Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session B29: Charged and Ion-Containing Polymers II |
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Sponsoring Units: DPOLY Chair: M. Muthukumar, Univ. of Massachusetts Room: LACC 504 |
Monday, March 21, 2005 11:15AM - 11:27AM |
B29.00001: Brownian Dynamics Studies of Morphology and Dynamics of Associative Ionomers Aniket Bhattacharya, Monojoy Goswami, Sanat K. Kumar We propose to utilize computer simulations to understand the morphology and the viscoelastic properties of melts of polymers which have charges on their backbone with small counterions being carried along for charge neutrality (``ionomers''). While there has been significant theoretical and experimental research performed on ionomers, little systematic simulation work has been conducted which explicitly incorporates the long range Coulomb interaction among the charges on the polymer backbone and the counterions. We shall utilize Molecular dynamics simulations to study the aggregation behavior and reversible gelation of these materials, particularly focusing on the molecular aspects which drive the formation of local clusters studied recently by transmission electron microscopy (STEM)$^\dagger$. We will also study the unusual viscoelastic response, shear induced morphologies, and melting of the Coulomb gel using non-equilibrium molecular dynamics (NEMD) simulations.\\ $^\dagger$B.~Kirkmeyer, A, Taubert, J-S Kim, K.~I. Winey, Macromolecules {\bf 35}, 2648 (2002). [Preview Abstract] |
Monday, March 21, 2005 11:27AM - 11:39AM |
B29.00002: Phase Behavior of Polyelectrolyte Solutions Chi-lun Lee, M. Muthukumar The coexistence and spinodal curves for macrophase separation in salty solutions of flexible polyelectrolytes will be presented in terms of the valency of salt ions, and the molar mass of the polyelectrolyte. [Preview Abstract] |
Monday, March 21, 2005 11:39AM - 11:51AM |
B29.00003: Phase diagram of solution of oppositely charged polyelectrolytes Rui Zhang, B. I. Shklovskii We study a solution of long polyanions (PA) with shorter polycations (PC) and focus on the role of Coulomb interaction. A good example is solutions of DNA and PC which are widely studied for gene therapy. In the solution, each PA attracts many PCs to form a complex. When the ratio of total charges of PA and PC in the solution, $x$, equals to 1, complexes are neutral and they condense in a macroscopic drop. When $x$ is far away from 1, complexes are strongly charged. The Coulomb repulsion is large and free complexes are stable. As $x$ approaches to 1, PCs attached to PA disproportionate themselves in two competing ways. One way is inter-complex disproportionation, in which PCs make some complexes neutral and therefore condensed in a macroscopic drop while other complexes become even stronger charged and stay free. The other way is intra-complex disproportionation, in which PCs make one end of a complex neutral and condensed in a small droplet while the rest of the complex forms a strongly charged tail. Thus each complex becomes a ``tadpole.'' We get a phase diagram of PA-PC solution in a plane of $x$ and inverse screening radius of the monovalent salt, which includes phases with both kinds of disproportionation. [Preview Abstract] |
Monday, March 21, 2005 11:51AM - 12:03PM |
B29.00004: Influence of Neutralization on Amorphous-Phase Properties in Semicrystalline Ionomers Katsuyuki Wakabayashi, Richard A. Register Ethylene-methacrylic acid (E-MAA) ionomers contain lamellar polyethylene crystallites, amorphous copolymer segments and ionic aggregates, each of which affects the mechanical properties of the material. For a quantitative assessment of the contributions from each of the three structural motifs, we measured the ionomer modulus at 70 $^{\circ}$C, where the materials still contain substantial crystallinity, and applied a two-phase composite treatment (Davies Model) to extract the modulus of the amorphous phase. The amorphous phase modulus at 70 $^{\circ}$C increases with neutralization level as a consequence of physical crosslinking by the ionic aggregates; amorphous phase moduli for ionomers with varying comonomer content and neutralization levels approximately collapsed when plotted against the number density of ionic groups, with the modulus increasing with ion content in general agreement with simple rubber elasticity theory. Between 25 and 70 $^{\circ}$C, the relaxation behavior of ionomers differs substantially from that for unneutralized E-MAA copolymers. The ionomers exhibit two-step drops in the storage modulus prior to primary crystal melting, which we attribute to melting of secondary crystallites and devitrification of the amorphous phase, whose glass transition is elevated by neutralization. [Preview Abstract] |
Monday, March 21, 2005 12:03PM - 12:15PM |
B29.00005: Toward Reconciliation of STEM and SAXS Data from Ionomers by Investigating Gold Nanoparticles Nicholas Benetatos, Brian Smith, Paul Heiney, Karen Winey We have recently pioneered the use of scanning transmission electron microscopy (STEM) for direct, model independent imaging of the nano-scale morphology of ionomers. To date, the sizes of ionic aggregates determined in STEM experiments are inconsistent with SAXS data interpreted by the Yarusso-Cooper model. To address this discrepancy we have investigated a pair of model nanoparticles (11 and 55 atom Au clusters) with both STEM and SAXS. Using this model system we have improved our method of measuring nanometer scale objects and evaluated the importance of STEM probe size and specimen thickness. While the size of the STEM probe was inconsequential, specimen thicker than 50 nm showed significant depreciation of image quality, which limits our ability to accurately measure particle size. SAXS was performed on dilute suspensions of nanoparticles and fit using a monodisperse, hard-sphere form factor model. For Au11, STEM finds a diameter of 1.3 nm + .14 and SAXS finds a diameter of 1.4 nm. Similarly, both STEM and SAXS determine a diameter of 1.7 nm for Au55. Analysis of these model systems have allowed us to evaluate several factors of potential importance in reconciling STEM and SAXS data from ionomers. [Preview Abstract] |
Monday, March 21, 2005 12:15PM - 12:27PM |
B29.00006: In-situ process for synthesis of monodispersed semiconducting nanoparticle in polyelectrolyte matrix Vivek Maheshwari, Ravi Saraf The properties of Nanoparticles (NP) are influenced by their interaction with the surroundings. These interactions can result in enhancement or quenching of the luminescence from nanoparticles. We present a simple method for synthesis of Cadmium sulfide (CdS) nanoparticles in a polyelectrolyte (PE) matrix at room temperature. The final product is 100 micron PE particles embedded with CdS nanoparticles. Absorption studies indicate a uniform size of 3-4nm for CdS NP. This allows a single step assembly of NP/PE into a layered structure from the solution, atomic force microscopy studies of assembled layers will be presented. Also presented will be the electroluminescence properties of films prepared from these composite particles and optical studies of the colloid solution. A 430{\%} increase in photoluminescence is observed from the composite in comparison to the nascent particles extracted from the same. [Preview Abstract] |
Monday, March 21, 2005 12:27PM - 12:39PM |
B29.00007: Model for periodic pattern formation in salt precipitates during drop evaporation. Vladimir A Belyi, M Muthukumar Recent works on evaporating liquid drops have led to qualitative understanding of the deposit growth and, in particular, formation of tall rim near the drop contact line. However, emergence of more complex patterns in the evaporation deposit still remains unexplained. In the present work we analyze formation of periodic salt deposits in the evaporating water-polyelectrolyte-salt systems. We propose a model that explains formation of concentric rings in the salt deposits, as well as transition between radial and tangential directions in the salt deposit growth. [Preview Abstract] |
Monday, March 21, 2005 12:39PM - 12:51PM |
B29.00008: Pattern Formation in Drying Drops of Polyelectrolyte - Salt Solutions Deniz Kaya, Vladimir A Belyi, M Muthukumar We use optical microscopy, AFM, and SEM to investigate salt patterns formed during evaporation of aqueous solutions of sodium poly(styrene sulfonate) and sodium chloride (NaPSS/NaCl). Observed patterns exhibit significantly larger variety than in the simple "drying coffee drop" experiments. We find that varying the concentration ratios of polyelectrolyte/salt solutions leads to formation of qualitatively different patterns, including radially grown salt deposits, concentric rings of salt and other structures. Our results indicate that these patterns are also sensitive to evaporation rate of the droplet. However molecular weight of the polymer appears to have little to no effect on the observed patterns. [Preview Abstract] |
Monday, March 21, 2005 12:51PM - 1:03PM |
B29.00009: Counterion effect on rheology and morphology of polydimethylsiloxane ionomers Claude Coehn, Ashish Batra, Hansoo Kim, Karen Winey We have synthesized a series of polydimethylsiloxane ionomers with control over spacing between ions, number of ions/chain and molecular weight. Freshly precipitated transition metal zinc and cobalt ionomers with less than one mol {\%} of ions flow at room temperature and exhibit a zero shear-rate viscosity. X-ray scattering data and scanning transmission electron microscopy (STEM) data do not show any evidence of ionic aggregates. These ionomers form a network on annealing and the time to network percolation follows an Arrhenius dependence with temperature. Annealed zinc and cobalt ionomers also do not show any evidence of ionic aggregates that could be detected by X-rays or STEM leading to the conclusion that individual ion pairs act as cross-link points. Under similar conditions of spacing between ions and number of ions, barium ionomers, on the other hand, precipitate as weak networks at room temperature and form stronger gels on annealing. STEM and X-ray scattering from these ionomers show aggregate formation. At the higher 8 mol{\%} zinc ions, these ionomers also precipitate as gels and show rod-like aggregates with an aspect ratio of 20 and a diameter of 1nm as observed by STEM. [Preview Abstract] |
Monday, March 21, 2005 1:03PM - 1:15PM |
B29.00010: Miscibility of Polystyrene and Lighted Sulfonated Polystyrene Blends N.C. Zhou, W.R. Burghardt, R.J. Composto, K.I. Winey The blend miscibility of deuterated polystyrene (dPS) and lighted sulfonated poly(styrene-ran-sulfonated polystyrene) (P (S-SS)) has been examined by forward recoil spectrometry (FRES). Equilibrium coexistence compositions were determined for dPS:P(S-SSx) blends where x is the mole percent of sulfonation.At x = 0.2%, the blends are fully miscible at 150°C to 190°C, while at x = 2.6% the system fully immiscible at the same temperatures. Intermediate levels of sulfonation (0.7, 1.0 and 1.2%) are partially miscible and exhibit an upper critical solution temperature (UCST). This behavior is attributed to the dilution of repulsive intra-molecular interaction between the ionic and non-ionic groups in the copolymer due to favorable interactions with the non-ionic group of the homopolymer PS. Estimates using the Flory-Huggins and the copolymer effect theories found a large (~20) positive monomer-monomer interaction parameter between styrene and styrene sulfonate. This large interaction parameter might drive phase separation within a compositionally disperse random copolymers sample. [Preview Abstract] |
Monday, March 21, 2005 1:15PM - 1:27PM |
B29.00011: The behavior of multivalent ions in binary polyelectrolyte mixtures Olena Zribi, Ramin Golestanian, Tannie Liverpool, Hee Kyung, Hyung S. Lee, Gerard C. L. Wong Multivalent ions can induce condensation of like-charged polyelectrolytes into compact states, a process that requires different ion valence for different polyelectrolyte species. We investigate the condensation behavior of binary anionic polyelectrolyte mixtures consisting of DNA coils and F-actin rods in the presence of different multivalent ions (such as spermidine and tobramycin, a multivalent antibiotic). The mixture phase can separate into coexisting finite-sized F-actin bundles and DNA toroids. Further, by increasing the DNA volume fraction in the mixture, condensed F-actin bundles can be completely destabilized, leading to only DNA condensation within the mixture. We examine a number of possible causes and propose a model based on polyelectrolyte competition for ions. [Preview Abstract] |
Monday, March 21, 2005 1:27PM - 1:39PM |
B29.00012: Molecular Dynamics Simulations of Polyelectrolyte Networks De-Wei Yin, Juan J. de Pablo Polyelectrolyte networks exhibit discontinuous volume transitions due to electrostatic interactions involving charged monomers and counterions. We have conducted molecular dynamics simulations of crosslinked polyelectrolyte networks of various molecular weights, counterion valencies, solvent dielectricities, and backbone charge densities. Counterions are modeled explicitly to overcome limitations imposed by the Debye--H\"{u}ckel approximation, and the solvent is treated implicitly. Our results show that the osmotic pressure of polyelectrolyte networks depends greatly on the strength of electrostatic interactions, and that an unstable regime develops along isotherms when the interaction is strong. The structures of constituent chains in polyelectrolyte networks are compared with those in neutral networks and those of uncrosslinked linear polyelectrolyte chains, and both similarities and differences are found. We also present our observations in the context of leading theories on the swelling of polyelectrolyte networks and on the condensation of counterions on rigid and flexible polyelectrolyte chains. [Preview Abstract] |
Monday, March 21, 2005 1:39PM - 1:51PM |
B29.00013: Test-charge theory for the planar electric double layer Yoram Burak, David Andelman, Henri Orland A new model for the ion distribution near a charged surface is presented, based on the response of the ions to the presence of a single test particle. Near an infinite planar surface this model produces the exact density profile, in the limits of weak and strong coupling, which correspond to zero and infinite values of the dimensionless coupling parameter; at intermediate values of the coupling parameter the model produces approximate density profiles that agree semi-quantitatively with recent Monte-Carlo simulations. The model also sheds light on the occurrence of a distance-dependent crossover from exponential to algebraic decay, even at very large values of the dimensionless coupling parameter. [Preview Abstract] |
Monday, March 21, 2005 1:51PM - 2:03PM |
B29.00014: Spin Lattice Relaxation as a Probe of Carrier Dynamics in Conducting Polymer Poly-3-methyl-thiophene Gerard Gaidos, W.G. Clark, S.E. Brown, Reghu Menon Measurements of the proton spin lattice relaxation rate (1/$T_{1})$ in the conducting polymer poly-3-methyl-thiophene doped with PF$_{6}$ are reported over the temperature ($T)$ and magnetic field ($B_{0})$ ranges 2-300 K and 0.9-9.0 T respectively. They yield information regarding local magnetic fluctuations from charge carrier dynamics. Their dependence on $T$ and $B_{0}$ deviate from the Korringa law for 1/$T_{1}$ in metals. Below 35 K, two values for 1/$T_{1}$ are observed. At higher $T$, a more uniform relaxation is observed. These results suggest that localized and itinerant electrons are present in different regions of the sample, depending on $T$ and the degree of sample disorder. This interpretation is further supported by magnetic susceptibility measurements, which demonstrate Fermi glass behavior at low $T$. From these 1/$T_{1}$ measurements, the disordered fraction of our samples is obtained. This work was supported by NSF Grants DMR-0334869 and INT-0225578 (WGC), and DMR-0203806 (SEB). [Preview Abstract] |
Monday, March 21, 2005 2:03PM - 2:15PM |
B29.00015: Capillary Force Driven Nanoactuator Gaurav Singh, Ravi Saraf By stimulating an aqueous drop trapped between a substrate and $\sim $30 nm thick polymer film with AC electric field, we have designed an actuator with a frequency response up to (at least) 100 KHz. The amplitude of vibration of the polymer film is sensitive to the surface chemistry of the substrate (such as polymer brush, etc.) and ion concentration. The device shows only first order response and the amplitude is proportional to the magnitude of the AC field. We will present our recent results on the frequency response as a function of ion content and dynamics of ionic polymer brush such as, tethered DNA. The data will be explained in terms of electro-wetting phenomena. [Preview Abstract] |
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B29.00016: Diffusion of Labeled Polyelectrolytes in an Unlabeled Polyelectrolyte Matrix Solution Paul Russo, Rongjuan Cong, Elena Temyanko Fluorescence photobleaching recovery (FPR) was used to investigate the diffusion of fluoresceinamine-labeled poly(styrene sulfonate sodium salt) (LNaPSS, various molecular weights) in a matrix of unlabeled poly(styrene sulfonate sodium salt) (NaPSS, $M_{w}$ = 990,000). FPR selectively monitors the optical tracer self-diffusion coefficient of LNaPSS ($D)$. No long-term aggregates were detected. The matrix polymer slowed the self-diffusion of LNaPSS. When measuring $D$ of LNaPSS with three different molecular weights over the same range of matrix concentration, the results depended on molecular weight of the LNaPSS. When the matrix concentration exceeded 20 mg/g of water, $D$ was almost inversely proportional to molecular weight. In-situ dialysis FPR studies show that with the addition of salt, $D$ decreases more dramatically with matrix than without matrix. [Preview Abstract] |
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