Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session A17: Charged and Ion - Containing Polymers |
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Sponsoring Units: DPOLY Chair: Bulent Ozbas, Princeton University Room: Colorado Convention Center 102 |
Monday, March 5, 2007 8:00AM - 8:12AM |
A17.00001: Solvent effects on polyelectrolyte charge and conformation in solution Ralph Colby, Shichen Dou We study partially quaternized poly(2-vinyl pyridine) in a wide range of solvents, with chloride or iodide counterions. Dielectric spectroscopy (conductivity) determines the effective charge on the polymer, which increases systematically with solvent dielectric constant, but is significantly smaller than the Manning prediction for strongly charged polyelectrolytes in high dielectric constant solvents. Small-angle X-ray scattering and specific viscosity are used to provide two independent measures of the correlation length. The results motivate us to include ion solvation effects and both ion-dipole and dipole-dipole attraction effects in the `solvent quality' of the Dobrynin scaling model. For instance, the stronger dipole of condensed iodide makes ethylene glycol a poor solvent, while it is a good solvent for the polymer with chloride counterions. [Preview Abstract] |
Monday, March 5, 2007 8:12AM - 8:24AM |
A17.00002: Electrostatic Properties of an Entirely Hydrophilic Polyelectrolyte. David Hoagland, Alexei Popov A new of class of polyelectrolyte ionenes is described, one with an entirely hydrophilic backbone of quaternized nitrogens connected by polyoxyethylene spacers of controlled length. The chemistry of these pegylated ionenes yields solubility at constant charge density in solvents of varying dielectric constant; it also allows for controlled variation of polyelectrolyte charge density through choice of monomers. Such features make the new ionenes ideal model polyelectrolytes on which to test theories for electrostatic properties of polyelectrolytes. In particular, we report on the use of electrophoresis to measure effective charge density for different charge spacings and dielectric constants. In conformance with previous results for aliphatic ionenes, we find counterion condensation for pegylated ionenes at conditions different than classical predictions. Counterion condensation -- a constant effective charge density - is encountered in univalent electrolyte by the lowering of dielectric constant even when the dimensionless charge density is less than unity; conditions for the condensation depend on counterion identity (size). Additional studies on various anionic polyelectrolytes dissolved in nonaqueous solvents reproduce the same trends, suggesting their universality. [Preview Abstract] |
Monday, March 5, 2007 8:24AM - 8:36AM |
A17.00003: Formation, Structure and Electrochemical Impedance Analysis of Microporous Polyelectrolyte Multilayers Jodie Lutkenhaus, Kathleen McEnnis, Paula Hammond Microporous networks are of interest as electrolyte materials, gas separation membranes and catalytic nanoparticle templates. Here, we create microporous polyelectrolyte networks of tunable pore size and connectivity using the layer-by-layer (LBL) technique. In this method, a film is formed from the alternate adsorption of oppositely charged polyelectrolytes from aqueous solution to create a cohesive thin film. Using poly(ethylene imine) (PEI) and poly(acrylic acid) (PAA), LBL thin films of variable composition and charge density were assembled; then, the films were treated in an acidic bath, which ionizes PEI and de-ionizes PAA. This shift in charge density induces morphological rearrangement realized by a microporous network. Depending on the assembly pH and acidic bath pH, we are able to precisely tune the morphology, which is characterized by atomic force microscopy and scanning electron microscopy. To demonstrate the porous nature of the polyelectrolyte multilayer, the pores were filled with non-aqueous electrolyte (i.e. ethylene carbonate, dimethyl carbonate and lithium hexafluorophosphate) and probed with electrochemical impedance spectroscopy. These microporous networks exhibited two time constants, indicative of ions traveling through the liquid-filled pores and ions traveling through the polyelectrolyte matrix. [Preview Abstract] |
Monday, March 5, 2007 8:36AM - 8:48AM |
A17.00004: Influence of humidity and crystallization time on the conductivity of nanoparticle-filled solid polymer electrolytes Susan Fullerton, Janna Maranas The purpose of this study is to investigate two conditions that influence the conductivity of solid polymer electrolytes [SPEs]: humidity and crystallinity. SPEs cannot currently be used in solid-state lithium ion batteries because low room-temperature conductivity precludes effective application. Many modifications have been made to improve the conductivity; however, conductivity results vary widely for the same system investigated within different studies. One explanation is that SPE conductivity is extremely sensitive to experimental conditions which are often not reported. We investigate the consequence of humidity on conductivity, and the time at which conductivity is measured following sample preparation. Specifically, we choose nanoparticle-filled SPEs as an example to demonstrate that various conclusions can be made regarding the influence of nanoparticles on conductivity, depending on the experimental conditions. [Preview Abstract] |
Monday, March 5, 2007 8:48AM - 9:00AM |
A17.00005: Counterion Effects on Ion Mobility and Mobile Ion Concentration of Doped Polyphosphazenes and Polyphosphazene Ionomers Jim Runt, Robert Klein Previous investigations have shed some light on the ion conduction process in polymer electrolytes, yet ion transport is still not well understood. Here, upon the application of a physical model of electrode polarization to two systems with nearly identical chemical structure, one composed of an ionomer (MI) with a single mobile cation, and the other a salt-doped polymer (M+S) with mobile cation and mobile anion, quantitative comparison of the conductivity parameters is achieved. The polymer electrolyte chemistries of both MI and M+S are based on poly(methoxyethoxy-ethoxy phosphazene) (MEEP). The glass transition was found to be an important factor governing the conductivity and ion mobility. However, even accounting for the glass transition, the mobility of ions in the M+S system is 10 times larger than that in the MI system, which must arise from faster diffusion of the anion than the cation. Values for mobile ion concentration are also approximately 10 times higher in M+S than MI. These differences originate from free volume available for diffusion and local environment surrounding the ion pairs, demonstrating that the location of the ion pairs in the polymer matrix has a crucial effect on both conductivity parameters. Research supported by NSF Polymers Program. [Preview Abstract] |
Monday, March 5, 2007 9:00AM - 9:12AM |
A17.00006: Ion mobility and mobile ion concentration in PEO-based polyurethane ionomers Daniel Fragiadakis, Shichen Dou, Ralph Colby, James Runt The conductivity of a series of single-ion conducting polyurethane ionomers, based on poly(ethylene oxide) (PEO) segments and containing Li$^{+}$ and Na$^{+}$ cations, was studied using dielectric spectroscopy. The application of a physical model of electrode polarization allows the separate determination of the ion mobility and the mobile ion concentration as a function of temperature. The influence of temperature, type of mobile cation, and water content on the parameters determining the ionic conductivity was investigated, in order to contribute to the understanding of the mechanisms of ion conduction. The conductivity is also discussed in relation to the glass transition and dielectric relaxation processes of the materials. The results are compared to those of previous studies on PEO-based polyester ionomers having a closely related chemical structure. [Preview Abstract] |
Monday, March 5, 2007 9:12AM - 9:24AM |
A17.00007: Conformational structures in dry ionomers Elshad Allahyarov, Philip Taylor The molecular architecture of polymer electrolyte membranes (PEM), which consist of hydrophobic and hydrophilic segments, leads to its own self-assembled structure through a partial phase segregation. Controlling these structures is necessary for improving the performance of fuel cells. We have used computer simulation to analyze the relationship between the hydrophilic cluster structure and the parameters describing the pendant side chains in dry Nafion-like materials. We investigate the morphology of a dry PEM system within different coarse-grained models: a free-proton model, a dipolar model for side chains, and a branched-chain model. We conclude that the free-proton model, where the proton-proton correlations are decoupled from the sulfonate-sulfonate correlations, has the potential to explain the experimentally observed conformational structures of PEM. We find that the geometry of domains with a high concentration of sulfonate groups depends only weakly on the form of the distance-dependent dielectric permittivity, but strongly depends on the partial charge and monomeric unit sequence distribution along the ionomer chain. We predict a nanophase separation with a lamellar-like morphology in ionomers carrying a divalent salt. [Preview Abstract] |
Monday, March 5, 2007 9:24AM - 9:36AM |
A17.00008: Water Diffusion in Ultrathin Ionomer Thin Films: Neutron Reflectivity Study Lilin He, Erik B. Watkins, Jaroslaw Majewski, Cy H. Fujimoto, Christopher J. Cornelius, Dvora Perahia The mechanism of penetration of solvents into ionic random co-polymers is a key to formation of polymeric membranes with selective transport. The pathways of diffusion depend on molecular parameters including the chemical structure, ionic strength and conformation of the polymer. The penetration of water into thin (on the order of magnitude of several R$_{g}$'s) highly rigid sulfonated polyphenlylene films, supported on SiOx substrate as a function of time was investigated by neutron reflectometry. The ionomer films were exposed to saturated vapor and to liquid water and reflectometry patterns were recorded until equilibrium was reached. Increase thickness due to swelling was observed in both cases whereas exposure to vapors results in reversible changes and contact with bulk water, transform the film permanently. The onset of the diffusion is Fickian, however the distribution of the solvent within in the film is not uniform. Clear interfacial segregation is denoted. [Preview Abstract] |
Monday, March 5, 2007 9:36AM - 9:48AM |
A17.00009: Nanoscale Morphology of Sulfonated Polystyrene Ionomers Nancy C. Zhou, Karen I. Winey We have applied our scanning transmission electron microscopy (STEM) methods to investigate the size, shape and spatial distribution of the ionic, nanoscale aggregates in poly(styrene-\textit{ran}-styrene sulfonate) (P(S-SS$_{x}))$ ionomers. This analytical electron microscopy method minimizes phase contrast that can obscure nano-scale features and accentuates differences in atomic number. We recently reported quantitative agreement between STEM and X-ray scattering results in a Cu-neutralized poly(styrene-\textit{ran}-methacrylic acid) (SMAA) ionomer with respect to the size of the ionic aggregates and their number density. For this study, P(S-SS$_{x})$ ionomers were prepared by solution neutralizing with metal acetates, solution casting, and annealing. Initial STEM results from P(S-SS$_{0.019})$ fully neutralized with Zn indicate a uniform distribution of monodisperse spherical aggregates. Combining direct imaging and X-ray scattering of P(S-SS$_{x})$ ionomers, we will investigate the effect of cation type and level of neutralization. [Preview Abstract] |
Monday, March 5, 2007 9:48AM - 10:00AM |
A17.00010: Morphology and Proton Transport in Polyimide-Polysiloxane Segmented Copolymers Lijun Zou, Mitchell Anthamatten Sulfonated polyimides are fuel cell candidates due to their good mechanical, chemical, and thermal stability, and their relatively high proton conductivity. Here we report the one-pot synthesis of sulfonated polyimide-polysiloxane segmented copolymers through the reaction of a dianhydride with a mixture of three diamines: a non-ionic aromatic diamine (4,4'-oxydianiline), a sulfonated diamine (4,4'-diamino-2,2'-biphenyldisulfonic acid), and a telechelic diamino polysiloxane. The presence of ionic clusters that are covalently connected to hydrophobic siloxane groups lead to interesting morphologies, swelling behavior, and proton transport characteristics. Equilibrium water sorption studies of cast films show that the presence of siloxane segments does not interfere with water swelling, suggesting microphase-segregation. TEM analysis shows evidence of phase-segregation in sulfonated polyimides and reveals that siloxane segments strongly affect ionic clustering. [Preview Abstract] |
Monday, March 5, 2007 10:00AM - 10:12AM |
A17.00011: Morphological Study of Model Poly(Ethylene-Acrylic Acid) Ionomers Christopher D. Chan, Travis W. Baughman, Kathleen L. Opper, Kenneth B. Wagener, Karen I. Winey We have synthesized \textit{linear} poly(ethylene-co-acrylic acid) (EAA) copolymers with precisely and randomly placed acid groups using ADMET (acyclic diene metathesis) and ROMP (ring opening metathesis polymerization). In the acid form, the EAA copolymers with precisely placed acid groups exhibit the typical orthorhombic PE crystal structure along with a new layered structure. The layered structures are more pronounced at lower acid content and have spacings consistent with the separation between acid groups; at 9.5mol{\%} acid the layer-to-layer spacing is 2.53 nm. Given the PE crystal lamellae spacing determined by SAXS, each PE lamellae contains 2 to 6 acid-rich layers. The EAA copolymers with random acid groups do not exhibit well-developed layered structures. When these linear EAA copolymers are neutralized with zinc acetate in solution, STEM and X-ray scattering are used to characterize the Zn-rich ionic aggregates. Preliminary results have indicated that the ionic interactions dominate and disrupt the acid-acid layered structure even at partial neutralization. [Preview Abstract] |
Monday, March 5, 2007 10:12AM - 10:24AM |
A17.00012: Proton Conducting Membranes from Fluorinated Poly(Isoprene)-\textit{block}-Sulphonated Poly(Styrene): Structure and Transport Properties. Akinbode Isaacs-Sodeye, Samuel Gido, Tianzi Huang, Jimmy Mays Proton Conducting Membranes used in Fuel Cells typically comprise of ionomers, having hydrophobic backbones and hydrophilic acid bearing side chains. Cell Efficiencies are determined by membrane morphology amongst other factors. Our work is aimed at optimizing the morphology and ultimately properties of our relatively cheaper fluorinated Poly(Isoprene)-block-sulphonated Poly(Styrene) block copolymer ionomer membranes, made from post polymerization modified PS-PI. Samples have been synthesized with two levels of sulphonation of polystyrene units (25mol{\%} and 50mol{\%}), and two counterions (Cesium and proton). Analysis of our membranes has been carried out using SAXS/SANS, Gravimetry, Diffusion Cells and Electrochemical Impedance Spectroscopy. SAXS and SANS data have shown a 63{\%} increase in domain spacing upon soaking the 50mole{\%} Acid form with heavy water for 16hours at 60oC. This sample also had a water uptake value of 595{\%} and an order of magnitude less methanol permeability than Nafion{\texttrademark} 112 at ambient temperature. [Preview Abstract] |
Monday, March 5, 2007 10:24AM - 10:36AM |
A17.00013: Polyelectrolyte Interfacial Swelling and Film Stability Vivek Prabhu, Ashwin Rao, Shuhui Kang, Eric Lin, Sushil Satija The phase stability of polyelectrolytes at interfaces and in thin films are of fundamental interest for the fabrication of high resolution features by photolithography. In this process, a latent chemical image is formed within a thin polymer film by exposure to light and subsequently resolved by selective dissolution. The selective dissolution occurs at a polyelectrolyte copolymer gradient comprised of hydrophilic (weakly acidic) and hydrophobic groups. The balance between the hydrophobicity and hydrophilicity (degree of ionization) controls the film stability when exposed to an aqueous hydroxide solution. The average copolymer content that dissolves away can be understood by phase diagrams, but a residual material that swells, but does not dissolve, occurs within the gradient interface. Controlling this swelling amplitude and depth is of technological interest to prepare high fidelity features of ever smaller dimensions. Contrast variant neutron reflectivity and quartz crystal microbalance quantify this nanometer-scale spatial distribution of polyelectrolyte and aqueous base. The swelling spatial extent measured during in situ dissolution, water rinse, and drying implies the polymer profile is dynamic on the nanometer scale. The profile control by ionic strength and charge valence will also be discussed. [Preview Abstract] |
Monday, March 5, 2007 10:36AM - 10:48AM |
A17.00014: ATRP-derived functional polymers for electronic applications Tracy Bucholz, Joung Eun Yoo, Sally Peng Li, Yueh-Lin Loo Traditionally, the controlled synthesis of functional polymers has been challenging due to the incompatibility of chemical functional groups with the propagating active centers during polymerizations. This barrier, however, has been overcome with the development of atom transfer radical polymerization (ATRP). Using this technique, in combination with ring-opening polymerization, we have successfully synthesized well-defined block copolymers containing polypentafluorostyrene (PPFS) and polylactide (PLA). Acid-catalyzed degradation of the PLA block yields PPFS films with nanoscale pores whose size and spacing are tunable through control of the diblock copolymer molecular weight and composition. The introduction of porosity to PPFS films lowers the dielectric constant, useful as isolation for interconnects. In addition, we used ATRP to synthesize well-defined homopolymers of and block copolymers containing poly(2-acrylamido-2-methyl-1-propanosulfonic acid). We used these polymers as templates for the subsequent polymerization of aniline (PANI) to create water-dispersible, directly patternable polymer conductors for thin film electronics. We can tune the conductivity of PANI through control over the molecular characteristics of the polymer acid template. [Preview Abstract] |
Monday, March 5, 2007 10:48AM - 11:00AM |
A17.00015: The nature of water in hydrated acid-form Nafion membranes G. Polizos, Z. Lu, D.D. Macdonald, E. Manias The nature of water in perfluorinated membranes in the acid form (Nafion) was quantified at several hydration levels by dielectric relaxation spectroscopy. Two different experimental setups were used to probe both the low frequencies (10$^{-2}$-10$^7$ Hz, -50 to 25$^{\circ}$C) and the microwave region (0.045-26 10$^9$Hz, 25 to 45$^{\circ}$C). The competition between sulfonic-group/water attraction and water/water hydrogen-bonding, in addition to confinement effects, give rise to three states of water, manifested through distinct dynamical behaviors: The cooperative relaxation time distribution of free (isotropic) water networks is identified as the fastest process, whereas water molecules strongly bound to the charged sulfonic groups correspond to the lowest frequencies. A third relaxation mode is also observed with relaxation times at high frequencies close to the bulk water, which is attributed to ``loosely'' bound water. These water states can be correlated with the respective Nafion phase separated morphologies and the corresponding proton conductivities. [Preview Abstract] |
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