Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session H24: Dillon Medal SymposiumFocus Prize/Award
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Sponsoring Units: DPOLY Chair: Timothy Lodge, University of Minnesota Room: New Orleans Theater C |
Tuesday, March 14, 2017 2:30PM - 3:06PM |
H24.00001: Interplay of Transport and Morphology in Nanostructured Ion-Containing Polymers Invited Speaker: Moon Jeong Park The global energy crisis and an increase in environmental pollution in the recent years have drawn the attention of the scientific community to develop innovative ways to improve energy storage and find more efficient methods of transporting the energy. Polymers containing charged species that show high ionic conductivity and good mechanical integrity are the essential components of these energy storage and transport systems. In this talk, first, I will present a fundamental understanding of the thermodynamics and transport in ion-containing block copolymers with a focus on the structure-property relationships. Tailoring the intermolecular interactions between the polymer matrix and the embedded charges appeared to be vital for controlling the transport properties. Particularly, the achievement of well-defined self-assembled morphologies with three-dimensional symmetries has proven to facilitate fast ion transport by constructing less tortuous ion-conducting pathways. Examples of attained morphologies include disorder, lamellae, gyroid, Fddd, hexagonal cylinder, body-centered cubic, face-centered cubic, and A15 phases. Second, various strategies for accessing high cation transference number as well as improved ionic conductivity from ionic-containing polymers are enclosed; (1) the inclusion of terminal ionic units as a new means to control the nanoscale morphologies and the transport efficiency of block copolymer electrolytes and (2) the addition of zwitterions that offered a polar medium close to water, and accordingly increased the charge density and ionic conductivity. The obtained knowledge on polymer electrolytes could be used in a wide range of emerging nanotechnologies such as fuel cells, lithium batteries, and electro-active actuators. [Preview Abstract] |
Tuesday, March 14, 2017 3:06PM - 3:18PM |
H24.00002: Toward Atomic-Resolution Electron Microscopy of Polymer Crystals Nitash Balsara, Xi Jiang, Douglass Greer, Andrew Minor, Kenneth Downing, Ronald Zuckermann We aim to produce images of synthetic polymers with atomic resolution using electron microscopy. This is inherently challenging because polymers are unstable under the electron beam. We are thus forced to use low exposure in order to minimize beam damage. Our experiments were conducted on crystalline sheets formed by self-assembly of an amphiphilic diblock copolypeptoids in water. Sophisticated averaging algorithms were used to extract high resolution information from low exposure images, where Fourier transforms along orthogonal directions will be used to align individual images. Super-position of images results in images that appear to represent atoms. On going work is aimed at confirming this. Methods to extend our work to other synthetic polymers will be discussed. [Preview Abstract] |
Tuesday, March 14, 2017 3:18PM - 3:30PM |
H24.00003: Conjugated block copolymers as model materials to examine charge transfer in donor-acceptor systems Enrique Gomez, Melissa Aplan, Youngmin Lee Weak intermolecular interactions and disorder at junctions of different organic materials limit the performance and stability of organic interfaces and hence the applicability of organic semiconductors to electronic devices. The lack of control of interfacial structure has also prevented studies of how driving forces promote charge photogeneration, leading to conflicting hypotheses in the organic photovoltaic literature. Our approach has focused on utilizing block copolymer architectures --where critical interfaces are controlled and stabilized by covalent bonds-- to provide the hierarchical structure needed for high-performance organic electronics from self-assembled soft materials. For example, we have demonstrated control of donor-acceptor heterojunctions through microphase-separated conjugated block copolymers to achieve 3{\%} power conversion efficiencies in non-fullerene photovoltaics. Furthermore, incorporating the donor-acceptor interface within the molecular structure facilitates studies of charge transfer processes. Conjugated block copolymers enable studies of the driving force needed for exciton dissociation to charge transfer states, which must be large to maximize charge photogeneration but must be minimized to prevent losses in photovoltage in solar cell devices. Our work has systematically varied the chemical structure, energetics, and dielectric constant to perturb charge transfer. As a consequence, we predict a minimum dielectric constant needed to minimize the driving force and therefore simultaneously maximize photocurrent and photovoltage in organic photovoltaic devices. [Preview Abstract] |
Tuesday, March 14, 2017 3:30PM - 3:42PM |
H24.00004: Unusual Semi-Crystalline Morphology of a Precise Carboxylic Acid Polyethylene Karen Winey, Edward Trigg, Robert Middleton Linear polyethylenes with precisely periodic functional groups (precise polyethylenes) exhibit novel morphologies, including a multi-layer adjacent reentry crystal structure in a carboxylic acid containing precise polyethylene. Here, we explore chain orientation within lamellae via X-ray scattering. A comparison of the long period (via SAXS) and the layer-layer correlation length (via the Scherrer equation) implies that the functional group layers are not coplanar with the lamellae, and may in fact be perpendicular. This finding also implies that the trans alkyl segments are oriented in (or near) the plane of the lamellae, in contrast with polyethylene. The implications of this finding are discussed with respect to prior work on morphological evolution during tensile deformation, and current work on transport of charged species through crystallites of precise polyethylenes. [Preview Abstract] |
Tuesday, March 14, 2017 3:42PM - 3:54PM |
H24.00005: Aqueous Lyotropic Liquid Crystalline Frank-Kasper Mesophases Mahesh Mahanthappa, Sung A Kim, Kyeong-Jun Jeong, Arun Yethiraj Amphiphilic molecules undergo water concentration-dependent self-assembly to form lyotropic liquid crystal (LLC) mesophases. LLC morphology selection is directed by cooperative optimization of preferred molecular packing arrangements, which stem from a subtle balance of local, non-covalent interactions. We recently discovered a class of amphiphiles that form a progression of discontinuous micellar LLCs, including two tetrahedrally-closest packed Frank-Kasper phases that exhibit exceptional long range order. This discovery complements recent reports of their formation in thermotropic liquid crystals, neat diblock and tetrablock polymers, and in lyotropic mesophases of block polymers in ionic liquids. Using a combination of MD simulations and experiments, we provide new insights into the mechanisms of formation for these low symmetry micelle phases. [Preview Abstract] |
Tuesday, March 14, 2017 3:54PM - 4:06PM |
H24.00006: The dependence of chain exchange in copolymer micelles on the chi parameter Timothy Lodge, Yuanchi Ma Chain exchange kinetics in diblock copolymer micelles with a lower critical micellization temperature (LCMT) were investigated using time-resolved small-angle neutron scattering (TR-SANS). In TR-SANS, a contrast-matching strategy was used to study the chain distribution in micelles as a function of time, and a relaxation function was defined to quantify the degree of chain exchange. In this work, the chain exchange rate among micelles was studied with respect to the Flory-Huggins interaction parameter between the solvent and the core block. Previous TR-SANS experiments have been interpreted in terms of an activation barrier for chain escape that increases linearly with chi. The results to be presented here, plus some further analysis, indicate that a more elaborate dependence is required. [Preview Abstract] |
Tuesday, March 14, 2017 4:06PM - 4:18PM |
H24.00007: Disordered bicontinuous nanostructures from randomly end-linked copolymer networks Ryan Hayward Self-assembly within randomly cross-linked copolymer networks can provide co-continuous nanometer-scale structures in a wide variety of material systems. Copolymer networks prepared by end-linking pairs of telechelic polymers in a common solvent are particularly attractive in this regard as systems with well-defined and easily tuned network parameters. For sufficiently high levels of immiscibility between the constituent polymers, removal of solvent leads to microphase separation into disordered nanoscale structures. Using copolymer networks with a glassy strand and an ion-conducting strand, we have found that disordered morphologies with well-percolated domains of both phases persist across a wide range of compositions of the two materials. Similarly, by including a degradable component, we have found that interpenetrating porous structures are formed over a wide range of loading. These materials show a narrow distribution of pore sizes that can be tuned by adjusting the molecular weight of the starting polymers. [Preview Abstract] |
Tuesday, March 14, 2017 4:18PM - 4:30PM |
H24.00008: Directing self-assembly of soft mesophases using orthogonal stimuli -- effective routes to biaxial control Chinedum Osuji Directed self-assembly (DSA) of soft mesophases has typically focused on controlling the orientation of anisotropic structures in a single direction, i.e. on uniaxial control. The question of biaxial control, and thereby developing single-crystal textures (in relevant mesophases) has been left largely unaddressed. We report recent progress in developing biaxial DSA in hexagonal mesophases using two routes. First, we explore localized field screening using magnetic nanoparticle arrays as a means of imposing lateral stresses to control lattice orientation in the presence of a magnetic field which otherwise controls the orientation of the long axes of the cylindrical microdomains. In the second we demonstrate the concurrent use of physical confinement and magnetic field alignment to independently control the orientation of cylinders axes and the orientation of their lattice planes, respectively, in a small molecule mesophase. Field control of the lattice orientation is possible due to a tilted arrangement of mesogens with tilt angles and therefore magnetic anisotropy coupled to the lattice orientation. X-ray scattering and TEM reveal the formation of a near single-crystal morphology. [Preview Abstract] |
Tuesday, March 14, 2017 4:30PM - 4:42PM |
H24.00009: Anisotropic Proton Conductivity in Thin Nafion Films Keiji Tanaka, Yudai Ogata, Norifumi Yamada, Daisuke Kawaguchi Proton conductivity of polyelectrolyte at the solid interface is a key for the performance of polyelectrolyte-based fuel cells. We present the impact of interfacial effect on proton conductivity of Nafion in thin films supported on quartz substrates. With decreasing film thickness, the in-plane and out-of-plane proton conductivity increased and decreased, respectively. Neutron reflectivity measurements confirmed that a hydrated multilamellar structure of Nafion was formed near the quartz interface. Finally, we demonstrate the enhanced proton conductivity by increasing the ratio of the interfacial area to the total volume. This finding should provide a new insight into the material design of polyelectrolytes for fuel cells. [Preview Abstract] |
Tuesday, March 14, 2017 4:42PM - 4:54PM |
H24.00010: Functional Materials from Polymeric Ionic Liquids Rachel Segalman, Gabriel Sanoja, Nicole Michenfelder-Schauser, Samir Mitragotri, Ram Seshadri Ionic liquids (IL's) have been suggested for applications as diverse as solubilizing cellulose, antimicrobial treatments, and electrolytes in batteries due to their molten salt properties. A polymeric cation (such as imidazolium) is an excellent host for \textit{any} associated anion. As a result, polymerized ionic liquids are not just solid counterparts to IL's, but are shown to be vectors for the inclusion of a wide variety of functionalities ranging from multi-valent ions to magnetic anions. Moreover, PIL block copolymers allow orthogonal control over mechanical and morphological properties, ultimately leading to a conceptual framework for processable, tunable, multifunctional materials. [Preview Abstract] |
Tuesday, March 14, 2017 4:54PM - 5:06PM |
H24.00011: Nanoparticlization and Morphological Change of Sulfur- and Fluorine-Containing Block Copolymers in Organic Solvent Kookheon Char, Jeewoo Lim, Yunshik Cho, Youngjin Kim The use of controlled polymerization technique allowed us to readily change the degrees of polymerization of constituent blocks by simply altering the monomer feed ratio. This also allowed for the control over size and, more importantly, sulfur/fluorine contents of the block copolymers (BCP) obtained. We have prepared BCPs containing either high sulfur or fluorine content through one-pot and mild ring-opening metathesis polymerization (ROMP). The low solubility of sulfur- and fluorine-rich blocks led to the \textit{in situ} formation of BCP nanoparticles during the polymerization. Furthermore, the variations of the degrees of polymerization of constituent blocks yielded various nanostructures such as rods and vesicles under non-aqueous environment without the need for extensive post-polymerization modification processes Such control over the sulfur or fluorine content also allowed for the control of refractive indices of drop-cast films of BCPs over a range greater than 0.2 [Preview Abstract] |
Tuesday, March 14, 2017 5:06PM - 5:18PM |
H24.00012: Polyampholyte Ionomer Networks Kevin Cavicchi, Guodong Deng Novel materials that can reversibly adapt to their environment are important as functional materials. In polymer networks, dynamic bonding of the crosslinks, which can break and reform under an external stimuli (e.g. heat or mechanical stress) are of interest for functional material properties (e.g. self-healing or shape memory) and enhanced mechanical properties (e.g. toughness, strength). One general route to introduce dynamic bonds is through non-covalent interactions. In this work, poly(butyl acrylate) networks crosslinked by vinyl benzyl tri-n-octyl ammonium/phosphonium styrene sulfonate ion pairs were prepared as model system to study the thermo-mechanical properties of polyampholyte networks as a function of the network parameters, including ion-pair chemistry and crosslink density. Results of rheological behavior, mechanical and thermal properties of these materials will be presented and compared to other ionic systems, such as ionomers with pendant counter ions. [Preview Abstract] |
Tuesday, March 14, 2017 5:18PM - 5:30PM |
H24.00013: Ionomers for Ion-Conducting Energy Materials Ralph Colby For ionic actuators and battery separators, it is vital to utilize single-ion conducting ionomers that avoid the detrimental polarization of other ions. Single-ion conducting ionomers are synthesized based on DFT calculations, with low glass transition temperatures (facile dynamics) to prepare ion-conducting membranes for battery separators that conduct Li$^{\mathrm{+}}$ or Na$^{\mathrm{+}}$. Characterization by X-ray scattering, dielectric spectroscopy, FTIR, NMR and linear viscoelasticity collectively develop a coherent picture of ionic aggregation and both counterion and polymer dynamics. $^{\mathrm{7}}$Li NMR diffusion measurements find that diffusion is \textit{faster} than expected by conductivity using the Nernst-Einstein equation, which means that the majority of Li diffusion occurs by ion pairs moving with the polymer segmental motion. Segmental motion only contributes to ionic conduction in the rare event that one of these ion pairs has an extra Li (a positive triple ion). This leads us to a new metric for ion-conducting soft materials, the product of the cation number density p$_{\mathrm{0}}$ and their diffusion coefficient D; p$_{\mathrm{0}}$D is the diffusive flux of lithium ions. This new metric has a maximum at intermediate ion content that corresponds to the overlap of ion pair polarizability volumes. At higher ion contents, the ion pairs interact strongly and form larger aggregation states that retard segmental motion$^{\mathrm{\thinspace }}$of both mobile ion pairs and triple ions. [Preview Abstract] |
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