Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session V56: Polymers for Energy Applications IFocus
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Sponsoring Units: DPOLY Chair: Christopher Evans, University of Illinois at Urbana-Champaign Room: LACC 515B |
Thursday, March 8, 2018 2:30PM - 2:42PM |
V56.00001: Understanding Morphology-Mobility Dependence in PEDOT:Tos Igor Zozoulenko, Nicolas Rolland, Juan Felipe Franco-Gonzalez, Riccardo Volpi, Mathieu Linares We develop a multi-scale model to calculate a charge carrier mobility in conducting polymer PEDOT, as a function of the physico-chemical properties of the system. We start by calculating the morphology using molecular dynamics simulations. Based on the calculated morphology we perform quantum mechanical calculation of the transfer integrals between states in polymer chains and calculate corresponding hopping rates using the Miller-Abrahams formalism. We then construct a transport resistive network, calculate the mobility using the Master Equations and analyze the calculated mobility in terms of transfer integrals distributions and percolation thresholds. Our results provide theoretical support for the recent study (Noriega et al., Nature Mat., 2013) explaining why the mobility in polymers rapidly increases as the chain length is increased and then saturates for sufficiently long chains. Our study also provides the answer to the long-standing question whether the enhancement of the crystallinity is the key to designing high-mobility polymers. We demonstrate, that it is the effective π-π stacking, not the long-range order that is essential for the material design for the enhanced electrical performance. |
Thursday, March 8, 2018 2:42PM - 2:54PM |
V56.00002: Organic Photovoltaics where Water is the Semiconducting Medium and Protons and Hydroxides are the Charge Carriers William White, Eric Schwartz, Lawrence Renna, Shane Ardo Electrochemical technologies require ion-conducting electrolytes that are passive in that electric bias drives ion migration in the thermodynamically favored direction. Recently, my group engineered two important features into passive ion-conducting polymers to introduce the active function of photovoltaic action due to ion transport. These features were covalent bonding of photoacid dyes to the polymers such that absorption of visible light resulted in liberation of protons, and synthesis of polymer membranes with charge-selective contacts to facilitate separation and collection of H+ and OH–. Joining a cation-selective polymer to an anion-selective polymer forms an ionically conductive bipolar membrane, which mimics a rectifying electronic semiconductor pn-junction diode in both form and function. Using a photoacid-dye-modified bipolar membrane, solar-simulated illumination generated a ~120 mV photovoltage. Insights into materials function were obtained using impedance spectroscopy, Mott-Schottky analysis, finite-element numerical modeling of photoacid kinetics, and analysis of drift–diffusion generation–recombination membrane physics. These photo-responsive ion-conducting polymers represent a new class of materials that we envision using for solar desalination of salt water. |
Thursday, March 8, 2018 2:54PM - 3:06PM |
V56.00003: Entropy Promotes Charge Separation in Organic Photovoltaics Eisuke Kawashima, Mikiya Fujii, Koichi Yamashita Morphology of organic photovoltaics (OPVs)—phase separation and miscibility of organic semiconductors—is considered as a key factor to improve device performance. For example, accessibility to interfaces and electrodes—the transport properties—determine exciton dissociation and charge collection efficiencies, respectively. The morphological effects, however, are unclear. |
Thursday, March 8, 2018 3:06PM - 3:42PM |
V56.00004: Charge Transfer and Mass Transport in Organic Radical Polymers Invited Speaker: Jodie Lutkenhaus Organic radical polymer batteries offer an intriguing path towards plastic energy storage. Organic radical polymers often consist of an aliphatic backbone and pendant stable radical groups. These electroactive polymers store charge by a reversible redox reaction, usually with near-100% Coulombic efficiency and extremely fast charge transfer kinetics. However, their performance is complicated by the generally insulating nature of the polymer backbone. Also, the general nature of this reaction is not completely understood, as it is fundamentally different from more traditional battery electrode materials and conjugated polymers. Here, we present electrochemical quartz crystal microbalance with dissipation (EQCMD) monitoring as a means to quantify ion transport, dynamic swelling, and mechanical properties of an organic radical polymer during electrochemical interrogation. We focus upon EQCMD characterization of the redox-active nitroxide radical polymer, poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) (PTMA). Upon oxidation, PTMA becomes positively charged, which requires the transport of a complementary anion into the polymer for electroneutrality. By EQCMD, we quantify anion transport and resultant swelling upon oxidation, as well as decoupling of contributions attributed to the ion and the solvent. We explore the effect of different lithium electrolyte salts in which each salt gives different charge storage and mass transport behavior. This is attributed to varied polymer-dopant and dopant-solvent interactions. |
Thursday, March 8, 2018 3:42PM - 3:54PM |
V56.00005: Characterization of PTMA for Organic Radical Batteries Using Small Angle Neutron Scattering Halie Martin, Barbara Hughes, Thomas Gennett, Mark Dadmun Stable radical polymers have become attractive as active layers in organic radical batteries. Specifically, (2,2,6,6-tetramethylpeperidinyloxy-4-yl methacrylate) (PTMA) is not a characteristic conductive material, however it exhibits extremely rapid electron charge kinetics, comparable to traditional transition metal ions. The feasibility of organic radical batteries is limited by the minimal knowledge of the correlation of functional efficiency and structural changes the polymer undergoes throughout the redox process during charging. Small angle neutron scattering is utilized to correlate structural changes of the PTMA polymer as the radical concentration is increased from 10% to fully saturated with radical moieties. These studies also investigate the structural changes and reorganization of the PTMA during the oxidation cycles. This analysis provides structural information on the flexibility of the polymer chains and the inter-chain interactions of radical groups between neighboring solvated chains. These studies provide integral insight that may be used to improve the performance of organic radical batteries by elucidating molecular structure-functional property relationships. |
Thursday, March 8, 2018 3:54PM - 4:06PM |
V56.00006: Methanol transport in Nafion investigated with a combination of theory, simulation, and experiment Marielle Soniat, Daniel Miller, Frances Houle Modeling the performance of selectively permeable polymer electrolyte membranes (PEMs) under realistic operating conditions is an unmet need in the renewable energy field. In particular, swelling and transport under non-steady-state conditions are rarely considered in simulation studies. This presentation will focus on methanol transport through Nafion(R) that is fully hydrated in liquid water, a situation that is applicable to membranes used in an aqueous phase solar fuels device for CO2 reduction. Theoretical and experimental values are used to inform a parameter-free reaction-diffusion mechanistic scheme, including swelling, uptake, and desorption. The scheme is validated by simulating new experimental data for time-dependent methanol permeation and sorption in Nafion(R), measured using Fourier transform infrared (FTIR) spectroscopy, as well as literature studies using FTIR attenuated total reflectance spectroscopy. Good agreement is observed for both steady-state and non-steady-state conditions. Key phenomena controlling transport in this type of system are identified, and their implications for membrane design are discussed. This work builds towards a general framework for understanding and modeling transport through PEMs at the level of fundamental physical chemistry. |
Thursday, March 8, 2018 4:06PM - 4:18PM |
V56.00007: Transport of Water and Salt Through Desalination Membranes: A Computational Study Dipak Aryal, Venkatraghavan Ganesan The dynamics of ions and solvent molecules in desalination membranes is key to water purification technologies in which selective transport of the different components are desired. Recent experimental results have shown that transport properties of ions in charged membranes are impacted by aqueous salt concentrations and ion identities. Motivated by such observations, here we have probed a series of atomistic molecular dynamics simulations of charged membranes in aqueous mono and divalent salt solutions at different concentrations (ranging from 0.06 to 1 M) to investigate the molecular level understanding the effects of multicomponent salt solutions on fundamental salt and water transport properties. Our finding shows that diffusion of salt ions and water are influenced by cation sizes, salt concentrations, and ionic strength of polymers. Divalent ions are more strongly coupled with ionic groups which reduce their motions as increasing concentration in fixed charged membranes. These simulations are in qualitative agreement with experimental results. Further, water molecules clustering around the ionic groups forms long-range networks in turn provide paths for salt transport and water diffusion. |
Thursday, March 8, 2018 4:18PM - 4:30PM |
V56.00008: Abstract Withdrawn
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Thursday, March 8, 2018 4:30PM - 4:42PM |
V56.00009: Solvation and Dilution Thermodynamics in Ion-Containing Block Copolymers: a Numerical SCFT Study Kevin Hou, Jian Qin Understanding the thermodynamics of ion-containing block copolymers is crucial for engineering the morphology of polymer electrolytes. We present a minimal model for the electrostatic interaction in these materials. Ion solvation energy and dielectric heterogeneity are treated explicitly, and the assumption that ions are bound to the conductive species is discarded. A symmetry-adapted solver for Poisson's equation is developed, enabling efficient exploration of parameter space and accurate resolution of bicontinuous morphologies. Complete phase diagrams are provided for varying salt concentrations and average dielectric permittivity. The resulting trends cannot be rationalized by an effective χ parameter. Two distinct regimes are identified, one dominated by ionic solvation effects and another by the translational entropy of ions. Canonical solid polymer electrolytes, such as PS-PEO/LiTFSI, appear to be in the solvation regime. |
Thursday, March 8, 2018 4:42PM - 4:54PM |
V56.00010: Dielectric enhancement in strongly dipolar polymers: mixing and free volume effects Bing Zhang, Yash Thakur, Rui Dong, Wenchang Lu, Ciprian Iacob, James Runt, Qiming Zhang, Jerry Bernholc Materials with high dielectric constant and low dielectric loss are desired for high performance capacitive energy storage. In dipolar polymer dielectrics, a relatively large free volume gives dipoles more freedom in responding to an external electric field and thus store more energy. An increased dielectric constant while maintaining low loss is achieved by mixing two strongly dipolar polymers: PEEU and ArPTU, both observed in experiments and simulated by molecular dynamics and quantum mechanics computations. Local dipolar disorder, polymer chain distortion, chain separation and free volumes are analyzed. |
Thursday, March 8, 2018 4:54PM - 5:06PM |
V56.00011: Dipolar interactions as the origin of excess scattering in concentrated solutions and melts of ionic polymers Rajeev Kumar, Brad Lokitz, Timothy Long, Bobby Sumpter Scattering is one of the most powerful characterization tools for probing structure and dynamics of polymers at different length and time scales. While the protocols for interpretting scattering from neutral polymers are fairly well-established, interpreting scattering of ionic polymers still pose a great challenge desipte decades of research. In this talk, we will present a generalized theory for studying static structure factor in concentrated solutions and melts of dipolar and ionic polymers. The theory captures the effects of electrostatic fluctuations on the structure factor and provides insights into the origin of excess scattering at ultralow wavevectors in salt-free ionic polymers. The excess scattering can originate from the dipolar interactions resulting from counterion adsorption on the polymers, which leads to screened charge-charge interactions mediated by non-local dielectric media. Also, it will be shown that the structure factor for dipolar polymers can exhibit a peak at a finite wavevector and excess scattering at ultralow wavevectors. |
Thursday, March 8, 2018 5:06PM - 5:18PM |
V56.00012: The Effective Flory-Huggins Parameter in Polarizable Polymeric Systems: One-loop Theory and Field-theoretic Simulations Douglas Grzetic, Kris Delaney, Glenn Fredrickson We apply a recently-introduced polarizable field theory to polymeric systems containing polarizable (and, optionally, charged) species. This framework, in which classical Drude oscillators are attached to the polymer segments, self-consistently incorporates dielectric response, van der Waals interactions and ion self-energies. The van der Waals interactions in a system with polarizability contrast give rise to an enhanced effective Flory-Huggins parameter, which we show can be estimated via a renormalized one-loop approximation. By complex Langevin sampling of the fully-fluctuating polarizable field theory, we simulate a diblock copolymer melt with species polarizability contrast and measure the enhancement of the Flory-Huggins parameter, finding excellent agreement with the renormalized one-loop theory. The effective Flory-Huggins parameter is sensitive to electrostatic screening, in a manner that is clarified by the one-loop theory. We discuss implications of this work for the phase behavior of polarizable and/or charged polymeric systems. |
Thursday, March 8, 2018 5:18PM - 5:30PM |
V56.00013: Molecular Dynamics of Ionic Block Copolymers in Thin Films under Electric Fields Wei Li, Brad Lokitz, Bobby Sumpter, Rajeev Kumar Understanding electromechanical responses of ionic block copolymers is a topic of great interest due to its fundamental and technological importance. We have investigated responses of thin films containing microphase separated ionic diblock copolymers to applied electric fields using coarse-grained molecular dynamics simulations. In this talk, we will present results highlighting the effects of the counterion size, film thickness, and the electrostatic interaction strength on the responses of the diblock copolymers to applied electric fields. Comparisons of the results from the molecular dynamics simulations with the neutron reflectometry measurements done on imidazolium based ionic block copolymers will also be presented. |
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