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Interactive Forces between SDS-Suspended Single-Wall Carbon Nanotubes and Agarose Gels

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Title:
Interactive Forces between SDS-Suspended Single-Wall Carbon Nanotubes and Agarose Gels
Physical Description:
Poster
Creator:
Clar, Justin G.
Publisher:
American Chemical Society
Place of Publication:
Journal of American Chemical Society

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Collected for University of Florida's Institutional Repository by the UFIR Self-Submittal tool. Submitted by Justin Clar.
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In Press

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University of Florida Institutional Repository
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University of Florida
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All rights reserved by the submitter.
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IR00003540:00001

MISSING IMAGE

Material Information

Title:
Interactive Forces between SDS-Suspended Single-Wall Carbon Nanotubes and Agarose Gels
Physical Description:
Poster
Creator:
Clar, Justin G.
Publisher:
American Chemical Society
Place of Publication:
Journal of American Chemical Society

Notes

Acquisition:
Collected for University of Florida's Institutional Repository by the UFIR Self-Submittal tool. Submitted by Justin Clar.
Publication Status:
In Press

Record Information

Source Institution:
University of Florida Institutional Repository
Holding Location:
University of Florida
Rights Management:
All rights reserved by the submitter.
System ID:
IR00003540:00001


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Interactive Forces between SDS Suspended Single Wall Carbon Nanotubes and Agarose Gels Justin G. Clar Carlos A. Silvera Batista Sejin Youn Jean Claude J. Bonzongo Kirk J. Ziegler Departments of Environmental Engineering Sciences and Chemical Engineering Universit y of Florida, Gainesville, Florida 32611, USA Inclusion of SWCNTs in a variety of applications and novel electronic devices has been challenging due to the presence of both Metallic ( m ) and Semiconducting ( s ) SWCNTs in as produced batches A method commonly used to produce large scale separations of the two fractions is column based using an agarose gel stationary phase 1 2 ( Figure 1 ) Prior studies have correctly attributed the mechanism of separation as the selective retention of s SWCNTs to the agarose gels, however, few details of the forces driving this selective adsorption are understood 3 4 Figure 1 : (left) Elution curves of SWCNTs suspended in 1 wt % SDS, using Dextran as medium Absorbance data points are at = 626 nm (right) VIS NIR absorbance spectra from the initial sample and the effluent at the first ( P 1 ) and second (P 2 ) peaks OBJECTIVES & GOALS Achieve a mechanistic understanding of the selective retention of SDS SWCNTs in agarose gel Specifically, to understand the dominant force(s) that drive the selective retention of s SWCNTS during separation This understanding will allow for process optimization that maximizes separation quality, and throughput SDS SWCNTs and agarose gels are complex system with many potential interactive forces between them Relative importance of each force can be evaluated by either inhibiting or promoting its significance during adsorption through gel functionalization and solution chemistry modification Forces investigated in both equilibrium (batch) and non equilibrium (column) studies include : van der Waals ( vdW ), Ionic (ion exchange), hydrophobic, and Ion Dipole Figure 2 : Physical and chemical structure of agarose (a) Monomeric unit of agarose chains (b) Polymers organize into double helices and are further stabilized by bundling to form aggregates various structure and size (c) Ligands added to agarose backbone after funtionalization The R group represents CH 2 CH(OH)CH 2 chains added during a glycidyl ether coupling reaction All gels were purchased from GE National Science Foundation (CBET 0853347) for support of this research .Prof. Yiider Tseng for access to the ultracentrifuge, The Richard Smalley Institute at Rice University for supplying SWCNTs GE for providing Sepharose 6 and 4 FF used in this study. 3.3 Ligand Density & Adsorption Sites 3.1 Hydrophobic Interactions Figure 4 : Non equilibrium retention behavior of a 1 wt % SDS SWCNT suspension in plain Sepharose 4 FF with that of Sepharose 4 FF functionalized hydrophobic ( octyl and butyl) groups Figure 3 : Equilibrium adsorption isotherms for SWCNTs in 1 wt % SDS Media are (a) plain Sepharose 4 FF ( ), (b) butyl Sepharose ( ) and (c) octyl Sepharose ( ) 3.2 Interactions Figure 5 : Equilibrium adsorption isotherms for SWCNTs in 1 wt % SDS The media are (a) plain Sepharose 6 FF ( ), (b) phenyl Sepharose LS ( ) and, (c) HS( ) Figure 6 : Non equilibrium retention behavior of a 1 wt % SDS SWCNT suspension in plain Sepharose 6 FF and with phenyl groups at LS and HS Sepharose functionalized with alkyl groups shows dramatic reduction in retention relative to the control ( 65 % and 27 % for octyl and butyl groups, respectively ) Increased density of hydrphobic groups should increase retention if hydrophobic interaction was the driving force of SDS SWCNT retention, a behavior not seen here Figure 3 demonstrates that the Langmuir model is not an adequate for these systems, although widely assumed in the literature 5 6 Reduced retention in both batch and columns studies suggest that purely hydrophobic interactions are not the dominate retention mechanism during separation Sepharose functionalized with phenyl groups shows dramatic reduction in retention relative to the control ( 54 % and 25 % for LS and HS respectively) If interactions were the dominate retention force, increased density of these groups would increase SDS SWCNT retention The opposite behavior is seen here Again, Langmuir behavior is not seen in phenyl substituted systems ( Figure 5 ) Reduced retention in both batch and column studies suggest that interactions are not the dominate retention mechanism during separation Inverse relationship between retention and ligand density ( Figure 7 ) Adsorption sites must be a key piece of agarose backbone found in different locations/confirmations on the surface given by isotherm shape Mechanism must account for : a) Importance of charged groups (SDS) b) OH group alteration decreases retention 4 .2 Role of SDS 4 .1 Mechanism & Selectivity During functionalization hydroxyl groups are moved/masked from the pristine surface (See Figure 2 ) We propose that OH groups are the active adsorption sites Dipoles on hydroxyl groups create the potential for an attractive interaction between the dipoles (H + ) and the negative charges on the SDS SWCNTs, i e ion dipole interactions Selectivity driven by inherent differences between m and s SWCNTs. Polarizability of m SWCNTs at least 3x > s SWCNTs creating increased magnitude image charge on m SWCNTs Larger charge has dual effects a) Direct repulsion from agarose surface by H + b) Increase in local charge screening increases ability of SDS to pack on m SWCNT surface increasing surfactant aggregation and limiting interactions with agarose surface. The proposed mechanism of selective retention for SDS SWCNTs on agarose gels is Ion dipole between ions of SDS head groups and known dipoles of agarose Selectivity is driven by the increased polarizability of the m SWCNTs species. Confirmation of hydroxyl groups on the agarose surface are an integral factor during the adsorption process. Traditional Langmuir isotherms may not be adequate to describe the sorption process during SDS SWCNT separations on agarose gels in all systems. 1: Hirano, A.; et al. J. Phys. Chem. C 2011 115 21723 21729. 2:Tanaka, T.; et al Appl. Phys. Express 2009 2 125002 1. 3: Liu, H.; et al. J. Phys. Chem. C 2010 114 9270 9276 4:Silvera Batista, C. A.; et al. J. Phys. Chem. C 2011 115 9361 9369. 5 : Hirano, A .; et al J Phys Chem C 2012 116 9816 9823 6 : Hirano, A .; et al ACS Nano 2012 6 10195 10205 7 : Kozinsky, B .; et al Phys Rev Lett 2006 96 166801 8 : Lu, W .; et al Nano Lett 2009 9 1668 1672 4: Discussion 7: Selected References 6: Acknowledgements 5: Conclusions 3: Selected Results 2: Methodology 1: Motivation & Objectives Krishnamoorti and co workers J Am Chem Soc 2004 126 9902 All ionic surfactants should create image charge No separation with SC SWCNTs Sodium Cholate (SC) Figure 7 : Relationship between ligand density and SWCNT retention (P 2 ) in non equilibrium experiments Ion dipole interactions account these observations: a) Permanent dipoles of different magnitude measured for agarose b) SDS SWCNTs are macro ions Differences in structure of surfactant SWCNT complex SDS/SC interact with SWCNT differently; effects water molecules. Enthalpic and entropic effects important for separation