Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session F31: Focus Session: Nano to Meso-Scale Structure in Ordered Soft Matter: Liquid Crystal Structure, Dynamics and Function II |
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Sponsoring Units: DPOLY Chair: Chinedum Osuji, Yale University Room: 339 |
Tuesday, March 19, 2013 8:00AM - 8:36AM |
F31.00001: POLYMER PHYSICS PRIZE BREAK
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Tuesday, March 19, 2013 8:36AM - 8:48AM |
F31.00002: Liquid Crystals of Disks of Controlled Aspect Ratios Zhengdong Cheng, Min Shuai, Andres F. Mejia Nanoparticles with quasi two-dimensional shapes serve as building blocks for discotic colloidal liquid crystals. However, due to difficulty of synthesis and especially shape-tuning of disk-shaped nanoparticles, good model systems for the study of discotic colloidal liquid crystals are hard to found. $\alpha $-zirconium phosphate (ZrP) crystals synthesized through hydrothermal treatment has regular disk shapes and controllable size, thickness, as well as size polydispersity. We experimentally illustrate that aqueous suspensions of these ZrP disks form stable liquid crystal phase easily. By choosing the thickness of the disks, an iridescent liquid crystal phase has been achieved. The critical concentration of the phase transition was found to be dependent on aspect ratios. We will also discuss our recent results on the phase diagram of discotic liquid crystals as a function of aspect ratio and particle concentration using ZrP monolayers and wax disks. [Preview Abstract] |
Tuesday, March 19, 2013 8:48AM - 9:00AM |
F31.00003: Synthesis and Self-Assembly Behaviors of Polyhedral Oligomeric Silsesquioxane Based Giant Molecular Shape Amphiphiles Kan Yue, Xinfei Yu, Chang Liu, Wen-Bin Zhang, Stephen Cheng Recently, our group has focus on the synthesis and characterization of novel giant molecular shape amphiphiles (GMSAs) based on functionalized molecular nanoparticles (MNPs), such as polyhedral oligomeric silsesquioxane (POSS), tethered with polymeric tails. A general synthetic method via the combination of sequential ?click? reactions has been developed and several model GMSAs with various tail lengths and distinct molecular topologies, which can be referred as the ?giant surfactants?, ?giant lipids?, ?giant gemini surfactants?, and ?giant bolaform surfactants? etc., have been demonstrated. Studies on their self-assembly behaviors in the bulk have revealed the formation of different ordered mesophase structures with feature sizes around 10 nanometers, which have been investigated in detail by small angle X-ray scattering (SAXS) technique and transmission electron microscopy (TEM). These findings have general implications on understanding the underlying principles of self-assembly behaviors of GMSAs, and might have potential applications in nano-patterning technology. [Preview Abstract] |
Tuesday, March 19, 2013 9:00AM - 9:12AM |
F31.00004: 2D Smectic of a T-shaped Liquid Crystal Mesogen D. Chen, D.A. Coleman, C. Zhu, N. Chattham, X. Cheng, C. Tschierske, J.E. Maclennan, M.A. Glaser, N.A. Clark We report structural studies of a T-shaped mesogenic molecule. Upon cooling from the isotropic, the molecules first form a lamellar phase, with the molecular tails organized into sheets and the head groups isotropic in the plane of the lamellae. On further cooling, the head groups self-assemble into phases with 2D nematic and smectic order. The 2D smectic has only short-range positional correlations, with dislocations in the layering. The development of the 2D smectic reduces the long-range correlations of the fundamental lamellar structure, with the system evolving into a biaxial nematic with the T-shaped molecules ordered in three dimensions but with only short-range correlations. [Preview Abstract] |
Tuesday, March 19, 2013 9:12AM - 9:48AM |
F31.00005: Hierarchical Structure in Liquid Crystalline Polymers and Block Copolymers Invited Speaker: Rajeswari Kasi We are interested in developing general molecular engineering approaches to liquid crystalline and semicrystalline brush random and block copolymers. These polymers self-assemble into hierarchical supramolecular nano structures with organization over several length scales that allows for evolution for unique property and function. In these polymeric libraries, we exploit liquid crystalline units for its responsive optical and mechanical features and semicrystalline brush units for its mechanical and thermal features. These materials are useful for applications in 1D photonic band gap materials as well as templates for preparation of nanoporous scaffolds. A series of liquid crystalline monomers and semicrystalline brush macromonomers are synthesized and polymerized by ring opening metathesis methods to prepare liquid crystalline random brush copolymers and liquid crystalline block brush copolymers. All these copolymers exhibit atleast two levels of hierarchy: LC mesophase assembly and brush microphase segregation due to incompatibility with the LC phase. We investigate the phase evolution of these materials based on composition, molecular weight and length of the semicrystalline brush and we map out the phase behavior by a variety of techniques including thermal analysis, UV visible analysis, polarized optical microscopy, temperature controlled small angle x-ray, wide-angle x-ray, electron microscopy, dynamic mechanical analysis. In addition to thermal and microstructural analysis, we determine the order-disorder transition of the self-assembled copolymers. In closing, by exploiting molecular architecture and composition to modulate the self-assembly, hierarchical structure at multiple length scales can be obtained and preserved which allows for the creation of unique 1D-photonic band gap materials as well as nanoporous scaffolds. [Preview Abstract] |
Tuesday, March 19, 2013 9:48AM - 10:00AM |
F31.00006: Triply Periodic Multiply Continuous Lyotropic Liquid Crystals Derived from Gemini Dicarboxylate Surfactants Gregory Sorenson, Mahesh Mahanthappa A delicate balance of non-covalent interactions drives the supramolecular assembly of hydrated small molecule amphiphiles into aqueous lyotropic liquid crystals (LLCs). High symmetry multiply continuous phases, exemplified by the gyroid phase, are particularly desirable for many applications due to their interpenetrating hydrophilic and hydrophobic domains with well-defined chemical functionality decorating the interface between the two domains. However, these high symmetry assemblies are often difficult to obtain due to limited levels of hydration and temperature ranges over which they are accessible. Recent work suggests that small molecule amphiphiles known as ``gemini'' surfactants readily form these lyotropic network phases. Herein we report the lyotropic phase behaviors of a new class of dicarboxylate gemini surfactants that form stable, multiply continuous, high symmetry network structures over broad hydration and temperature ranges. [Preview Abstract] |
Tuesday, March 19, 2013 10:00AM - 10:12AM |
F31.00007: Alignment and Stiffening of Liquid Crystal Elastomers under Dynamic Compression Aditya Agrawal, Prabir Patra, Pulickel Ajayan, Walter Chapman, Rafael Verduzco Biological tissues have the remarkable ability to remodel and repair in response to disease, injury, and mechanical stresses, a phenomenon known ``functional adaptation'' or ``remodeling''. Herein, we report similar behavior in polydomain liquid crystal elastomers. Liquid crystal elastomers dramatically increase in stiffness by up to 90 {\%} under low-amplitude, repetitive (dynamic) compression. By studying a systematic series of materials, we demonstrate that the stiffness increase is directly influenced by the liquid crystal content of the elastomers, the presence of a nematic liquid crystal phase and the use of a dynamic as opposed to static deformation. Through a combination of rheological measurements, polarizing optical microscopy and 2-D X-ray diffraction, we demonstrate that self-stiffening arises due to rotations of the nematic director in response to dynamic compression, and show that the behavior is consistent with the theory for nematic rubber elasticity. Previous work with liquid crystal elastomers has focused primarily on `soft elastic' deformations at large strains, but our findings indicate rich behavior at previously overlooked low-strain, dynamic deformations. [Preview Abstract] |
Tuesday, March 19, 2013 10:12AM - 10:24AM |
F31.00008: Large area Magnetic alignment of a Cylindrical liquid crystalline Brush Block Copolymer for Generating Nanoporous Templates Manesh Gopinadhan, Prashant Deshmukh, Pawel Majewski, Rajeswari Kasi, Chinedum Osuji Magnetic fields have been shown to be a facile route to directing the self-assembly of both lamellar and cylinder forming diamagnetic block copolymer nanostructures over macroscopic areas. Here we present magnetic field directed self-assembly of a novel strongly segregated cylindrical block copolymer with polynorbonene backbone bearing a poly(lactic acid) PLA minority cylindrical brush block which is amenable to selective removal by chemical etching while a ciano-biphenyl species forms the liquid crystalline magneto-responsive block. We found that the PLA brush length is critical to obtain hexagonally packed cylindrical domains, while the system was not susceptible to magnetic field alignment due to large separation of LC clearing transition and order-disorder transition temperatures. Surprisingly, doping a small amount of free ciano-biphenyl mesogens induces strong and fast alignment of block copolymer microdomains under 5T magnetic field. Subsequent etching of the PLA block from the aligned material and cross-linking norbonene backbone by thiol-ene chemistry yield highly aligned nanoporous membranes which could potentially serve as templates for the synthesis of nanomaterials. Magnetic field directed self-assembly thus offer a simple route to generate nanoporous templates where porosity and the dimensions can be controlled by the molecular parameters. [Preview Abstract] |
Tuesday, March 19, 2013 10:24AM - 10:36AM |
F31.00009: Observations of phase behavior of chiral mesogens in diastereomeric domains of bent-core helical nanofilament networks B. Horanyi, D. Chen, E. Korblova, D.M. Walba, J.E. Maclennan, M.A. Glaser, N.A. Clark Blends of NOBOW, a helical nanofilament-forming B4 bent-core liquid crystal with organic guest molecules are completely mixed in the high temperature, isotropic phase. Upon cooling, the B4 filaments nucleate from the isotropic melt and grow into a homochiral dendritic network which acts as a porous medium of large internal area, with the guest material confined to nanoscale interstitial volumes between the twisted filaments. A typical sample is a conglomerate of independently nucleated left- and right-handed B4 domains many tens of $\mu $m across. Polarized optical microscopy reveals that chiral liquid crystal guest materials nanoconfined in the helical nanofilament networks form diastereomeric domains with distinct thermal behavior. [Preview Abstract] |
Tuesday, March 19, 2013 10:36AM - 10:48AM |
F31.00010: The Role of Confinement on Biologically Derived Liquid Crystals Marguerite Brown, Daniel Blair Suspensions of stabilized, dilute microtubules provide a versatile model system for understanding the structure of confined liquid crystals. Microtubule solutions are easily transported as a simple monomeric fluid that can easily be polymerized into rod-like macromolecules after they are confined within quasi-2D geometries (microfluidics). Using polarization and confocal microscopy, we analyze the structure of liquid crystals in a variety of geometries. We will present results on the role of confinement, boundary conditions and concentration, specifically discussing how each variable alters nematic ordering. [Preview Abstract] |
Tuesday, March 19, 2013 10:48AM - 11:00AM |
F31.00011: Bio-based liquid crystalline polyesters Carolus Wilsens, Sanjay Rastogi The reported thin-film polymerization has been used as a screening method in order to find bio-based liquid crystalline polyesters with convenient melting temperatures for melt-processing purposes. An in depth study of the structural, morphological and chemical changes occurring during the ongoing polycondensation reactions of these polymers have been performed. Structural and conformational changes during polymerization for different compositions have been followed by time resolved X-ray and Infrared spectroscopy. In this study, bio-based monomers such as vanillic acid and 2,5-furandicarboxylic acid are successfully incorporated in liquid crystalline polyesters and it is shown that bio-based liquid crystalline polymers with high aromatic content and convenient processing temperatures can be synthesized. [Preview Abstract] |
Tuesday, March 19, 2013 11:00AM - 11:12AM |
F31.00012: The liquid-crystal phase transition in suspensions of soft particles Miguel Pelaez-Fernandez, Anton Souslov, L. Andrew Lyon, Paul M. Goldbart, Alberto Fernandez-Nieves We experimentally determine the equation of state of swollen microgel suspensions: $\pi=\pi(\zeta, N_c)$, with $\pi$ the suspension osmotic pressure, $\zeta$ the generalized volume fraction and $N_c$ the number of chains per particle, which determines the microgel stiffness. We find that the melting and freezing lines shift to higher $\zeta$ as the particle becomes softer. Concomitantly, the liquid-crystal coexistence region becomes wider. We suggest that this behavior is due to the internal degrees of freedom of the microgel particles, which increase as the particle becomes softer. In this case, crystallization requires freezing some of these additional degrees of freedom resulting in the observed widening of the coexistence region. Our experiments provide the starting point to understand how the single-particle elasticity affects the phase behavior of colloidal suspensions. [Preview Abstract] |
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