Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session J20: Invited Session: Dillon Medal Symposium |
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Sponsoring Units: DPOLY Chair: Rachel Segalman, University of California, Santa Barbara Room: Ballroom B |
Tuesday, March 3, 2015 2:30PM - 3:06PM |
J20.00001: John H. Dillon Medal Lecture: Magnetic Field Directed Self-Assembly of Block Copolymers and Surfactant Mesophases Invited Speaker: Chinedum Osuji Molecular self-assembly of block copolymers and small molecule surfactants gives rise to a rich phase behavior as a function of temperature, composition, and other variables. We consider the directed self-assembly of such soft mesophases using magnetic fields, principally through the use of \textit{in situ} x-ray scattering studies. Field alignment is predicated on a sufficiently large product of magnetic anisotropy and grain size to produce magnetostatic interactions which are substantive relative to thermal forces. We examine the role of field strength on the phase behavior and alignment dynamics of a series of soft mesophases, outlining the possibility to readily create highly ordered functional materials over macroscopic length scales. We show that magnetic fields as large as 10 T have little discernable impact on the stability of block copolymer systems considered, with shifts in order-disorder transition temperatures of roughly 5 mK or smaller. Consequently, directed self-assembly in these systems proceeds by nucleation of randomly aligned grains which thereafter rotate into registry with the field. We highlight the tradeoff between decreasing mobility and increasing anisotropic field interaction that dictates alignment kinetics while transiting from a high temperature disordered state to an ordered system at lower temperatures. [Preview Abstract] |
Tuesday, March 3, 2015 3:06PM - 3:18PM |
J20.00002: Directed Assembly of Block Polymers Edwin Thomas Various types of boundary conditions and applied fields can be used to impose constraints on how the micro domain organize. In some cases the constraints serve to remove degenerate patterns which serves to eliminate defects that occur at the boundaries between energetically equivalent patterns. In other cases, either new micro domain patterns emerge or certain types of defects are created at special locations depending on the global and local symmetries of both the imposed constraints and the micro domains themselves. Addition of nano particles to a block polymer brings in additional considerations for the overall pattern of the system. Additive size, shape and surface chemistries relative to those of the block polymer influence their location in the overall pattern. By providing commensuration of block polymer period(s) as well as compatibility of the point group symmetries of both the particle(s) and domain(s), help realize systems where the equilibrium microstructure enables multifunctional physical properties. [Preview Abstract] |
Tuesday, March 3, 2015 3:18PM - 3:30PM |
J20.00003: Failure of Batteries with Block Copolymer Electrolytes and Lithium Metal Anodes Nitash Balsara, Didier Devaux, Katherine Harry, Dilworth Parkinson, Rodger Yuan, Daniel Hallinan, Alastair MacDowell Solid block copolymer electrolytes are promising candidates for the development of high performance rechargeable batteries comprising a lithium metal anode due to their chemical stability toward lithium and their mechanical resistance to dendrite growth. The application of a solid polystyrene-b-poly(ethylene oxide) (SEO) block copolymer electrolyte in lithium symmetric cells permits to study the formation and growth of lithium dendrites by a non-destructive tool, hard X-ray microtomography. All solid-state batteries comprising a Li metal anode, a SEO electrolyte layer and a composite cathode were assembled and cycled. The cathode contains lithium iron phosphate as active material, SEO electrolyte as binder, and carbon black. Hard X-ray microtomography enables to visualize the microstructural changes at the Li/SEO and SEO/cathode interfaces to get insight on the battery failure mechanisms. [Preview Abstract] |
Tuesday, March 3, 2015 3:30PM - 3:42PM |
J20.00004: Polymer Dynamics under Cylindrical Nano-Confinement Karen Winey, Wei-Shao Tung, Robert Riggleman Polymer melts under cylindrical confinement have previously been shown to exhibit chain conformations elongated parallel to the cylinder axis and compressed perpendicular to the cylinder. Further, simulations and theory found that the number of entanglements per chain decreases as the cylinder diameter decreases. This talk presents the local dynamics and polymer diffusion under cylindrical nanoconfinement using simulations and experiments. For the molecular dynamics simulations, an entangled polymer is confined by an amorphous cylindrical confinement. Local dynamics and local packing of monomers are affected by the cylindrical confinement and an anisotropic mean-squared displacement is observed with faster motion along the cylinder axes that increases with increasing confinement. Using elastic recoil detection experiments, polymer diffusion coefficients along cylindrical nanopores were measured for deuterated polystyrene diffusing into nanoporous membranes infiltrated with polystyrene. The tracer diffusion coefficient increased with decreasing pore size, although the increase is less pronounced than found in the simulations. Results will be discussed in terms of the reptation model. [Preview Abstract] |
Tuesday, March 3, 2015 3:42PM - 3:54PM |
J20.00005: The physical aging of star-shaped macromolecules: role of functionality Peter Green, Bradley Frieberg, Emmanouil Glynos, Georgios Sakellariou The phenomenon of physical aging, structural relaxations that enable the return of a polymer, quenched to a temperature $T_{age}$ below its glass transition temperature $T_g$, to equilibrium, was investigated in a series of star-shaped macromolecules. These macromolecules possessed functionalities that varied from $f=3$ to $f=64$, and their degrees of polymerization per arm $N$ were all comparable ($N\sim100$). The aging of these star-shaped macromolecules is qualitatively similar to that of linear chain polymers, with their aging rates $K$ exhibiting maxima at threshold temperatures $T_{tr}$. The aging rates of the star-shaped molecules, however, are slower than their linear analogs. Moreover, $T_{tr}$ decreased with increasing $f$, and $K$ increased with increasing $f$ for $T_{age} < T_{tr}$. Our results are, in part, rationalized in terms of dynamic percolation models. [Preview Abstract] |
Tuesday, March 3, 2015 3:54PM - 4:06PM |
J20.00006: Solvent, Thermal and Solvent-Thermal Methods on Block Copolymer Thin Films Thomas Russell, Xiaodan Gu, Ilja Gunkel, Alexander Hexemer Real-time grazing-incidence small-angle X-ray scattering experiments were used to study block copolymer self-assembly in thin films during thermal and solvent vapor annealing, where copolymer thin films were exposed to the vapor of a solvent having near equal interactions with the blocks and to elevated temperature in an inert gas atmosphere, respectively. Similarities between both annealing techniques were identified and advantages and disadvantages of each annealing method are discussed. We show that the product of the effective Flory-Huggins interaction parameter, $\chi$, and the degree of polymerization, N, determines the grain size, irrespective of the specific annealing technique. Thermal-solvent annealing, where the thin films were exposed to solvent vapors at elevated temperatures, is also discussed and compared to solvent vapor and thermal annealing. [Preview Abstract] |
Tuesday, March 3, 2015 4:06PM - 4:18PM |
J20.00007: Predicting the distribution of functional nanoparticles in block polymers Robert Riggleman Polymer nanocomposites continue to find new applications, and it has become clear that controlling the dispersion state of the nanoparticles plays a key role in their ultimate performance. For optical properties it is crucial to control the particle spacing and mutual orientation, while mechanical properties seem to be dictated by the size and shape of any aggregates that form. However, predicting the equilibrium structure and assembly of nanoparticles as a function of their size, shape, surface functionality, and interactions with the matrix polymers remains a significant challenge. In this talk, I will describe our recent efforts to extend polymer field theory to describe the thermodynamics of polymer nanocomposite materials. Our approach does not require the mean-field approximation, and we can describe nanoparticles with a wide range of surface functionality, including grafting with various polymer architectures and strong wetting with a matrix polymer. [Preview Abstract] |
Tuesday, March 3, 2015 4:18PM - 4:30PM |
J20.00008: Coarse-Grained Simulation of Ion Diffusion in Polymer Melts: Effect of Physical Crosslinking and Finite Concentration Zhen-Gang Wang, Umi Yamamoto We present a coarse-grained simulation framework to study long-time dynamics of lithium ions in unentangled polymer melts. Effects of strong cation-monomer binding are modelled by formation of reversible bonds, and monomer-specific binding features enter via bond lifetime and coordination number, which can be estimated from atomistic simulations. Two competing mechanisms control the cation transport: successive replacement of dynamic bonds, and motion of the ``branched'' polymer cluster formed by a cation. Either channel can dominate the long-time diffusion depending on chain lengths and/or the bond lifetime relative to the Rouse time. At high concentrations, cations crosslink the polymers into a transient network, which significantly slows down the relaxation of the polymers, resulting in the non-monotonic dependence of ion conductivity on concentration, in qualitative agreement with experiment. [Preview Abstract] |
Tuesday, March 3, 2015 4:30PM - 4:42PM |
J20.00009: Thermodynamics and Kinetics of Defect Annihilation in Block Copolymer Assembly Juan de Pablo Directed copolymer seassembly (DSA) offers a promising alternative for patterning at sub-lithographic length scales. Much progress has been made over the past decade, but a number of significant challenges remain. In particular, it is essential that the concentration of defects in self-assembled block polymer films be brought down to levels that are compatible with semiconductor fabrication requirements. Recent work has shown that many of the defects that arise in block copolymer films assembled on nano-patterned substrates represent highly unfavorable non-equilibrium states that are stabilized by large free energy barriers. It is therefore of interest to identify the kinetic mechanisms that may lead to elimination of such barriers. In this work we use theory and simulations to determine the pathways through which defects are annealed or annihilated in directed copolymer assembly processes. We examine the effects of composition, pattern characteristics, solvent concentration and general material characteristics on directed assembly, and propose general guidelines and fabrication strategies that are likely to lead to defect-free assembly of block polymers on lithographically patterned substrates. [Preview Abstract] |
Tuesday, March 3, 2015 4:42PM - 4:54PM |
J20.00010: Polymer stability and function for electrolyte and mixed conductor applications Paula Hammond, Nicole Davis, David Liu, Chibueze Amanchukwu, Nate Lewis, Yang Shao-Horn Polymers exhibit a number of attractive properties as solid state electrolytes for electrochemical energy devices, including the light weight, flexibility, low cost and adaptive transport properties that polymeric materials can exhibit. For a number of applications, mixed ionic and electronic conducting materials are of interest to achieve transport of electrons and holes or ions within an electrode or at the electrode-electrolyte interface (e.g. aqueous batteries, solar water splitting, lithium battery electrode). Using layer-by-layer assembly, a mode of alternating adsorption of charged or complementary hydrogen bonding group, we can design composite thin films that contain bicontinuous networks of electronically and ionically conducting polymers. We have found that manipulation of salt concentration and the use of divalent ions during assembly can significantly enhance the number of free acid anions available for ion hopping. Unfortunately, for certain electrochemical applications, polymer stability is a true challenge. In separate studies, we have been investigating macromolecular systems that may provide acceptable ion transport properties, but withstand the harsh oxidative environment of lithium air systems. An investigation of different polymeric materials commonly examined for electrochemical applications provides insight into polymer design for these kinds of environments. [Preview Abstract] |
Tuesday, March 3, 2015 4:54PM - 5:06PM |
J20.00011: Structural evolution of polyelectrolyte-complex-core micelles and ordered-phase bulk materials Matthew Tirrell, Daniel Krogstad, Edward Kramer The kinetics of formation and structural evolution of novel polyelectrolyte complex materials formed by the assembly of water-soluble di- and tri-block copolymers, with one neutral block and one block either cationic or anionic, have been investigated. The mechanism and speed of the assembly process, and the organization of these domains, were probed using dynamic mechanical spectroscopy and small angle X-ray scattering (SAXS). SAXS revealed that the equilibrium morphologies of both the di-block copolymer and the tri-block copolymer materials were generally qualitatively the same with some apparent quantitative differences in phase boundaries, possibly attributable to lack of full equilibration. Slow kinetics and difficulties in reaching equilibrium phase structures, especially in tri-block materials, is a principal message of this article. Detailed analysis of the SAXS data revealed that the tri-block copolymer materials formed ordered phases via a nucleation and growth pathway and that the addition of small amounts ($\sim$20{\%}) of corresponding di-block copolymers increased the rate of structure formation and enhanced several key physical properties. [Preview Abstract] |
Tuesday, March 3, 2015 5:06PM - 5:18PM |
J20.00012: Flexible Battery Cathodes Enabled by Conductive Block Copolymers Jodie Lutkenhaus, Rafael Verduzco, Hyosung An, Yen-Hao Lin Alone, or as part of hybrid electrodes, conductive polymers are poised to play an integral role in the new and growing field of flexible or ``plastic'' power. Here we demonstrate that even small amounts of a poly(3-hexylthiophene)-block-poly(ethylene oxide) (P3HT-b-PEO) block copolymer, acting as an ion and electron conductor, can bring about significant improvements in energy storage and mechanical flexibility for V$_{2}$O$_{5}$ hybrid cathodes for Li-ion batteries. By following this approach, traditional inert polymer binders and carbon black additives are not needed. V$_{2}$O$_{5}$ alone has a high theoretical capacity that is limited in practical application by low conductivity. Further, V$_{2}$O$_{5}$ alone is brittle and breaks upon repeated flexure. P3HT-b-PEO serves to address both these issues. This presentation will cover how these hybrid electrodes are formed and the resulting physicochemical properties that lead to its enhanced flexibility and energy storage. [Preview Abstract] |
Tuesday, March 3, 2015 5:18PM - 5:30PM |
J20.00013: Swelling of polyelectrolyte and polyzwitterion brushes by humid vapors Jan Genzer, Casey Galvin, Michael Dimitriou, Sushil Satija Swelling behavior of polyelectrolyte and polyzwitterion brushes derived from poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) in water vapor is investigated using a combination of neutron and X-ray reflectivity and spectroscopic ellipsometry over a wide range of relative humidity (RH) levels. The extent of swelling depends strongly on the nature of the side-chain chemistry. For parent PDMAEMA, there is an apparent enrichment of vapor at the polymer/air interface. Despite extensive swelling at high humidity level, no evidence of charge repulsion is found in weak or strong polyelectrolyte brushes. Polyzwitterionic brushes swell to a greater extent than the quaternized brushes studied. However, for RH levels beyond 70{\%}, the polyzwitterionic brushes start to exclude water molecules, leading to a decline in water volume fraction from the maximum of 0.30 down to 0.10. Using a gradient in polymer chain grafting density, we provide evidence that this behavior stems from the formation of inter- and intramolecular zwitterionic complexes. [Preview Abstract] |
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