Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session B33: Focus Session: Dielectric and Ferroelectric Polymers for Electrical Applications: Ferroelectrics |
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Sponsoring Units: DPOLY DMP Chair: Philip Taylor, Case Western Reserve University Room: 341 |
Monday, March 18, 2013 11:15AM - 11:51AM |
B33.00001: Phase Transitions as a Novel Mechanism for High-Speed Energy Storage Invited Speaker: Jerry Bernholc In many energy applications there is an urgent need to store and quickly discharge large amounts of electrical energy. Since capacitors can be discharged far quicker than batteries and fuel cells, they have much higher power densities. At present, highly insulating polymers with large breakdown fields, such as polypropylene, are the dielectrics of choice in high-power capacitors. However, their energy densities are quite low because of small dielectric constants. Ferroelectric polymers from the PVDF family have significantly larger dielectric constants, yet their energy densities are still rather low. This can be traced to early saturation of their displacement fields with the applied electric field, and to somewhat lower breakdown fields. However, an admixture of a small amount of another polymer, such as CTFE, results in a dramatic increase in the stored energy [1]. We show that this highly non-linear increase in the energy density is due to the formation of disordered nanodomains with different copolymer concentrations, which undergo first-order non-polar to polar phase transitions with an increase of the applied field. The resulting energy density profile reproduces well the experimental data, while its variation with co-polymer concentration and distribution suggest avenues for additional substantial improvements in the stored energy [2]. Most recently, we have identified a low-activation-energy pathway for these successive phase transformations [3]. It provides further confirmation of the viability of the suggested energy storage mechanism and also enables fine-tuning of the kinetics of energy release by informed choices of suitable co-polymers.\\[4pt] [1] Chu et al, Science 313, 334 (2006).\\0pt] [2] V. Ranjan L. Yu, M. Buongiorno-Nardelli, and J. Bernholc, PRL 99, 047801 (2007).\\[0pt] [3] V. Ranjan, M. Buongiorno Nardelli, and J. Bernholc, PRL 108, 087802 (2012). [Preview Abstract] |
Monday, March 18, 2013 11:51AM - 12:03PM |
B33.00002: Constrained Molecular Dynamics Modeling of Dielectric Response in Polar Polyethylene Analogs and Poly(vinylidene flouride) Jeffrey Calame A simplified molecular dynamics formalism for polymers, having united atoms with constrained bond lengths and bond angles along the backbone but allowing torsional motion, has been developed to model the dielectric response and ferroelectricity in polymers with permanent dipoles. Analytic relations existing on the backbone geometry and associated dihedral motion allow elimination of many dot and cross product evaluations. Also, constraint error correcting forces, symplectic integration with velocity prediction, random force excitation with damping and a momentum-conserving thermostat, and rapid neighbor list and long range force computation allow efficient computation and time steps as large as 20 fs to enable the study of relatively long time scale dielectric phenomena. Studies are performed on non-polar polyethylene for benchmarking, followed by a model system (polar polyethylene) which retains the molecular structure, dihedral potentials, and non-bonded interactions of polyethylene, except artificial partial charges are placed on the united atoms. The modeling is extended to poly(vinylidene fluoride) by changes to the molecular structure, potentials, and charges. Heterogeneous systems containing crystalline and amorphous arrangements of polymer chains are studied. [Preview Abstract] |
Monday, March 18, 2013 12:03PM - 12:15PM |
B33.00003: Crystal Orientation and Temperature Effects on the Double Hysteresis Loop Behavior of a PVDF-$g$-PS Graft Copolymer Lei Zhu, Lianyun Yang, Fangxiao Guan In a recent report, double hysteresis loop behavior is observed in a nanoconfined poly(vinylidene fluoride-\textit{co}-trifluoroethylene-\textit{co}-chlorotrifluoroethylene)-\textit{graft}-polystyrene [P(VDF-TrFE-CTFE)-$g$-PS] copolymer. It is considered that the PS grafts are capable of reducing the compensation polarization and thus the polarization electric field during the reverse poling process, resulting in the double hysteresis loop behavior. In this study, we further investigated crystal orientation and temperature effects on this novel ferroelectric behavior. It is observed that with increasing the orientation factor, the electric displacement-electric field (D-E) loop changes from linear for non-oriented film to double loop for the well-oriented film. With increasing the temperature, the double hysteresis loop is gradually replaced by the single and open loop, which is attributed to the impurity ion migrational loss in the sample. [Preview Abstract] |
Monday, March 18, 2013 12:15PM - 12:27PM |
B33.00004: Polarization Mapping in Ferroelectric Polymer Thin Films by Pyroelectric Scanning Microscopy Jingfeng Song, Stephen Ducharme High-resolution mapping of polarization distribution in P(VDF-TrFE) Langmuir-Blodgett film was carried out through pyroelectric scanning microscopy with a focused 405nm blue diode laser beam. A lateral resolution of 500 nm was achieved by modulating the laser power at high frequency. At frequencies above 1 MHz, the laser spot size, rather than the thermal diffusion, becomes the limiting factor in the lateral resolution. The experimental results were compared to computer models developed with the finite element method. [Preview Abstract] |
Monday, March 18, 2013 12:27PM - 12:39PM |
B33.00005: Interfacial polarization and internal electron tunneling effect on dielectric properties of multilayer polymer films Jung-Kai Tseng, Zheng Zhou, Matt Mackey, Joel Carr, Eric Baer, Lei Zhu Due to large contrasts in dielectric constant and volumetric conductivity, Maxwell-Wagner-Sillars interfacial polarization is observed in poly(vinylidene fluoride) (PVDF) based multilayer films. This interfacial polarization is helpful to enhance the breakdown strength of multilayer films, because they serve as electron traps to prevent hot electron thermal runaway. In this study, the relationship between volumetric resistivity and internal electron tunneling in polysulfone (PSF)/(PVDF) multilayer film is reported. In general, resistivity decreases with decreasing the thickness of the insulating PSF layer. This is attributed to the internal electron tunneling in thin PSF layers. As a result, the electron-hole neutralization via the PSF layer decreases the interfacial polarization in the PVDF layer, resulting in a lower volumetric resistivity. [Preview Abstract] |
Monday, March 18, 2013 12:39PM - 12:51PM |
B33.00006: Ab-initio study of high energy storage in polymers: PVDF-BTFE Rui Dong, V. Ranjan, M. Buongiorno-Nardelli, J. Bernholc Previous experiments [1] and our theoretical work [2] have indicated that introducing CTFE monomers in polyvinylidene fluoride (PVDF) in small concentration can lead to ultra high density capacitive energy storage. Our previous work indicates that this is due to (i) formations of domains with different impurity concentrations, and (ii) existence of a low energy barrier path connecting ground state non-polar phase to a polar phase. We are now investigating bromo-triflouroethylene (BTFE) in a PVDF-BTFE as a potential high energy density material. Our results show that PVDF-BTFE prefers the nonpolar phase up to a higher concentration of 33\%, as compared to PVDF-CTFE(17\%). This could lead to a higher proportion of PVDF sample being available for phase transition under the electric field. The calculated energy barriers for the electric-field-induced phase transition are also low and comparable to PVDF-CTFE. We will discuss the calculated phase equilibria and the potential of PVDF-BTFE for high density capacitive energy storage.\\[4pt] [1] B. Chu et al., Science 313, 334 (2006).\\[0pt] [2] V. Ranjan et al., PRL 108, 087802 (2012); PRL 99, 47801 (2007). [Preview Abstract] |
Monday, March 18, 2013 12:51PM - 1:03PM |
B33.00007: Effect of crystal isomorphism on novel ferroelectric behaviors of P(VDF-TrFE)-based copolymers Lianyun Yang, Xinyu Li, Qiming Zhang, Lei Zhu Novel ferroelectric behaviors of poly(vinylidene fluoride-\textit{co}-trifluoroethylene) [P(VDF-TrFE)]-based copolymers, including relaxor ferroelectric and double hysteresis loop behaviors, have drawn great attention in research. Despite of a great amount of work have been done over the last two decades, the fundamental understanding of these behaviors is still lacking. In this work, the physics behind these novel ferroelectric behaviors are discussed based on the studies of P(VDF-TrFE)-based terpolymers and e-beam irradiated P(VDF-TrFE). We find that crystal isomorphism in P(VDF-TrFE)-based copolymers has a significant effect on the dielectric properties. This is achieved by pinning the polymer chains with structural defects. Consequently, nanodomains and easy dipole switching are responsible for the novel ferroelectric behaviors. This understanding will help us to further design new polymers with better dielectric/ferroelectric properties. [Preview Abstract] |
Monday, March 18, 2013 1:03PM - 1:15PM |
B33.00008: Ferroelectric Polymer Composite with Enhanced Breakdown Strength Kuo Han, Matthew Gadinski, Qing Wang Numerous efforts have been made in the past decades to improve the energy storage capability of dielectric capacitors by incorporating ceramic addictives into polymers. Ferroelectric polymers have been particularly interesting as matrix for dielectric composites because of their highest dielectric permittivity and energy density. However, most polymer composites suffer from significantly reduced breakdown strength, which compromises the potential gain in energy density. In this work, various metallic alkoxide were introduced into the functionalized ferroelectric poly(vinylidene fluoride-\textit{co}- chlorotrifluoroethylene), P(VDF-CTFE), via covalent bonding. The composite with the optimized composition exhibited the Weibull statistical breakdown strength of 504.8 MV/m, 67.6 {\%} higher than the pristine polymer. The enhanced breakdown strength was mainly ascribed to the cross-linking and the formation of deep traps, which effectively reduced the conduction and further lowered the energy loss. Additionally, the homogeneous dispersion of the inorganic phase and the small contrast in permittivity between the polymer and amorphous oxides also contribute to the improved dielectric strength. The dielectric spectra of the composites have been recorded at varied temperatures and frequencies, which revealed the presence of the interfacial polarization layer in the composites. [Preview Abstract] |
Monday, March 18, 2013 1:15PM - 1:27PM |
B33.00009: Effect of Polymer Blocking Layer and Processing Method on the Breakdown Strength and the Extractable Energy Density of Barium Titanate/poly(vinylidene fluoride-co-hexafluoropropylene) Nanocomposite Thin Film Capacitors Yunsang Kim, Mohanalingam Kathaperumal, O'Neil Smith, Ming-Jen Pan, Joseph Perry Polymer-metal oxide nanocomposites are of great interest because of their high energy density and easy processability, which make them candidate materials for energy storage applications. Although loading of high-k filler in polymer matrix is desirable to maximize energy density of nanocomposites, the decrease of breakdown strength at higher loading compromises a potential gain in energy density. In this work, we investigate the effect of a fluoropolymer (CYTOP) blocking layer in BaTiO$_{3}$/poly(vinylidene fluoride-co-hexafluoro propylene) nanocomposite films on the improvement of breakdown strength and energy storage density. The introduction of blocking layer may serve to prevent moisture absorption and charge injection from electrode, thereby decreasing the probability of catastrophic breakdown events. We also examine the influence of processing method, i.e. spin- or blade-casting, on the performance of bilayer films. The charge-discharge method shows about a twofold increase in extractable energy density (from 2 to 3.7 J/cm$^{3}$) of bilayer films fabricated by blade-casting compared to single layer film by spin-casting because of improved breakdown strength. The results will be discussed in regards to morphology, electric field distribution, and loss of bilayer films. [Preview Abstract] |
Monday, March 18, 2013 1:27PM - 1:39PM |
B33.00010: Relaxor Ferroelectric Behavior in Poly(vinylidene fluoride-co-bromotrifluoroethyene) Matthew Gadinski, Qing Wang Copolymers of vinylidene fluoride (VDF) and bromotrifluoroethylene (BTFE) were prepared over a composition range up to the disappearance of crystallinity ($\sim$ 9 mol {\%} BTFE). The resulting copolymers were characterized by $^{19}$F NMR to elucidate composition and quantify the linkage defects of the polymer chain. Chain conformations were analyzed by FTIR analysis and crystal structures were studied by DSC and WAXD. The dielectric properties were evaluated by dielectric spectroscopy as a function of frequency and temperature and at high fields to investigate the influence of BTFE on dielectric behavior. The results indicate that the P(VDF-BTFE) copolymers exhibit relaxor ferroelectric behavior similar to those reported in PVDF terpolymers resulting from a mixed $\alpha $/$\gamma $ crystalline phase. Effects of processing such as stretching and crosslinking have also been studied with respect to the relaxor ferroelectric properties of the copolymers. Stretching was found to improve the breakdown strength of the films along with enhancing both the stored and discharged energy density. Preliminary crosslinking results indicate that stretched and cross-linked polymer show a reduced remnant polarization. [Preview Abstract] |
Monday, March 18, 2013 1:39PM - 1:51PM |
B33.00011: BaTiO3 and polypropylene nanocomposites for capacitor applications Daxuan Dong, Longxiang Tang, Lei Zhu, Je Kyun Lee A novel strategy to uniformly disperse 70-nm BaTiO3 ferroelectric nanoparticles in a dielectric polypropylene (PP) matrix is developed in order to achieve high dielectric constant and high energy density for capacitor applications. By modifying BaTiO3 surface with a bis-phosphonic acid-terminated polyhedral oligomeric selsisquioxane (POSS), a nanocomposite with BaTiO3@POSS uniformly dispersed in PP matrix was achieved. The nanocomposite film containing a high nanoparticle content of 30 vol.{\%} exhibited a high dielectric constant of 32 and a breakdown voltage of 220 MV/m, but with a high energy loss. Improvement of this nanocomposite by understanding the interfacial polarization is carried out in this work. The dielectric constant difference between BaTiO3 and PP can generate interfacial polarization and subsequent internal conduction in BaTiO3 particles upon bipolar polarization. Reduction of this internal conduction mechanism will significantly reduce the hysteresis loss in polymer nanodielectrics. [Preview Abstract] |
Monday, March 18, 2013 1:51PM - 2:03PM |
B33.00012: Dielectric Bilayer Films Comprising Polar Cyanolated Silica Sol-Gel and Nanoscale Blocking Layer for Energy Storage Applications Mohanalingam Kathaperumal, Yunsang Kim, O'Neil Smith, Amir Dindar, Canek Fuentes-Hernandez, Do-Kyung Hwang, Ming-Jen Pan, Bernard Kippelen, Joseph Perry Organic-inorganic hybrid sol-gel containing polar groups, which can undergo orientational polarization under the influence of an electric field, provide a potential route to processable and rational design of materials for energy storage applications. However, the porous nature of sol-gel films, which significantly lowers breakdown strength, limits the potential of this material for energy storage particularly in high-field applications. In this work, we fabricate and characterize dielectric bilayer films comprising cyanolated silica sol-gel film prepared from 2-cyanoethyltrimethoxysilane (CNETMS) precursor and nanoscale blocking layers, which include amorphous fluoropolymer, SiO$_{2}$, Al$_{2}$O$_{3}$ and ZrO$_{2}$ deposited by spin casting, electron beam evaporation or atomic layer deposition (ALD). CNETMS films with 50 nm ZrO$_{2}$ blocking layer exhibit an extractable energy density of 13 J/cm$^{3}$, which is about a twofold enhancement compared to CNETMS films without blocking layer. The effect of the blocking layer will be discussed in terms of surface morphology, dielectric contrast, i.e. the ratio of relative permittivity between oxide layer and sol-gel film, electric field distribution, breakdown strength and statistics, bias polarity, and loss of the bilayer films. [Preview Abstract] |
Monday, March 18, 2013 2:03PM - 2:15PM |
B33.00013: A variational formulation of electrostatics for heterogeneous dielectric media Francisco Solis, Vikram Jadhao, Monica Olvera de la Cruz Many biological and synthetic soft matter systems involve fixed or mobile charges. The electrostatic interactions between these charges often play crucial roles in determining the structural properties and physical behavior of these systems. Coarse-graining of the properties of these systems often leads to consideration of free charges embedded in a medium with varying dielectric permittivities. Investigation of the behavior of these systems by theoretical or computational methods requires, therefore, formulations of their electrostatic properties that suitably address the properties of the medium. In this talk we present a new and powerful variational formulation of the electrostatics of charged particles in heterogenous media. Our formulation replaces the electric and polarization vector fields for the induced polarization charge density at interfaces. In addition, this variational principle has the property of evaluating to the true free energy of the system at its minimum; a property not found in many other variational formulations. We discuss the application of this functional to a variety of electrostatic problems and show how it allows the development of new algorithms for simulation of charged systems in heterogeneous media. [Preview Abstract] |
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