Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session S37: Liquid Crystals, Membranes, Micelles and Vesicles |
Hide Abstracts |
Sponsoring Units: GSOFT Chair: L J Martinez-Miranda, University of Maryland, College Park Room: 340 |
Thursday, March 17, 2016 11:15AM - 11:27AM |
S37.00001: \textbf{Tetratic, triatic and nematic liquid crystals on a complex plane} Oksana Manyuhina, Mark Bowick Liquid crystals are elastic materials able to resolve geometric and topological frustration by creating disclinations, discontinuities in their continuous orientation field.~ The strength and the nature of disclinations depend on the symmetry of elements forming liquid crystal phase. Several examples of confined nematic (director field), triatic (Y-field) and tetratic (cross-field) liquid crystals will be considered to show that their ground state contains topological defects. Next, we analyze shape variation of the boundary, enclosing different defect textures. We argue that topological defects can capture essential features of macroscopic shape and relate it to microscopic order, providing a natural way to connect different length scales and to account for large deformations in soft and biological systems. [Preview Abstract] |
Thursday, March 17, 2016 11:27AM - 11:39AM |
S37.00002: Nano-electromechanical Rotation of Graphene and Giant Enhancement in Dielectric Anisotropy in a Liquid Crystal Rajratan Basu, Daniel Kinnamon, Alfred Garvey A nematic liquid crystal (LC) is doped with dilute concentrations of pristine monolayer graphene flakes (GP), and the LC$+$GP hybrids are found to exhibit a dramatic increase in the dielectric anisotropy. Electric field-dependent conductance studies reveal that the graphene flakes follow the nematic director that mechanically rotates on increasing an applied electric field. Further studies show that the $\pi -\pi $ electron stacking, between the graphene's honeycomb structure and the LC's benzene rings, stabilizes \textit{pseudo-nematic} \textit{domains} that collectively amplify the dielectric anisotropy by improving the orientational order parameter in the nematic phase. These anisotropic domains interact with the external electric field, resulting in a \textit{nonzero }dielectric anisotropy in the isotropic phase as well. The enhancement in dielectric anisotropy, due to the LC -- graphene coupling, is found to have subsequent positive impacts on the LC's orientational threshold field and elasticity that allows the nematic director to respond quicker on switching the electric field off. [Preview Abstract] |
Thursday, March 17, 2016 11:39AM - 11:51AM |
S37.00003: Smectic Liquid Crystal-Nanoparticle arrangement observed with X-ray Scattering Luz J Martinez-Miranda, Patricio Romero-Hasler, Ariel Meneses-Franco, Eduardo A. Soto-Bustamante We observed the alignment of two different monomeric liquid crystals combined with TiO$_{2\, }$in a concentration of 0.3 wt of TiO$_{2}$. The liquid crystals are M6R8 and I6R8. These two monomeric compounds have a crystal-SmC-SmA-isotropic phase progression. The two monomeric compounds differ in the final group at the end of one of the carbon chains. The nanoparticle ties itself to the monomers through hydrogen bonding. The difference in the final group determines where the nanoparticle attaches to the liquid crystal molecule. This difference in the way it attaches can be observed using X-ray scattering. The way the nanoparticle attaches has consequences in the current-voltage curve obtained [1]. Under the influence of an electric field, the M6R8 polymerizes. We observe by X-ray scattering that the nanoparticles migrate and the scan is very similar to the scan of the I6R8 monomer with the nanoparticle. In addition the nanoparticle is ordered along one direction and does not seem as ordered in the direction perpendicular to this direction. [1] A. Meneses-Franco, J. Mater. Chem. C, 2015, 3, 8566. [Preview Abstract] |
Thursday, March 17, 2016 11:51AM - 12:03PM |
S37.00004: ABSTRACT WITHDRAWN |
Thursday, March 17, 2016 12:03PM - 12:15PM |
S37.00005: Effects of graphene on in-plane electro-optic switching for a nematic liquid crystal Daniel Kinnamon, Nicole Skaggs, Alfred Garvey, Rajratan Basu A small quantity of graphene flakes was doped in a nematic liquid crystal (LC), and the in-plane electro-optic switching was found to be significantly faster in the LC$+$graphene hybrid than that of the pure LC. Additional studies revealed that the presence of graphene reduced the rotational viscosity and the twist elastic constant of the LC, allowing the nematic director to respond faster on switching the electric field on. [Preview Abstract] |
Thursday, March 17, 2016 12:15PM - 12:27PM |
S37.00006: Flow of anisotropic and isotropic objects in quasi-twodimensional fluids Ralf Stannarius, Alexey Eremin, Sarah D\"olle, Kirsten Harth, Christoph Klopp We study the motion of microscopic objects in very thin freely suspended smectic liquid-crystal films. The aspect ratios of these films are of the order of 1:10$^6$. Hydrodynamic motion is restricted to the film plane. Thus such films represent quasi-twodimensional fluids. Not only do they provide the opportunity to test theoretical models on mobilities in thin membranes, they also allow access to viscosity parameters of in-plane isotropic (smectic A) and anisotropic (smectic C) fluids. Combinations of these environments with isotropic and anisotropic geometries of inclusions provide rich information about interactions of rotational and translational particle motions, the anchoring-induced and flow-induced alignments of the embedding fluid, and interactions of particles via flow and director fields. Thermal diffusion in horizontal films as well as controlled effective gravity in tilted films are explored. [Preview Abstract] |
Thursday, March 17, 2016 12:27PM - 12:39PM |
S37.00007: ABSTRACT WITHDRAWN |
Thursday, March 17, 2016 12:39PM - 12:51PM |
S37.00008: Field-driven dynamics of microcapillaries filled with nematic liquid crystal Fred Fu, Pouya Khayyatzadeh, Nasser M Abukhdeir Polymer-dispersed liquid crystal (PDLC) composites have long been a focus of study for their unique electro-optical properties and the feasibility of manufacturing them on a large scale, resulting in applications such as switchable windows. LC domains within PDLCs are typically spheroidal, as opposed to rectangular in LCD technology, and thus exhibit substantially different behaviour in the presence of an external field. In this work, continuum simulations were performed in order to capture the complex formation and electric field-driven switching dynamics of approximations of PDLC domains. A simplified elliptic cylinder (microcapillary) geometry is used and the effects of varying aspect ratio, surface anchoring, and external field strength were studied using the Landau--de Gennes model. The observed nematic formation and reorientation dynamics were found to be governed by the presence and motion of defects within the domain. Aspect ratio was found to strongly influence domain texture by providing regions of high curvature to which defects are attracted. Simulations also predict the presence of a geometry-controlled transition from nematic order enhanced by an external field (low aspect ratio) to nematic order frustrated by an external field (high aspect ratio). [Preview Abstract] |
Thursday, March 17, 2016 12:51PM - 1:03PM |
S37.00009: \textbf{Structural organization of liquid crystals at liquid crystal-air interface: Synchrotron X-ray reflectivity and computational simulations} Monirosadat Sadati, Hadi Ramezani-Dakhel, Wei Bu, Emre Sevgen, Zhu Liang, Cem Erol, Nader Taheri Qazvini, Mohammad Rahimi, Binhua Lin, Benoit Roux, Mark Schlossman, Juan J. de Pablo Numerous applications of liquid crystals (LC) rely on control of molecular orientation at an interface. However, little is known about the precise molecular structure of such interfaces. In this work, we have performed synchrotron X-ray reflectivity measurements accompanied by an advanced theoretical and computational analysis to study the structural organization of liquid crystals at the air-liquid crystal interface. The X-ray reflectivity was measured from two nematic (5CB) and smectic (8CB) liquid crystals at several temperatures, in the nematic phase and above the nematic-isotropic transition. Our computational simulations and X-ray reflectivity results indicate that in the case of 8CB nematic phase, incipient bulk smectic fluctuations are pinned at the interface to form temperature-dependent multilayers at the interface. Such layers can extend far from the interface. However, the interface of 5CB in the nematic phase exhibits a relatively small number of layers. These measurements will be extended to the study of the LC-aqueous electrolyte interfaces to understand the effects of electrostatic interactions and external stimuli on the interfacial anchoring energy and LC orientational ordering. [Preview Abstract] |
Thursday, March 17, 2016 1:03PM - 1:15PM |
S37.00010: Gold nanoparticle encapsulation into a mixed lipid nanodisk: molecular dynamics simulations HARI SHARMA, Zilu Wang, Elena Dormidontova There is a growing interest in applications of nanoparticles in biomedicine. For practical applications of gold nanoparticles it is often desirable to encapsulate them into lipid nanocarriers. To this end it is important to understand gold-lipid interactions at the molecular level. We have performed coarse grained molecular dynamics simulations using a MARTINI force field of a lipid nanodisk composed of long and short tail lipids, DPPC and DHPC mixed in the ratio of 3:1 and studied its interaction with small gold nanoparticles (AuNP) functionalized with hydrophobic alkane tethers. We found that the inhomogeneous distribution of lipids in the nanodisk affects the outcome the AuNP-nanodisk interaction. The ordered arrangement of long chain lipids forming the interior region of the nanodisk are found to be less accessible for AuNP penetration compared to the rim of the nanodisk, where more mobile short lipids are located. Once encapsulated into a nanodisk, AuNP's have tendency to aggregate, especially if temperature is not too low. The results of computer modeling will be compared to experiment and the implications of our findings for experimental design of lipid nanocarriers for AuNP delivery will be discussed. [Preview Abstract] |
Thursday, March 17, 2016 1:15PM - 1:27PM |
S37.00011: Nanoscale Membrane Curvature detected by Polarized Localization Microscopy Christopher Kelly, Abir Maarouf, Xinxin Woodward Nanoscale membrane curvature is a necessary component of countless cellular processes. Here we present Polarized Localization Microscopy (PLM), a super-resolution optical imaging technique that enables the detection of nanoscale membrane curvature with order-of-magnitude improvements over comparable optical techniques. PLM combines the advantages of polarized total internal reflection fluorescence microscopy and fluorescence localization microscopy to reveal single-fluorophore locations and orientations without reducing localization precision by point spread function manipulation. PLM resolved nanoscale membrane curvature of a supported lipid bilayer draped over polystyrene nanoparticles on a glass coverslip, thus creating a model membrane with coexisting flat and curved regions and membrane radii of curvature as small as 20 nm. Further, PLM provides single-molecule trajectories and the aggregation of curvature-inducing proteins with super-resolution to reveal the correlated effects of membrane curvature, dynamics, and molecular sorting. For example, cholera toxin subunit B has been observed to induce nanoscale membrane budding and concentrate at the bud neck. PLM reveals a previously hidden and critical information of membrane topology. [Preview Abstract] |
Thursday, March 17, 2016 1:27PM - 1:39PM |
S37.00012: Membrane Domain Formation on Nanostructured Scaffolds Charles Collier, Fangjie Liu, Bernadeta Srijanto The spatial organization of lipids and proteins in biological membranes seems to have a functional role in the life of a cell. Separation of the lipids into distinct domains of greater order and anchoring to the cytoskeleton are two main mechanisms for organizing the membrane in cells. We propose a novel model membrane consisting of a lipid bilayer suspended over a nanostructured scaffold consisting of arrays of fabricated nanopillars. Unlike traditional model membranes, our model will have well-defined lateral structure and distributed substrate attachments that will emulate the connections of cellular membranes to the underlying cytoskeleton. Membranes will be characterized using neutron reflectometry, atomic force microscopy and fluorescence to verify a suspended, planar geometry with restricted diffusion at suspension points, and free diffusion in between. This architecture will allow the controlled study of lipid domain reorganization, viral infection and signal transduction that depend on the lateral structure of the membrane. [Preview Abstract] |
Thursday, March 17, 2016 1:39PM - 1:51PM |
S37.00013: Structure and dynamics of a hydrated phospholipid bilayer in the presence of a silica substrate Matthew McCune, Ioan Kosztin We study the structure and dynamics of a hydrated diyristoyl-phosphatidycholine (DMPC) lipid bilayer supported on a silica substrate using all-atom molecular dynamics (MD) simulation. A similar MD simulation of a freestanding DMPC bilayer is used as a reference to determine changes to both lipid and hydration water properties due to the introduction of the substrate. Long time (0.1 microsecond) MD trajectories were used to investigate the effect of the substrate on the structure and dynamics of the lipid bilayer by determining (i) the spatial distribution of water molecules and selected lipid atoms; (ii) the out of plane fluctuations of the lipid molecules; (iii) the dipole moment orientation of hydration waters; and (iv) the lateral mean-square-displacement of both lipid and water molecules. The obtained results suggest that (i) at equilibrium the space between the substrate and lipid bilayer is filled by only hydration water; (ii) the presence of the substrate has no major influence on the structure of hydration water layers and on the out-of-plane fluctuations of the lipids; and (iii) the silica substrate alters considerably the lateral diffusion of the lipids in the closest bilayer leaflet and the hydration waters between the substrate and DMPC membrane. The reported results appear to be consistent with previous MD and neutron scattering studies. [Preview Abstract] |
Thursday, March 17, 2016 1:51PM - 2:03PM |
S37.00014: Insight into cholesterol transport in different lipid environments: a simulation study Klas Karis, Ursula Perez-Salas, Fatemeh Khalili-Araghi With molecular dynamics simulations employing the MARTINI coarse grained force field, we investigate the difference in the dynamic behavior of cholesterol, linked to the absorption and desorption of cholesterol in two phospholipid environments consisting of either an uncharged, zwitterionic lipid (POPC) or the charged counterpart (POPS). The work is motivated by results from recent neutron scattering experiments measuring the transfer rate of inter-membrane cholesterol transfer, revealing that cholesterol inter-membrane transport is significantly slower in lipid membranes composed of charged lipids, than in membranes composed of uncharged lipids. By systematically investigating dynamical and equilibrium parameters such as the free energy of desorption, lateral diffusion, tilt angle distribution, structural parameters and estimated absorption rates, we map the key differences in interaction of the two lipid species with cholesterol. Results point towards a shift in cholesterol absorption rates for POPS compared to POPC. [Preview Abstract] |
Thursday, March 17, 2016 2:03PM - 2:15PM |
S37.00015: Phase separation in artificial vesicles driven by light and curvature Melissa Rinaldin, Wim Pomp, Thomas Schmidt, Luca Giomi, Daniela Kraft The role of phase-demixing in living cells, leading to the lipid-raft hypothesis, has been extensively studied. Lipid domains of higher lipid chain order are proposed to regulate protein spatial organization. Giant Unilamellar Vesicles provide an artificial model to study phase separation. So far temperature was used to initiate the process. Here we introduce a new methodology based on the induction of phase separation by light. To this aim, the composition of the lipid membrane is varied by photo-oxidation of lipids. The control of the process gained by using light allowed us to observe vesicle shape fluctuations during phase-demixing. The presence of fluctuations near the critical mixing point resembles features of a critical process. We quantitatively analyze these fluctuations using a 2d elastic model, from which we can estimate the material parameters such as bending rigidity and surface tension, demonstrating the non-equilibrium critical behaviour. Finally, I will describe recent attempts toward tuning the membrane composition by controlling the vesicle curvature. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700