1220 0.062


alnterpolated value


SOh = 1.2, We = 5.4
Oh 0.2, We 6.5


10-2 10 1 100
Ut/D


101 10:


Figure 6: Ejection sequence of #5, 10%. Time interval
between each frame is 31 ps


quence of ejection of coating #5, I1 r. solids from the
piezo nozzle is shown in Fig. 6
At this point, the generation of micron sized droplets
is produced at the expense of droplet speed and thus
we are limited to We ~ 1 10 for micron drop im-
pacts. Furthermore, limited temporal resolution of our
high speed technology precludes us from obtaining pre-
cise dynamic behavior of the impacted droplet at early
times t < D/U. However we are able to obtain spread-
ing histories for t > D/U. The ejection of higher speed
droplets will be the focus for future work.


Results

The following set of results is quantified in terms of
the spreading diameter, d(t), and the centerline height,
h(t), upon impact and spreading, Fig. 2. The increasing
and decreasing curves define the spreading diameter and
centerline height, respectively.
From our mm drop impacts we we able to observe


Figure 7: Continuation of spreading from mm to mum
drop impacts of colloidal dispersion #4, 15' .
O are from micron drop impacts and A are
from mm drop spreading.


the impact of colloidal dispersions at We ~ 300 at
speeds U ~ 2 m/s. In this regime the spreading time,
t ~ D/U z 1-4. When We is small, inertial, surface
tension, and viscosity are all comparable (Oh ~ 1) while
gravity is assumed negligible. Unfortunately for mm
size drops, the Bo ~ 1 which identifies gravity as a non-
negligible factor. However, micron sized drops provide
Bo <1 thus justifying the neglect of gravity. We ex-
plore the impact and spreading of highly viscous micron
sized drops of Newtonian and complex rheology at im-
pact times t > D/U where the dominant balance is be-
tween capillarity and viscosity. The spreading from both
mm and micron sized drops is shown in Fig. 7 which
demonstrates the match between early times (t < D/U)
from a mm size drop to later times (t > D/U) from a
pm size drop. It is important to note that the time scale
T D/U is valid for impact driven spreading but for
We ~ 1 we expect a viscosity and capillary driven time
scale, Tvise = D/o. It is clear from Fig. 7 that the
spreading diameter, 3(t) d(t)/D, continues after a
short delay when capillarity acts to spread the drop to
equilibrium. We now focus our attention to spreading
from low We impacts of both colloidal dispersions and
viscous Newtonian solutions.


1 1 I
I I


A-
A








7th International Conference on Multiphase Flow,
ICMF 2010, Tampa, FL, May 30 -June 4, 2010


0 Oh = 1.2, We = 5.4 (#
A Oh = 1.1, We = 0.37 (>






O OO


IV


10-1 100
t (l(D a)


Figure 8: Capillary driven spreading on mica with 0 =
15.





Spreading of colloidal dispersions

Fig 8 demonstrates the effect of the We on spreading
as we see that for higher We we see increased spreading
for #4, 5i solids. Moreover, the effect of inertia is
negligible in this regime where the We ~ 1. Notice
that the time is scaled by the impact velocity, U, and the
initial diameter of the drop, D. This scale is most likely
physically inaccurate, but serves as a first approximation
for direct comparison, t < D/U shown later. A viscous
and capillary time scale is of the form t ~ pD/a for
Oh > 1 and We < 1 or t ~ p/pU2 for We > 1 and
Oh > We1/2. Since we are focused on the later stages
of impact the rTise is the appropriate time scale.

We observe counterintuitive behavior in Fig. 9 where
faster spreading occurs for the lowest We. The higher
shear rates generated upon impact for We = 0.96 may
counteract spreading at these time scales and lead to a
delayed spreading compared to smaller We. Since the
work done by viscous dissipation goes quadratic with
the shear rate, spreading may be resisted by the inertia
at these time scales for We ~ 1. We investigate the role
of colloidal particles closer by observing the spreading
of equivalently viscous Newtonian liquids.

We observe faster spreading for 7 '. glycerol/water
solutions lower We but countering this trend we ob-
serve increased spreading with We for I' glycerol so-
lutions as seen in Figs. 10 and 11. When comparing
equivalently viscous glycerol/water and colloidal disper-
sions we observed increased resistance to spreading in
the non-Newtonian liquids as observed in Fig. 12. This
behavior is further confirmed in Fig. 13.


Figure 9: Capillary driven spreading on mica with 0 =
13.


0 Oh = 0.41, We 0.81 (75%
A Oh = 0.41, We = 0.53 (75%
Oh = 0.41, We = 3.71 (75%


10-1 100
t/(pD/a)


101 10:


Figure 10: Spreading on mica with 0 = 13'


0 Oh
A Oh
Oh


1.1, We = 0.43 (85% glycerol)
1.1, We = 1.1 (85% glycerol)
1.1, We = 2.6 (85% glycerol)


1.5 I


t/(pD/a)


Figure 11: Spreading on mica with 0 = 16'


1.6

1.4

1.2

1

0.8
z


O Oh
A Oh
Oh


t/(pD/a)


101 10:







7th International Conference on Multiphase Flow,
ICMF 2010, Tampa, FL, May 30 -June 4, 2010


Conclusions


0 Oh=
A Oh=


0.5


10-1 100
t/(pD/a)


Figure 12: Effect of colloidal particles 1
person #5, 10% and 6'.
with contact angles of 0 of
spectively.


To date, we have confirmed from both mm and micron
sized impacts that the effects of colloidal particles act to
resist spreading at least at low We. Additionally from
cerol early impact times where t < D/U, the solid/liquid
rinterfacial energy is negligible and the impact is dom-
Sinated by the balance between inertia and surface ten-
sion/viscosity. We hypothesize that non-Newtonian ef-
fects will be ign ilik.iili in the spreading of micron-sized
droplets (Oh ~ 1-10) for larger impact We. This may
help elucidate the counterintuitive behavior we observed
for high Oh and low We impacts.
We have restricted this study to an ideal, perfectly
flat surface with almost perfect wettability (mica, 0 =
15). We will explore the impact of these highly viscous
101 102 Newtonian and non-Newtonian liquids on hydrophobic
and rough surfaces. Additionally, increasing the impact
speed may further validate the foregoing conclusions.
for colloidal dis- Increasing the speed will also act to increase the shear
glycerol/water rate and may act to provide differing effects in those
13' and 16', re- compared to similar We from mm drop impacts. Con-
ducting further rheology measurements to measure os-
cillatory behavior will also provide insight into assessing
non-Newtonian qualities. These and other efforts will be
the focus of future investigation.


Acknowledgements


1.8


SOh = 1.1, We = 0.37 '4 15%)
Oh 1.3, We = 0.43 glycerol)


10.

10 1


t/( D/u)


Figure 13: Effect of colloidal particles for colloidal dis-
persion #4, 15'. and i'. glycerol/water
with contact angles of 0 of 15 and 16, re-
spectively.


The authors extend appreciation to Pankaj Doshi and
Doug Kremer at Pfizer, Inc. for their support in this ef-
fort. We have also benefitted greatly from our collabo-
rators at UCSD, Juan C. Lasheras and Katie Osterday.
We appreciate D. Pozzo and J.C. Berg at the University
of Washington for the use of the rheometer and the con-
tact angle measurement apparatus as well as insightful
comments.


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7th International Conference on Multiphase Flow,
ICMF 2010, Tampa, FL, May 30 -June 4, 2010


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