Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session J21: Focus Session: Polymers for Energy Storage and Conversion I- Capacitors and Fuel Cells |
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Sponsoring Units: DPOLY GERA Chair: Michael Chabinyc, University of California, Santa Barbara Room: 406 |
Tuesday, March 4, 2014 2:30PM - 3:06PM |
J21.00001: DILLON MEDAL SYMPOSIUM BREAK |
Tuesday, March 4, 2014 3:06PM - 3:18PM |
J21.00002: Effect of Dipolar Orientational Polarization on Electronic Conductivity in Ferroelectric Polymer Electrets Lianyun Yang, Lei Zhu The leakage current, ion migration, and dipolar orientational polarization are major losses in ferroelectric polymers. The loss from the leakage current originates from electronic conduction and its behavior could be significantly affected by the internal electric field, which is induced by the dipolar orientational polarization. In this work, the leakage current in the corona charged PVDF electrets is studied under different external electric fields. Under low applied electric field, when no or very few dipoles could flip, the conductivity from the leakage direct current increases upon increasing the electric field. Under higher electric field, the aligned dipole-induced internal field would prevent the electrons from going through so that the conductivity decreases. After all the dipoles are aligned with the external electric field, the conductivity can increase again. This study will help us better understand the interplay between electronic conduction and dipolar orientation in ferroelectric materials. [Preview Abstract] |
Tuesday, March 4, 2014 3:18PM - 3:30PM |
J21.00003: Structural and Interfacial Effects on the Dielectric Properties of PVDF and its Composites for Energy Storage Jennifer Jones, Anthony Mayo, Lei Zhu, Norman Tolk, Richard Mu High energy density capacitors based on dielectric polymers are a focus of increasing research effort motivated by the possibility to realize compact and flexible energy storage devices. Multilayered ferroelectric polyvinylidene fluoride (PVDF) systems are fabricated using enabling technology in co-extrusion for increased energy storage efficiency. These micro- and nano-layered polymeric systems result in much improved device performance and a three-time enhancement of capacitive electrical energy density has been demonstrated. PVDF thin film nanocomposites with ZnO nanofillers have also been fabricated and evaluated for further enhancement of energy density storage. To understand the physics of why these multilayered and nanocomposite systems perform better than single layer PVDF we are developing characterization techniques using confocal second harmonic generation (SHG), electric field induced second harmonic (EFISH) and Raman laser spectroscopy. Our results have shown that the combination of Raman and SHG is a very sensitive, non-destructive and versatile technique that can be used to study the ferroelectric and structural properties of these systems. The addition of the EFISH technique allows the interrogation of structural and dielectric properties within individual layers and at the interfaces. [Preview Abstract] |
Tuesday, March 4, 2014 3:30PM - 3:42PM |
J21.00004: Multiscale simulations of polyurea-based dielectrics for capacitive energy storage Rui Dong, Vivek Ranjan, Marco Buongiorno Nardelli, Jerzy Bernholc In high energy capacitors, bi-axially oriented polypropylene is the preferred the state-of-art low loss dielectric. However, its energy density only reaches 4 J/cm$^3$ at 600 MV/m with 85\% efficiency, while the recently synthesized polythiourea reaches 8 J/cm$^3$ with 95\% efficiency under the same conditions [1]. Members of the aromatic polyurea family [2] have also been reported to have similarly high energy densities. We have performed multiscale simulations to investigate several members of the polyurea/ polythiourea family, focusing on their structural and dielectric properties. Antiparallel packing of urea/thiourea units is found to be preferred energetically, but the energy surfaces are remarkably flat overall, with several distorted and disordered structures being energetically close. Nevertheless, microscopic geometries are found to be critical for the ionic response. Local disorder leads to larger permittivities, but also increased losses. [1] Wu et al, Advanced Material, 25, 1734 (2013). [2] Wang et al, APL 94, 202905 (2009). [Preview Abstract] |
Tuesday, March 4, 2014 3:42PM - 3:54PM |
J21.00005: Effect of Organic Blocking Layer on the Energy Storage Characteristics of High-Permittivity Sol-Gel Thin Film Based on Neat 2-Cyanoethyltrimethoxysilane Yunsang Kim, Mohanalingam Kathaperumal, Ming-Jen Pan, Joseph Perry Organic-inorganic hybrid sol-gel materials with polar groups that can undergo reorientational polarization provide a potential route to dielectric materials for energy storage. We have investigated the influence of nanoscale polymeric layer on dielectric and energy storage properties of 2-cyanoethyltrimethoxysilane (CNETMS) films. Two polymeric materials, fluoropolymer (CYTOP) and poly(p-phenylene oxide, PPO), are examined as potential materials to control charge injection from electrical contacts into CNETMS films by means of a potential barrier, whose width and height are defined by thickness and permittivity. Blocking layers ranging from 20 nm to 200 nm were deposited on CNETMS films by spin casting and subjected to thermal treatment. Polarization-electric field measurements show 30\% increase in extractable energy density with PPO/CNETMS bilayers, relative to CNETMS alone, due to improved breakdown strength. Conduction current of the bilayers indicate that onset of charge conduction at high field is much delayed, which can be translated into effective suppression of charge injection and probability of breakdown events. The results will be discussed in regards to film morphology, field partitioning, width and height of potential barrier, charge trapping and loss of bilayers. [Preview Abstract] |
Tuesday, March 4, 2014 3:54PM - 4:06PM |
J21.00006: Structured block copolymer thin film composites for ultra-high energy density capacitors Saumil Samant, Shimelis Hailu, Christopher Grabowski, Michael Durstock, Dharmaraj Raghavan, Alamgir Karim Development of high energy density capacitors is essential for future applications like hybrid vehicles and directed energy weaponry. Fundamentally, energy density is governed by product of dielectric permittivity $\varepsilon $ and breakdown strength V$_{bd}$. Hence, improvements in energy density are greatly reliant on improving either $\varepsilon $ or V$_{bd}$ or a combination of both. Polymer films are widely used in capacitors due to high Vbd and low loss but they suffer from very low permittivities. Composite dielectrics offer a unique opportunity to combine the high $\varepsilon $ of inorganic fillers with the high V$_{bd}$ of a polymer matrix. For enhancement of dielectric properties, it is essential to improve matrix-filler interaction and control the spatial distribution of fillers for which nanostructured block copolymers BCP act as ideal templates. We use Directed Self-assembly of block copolymers to rapidly fabricate highly aligned BCP-TiO2 composite nanostructures in thin films under dynamic thermal gradient field to synergistically combine the high $\varepsilon $ of functionalized TiO2 and high V$_{bd}$ of BCP matrix. The results of impact of BCP morphology, processing conditions and concentration of TiO2 on capacitor performance will be reported. [Preview Abstract] |
Tuesday, March 4, 2014 4:06PM - 4:18PM |
J21.00007: Development of In-situ Resonant Soft X-ray Scattering for Soft Materials at Advanced Light Source Cheng Wang, Alexander Hexemer, Anthony Young, Howard Padmore Resonant Soft X-ray Scattering was developed at ALS over the past a few years. It combines soft x-ray spectroscopy with x-ray scattering and offers statistical information for 3D chemical morphology over a large sample area. Its unique chemical sensitivity, large accessible size scale, polarization control and high coherence make it a powerful tool for mesoscale chemical/morphological structure characterization for many classes of materials. However, in order to study sciences in naturally occurring conditions, we need to overcome the sample limitations set by the low penetration depth of soft x-rays and requirement of high vacuum. Adapting to the evolving environmental cell designs utilized increasingly in the Electron Microscopy community, we will report our development of customize design liquid/gas environmental cells that will enable soft x-ray scattering experiments on biological, electro-chemical, self-assembly, and hierarchical functional systems in both static and dynamic fashion. Initial RSoXS result of solar fuel membrane assembly/fuel-cell membrane structure in wet cell will be presented. [Preview Abstract] |
Tuesday, March 4, 2014 4:18PM - 4:30PM |
J21.00008: Structure and Water Transport in Nafion Nanocomposite Membranes Eric Davis, Kirt Page Perfluorinated ionomers, specifically Nafion, are the most widely used ion exchange membranes for vanadium redox flow battery applications, where an understanding of the relationship between membrane structure and transport of water/ions is critical to battery performance. In this study, the structure of Nafion/SiO$_{2}$ nanocomposite membranes, synthesized using sol-gel chemistry, as well as cast directly from Nafion/SiO$_{2}$ nanoparticle dispersions, was measured using both small-angle neutron scattering (SANS) and ultra-small-angle neutron scattering (USANS). Through contrast match studies of the SiO$_{2}$ nanoparticles, direct information on the change in the structure of the Nafion membranes and the ion-transport channels within was obtained, where differences in membrane structure was observed between the solution-cast membranes and the membranes synthesized using sol-gel chemistry. Additionally, water sorption and diffusion in these Nafion/SiO$_{2}$ nanocomposite membranes were measured using in situ time-resolved Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy and dynamic vapor sorption (DVS). [Preview Abstract] |
Tuesday, March 4, 2014 4:30PM - 4:42PM |
J21.00009: Role of Substrate/Film interactions in Controlling Structure and Swelling of Nafion Thin Films Adam Weber, Ahmet Kusoglu, Michael Hickner, Kunal Karan Nafion is the prototypical ionomer in electrochemical energy devices due to its good ionic conductivity and permselectivity. In most devices, bulk ionomers are in contact with the catalysts. When confined to nanometer-thick 'thin' films, Nafion's structure/property relationship deviate from bulk, resulting in a complex polymer behavior dependent on thickness, environmental and casting conditions, and substrate material. In this talk, results of a systematic investigation on the substrate/film interactions of Nafion will be presented. The nanostructure of hydrated films is studied by Grazing-incidence X-Ray Scattering and analyzed along with swelling and water uptake measured by ellipsometry and QCM. Overall, films exhibit phase-separation with 4 to 6nm water-domain spacing and 10 to 15{\%} swelling. Film thickness has a universal impact on properties such that thicker films (ca. 100nm) behave like bulk, whereas thin films (20 to 100nm) exhibit confinement effects with reduced swelling, regardless of the substrate. However, thin(ner) films (ca. 20nm) have no separated-structure and demonstrate significant swelling. Moreover, metallic substrates induce more ordered and anisotropic structure accompanied by additional reduction in swelling. [Preview Abstract] |
Tuesday, March 4, 2014 4:42PM - 4:54PM |
J21.00010: Analytical model describes ion conduction in fuel cell membranes Daniel Herbst, Steve Tse, Thomas Witten Many fuel cell designs employ polyelectrolyte membranes, but little is known about how to tune the parameters (water level, morphology, etc.) to maximize ion conductivity. We came up with a simple model based on a random, discrete water distribution and ion confinement due to neighboring polymer. The results quantitatively agree with molecular dynamics (MD) simulations and explain experimental observations. We find that when the ratio of water volume to polymer volume, $V_{w}/V_{p},$ is small, the predicted ion self-diffusion coefficient scales roughly as $D_{w}\left(T\right)\sqrt{V_{w}/V_{p}}\exp(-\cdots V_{p}/V_{w}),$ where $D_{w}\left(T\right)$ is the limiting value in pure water at temperature $T.$ At high water levels the model also agrees with MD simulation, plateauing to $D_{w}\left(T\right).$ The model predicts a maximum conductivity at a water level higher than is typically used, and that it would be beneficial to increase water retention even at the expense of lower ion concentration. Also, membranes would conduct better if they phase-separated into water-rich and polymer-rich regions. [Preview Abstract] |
Tuesday, March 4, 2014 4:54PM - 5:06PM |
J21.00011: Thermal-induced changes in Transport Properties of PFSA Ionomers Ahmet Kusoglu, Adam Weber Perfluorosulfonic-acid ionomers are widely used as the solid-electrolyte in electrochemical energy applications due to their remarkable conductivity and chemical/mechanical stability. Driven by achieving even higher conductivities, it is of interest to increase ion-exchange capacities without deteriorating the mechanical stability. Heat-treatments are commonly employed to change the balance between chemical and mechanical properties, where the latter can be enhanced by annealing-induced crystallinity at the expense of reduced conductivity. In this talk, we focus on how the annealing time membrane undergoes results in non-monotonic changes in its nanostructure, crystallinity and ion conductivity. Hydrophilic domains and crystallinity of the annealed samples, studied by Small- and Wide-angle X-Ray scattering, are correlated to their swelling and conductivity. Our results suggest that the conductivity can be enhanced by optimizing the annealing procedure for the ionomer. However, over a long period of annealing, conductivity and crystallinity of the ionomer appear to decrease and increase, respectively, although by preserving the overall chemical/mechanical balance. Our findings provide new insights into the thermal treatments in altering the structure/function relationship of ionomers due to their non-equilibrium state. [Preview Abstract] |
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