Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session X17: Charged and Ion-Containing Polymers I |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Jodie Lutkenhaus, Yale Room: B116 |
Thursday, March 18, 2010 2:30PM - 2:42PM |
X17.00001: The slow relaxation mode - from solutions to gel networks Chi Wu In dynamic laser light scattering (LLS), we measure how long a scattering object takes to ``move'' (relax) a distance of 1/q (the LLS observation length), where q is the scattering vector and $\sim $35 nm $<$ 1/q $< \quad \sim $190 nm. Recently, by using the Staudinger ligation to attach special functional groups to a copolymer, PAMS-\textit{co}-PS, we prepared a novel polymer that can undergo a neutral-charged-neutral transition in DMF with 0.5{\%} H$_{2}$O when the solution is alternatively bubbled with CO$_{2}$ and N$_{2}$. Armed with this polymer, we re-examined dynamics of salt-free polyelectrolyte dilute solutions by using laser light scattering (LLS). As expected, there exists only one diffusive relaxation mode in the neutral state. The bubbling of CO$_{2}$ decreases the scattering intensity and splits this initial diffusive relaxation mode into a fast and a slow diffusive mode. One common perception is that a slowly moving subject is larger. However, we found that the intensity contribution of the slow mode is independent of the scattering angle, indicating that it is not related to some scattering objects larger than 1/q. Combining our current and previous results of semi-dilute solutions and gel networks, we can generalize the slow mode as hindered motions of interacting polymer chains even though the nature of interaction can be very different, including electrostatic, segment-segment interaction in a less good solvent, and even chemical cross-linking. We wish to acknowledge the HKSAR RGC Earmarked Grant. [Preview Abstract] |
Thursday, March 18, 2010 2:42PM - 2:54PM |
X17.00002: Viscosity and scattering function of dilute, semidilute and concentrated polyelectrolyte solution: Molecular dynamics simulations Qi Liao We present the results of viscosity and scattering function of polyelectrolyte solutions in different solvent conditions for polymer backbone by molecular dynamics simulations. Polyelectrolyte solutions are modeled as an ensemble of bead-spring chains of charged Lennard-Jones particles with explicit counterions. Simulations were performed for both fully and partially charged polyelectrolyte chains with the number of monomers in the range of polymer concentrations covering both dilute and semidilute regime, even to the concentrated regime. The crossover behaviors of different regimes observed in the experiments are repeated quantitatively in our simulations. [Preview Abstract] |
Thursday, March 18, 2010 2:54PM - 3:06PM |
X17.00003: Persistence length of a linear polyelectrolyte in the presence of salt Wei Qu, Erik Luijten The conformational behavior of polyelectrolytes is important in various contexts, including the self-assembly behavior of biopolymers and their properties under confinement. A key parameter is the persistence length, which quantifies the rigidity of the polyelectrolyte. Despite much study, a debate exists about the dependence of the electrostatic persistence length on the Debye screening length. Since most theories and simulation studies treat the electrostatic interaction via the Debye--H\"{u}ckel potential, a mean-field approximation, these may not fully resolve the role of salt concentration. In this study, we simulate a polyelectrolyte with \emph{explicit} counterions and salt. The response of the persistence length to variation in ionic strength is compared to the Odijk--Skolnick--Fixman theory. [Preview Abstract] |
Thursday, March 18, 2010 3:06PM - 3:18PM |
X17.00004: Polyelectrolyte Complexation: A Field-Theoretic Description of Phase Behavior Debra Audus, Glenn Fredrickson Our research focuses on a type of polyelectrolyte complexation called complex coacervation where two oppositely charged polymers in solution phase separate to form a dense polymer phase, known as the coacervate, and a supernatant, which typically has very low concentrations of polymer. To understand the effects of various parameters on coacervation, we previously developed a simple analytic theory for flexible polymers and small ions, which reproduces many general experimental trends. However, this theory is only valid for symmetric oppositely charged polymers, which limits its direct applicability to many experimental systems. Consequently, we have extended this theory to describe more complicated experimental systems where salt concentrations are high, pH equilibria shift with the complexation process, polymer concentrations are highly asymmetric, and counterion condensation may play an important role. To validate the modified theory, we compare our predictions with an exhaustive study of the phase behavior of polyacrylic acid and polyallylamine hydrochloride. [Preview Abstract] |
Thursday, March 18, 2010 3:18PM - 3:30PM |
X17.00005: ABSTRACT WITHDRAWN |
Thursday, March 18, 2010 3:30PM - 3:42PM |
X17.00006: Transverse migration of a polyelectrolyte driven by electric and pressure-driven flow fields Rahul Kekre, Tony Ladd, Jason Butler Capillary electrophoresis experiments show that a flexible polyelectrolyte migrates under the combined action of electric and pressure-driven-flow fields [1]. When the fields act in conjunction, the polymer migrates to the center of the channel, but when the pressure gradient and external force act in opposite directions, the polymer migrates towards the boundaries. We have previously proposed that this is caused by long-range dipolar interactions between segments of the polyelectrolyte chain [2]. Due to the stretching and orientation of the chain by the local shear flow, there is a net motion transverse to the flow and field lines. Here I will describe a coarse-grained simulation of polyelectrolyte migration, including hydrodynamic interactions from the imposed flow and electric fields. The effects of the no-slip condition on the walls are included by regularized Green's functions. Our results explain the experimentally observed migration under different combinations of flow and electric field. [1] J. Zheng and E. S. Yeung. Anal. Chem., 74:4536, 2002; 75:3675, 2003. [2] O. B. Usta, J. E. Butler and A. J. C. Ladd. Phys. Rev. Lett., 98:098301, 2007. [Preview Abstract] |
Thursday, March 18, 2010 3:42PM - 3:54PM |
X17.00007: Stretching a strong polyelectrolyte chain under AC-electric fields: A molecular dynamics simulation study Hongjun Liu, Edward Maginn, Y. Elaine Zhu We use a coarse-grained molecular dynamics method to study the structural dynamics of a single strong polyelectrolyte in an explicit salt solution under AC-electric fields. The conformational dimension of the polyelectrolyte chain in aqueous solutions added with trivalent counterions is investigated as a function of AC-electric field strength and frequency. Our simulation results show that the polyelectrolyte chain can be stretched when the applied AC-field strength exceeds a critical value at the AC frequency range comparable to or smaller than the reciprocal of the relaxation time of the polyelectrolyte chain. We also observe the curious breathing mode of the stretched polyelectrolyte with the applied AC-electric oscillation, which could be applied to effectively manipulate and assemble charged polymers and biopolymers with desirable structures by varied electric fields. [Preview Abstract] |
Thursday, March 18, 2010 3:54PM - 4:06PM |
X17.00008: Ion Diffusion in polyelectrolyte solution Pengxiang Jia, Jiang Zhao We use fluorescence correlation spectroscopy to study diffusion of sparse charged fluorescent molecules as probes of ions in the solution of polystyrene sulfonate (PSS-Na+). The diffusion of the probe was found to depend strongly on its charged state. More importantly, the diffusion of positively charged probes depends strongly the concentration and molecular weight of PSS- Na+. The results show that the fraction of free ``counterions'' in the solution decreases sharply with the increase of the polymer concentration and the molecular weight, showing the role of entropy and electrostatic interaction in the distribution of counterions around the polyelectrolyte chains. [Preview Abstract] |
Thursday, March 18, 2010 4:06PM - 4:18PM |
X17.00009: Tribological and Rheological Properties of a Synovial Fluid Model Rebecca Klossner, Jing Liang, Wendy Krause Hyaluronic acid (HA) and the plasma proteins, albumin and globulins, are the most abundant macromolecules in synovial fluid, the fluid that lubricates freely moving joints. In previous studies, bovine synovial fluid, a synovial fluid model (SFM) and albumin in phosphate buffered saline (PBS) were observed to be rheopectic---viscosity increases over time under constant shear. Additionally, steady shear experiments have a strong shear history dependence in protein-containing solutions, whereas samples of HA in PBS behaved as a ``typical'' polyelectrolyte. The observed rheopexy and shear history dependence are indicative of structure building in solution, which is most likely caused by protein aggregation. The tribology of the SFM was also investigated using nanoindenter-based scratch tests. The coefficient of frictions ($\mu )$ between the diamond nanoindenter tip and a polyethylene surface was measured in the presence of the SFM and solutions with varied protein and HA concentrations. The lowest $\mu $ is observed in the SFM, which most closely mimics a healthy joint. Finally, an anti-inflammatory drug, hydroxychloroquine, was shown to inhibit protein interactions in the SFM in rheological studies, and thus the tribological response was examined. We hypothesize that the rheopectic behavior is important in lubrication regimes and therefore, the rheological and tribological properties of these solutions will be correlated. [Preview Abstract] |
Thursday, March 18, 2010 4:18PM - 4:30PM |
X17.00010: Effects of Salts and Ionic Liquids on the Thermodynamics of Poly(ethylene oxide)-Containing Block Copolymers Nisita Wanakule, Justin Virgili, Alexander Teran, Nitash Balsara We explore the thermodynamics of block copolymers doped with the salt, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and the ionic liquid, imidazolium bis(trifluoromethanesulfonyl) imide ([Im][TFSI]). The block copolymers comprise of polyethylene oxide (PEO), a polymer with a higher dielectric constant, and polystyrene (PS), a polymer with a lower dielectric constant. A combination of small-angle x-ray scattering (SAXS) and birefringence was used to determine morphology and order-to-disorder transition temperatures (ODT). Leibler's theory for microphase separation was employed to determine the effective Flory-Huggins interaction parameter. These values are compared to theoretically-determined values of the effective interaction parameter which were calculated with no adjustable parameters using a theory developed by Zhen-Gang Wang. [Preview Abstract] |
Thursday, March 18, 2010 4:30PM - 4:42PM |
X17.00011: Morphology effects on the ionic conductivity of PEO-containing block copolymers Wen-Shiue Young, Thomas Epps Salt-doped poly(ethylene oxide)-based block copolymers have attracted significant interest, as nanoscale ordered structures offer ideal platforms for the design of electrolytes for lithium battery membranes. Because the electrolyte conductivity is strongly dependent on the nature of the conducting pathways, it is important to understand how copolymer morphology affects electrolyte performance. We obtained different morphologies of lithium perchlorate-doped poly(styrene-b-ethylene oxide) by adjusting the amount of the lithium salt and the volume fractions of the copolymer blocks. A homemade ionic conductivity measurement cell allowed us to monitor the ionic conductivity changes while simultaneously using temperature-dependent small angle X-ray scattering to examine the electrolyte nanostructure. We compare the ionic conductivities of the copolymer electrolytes, which have the same salt concentrations ([Li]/[EO]) and similar molecular weight but different microstructures (lamellae, gyroid, and cylinders), to determine the morphology effects. Our results provide engineering parameters useful in the design of high-performance copolymer electrolytes. [Preview Abstract] |
Thursday, March 18, 2010 4:42PM - 4:54PM |
X17.00012: Morphologies in Diblock Copolymer and Ionic Liquid Mixtures Jae-Hong Choi, Liang Gwee, Yossef A. Elabd, Karen I. Winey The morphologies of mixtures of a poly(methyl methacrylate-$b$-styrene) diblock copolymer and an ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, have been studied with different ionic liquid contents. The solution cast block copolymer-ionic liquid mixture films appear transparent, because the ionic liquid EMIm-TFSI is preferentially compatible to the MMA phase. The ordered microphase separation structures in the films were characterized via small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The block copolymer and ionic liquid mixtures show ordered structures typical of block copolymers: hexagonally ordered cylinders and lamellae. The swelling behavior of block copolymer in ionic liquid as ionic liquid contents will be discussed. Also, the structure of mixture and ion transport property will be correlated. [Preview Abstract] |
Thursday, March 18, 2010 4:54PM - 5:06PM |
X17.00013: Homopolymer Dissolution in a Hydrophilic Ionic Liquid David Hoagland, John Harner Dissolution, structure, and dynamics of both neutral and charged polymers dissolved in a hydrophilic room temperature ionic liquid (IL), ethylmethylimidazolium ethyl sulfate [EMIM][EtSO4], have been studied by classical physicochemical methods (static and dynamic light scattering, intrinsic viscosity, refractometry) to determine differences in solution behavior from conventional aqueous and organic solvents. This IL is water miscible. Many neutral polymers and charged polymer salts molecularly dissolve, although solubility doesn't correlate with polymer hydrophilicity. Model neutral soluble polymers are polyvinylpyrrolidone and hydroroxyethyl cellulose while sodium poly(styrene sulfonate) and the iodo salt of methyl-quaternized poly(vinyl pyridine) fill the same role for charged polymers. The latter display none of the polyelectrolyte effects found in low ionic strength water, consistent with strong electrostatic screening in IL. In virial coefficient and coil size, the IL acts for these neutral and charged polymers as a classical good solvent. (Support: UMass MRSEC) [Preview Abstract] |
Thursday, March 18, 2010 5:06PM - 5:18PM |
X17.00014: Thermoreversible Ion Gels from Supramolecular Assembly via Hydrogen Bonding in Ionic Liquids Yu Lei, Timothy Lodge Ion gels are a novel class of functional materials of broad interest for advanced applications. We have developed a thermoreversible ion gel from a supramolecular system consisting of a poly(2-vinylpyridine-b-ethylene oxide-b-2- vinylpyridine) (P2VP-PEO-P2VP) triblock copolymer and a poly(4- vinylphenol) (PVPh) homopolymer dissolved in an ionic liquid, where the P2VP endblocks are capable of forming hydrogen bonds with the PVPh ``crosslinkers.'' Rheology and small angle X-ray scattering (SAXS) were employed to elucidate the gelation and relaxation mechanisms. Interestingly, the rheological data extend over 15 orders of magnitude along the reduced frequency axis, which we ascribed to the strong temperature dependence of hydrogen bonding. We have investigated how the stoichiometry between 2-vinylpyridine and 4-vinylphenol affects the gel quality. We have also investigated how the longest relaxation time and gel point depend on the length of P2VP endblock. The thermal stability and wide liquid temperature range of ionic liquids allow us to explore the fundamental response of this system in greater detail. [Preview Abstract] |
Thursday, March 18, 2010 5:18PM - 5:30PM |
X17.00015: Thermodynamics and Mechanism of the Block Copolymer Micelle Shuttle between Water and an Ionic Liquid Zhifeng Bai, Timothy Lodge The micelle shuttle, whereby amphiphilic poly((1,2-butadiene)-b- ethylene oxide) (PB-PEO) block copolymer micelles reversibly transfer between water and a hydrophobic ionic liquid upon a temperature stimulus, is of interest in delivery, reaction and separations in synthesis and biphasic catalysis involving ionic liquids. A solvophobic dye-labeled short PB homopolymer is loaded into the PB-PEO micelles and quantitatively shuttled between the two fluids. The micelle distribution in the biphasic system has a favorably strong temperature dependence as revealed by quantitative fluorescence analysis, which is further used to extract the standard Gibbs free energy change ($\Delta$G$^{\circ}$), enthalpy change ($\Delta$H$^{\circ}$) and entropy change ($\Delta$S$^{\circ}$) of the transfer. The slow yet spontaneous micelle shuttle is explored under quiescent conditions to understand the transfer kinetics. A detailed mechanism for the transfer is proposed. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700