Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session K25: Polymer Electrolytes and Conduction |
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Sponsoring Units: DPOLY Chair: Bulent Ozbas; Princeton University Room: Baltimore Convention Center 322 |
Tuesday, March 14, 2006 2:30PM - 3:06PM |
K25.00001: BREAK
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Tuesday, March 14, 2006 3:06PM - 3:18PM |
K25.00002: Conformational transition of polybenzimidazole in N,N-Dimethylacetamide/lithium chloride. Christopher Shogbon, Haifeng Zhang, Brian Benicewicz, Yvonne Akpalu, Jean-Luc Brousseau Static light scattering and circular dichroism techniques have been used for the first time to study the chain conformation of a previously synthesized $m$-PBI sample in DMAc/LiCl. The chain conformation was studied as a function of a) polymer concentration (0.1 to 20 mg/mL) at a fixed salt concentration of 4 {\%} LiCl and b) salt concentration (0.05 to 7 {\%}) at a fixed polymer concentration of 0.3 mg/mL. As polymer or salt concentration was increased, the chains collapsed initially, and then underwent fluctuations in size without a significant decrease in their average size. The collapse was associated with a conformational transition from random coil to an ``extended wormlike'' chain. At polymer concentrations greater than 9 mg/mL, the average size of the polymer chain is relatively constant at 31.2 $\pm $ 1.7 nm. Circular dichroism measurements confirmed the conformational transitions that had been observed by indicating optical activity at polymer concentrations above 2 mg/mL. These results contribute to our overall understanding of chain stiffness and conformational transitions in PBI polymers, which may play an important role in the preparation of polymer electrolyte membranes via sol-gel processing. [Preview Abstract] |
Tuesday, March 14, 2006 3:18PM - 3:30PM |
K25.00003: Nanostructured Polymer Electrolytes Omolola Odusanya, Mohit Singh, Nitash Balsara We present results on work on polystyrene-b-polyethyleneoxide copolymer electrolyte membranes. The volume fraction of the ethylene oxide block is 0.38 and molecular weight of each block is 36 kg/mol and 25 kg/mol respectively for the polystyrene and ethyleneoxide blocks. These electrolytes were made by doping with lithium bis(trifluoromethylsulfonyl)imide salt with the ratio of Li ion / ethylene oxide units ranging from 0.02 to 0.1. The salt/polymer samples were pressed into 1.0mm thick and 4.0 mm ID pellets in an air-free environment and measurements were made from 80$^{o}$C to 120$^{o}$C. Transmission Electron Microscopy and Small Angle X-ray Scattering experiment results indicate that our samples have a perforated hexagonal morphology. Conductivity results using AC impedance spectroscopy show that we are able to achieve values of $\sim $ 0.0001 S/cm, well within the theoretical upper limit expected for these samples while maintaining a high mechanical integrity of about 0.1GPa as determined from rheology. Achieving the combination of high conductivity with mechanical strength, which we observe in our results, has been a major problem in the battery research community. [Preview Abstract] |
Tuesday, March 14, 2006 3:30PM - 3:42PM |
K25.00004: Proton Conducting Membranes from Fluorinated Poly(Isoprene)-\textit{block}-Sulphonated Poly(Styrene): A Structure Vs Property Study. 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 limited by membrane morphology amongst other things. This study is a step towards tuning 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. Work on random and graft copolymer ionomers especially Nafion $^{TM}$ have shown that morphologies of membranes from such materials vary with temperature, water content, counterion and No. of acid groups per chain etc. Analysis of our membranes using USAXS and SANS aims to explore the above mentioned variables; furthermore methanol permeability and proton conductivity will be studied using a diffusion Cell and impedance spectroscopy respectively. [Preview Abstract] |
Tuesday, March 14, 2006 3:42PM - 3:54PM |
K25.00005: Proton transport through polymeric membranes Xinyu Wang, Rich Woudenberg, Ozgur Yavuzcetin, Sergio Granados, Bryan Coughlin, Mark Tuominen Hydrogen fuel cells have drawn increasing attention from researchers because of the steadily declining supply of fossil fuels. A key component of a fuel cell is a membrane that is an efficient conductor of protons, but not electrons or molecules. Nafion currently is the dominant material chosen for this purpose, with proton conductivity facilitated by an imbibed network of water. Unfortunately, this material loses its conductivity as it becomes dehydrated at elevated temperatures. In this work we make a detailed examination of the physics of proton conductivity in anhydrous polymeric membranes though temperature-dependent DC current-voltage characterization, AC impedance spectroscopy and Hall effect measurements. We assess the relevance of fundamental proton conductivity models involving thermo-mechanical and electro-mechanical transport mechanisms. This work is supported by DOE grant 10759-001-05, NSF grant DMR-0306951 and MRSEC. [Preview Abstract] |
Tuesday, March 14, 2006 3:54PM - 4:06PM |
K25.00006: Performance of Nanostructured Polymer Electrolytes in Li Batteries Mohit Singh, Lola Odusanya, Nitash Balsara Batteries that employ Li anodes for high energy density applications suffer from failures due to side reactions and dendrite growth on the Li electrodes. A recent theory by Newman and Monroe (2005) shows that dendrite formation can be prevented if the shear modulus of the electrolyte can be increased by several orders of magnitude without a concomitant decrease in conductivity. The nanostructured polymer electrolyte (PE) in our study has a modulus of a glassy polymer. AC impedance measurements on Li/PE/Li systems show that the PE has high ionic conductivity. We present experimental data on the performance of a novel nanostructured dry PE in a Li/PE/Li battery. We report the DC cycling measurements, interfacial resistance measurements, and dendrite growth characteristics in Li/PE/Li cells. The performance of the nanostructured PE is compared with that of PE based on the homopolymer poly(ethylene oxide), which is a benchmark for dry polymer electrolytes. [Preview Abstract] |
Tuesday, March 14, 2006 4:06PM - 4:18PM |
K25.00007: PEO mobility in nanoparticle-filled polymer electrolytes as measured by neutron scattering Susan Fullerton, Janna Maranas, Victoria Garcia Sakai The mobility of poly(ethylene oxide) [PEO] is measured for solid polymer electrolyte systems of PEO/LiClO4 and PEO/LiClO4/Al2O3, where LiClO4 is the lithium salt and Al2O3 is the nanoparticle filler. While the addition of nanoparticles has been shown to improve conductivity in solid polymer electrolytes, the molecular mechanism is unclear. Some suggest the addition of nanoparticles increases PEO mobility, while others suggest nanoparticles act like crosslinkers, pinning PEO at the ether oxygen atoms - decreasing PEO mobility. The glass transition temperatures of polymer electrolytes filled and unfilled with nanoparticles differs by only a few degrees, making it difficult to interpret the influence of nanoparticle fillers on PEO mobility. However, mobility can be directly measured by quasielastic neutron scattering, and has previously been used to measure a system of PEO/LiClO4. We measure PEO mobility using the High-Flux Backscattering Spectrometer [HFBS] and the Disk Chopper Time-of-Flight Spectrometer [DCS] at the NIST Center for Neutron Research in Gaithersburg, Maryland. The two techniques measure motion on a timescales ranging from 240 ps to 2 ns, and 0.1 ps to 40 ps respectively. PEO mobility is measured for filled and unfilled solid polymer electrolytes at 323K. The addition of LiClO4 imparts a second, slower process, and the addition of nanoparticle fillers increases PEO mobility. [Preview Abstract] |
Tuesday, March 14, 2006 4:18PM - 4:30PM |
K25.00008: Effects of Temperature and Dissolved LiClO$_{4}$ on the Viscoelastic and Dynamic Properties of Poly(ethylene oxide), (PEO) Melts R.B. Bogoslovov, J.C. Selser, S. Peng Poly(ethylene oxide)/lithium perchlorate (PEO/LiClO$_{4})$ complexes are widely studied as a prototype solid polymer electrolyte in rechargeable lithium-polymer batteries. Characterizing the structure and dynamics of the system in its molten state is important for understanding the role of the polymer environment in lithium ion transport and conductivity. A fiber-optic coupled Fabry-Perot interferometer is employed in the investigation of the electrolyte viscoelastic and dynamic properties, which are both related to the intrachain local mobility and therefore to ion diffusion. The properties of the system are studied as a function of composition, temperature, and frequency. Structural relaxation processes are observed both in the neat polymer melt and in the salt containing electrolytes. A unique $q$-dependent measurement is performed, allowing the investigation of the Brillouin frequency and linewidth as a function of frequency. It revealed a double-step relaxation in the gigahertz frequency range. The two relaxations are identified as secondary relaxations with Maxwell-Debye character. [Preview Abstract] |
Tuesday, March 14, 2006 4:30PM - 4:42PM |
K25.00009: Local Ion Motion and Interactions in Single-Ion Polymer Electrolytes via Dielectric Spectroscopy Robert Klein, Shihai Zhang, Shichen Dou, Ralph Colby, James Runt A novel method is presented whereby the parameters quantifying the conductivity of polymer electrolytes can be extracted from the phenomenon of electrode polarization in dielectric spectroscopy. The validity of the model was confirmed by examining the effects of sample thickness and temperature, as well as by comparison of predicted and measured conductivities. Ion mobilities and mobile ion concentrations of neat and `gel' forms are compared for poly(ethylene oxide)-based sulfonated ionomers. The mobile ion concentration of the neat ionomers was found to be a surprisingly low fraction of the total ion concentration, but increases substantially in the gel ionomers. Furthermore, the temperature dependence of mobility changes from VFT-like for the neat ionomers, to more Arrhenius-like for the gel ionomers. In addition, adding plasticizers to the ionomer significantly influences the local beta process, and the effects are quantified as a function of the dielectric constant and donor number of the plasticizer, and related to the conductivity. [Preview Abstract] |
Tuesday, March 14, 2006 4:42PM - 4:54PM |
K25.00010: Confined Water in Ionic Membranes: Studied by NMR Lilin He, Cy Fujimoto, Christopher Cornelius, Dvora Perahia Proton NMR studies have been carried out to identify the location and dynamics of water confined within highly rigid sulfonated ionomer membranes. Understanding the dynamics and location of water molecules within polymeric ionic membrane, is critical to their many potential uses from fuel cell application to water purifying membranes. The magnetic relaxation times are sensitive to the degree of confinement of the molecules and the chemical environment affects the resonance frequency (chemical shift) of the water. Three different environments have been identified, highly mobile, almost free water molecules, partially confined in hydrophilic environment and water molecule that penetrated into the hydrophobic regime. Where surprisingly no fast exchange between these sites was detected even at room temperature. The distribution between these sites strongly depend on the degree of ionization of the polymers. [Preview Abstract] |
Tuesday, March 14, 2006 4:54PM - 5:06PM |
K25.00011: E-Field Dependent Conduction Mechanisms in Low Density Polyethylene Jerilyn Brunson, J.R. Dennison Successful conduction mechanisms have been developed for amorphous solids and semi-conductors for electric field dependent charge carrier mobility. Where electrons are the primary charge carriers, their mobility is dependent on their probability of hopping between potential well trapping sites. Extending these conduction mechanisms to polymers, resistivity can be directly related to carrier mobility within the bulk. A series of low electric field resistivity measurements at constant temperature have been made to test the Poole-Frenkel theory of field-enhanced hopping conduction in low density polyethylene. [Preview Abstract] |
Tuesday, March 14, 2006 5:06PM - 5:18PM |
K25.00012: Ab initio study of a class of metalorganic systems Harald O. Jeschke, L. Andrea Salguero, Roser Valenti, Badiur Rahaman, Tanusri Saha-Dasgupta, Christian Buchsbaum, Martin U. Schmidt, Matthias Wagner We use first principles methods to study the electronic properties of a Cu(II) coordination polymer. We have introduced two substitutions on the polymer in order to investigate the influence of the change of constituents in the hydroquinone molecule on the interactions between the metal centers. Furthermore, we have introduced two different ligand molecules in order to simulate the effect of satellite molecules in a real sample in the laboratory. In the preparation and analysis of the structures, we optimize computational efficiency and precision by employing four different methods: We initially prepare structures with classical force field methods, then we relax the rough structure by ab initio molecular dynamics. The analysis is done with a full-potential linearized augmented plane-wave (LAPW) method and by downfolding with the N-th order muffin tin orbitals (NMTO) method. We find subtle changes of the interaction between the metal centers and of the band structure with each substituent or ligand molecule. [Preview Abstract] |
Tuesday, March 14, 2006 5:18PM - 5:30PM |
K25.00013: Computer simulation of supramolecular assembly by metal-ligand complexation Shihu Wang, Chun-Chung Chen, Elena E. Dormidontova Monte Carlo simulations were employed to study the supramolecular assembly of oligomers end-functionalized by ligands capable of complexation with metal ions. The properties of these metallo-supramolecular polymers strongly depend on the oligomer concentration, strength of complexation, and metal-to- ligand ratio. At high oligomer concentration the average molecular weight exhibits a maximum near the stoichiometric composition and decreases for higher or lower metal content. On the other hand, at low oligomer concentration the molecular weight shows a local minimum around the stoichiometric composition. This unusual behavior is attributed to the larger population of small rings around the stoichiometric composition, which make up a significant fraction of the overall molecular weight at low oligomer concentration. This effect is especially pronounced at low temperature, where the fraction of rings is higher. The fraction of chains and rings for different concentrations, temperatures and oligomer lengths were calculated and compared with experimental data. [Preview Abstract] |
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