Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session E16: Liquid Crystals III & Membranes, Vesicles and Miscelles I |
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Sponsoring Units: GSOFT Chair: Cheol Park, University of Colorado Room: 275 |
Tuesday, March 14, 2017 8:00AM - 8:12AM |
E16.00001: Spontaneous emergence of twist and formation of monodomain in lyotropic chromonic liquid crystals confined to capillaries. jinxin fu, Karthik Nayani, Jung Ok Park, Mohan Srinivasarao Unlike conventional nematics, lyotropic chromonic liquid crystals are notoriously hard to align. We report on the homogeneous planar alignment of Sunset Yellow in a flat rectangular capillary. Remarkably, the in-plane director aligns perpendicular to the long axis of the rectangular capillary resulting in a counterintuitive configuration. We rationalize the evolution of this configuration from a metastable doubly-twisted configuration by considering the coupling of the curvature of the edges of the rectangle to the Frank free energy via the saddle-splay contribution. In contrast, for a square capillary, the doubly-twisted configuration is the final ground state. Using a simple scaling argument, we show that the aspect ratio of the confining geometry determines the ground state. [Preview Abstract] |
Tuesday, March 14, 2017 8:12AM - 8:24AM |
E16.00002: Chiral amplification and sensing of chirality with lyotropic chromonic liquid crystals. Mohan Srinivasarao, Jung Ok Park, Jinxin Fu, Karthik Nayani, Rui Chang Due to the anisotropic elastic properties of lyotropic chromonic liquid crystals (LCLCs), a spontaneously twisted chiral structure has been reported in the achiral LCLCs system under cylindrical confinement. It is found that the handedness of chirality could be biased with a minute amount of a chiral additive. The entire system becomes ``homochiral'' and takes on the handedness of the additive. When 1{\%} by weight of L-glutamic acid was added to LCLCs in a cylinder, the LCLC sbecomes homochiral and possesses giant optical rotation. We explore the mechanism for this based on the ``sergeants-and-soldiers'' and the ``majority-rule'' principles known for organic molecular systems. [Preview Abstract] |
Tuesday, March 14, 2017 8:24AM - 8:36AM |
E16.00003: Configurational changes in chromonic tactoids upon the addition of polyethylene glycol and salt Rui Chang, Karthik Nayani, Jinxin Fu, Elsa Reichmanis, Jung Ok Park, Mohan Srinivasarao Lyotropic chromonic liquid crystals differ from conventional nematics in that the aggregation process of the plank-like molecules is affected by temperature, concentration, and additives. We study the effects of adding neutral polymer and ionic additives on the aggregation behavior by observing the optical textures of chromonic tactoids. When the aggregates are short, tactoids exhibit the well-known bipolar configuration with the two boojums at the poles. Longer aggregates increase the splay energy close to the boojums and drive an achiral symmetry-breaking transformation. The tactoids then conform to twisted bipolar and escaped-concentric configurations to relieve splay energy via twist and bend distortions. Neutral polymers and ionic additives significantly change the tactoid configurations. The fraction of escaped-concentric tactoids and the twist angle of twist bipolar tactoids increase with the addition of polyethylene glycol (PEG). The condensing effect of PEG elongates the aggregates and facilitates the formation of twist bipolar and escape concentric tactoids. The effects of NaCl on the tactoidal configuration depend on both sample and salt concentrations. The configurational transformation is rationalized by the screening of electrostatic repulsion by NaCl. [Preview Abstract] |
Tuesday, March 14, 2017 8:36AM - 8:48AM |
E16.00004: Toward molecular engineering of liquid crystal elasticity: a predictive study of nCB homologues Hythem Sidky, Jonathan Whitmer The difficulties associated with laboratory measurement of elastic constants present computational methods as an attractive option for understanding the elastic properties of new molecules. Free energy perturbation (FEP) has emerged as a powerful and effective method to obtain liquid crystal elasticities from molecular simulation. However, to date, this method has only been applied to coarse-grained models. Here, we extend this method to the \textit{in silico} measurement of molecular 5CB and its homologues, obtained from simulation using a combination of FEP methods. This represents a milestone in material property prediction and lays the foundation for computationally-guided molecular design of novel mesogenic compounds. [Preview Abstract] |
Tuesday, March 14, 2017 8:48AM - 9:00AM |
E16.00005: Temperature-gradient-induced} \textbf{Thermomigration and Thermal Convection in Freely-Suspended Smectic Liquid Crystal Films and Bubbles in Microgravity Cheol Park, Matt Glaser, Joe Maclennan, Noel Clark, Torsten Trittel, Ralf Stannarius Freely-suspended smectic films of sub-micrometer thickness and lateral extensions of several millimeters were used to study thermally driven migration and convection in the film plane. Film experiments were performed during the 6 minute microgravity phase of a TEXUS suborbital rocket flight (Texus 52, launched April 27, 2015). We have found an attraction of the smectic material towards the cold edge of the film in a temperature gradient, similar to the Soret effect. This process is reversed when this edge is heated up again. Thermal convection driven by two thermocontacts in the film is practically absent, even at temperature gradients up to 10 K/mm, with thermally driven convection only setting in when the hot post reaches the transition temperature to the nematic phase. The Observation and Analysis of Smectic Islands in Space (OASIS) flight hardware was launched on SpaceX-6 in April 2015 and experiments on smectic bubbles were carried out on the International Space Station using four different smectic A and C liquid crystal materials in separate sample chambers. We observed that smectic islands on the surface of the bubbles migrated towards the colder part of the bubble in a temperature gradient. [Preview Abstract] |
Tuesday, March 14, 2017 9:00AM - 9:12AM |
E16.00006: Measurements of Translational and Rotational Mobilities of Inclusions near a Boundary in TiltedFreely-Suspended Smectic Liquid Crystal Films Ian Cadenhead, Adam Green, Cheol Park, Matt Glaser, Joe Maclennan, Noel Clark Freely-suspended liquid crystal films serve as an excellent model system for investigating two-dimensional hydrodynamics, including the study of inclusion mobilities near fixed boundaries. We present experimental measurements using digital video microscopy of the translational and rotational mobilities of smectic islands near the boundary of a rectangular smectic A film a few molecular layers thick. The islands are thicker, circular domains that behave as large particles embedded in the film. Tilting the film causes the islands to drift under gravity. Measuring the diffusion and velocities of~these islands allows us to extract the translational and rotational mobilities of the inclusions as a function of distance from the film boundary. The results are compared to Saffman-Delbr\"{u}ck theory using the general approach of Levine and MacKintosh. [Preview Abstract] |
Tuesday, March 14, 2017 9:12AM - 9:24AM |
E16.00007: Layer Dynamics in Free Standing Membranes of Smectic Liquid Crystals Shokir Pardaev, Zeinab Parsouzi, Alan Baldwin, James Gleeson, Antal Jakli, Samuel Sprunt We studied the layer dynamics of free-standing smectic liquid crystal membranes with particular focus on the surface parameters that control these dynamics. Photon correlation spectroscopy reveals the contribution of distinct under- and overdamped processes. The frequency and damping rate of the former scale with scattering wavenumber in a manner that can be explained by the effect of a surface elastic constant (associated with gradients in surface tension) in addition to the average surface tension. The damping is shown to be quite sensitive to the presence of an atmosphere surrounding the film. The dispersion of the overdamped mode, observed in sufficiently thick films, can be explained as a composite of a surface elastic mode (hydrodynamic mode) and surface molecular tilt (non-hydrodynamic mode). [Preview Abstract] |
Tuesday, March 14, 2017 9:24AM - 9:36AM |
E16.00008: A chiral minimal surface from space group symmetries Shashank Markande, Gerd E. Schr\"oder-Turk, Vanessa Robins, Elisabetta A. Matsumoto Triply periodic minimal surfaces form the interface between bicontinuous structures in diblock copolymers and lipid bilayers in the membranes of certain organelles. Here we study a one parameter family of chiral triply periodic minimal surfaces which partition space into two disjoint regions, enclosing a quartz network on one side and its dual qzd network on the other. The three dimensional orbifold of the underlying space group, $P6_{2}22$, is used to analyze the symmetries of the surface. The symmetry elements combined with the flat points of the surface are used to obtain a regular parametrization known as the Weierstrass-Ennepper representation. [Preview Abstract] |
Tuesday, March 14, 2017 9:36AM - 9:48AM |
E16.00009: Stimuli-responsive cellulose-based nematogels Qingkun Liu, Ivan Smalyukh Physical properties of composite materials can be pre-engineered by controlling their structure and composition at the mesoscale. Yet, approaches for achieving this are limited and rarely scalable. We introduce a new breed of self-assembled nematogels formed by an orientationally ordered network of thin cellulose nanofibers infiltrated with a thermotropic nematic fluid. The interplay of orientational ordering within the nematic network and that of the small-molecule liquid crystal around it yields a composite with highly tunable optical properties. By means of combining experimental characterization and analytical modeling, we demonstrate sub-milisecond electric switching of transparency and also facile response of the composite to temperature changes and light illumination. Finally, we discuss a host of potential technological uses of these self-assembled nematogel composites, ranging from smart and privacy windows to novel flexible display modes. [Preview Abstract] |
Tuesday, March 14, 2017 9:48AM - 10:00AM |
E16.00010: Abstract Withdrawn
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Tuesday, March 14, 2017 10:00AM - 10:12AM |
E16.00011: Effect of negative curvature on the interaction of amphipathic $\alpha $-helix model protein with an oil/buffer interface Mona Mirheydari, Elizabeth K. Mann, Edgar E. Kooijman Lipid droplets, are dynamic cell organelles that play roles in biological processes. The biophysics of lipid droplets are studied with a model system consisting of a triolein drop formed in a physiologically-relevant buffer and covered with phospholipid monolayer. Interfacial tension is used to characterize the droplet surface after addition of the protein to the buffer. ApoLp-III serves as a model protein for the amphipathic $\alpha $-helix bundle domain in proteins associated with lipid droplets. Previous work use POPC to form the phospholipid monolayer surrounding the oil droplet. Here, we used POPC, and mixtures of POPC and other lipids to study the effect of effective molecular shape, headgroup charge and size in protein binding to the oil/buffer interface. Our data shows that the affinity of the protein binding to the interface increases for monolayer made up of POPC lipid mixed with negatively charged lipids. We compared the results for native and folded apoLp-III (which contains a disulfide bond) to explore the role of unfolding on the protein affinity with a POPC monolayer. Experiments are done using our home-build droplet tensiometer in a temperature controlled room. [Preview Abstract] |
Tuesday, March 14, 2017 10:12AM - 10:24AM |
E16.00012: Structural modification of unilamellar and multilamellar vesicles in the presence of vitamin D A. Devarajan, Y. A. Raouf, S. Rashid, R. L. Law, V. Stojanoff, A. F. Isakovic, D. L. Gater Chronic vitamin D deficiency is increasingly associated with a range of health conditions, such as cardiovascular disease, diabetes and certain cancers. Our report contributes to a mechanistic understanding of these associations. Vitamin D is a lipophilic compound that is synthesized in the skin by the action of UV light on 7-dehydrocholesterol and obtained from dietary sources. We look at how vitamin D could be extracted from either skin membranes or therapeutic liposomes and transported through the body by its associated proteins. A variety of physical techniques (FTIR, DLS, UV-Vis spectroscopy, NMR, XRD) are brought to investigate: (a) the behavior of vitamin D in model membranes, and (b) the effect of vitamin D-associated proteins on membrane structure. Our results include: (1) vitamin D can be incorporated into DOPC membranes up to 40mol{\%} with only minor changes in the dynamics of the lipid acyl chains; (2) liposomes containing larger quantities of vitamin D may have reduced stability over time; (3) the vitamin D binding protein and the vitamin D receptor do associate with and alter the behavior of model membranes, including systems that do not contain vitamin D.~ [Preview Abstract] |
Tuesday, March 14, 2017 10:24AM - 10:36AM |
E16.00013: Lipid and protein composition as driving force for multiple sclerosis Roy Beck, Rona Shaharabani Physical models and experiments often reduce the number of components aiming to address the fundamental mechanisms. Nevertheless, the inherent heterogeneity is an essential ingredient in the biological context. We present our recent efforts to model and understand the development of multiple sclerosis (MS) from a biophysical perspective. Myelin sheath is a multilamellar complex of various lipids and proteins that surround axons and acts as an insulating layer for proper nerve conduction. In MS the myelin structure is disrupted impairing its function. Previous studies showed that MS is correlated with small lipid composition variation and reduction in the adhesive myelin basic protein. We found that such alterations result in pathological phase transition from a lamellar to inverted hexagonal that involve enhanced local curvature .\footnote{ Shaharabani et al., \textbf{ J. Am. Chem. Soc.} 138, 12159 (2016)} Similar curvatures are also found in vivo in diseased myelin sheaths. Since the etiology and recovery pathways of MS are currently unclear, these findings delineate novel functional roles to dominant constituents in cytoplasmic myelin sheaths, shed new light on mechanisms disrupting lipid-protein complexes, and suggest new courses for diagnosis and treatment for MS. [Preview Abstract] |
Tuesday, March 14, 2017 10:36AM - 10:48AM |
E16.00014: Study of the Interaction of the HIV-1 Fusion Peptide with Lipid Bilayer Membranes William Heller, Durgesh Rai HIV-1 undergoes fusion with the cell membrane through interactions between its coat proteins and the target cell. Visualization of fusion with sufficient detail to determine the molecular mechanism remains elusive. Here, the interaction between a synthetic variant of the HIV-1 gp41 fusion peptide with vesicles composed of dimyristoyl phosphatidylcholine (DMPC) and dimyristoyl phosphatidylserine (DMPS) was studied. The peptide was observed to undergo a concentration-dependent conformational transition between an $\alpha $-helix and an antiparallel $\beta $-sheet that is accompanied by a transition in the structure of the lipid bilayer vesicle. The peptide changes the distribution of lipids between the vesicle leaflets. Further, it creates two regions having different thicknesses. The results shed new light on how the peptide modifies the membrane structure to favor fusion. A portion of this research was sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy. Research at Oak Ridge National Laboratory's Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U. S. Department of Energy. [Preview Abstract] |
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