Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session A16: New Mesophase Symmetries and Topologies in Self-Assembled Soft MatterFocus
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Sponsoring Units: GSOFT DBIO Chair: Cecilia Leal, University of Illinois Urbana-Champaign Room: 275 |
Monday, March 13, 2017 8:00AM - 8:36AM |
A16.00001: Formation of Low Symmetry Ordered Phases in Block Polymer Melts Invited Speaker: Frank Bates Until recently the phase behavior of asymmetric AB diblock copolymers in the melt state was universally accepted as a solved problem: spherical domains packed on a body centered cubic (BCC) lattice. Recent experiments with low molecular weight diblocks have upended this picture, beginning with the discovery of the Frank-Kasper sigma phase in poly(isoprene)-$b$-poly(lactide) (PI-PLA) followed recently by the identification of a dodecagonal quasicrystal phase (DDQC) as a metastable state that evolves from the supercooled disordered liquid. Self-consistent mean-field theory shows that introducing conformational asymmetry ($b_{A}$ \textgreater $b_{B}$ where $b$ is the statistical segment length) opens a window in the phase portrait at $f_{A}$ \textless \textless 1/2 that supports the formation of various low symmetry ordered phases. However, contrary to the widely accepted mean-field picture, the disordered state near the order-disorder transition (ODT) is highly structured and rapid cooling of this micellar fluid several tens of degrees below the ODT temperature arrests macromolecular chain exchange transitioning the material from an ergodic to non-ergodic state. We have explored the evolution of order following such temperature quenches and during subsequent reheating using synchrotron small-angle X-ray scattering (SAXS) revealing surprising analogies with the behavior of metal alloys. This presentation will associate the formation of ordered low symmetry phases with the concept of sphericity, the tendency for the self-assembled nanoparticles to be spherical in competition with the constraints imposed by periodic and aperiodic packing without voids and subject to the condition of incompressibility. This work was conducted in collaboration with Kyungtae Kim, Morgan Schulze, Akash Arora, Ronald Lewis, Timothy Gillard, Sangwoo Lee, Kevin Dorfman and Marc Hillmyer. [Preview Abstract] |
Monday, March 13, 2017 8:36AM - 8:48AM |
A16.00002: Frank Kaspar Phases of Block Copolymers and the Kelvin Problem: Is it all about Area? Gregory Grason, Michael Buckley, Abhiram Reddy Observations and predictions of Frank Kaspar phases of spherically-ordered assemblies of amphiphillic molecules, and block copolymers in particular, continue to beg questions about the physical mechanisms that stabilize complex symmetries, like the A15 or $\sigma$ lattices. In this talk we revisit previous heuristic and quantitative arguments about the role of lattice symmetry, and the geometry of Voronoi cells in particular, in selecting the minimal free energy packings of ``squishable" spherical domains. We focus on what might be called a ``diblock foam” model that maps the free energy of competing sphere phases directly onto two geometric moments of the cell distributions, the reduced area and the moment of inertia, which measure the respective costs of inter-domain repulsions and entropic stretching of constituent chains. Surface Evolver optimizations of the this purely geometric model are performed for BCC, A15, $\sigma$ and a broader array of competing Frank Kasper structures. These results, which we compare to SCFT studies, shed a critical light on the relative importance of optimal area vs. optimal stretching vs. optimal volume partitioning among cells in selecting among complex sphere phases, and further, suggests previously unstudied candidate phases. [Preview Abstract] |
Monday, March 13, 2017 8:48AM - 9:00AM |
A16.00003: Coupling mesodomain positional ordering to intra-domain orientational ordering in block copolymer assembly Christopher Burke, Abhiram Reddy, Ishan Prasad, Gregory Grason Block copolymer (BCP) melts form a number of symmetric microphases, e.g. columnar or double gyroid phases. BCPs with a block composed of chiral monomers are observed to form bulk phases with broken chiral symmetry e.g. a phase of hexagonally ordered helical mesodomains. Other new structures may be possible, e.g. double gyroid with preferred chirality which has potential photonic applications. One approach to understanding chirality transfer from monomer to the bulk is to use self consistent field theory (SCFT) and incorporate an orientational order parameter with a preference for handed twist in chiral block segments, much like the texture of cholesteric liquid crystal. Polymer chains in achiral BCPs exhibit orientational ordering which couples to the microphase geometry; a spontaneous preference for ordering may have an effect on the geometry. The influence of a preference for chiral polar (vectorial) segment order has been studied to some extent, though the influence of coupling to chiral tensorial (nematic) order has not yet been developed. We present a computational approach using SCFT with vector and tensor order which employs well developed pseudo-spectral methods. Using this we explore how tensor order influences which structures form, and if it can promote chiral phases. [Preview Abstract] |
Monday, March 13, 2017 9:00AM - 9:12AM |
A16.00004: Process-accessible structures in block copolymers Marcus Mueller, De-Wen Sun Process-directed assembly copolymers refers to thermodynamic processes that reproducibly direct the kinetics of structure formation from an initial, unstable state into a selected metastable structure. Specifically we investigate the spontaneous structure formation of ACB triblock copolymers after a rapid transformation of the middle block C from A to B. This prototypical process (e.g., photochemical transformation), which occurs on a time scale faster than the molecular relaxation time, convert the initial equilibrium structure of the AAB block copolymer into a well-defined but unstable structure of the ABB copolymer. The spontaneous structure formation that ensues from this unstable state becomes trapped in a metastable morphology, and we systematically explore, which metastable structures can be fabricated by varying the block copolymer composition of the initial and final state. In addition to the equilibrium structures linear diblock copolymers we find 6 metastable periodic structures, inter alia, Schoen’s F-RD periodic minimal surface. Generally, we observe that the metastable structure of the ABB copolymer possesses the same symmetry as the initial equilibrium structure of the AAB material. [Preview Abstract] |
Monday, March 13, 2017 9:12AM - 9:24AM |
A16.00005: Stability of sphere-forming phases in diblock copolymers: Assessment of lattice-partition theories Akash Arora, Frank S. Bates, Kevin D. Dorfman The recent experimental discovery of a Frank-Kasper $\sigma$ phase in block copolymers has significantly altered our understanding of the sphere-forming region of the phase diagram. The $\sigma$ phase possesses a large tetragonal unit cell containing 30 particles of different shapes and sizes, arranged in three different coordination environments. Although self-consistent field theory (SCFT) calculations have successfully identified the importance of conformational asymmetry on the relative stability of body-centered cubic (BCC) and the $\sigma$ phase, the dependence of stability of the $\sigma$ phase to its space-filling or lattice-partition principles remains an open question. In this study, we examine different geometrical theories in literature that attempt to predict the stable phase directly from the shapes and sizes of different Wigner-Seitz cells comprising the lattice. Specifically, we compare the predictions from these theories for four phases, fcc, bcc, $\sigma$, and A15 in diblock copolymers, to the results of SCFT calculations over a wide range of the sphere-forming region of the phase diagram. Our results bring to the fore both the successes and failures of purely geometric theories to predict the relative stability of these phases in diblock copolymers. [Preview Abstract] |
Monday, March 13, 2017 9:24AM - 9:36AM |
A16.00006: Role of Polymer-grafted Nanoparticle Interactions in Supercrystal Self-Assembly Nathan Horst, Curt Waltmann, Alex Travesset Many successful strategies are available for the programmable self-assembly of nanoparticle superlattices. In this talk, we discuss the the case of nanoparticles with grafted polymer ligands. For very short polymers, the phase diagram is rationalized by borrowing results from hard-sphere packing models. Although a clear correlation exists between the maximum of the packing fraction of hard spheres and supercrystal equilibrium phases found experimentally, these systems are flexible, which leads to clear deviations from the sphere packing model. Using theoretical and computational models, we present an investigation of the interactions of polymer-grafted nanoparticles, focusing on the role of the rigidity of the chain, and how it affects the resulting two and three-dimensional superlattice structures. Comparison with an experimental system of gold nanoparticles grafted with polyethylene glycol is also presented. [Preview Abstract] |
Monday, March 13, 2017 9:36AM - 9:48AM |
A16.00007: Direct Nanoscopic Imaging of Mesophase Formation from Anisotropic Nanoparticles Zihao Ou, Ziwei Wang, Erik Luijten, Qian Chen We utilize the emergent nanoscopic imaging technique, liquid phase transmission electron microscopy, to suggest a paradigm shift from imaging the dynamics and transformations of micron-sized systems to nanoscale objects in liquids. Here highly anisotropic nanoparticles are used as a prototypical system and are observed to assemble into a non-trivial mesophase, a plastic crystal with positional order and orientational disorder which has been predicted to be impossible for this shape using hard colloidal models. With a combination of direct imaging and Monte Carlo simulation, we show that the nanoscale ``non-hard'' interactions render configurational entropy sufficient to randomize nanoparticle orientations and induce the crystallization into a 3D hierarchical plastic crystal. The long-standing hypothesized kinetic intermediates in nanoscale crystallization is also visualized and analyzed for the first time. [Preview Abstract] |
Monday, March 13, 2017 9:48AM - 10:00AM |
A16.00008: Chiral Liquid and Liquid Crystal Phases from Achiral Molecules Goran Ungar, Huanjun Lu, Xiangbing Zeng, Christian Dressel, Carsten Tschierske There is a growing number of examples where chirality in mesophases is induced in non-chiral compounds, due to the mesophase structure (C. Tschierske, G. Ungar , \textit{ChemPhysChem} 2016, \textit{17}, 9.). The induced chirality often emerges due to synchronized selection of one of the two enantiomeric conformers of a bistable molecule that are separated by a sizeable but not unsurmountable energy barrier. Recent studies have revealed more complex and puzzling cases. Thus it was found that some long known cubic liquid crystal phases are always optically active, while others, like the ``double gyroid'', often appearing in the same non-chiral compound, never are (C. Dressel \textit{et al}., \textit{Angew. Chem. Int. Ed.,} 2014, \textit{53}, 13115). Even more puzzling is the recent discovery of a liquid phase, Iso*, containing no chiral molecules and having no long range positional or orientational order whatsoever, yet displays strong optical activity. The induced chirality in such a liquid develops over virtually unlimited distances (C. Dressel \textit{et al}., \textit{Nat. Chem}. \textbf{2014}, \textit{6}, 971). The nature of these and some new phases and of their transitions will be discussed. [Preview Abstract] |
Monday, March 13, 2017 10:00AM - 10:12AM |
A16.00009: Bottom-up preparation and structural study of monodispersed lipid particles with internal structure Hojun Kim, Alana Alfeche, Cecilia Leal Lipid based nanoparticles having internal bicontinuous cubic phases, also known as cubosomes, are becoming increasingly interesting drug delivery platforms. Compared to the liposomes, they offer an augmented surface area for drug encapsulation. However, this simple argument is insufficient to explain the cellular delivery performance of cubosomes compared to other lipid-based nanoparticles. One could argue that their topology facilitates membrane fusion and endosomal escape but at the moment the exact mechanism of cubosome cellular internalization and endosomal escape is still unknown. This is partially because the practical use of cubosomes has been limited due to hurdles of uncontrollable size and shape distributions. The conventional top-down preparation methods (sonication/homogenization) yield large and polydisperse particles. In this presentation we introduce a new system based on microfluidic devices to prepare small (200 nm) and monodisperse cubosomes with a quality not possible using conventional methods. With this approach, we successfully prepared spherical and monodisperse cubosomes (PDI: 0.01) with and without drug loading. To characterize the cubosomes and the formation mechanisms, we utilize Small Angle X-ray Scattering (SAXS) and Cryogenic TEM. [Preview Abstract] |
Monday, March 13, 2017 10:12AM - 10:24AM |
A16.00010: MD Simulations of the Mesostructure Phase of Microspheres at an Air-Water Interface Roy M. Lindsay, Daniel W. Sinkovits The interaction between like-charged particles in a bulk-phase system is adequately described by the standard Derjaguin-Landau-Overbeek-Verwey (DLVO) theory, but the interactions between particles trapped at an interface cannot be readily described by DLVO theory. Theoretical and experimental research over the past three decades has elucidated the dominant phenomena governing these interactions, but puzzles remain, including an experimentally observed mesostructure phase. In this project, we introduce a 4-term pair potential function in the molecular dynamics simulation to incorporate both short and long range repulsive and attractive forces. We reproduce an experimentally observed surface-area isotherm, and we attempt to reveal the dominant forces governing the formation of the mesostructure phase in these interfacial particle arrays. [Preview Abstract] |
Monday, March 13, 2017 10:24AM - 10:36AM |
A16.00011: Patterns on Pollen: a polysaccharide phase transition process Asja Radja, Maxim Lavrentovich, Eric Horsley, Randall Kamien, Alison Sweeney Pollen grains are famous for the beauty and diversity of the micron-scale patterns decorating their tough outer coating. These patterns are extraordinarily robust and reproducible within a species, yet different species have extremely variable patterns. Previously, we showed that these patterns could result from a first-order phase transition on a sphere, and this mechanism also informs the pattern reproducibility within a species as well as variation across species. Here we present micrographic evidence that the phase-transitioning material responsible for pattern formation is a polysaccharide mesh deposited on the cell surface prior to pattern development. We found that the phase transition of this material creates the negative spatial template of the final pattern observed on the mature cell. We also analyzed the various monosaccharide components of the polysaccharide mesh of two different species (and therefore pattern types) to investigate the linkage between a species' polysaccharide composition and its phase behavior. Finally, we calculated a phase diagram of possible pollen patterns given the theoretical statement of pattern formation in our previous work, and discussed how parameters from the existing theory map to the biological materials we observe. [Preview Abstract] |
Monday, March 13, 2017 10:36AM - 10:48AM |
A16.00012: Packing Structures of Soft Particles by Compression Sangwoo Lee, Liwen Chen Recent discovery of Frank-Kasper phases in self-assembling materials stimulates exploration of new crystal structure to understand the origin of the complex packing structures nature selects. We investigated packing structures by block copolymer micelles in an aqueous/organic solvent mixture. The micellar solution showed two phase states of globular polymer phase and liquid phase containing homogeneously dispersed polymeric micelles. The micelles developed a close-packed order which transforms into a Frank-Kasper C14 phase as the concentration of block copolymer surfactant increases. This transition aligns with the sphericity criteria. [Preview Abstract] |
Monday, March 13, 2017 10:48AM - 11:00AM |
A16.00013: TOPOLOGICAL CRYSTALS Satoshi Tanda We report the discovery of Mobius, Figure-8, Hopf-link Crystals in NbSe3[1,2]. We reveal their formation mechanisms of which two crucial components are the spherical selenium (Se) droplet, which a NbSe3 fiber wraps around due to surface tension, and the monoclinic (P2(1)/m) crystal symmetry inherent in NbSe3, which induces a twist in the strip when bent. Our crystals provide a non-fictitious topological Mobius world governed by a non-trivial real-space topology. We classified these topological crystals as an bridge between condensed matter physics and mathematics using concept of embedding. Moreover, we have investigated physical properties on the loop CDW systems. We discovered results by measurement of topological Ahoronov-Bohm interference effect of CDW, Shapiro steps utilizing high-frequency resistance, , and synchrotron X-ray diffraction. We will introduce a new perspective from these results of topological crystals studies[3,4,5]. \\\\ $[1]$ S. Tanda,et.al., Nature 417, 397 (2002). \\ $[2] $T.Matsuura,et.al., PRB 73, 165118 (2006).\\ $[3]$ J. Ishioka, et.al.,PRL 105, 176401 (2010)\\ $[4]$ Aharonov-Bohm effect in charge-density wave, M. Tsubota, K. Inagaki, T. Matsuura and S. Tanda, Europhys. Lett. 97, 57011 (2012)\\ $[5]$K. Inagaki,et.al.,PRB 93, 075423 (2016) [Preview Abstract] |
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