Liquid state theory has been developed for the structure and thermodynamics equilibrium of multiblock copolymer and ionomer solutions and melts. Local structural correlations and small-angle scattering profiles are studied using the multiblock polymer reference interaction site model (PRISM) integral equation theory for both ionomers with different fractions of strongly attractive, regularly spaced groups, and telechelics. In the low temperature regime, strong concentration fluctuations develop and small microphase separated ionic domains are formed. Cluster size and interfacial width in the strong segregation regime can be determined from examination of the partial collective structure factors and pair correlation functions in real-space. Qualitative, and sometimes quantitative, agreement with experimental scattering data has been demonstrated.
[G'30.02] The Cation Environment in a LiI Doped PEO melt via Neutron Scattering and MD Simulations
J. D. Londono, B. K. Annis (Oak Ridge Nat. Lab.), O. Borodin, G. D. Smith (Univ. of Miss.-Columbia)
Neutron scattering isotopic substitution (NSIS) experiments were performed, and the atomic partial radial distribution function [\deltaG(r)] about Li^+ in amorphous PEO/LiI (5:1) was obtained. The amorphous fraction in Li^+ doped PEO is thought to play a major role in the conductivity, and the atomic structure about the cation is important in modelling this quantity. Measurements were performed on ^6LiI and ^natLiI in deuterated PEO of about 50K MW at 90\degC. Results suggest a highly structured cation environment below 6-7ÅThe first peak in \deltaG(r) is at 2.05Åclose to the Li^+ to ether oxygen (EO) distances in analogous crystalline materials. MD yields a similar structure for \deltaG(r) if polarization effects are considered. The number of EO about Li^+ is similar in both sets of results (MD: 3.5-4; NSIS: 3 EO per Li^+). Sponsored by Div. of Mat. Sci., Basic Energy Sciences, USDOE, contract DE-AC05-96OR22464 with Oak Ridge Nat. Lab., managed by Lockheed Martin Energy Research Corp. and by NASA Grant NCC 1701 (Univ. of Miss.-Columbia).
[G'30.03] Polyelectrolyte Brushes: Novel Synthesis, Surface Force and Ellipsometric Study.
Svetlana Sukhishvili, Steve Granick (University of Illinois at Urbana-Champaign), Carl Kessel (3M Company, St. Paul, MN.)
We decribe a new versatile synthesis of polyelectrolyte brushes, which includes: self-assembly of vinyl-terminated alkyltriethoxysilane molecules on the substrate surface; (2) UV-initiated attachment of poly-4-vinylpyridine macromonomer to the surface vinyl groups, and (3) quaternization of pyridine rings with methyl iodide. Using FTIR-ATR spectroscopy and ellipsometry, we show that in this way the brushes with desired grafting and charge densities can be obtained. Increased grafting densities were obtained upon worsening the solvent quality. Importantly, this method allows use of the substrates, that do not bear surface hydroxyl groups, such as mica. Combining Surface Force and ellipsometry, we have undertaken the study of the obtained brushes in aqueous salt solutions at various grafting and charge densities.
[G'30.04] Solvent Polarity Effects in Ionomer Solutions.
Srinivas Nomula, Stuart Cooper (Department of Chemical Engineering, University of Delaware, Newark, DE.)
Model polyurethane ionomers are synthesized with regularly spaced ionic groups along the polymeric backbone. Dynamic Light Scattering applied to the ionomer solutions reveals two diffusive modes in non-polar as well as polar solvents. Only one diffusive mode is obtained for the underivatized polyurethane. The two modes, a fast mode (of the order of 10^-6 cm^2/s ) and a slow mode (of the order of 10^-8 cm^2/s ), differ by two orders of magnitude. In a non-polar solvent, toluene, the fast mode and slow mode correspond to the diffusion of single chains and aggregated ionomer chains in solution respectively. In polar solutions, the fast mode diffusion coefficient is seen to increase with the polarity of the solvent showing that diffusion coefficient of single polyions is enhanced by electrostatic interactions. The slow mode is found to be due to structures which are easily disrupted. This talk will discuss the effect of polarity of the solvent on the structures in ionomer solutions. In toluene, the aggregates consist of physically crosslinked chains where as in dimethylacetamide, the aggregates consist of polyions and counterions held together due to electrostatic interactions.
[G'30.05] Integral Equation Theory for the Conformational Properties and Static Structure Factor of Polyelectrolyte Solutions
Arun Yethiraj, Chwen-Yang Shew (Department of Chemistry, University of Wisconsin, Madison WI 53706.)
A theory is presented for the conformational properties and static structure factor of polyelectrolyte solutions. The polymer molecules are modeled as flexible chains that interact via a screened Coulomb site-site potential. In the theory, the many chain system is replaced by a single chain whose beads interact via the bare interaction plus a solvent-induced potential that approximately accounts for the presence of the other molecules. The solvent-induced potential and chain conformations are determined in a self-consistent fashion. The intramolecular correlation functions for a given solvent-induced potential are obtained either via a single chain Monte Carlo simulation or via a field theoretic approach. The predictions of the theory for the end-to-end distance and the static structure factor are in quantitative agreement with molecular dynamics simulations with no adjustable parameters. The predictions of the theory for the scaling of the peak in the structure factor with composition and charge fraction are consistent with experiments.
[G'30.06] The Structure of Flexible Polyelectrolytes at Non-zero Concentrations.
James P. Donley, Andrea J. Liu (U. C. Los Angeles^1)
Recently, we formulated a version of Debye-Hückel theory for polymers in solution at non-zero concentration.\footnotemark[2] Making use of the RPA, the theory captures the non-local aspect of the Debye screening length, which depends upon the structure of the molecules. We modelled the polymer structure itself as a semi-flexible chain with a single persistence length and solved for this parameter self-consistently. Our results are in reasonable quantitative agreement with simulation for the polymer end-to-end distance. Our present work goes beyond this generalized Debye-Hückel theory to elucidate the importance of: 1) modeling the polymer chain with a wave-vector dependent persistence length rather than just a constant; 2) incorporating explicit hard-core interactions; and 3) including higher order fluctuation corrections to our previous RPA treatment. We compare our results with recent simulations and experiment. \footnotetext[1]This work is supported by NSF grant CHE-9624090. \footnotetext[2]J.P. Donley, J. Rudnick and A.J. Liu, Macromolecules, in press.
[G'30.07] Phase Behavior of Ionomer Solutions in Non-polar Solvents
R. A. Weiss, K. Chakrabarty, T. A. P. Seery (University of Connecticut)
The phase behavior of solutions of the free acid and sodium salt derivatives of lightly sulfonated polystyrene in decalin were determined using light scattering. In general, association of the polar functional groups increases the upper critical solution temperatures for the solutions. The effects of sulfonation level and molecular weight of the polymers were also evaluated. In some cases, gelation of the solution preceded phase separation as the solution was cooled, which is in qualitative agreement with the theory of Joanny. Dynamic light scattering studies indicated that the formation of multichain aggregates precedes phase separation.
[G'30.08] Theory of Inhomogeneous Weakly Charged Polyelectrolytes
An-Chang Shi, Jaan Noolandi (Xerox Research Centre of Canada)
A theory of inhomogeneous multicomponent systems containing weakly charged polyelectrolytes is developed. The theory treats the polymer conformation and the electrostatics simutaneously using a functional integral representation of the partition function. A mean-field approximation to the theory leads to two sets of coupled mean-field equations: a generalized Poisson-Boltzmann equation describing the electrostatic potential, and a set of self-consistent field equations describing the equilibrium densities. The theory can be used to study the interfacial properties, microphase structures, and adsorptions of a variety of weakly charged polyelectrolyte systems. As a simple application, the interfaces between the polymer-rich and polymer-poor phases of a polyelectrolyte solution is studied.
[G'30.09] Conformational Properties of Charged Polymers in Poor Solvents
Chwen-Yang Shew, Arun Yethiraj (Department of Chemistry, University of Wisconsin, Madison WI 53706)
A simple theory is presented for the conformational properties of charged polymers in poor solvents. The theory extends an approach pioneered by diMarzio for neutral polymers to charged polymers. The starting point is an expression for the free energy in terms of the average polymer size, which is minimized with respect to the size to obtain the equilibrium conformations. For poor enough solvents the theory predicts a discontinuous transition from an extended to a collapsed state as the solvent quality is decreased. For high enough charge fractions the theory predicts a discontinuous transition from an extended to a collapsed as the solvent quality is decreased. The chain size probability distribution function is bimodal in the neighborhood of these transitions. These predictions are verified via computer simulations.
[G'30.10] Origin of Attractive Interactions between Two Like-charged Rods
Bae-Yeun Ha, Andrea J. Liu (UCLA)
Recent numerical simulations by Jensen, et al.(N. Gronbech-Jensen, R. J. Mashl, R. F. Bruinsma and W. M. Gelbart, preprint.) show that two like-charged rods (with associated counterions) can attract each other at low temperatures. Here we present a systematic theory to investigate this system. We model each rod together with its condensed counterions as the sum of a rod uniformly charged with the net charge, and a rod with a random, fluctuating distribution of charges of both signs and zero net charge. We find that at long distance, the interaction between two rods is repulsive due to the net charge on the rods. At short distances and at low temperatures, however, the interaction is attractive due to the charge fluctuations. We show that the charge fluctuations also give rise to additional counterion condensation; in other words, that there is a fluctuation correction to the limiting law due to Manning.
[G'30.11] Microphase Behavior Of Hydrogen Bonded Polystyrenesulfonate Ionomers From Dynamic Light Scattering Measurements
Thomas A. P. Seery, Kaushik Chakrabarty, Amit Sehgal, Robert A. Weiss (Polymer Program, University of Connecticut, Storrs CT)
Dynamic light scattering was used to investigate the phase diagram of a lightly sulfonated (< 2been previously characterized and the phase boundary obtained by cloudpoint measurements. The hydrogen bonding of the sulfonate groups is considered to be the driving force behind intermolecular aggregation that leads to phase separation at the cloupoint. Dynamic light scattering measurements exhibited multiple relaxation times at temperatures somewhat above the cloudpoints. The longer relaxation times correspond to multichain aggregates. Parallel measurements of the parent polystyrene provided a measure of chain expansion and a means of accounting for changing solvent quality for the chain backbone.
[G'30.12] Entangled States of Charged Polymers
Namkyoung Lee, Sergei Obukhov (University of Florida, Gainesville, FL 32611), Michael Rubinstein (University of North Carolina, Chapel Hill, NC 27599)
This abstract was not submitted electronically.