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Full-Text Articles in Physics

Elasticity Of Lyotropic Chromonic Liquid Crystals Probed By Director Reorientation In A Magnetic Field, Shuang Zhou, Yuriy A. Nastishin, M. M. Omelchenko, L. Tortora, V. G. Nazarenko, O. P. Boiko, T. Ostapenko, T. Hu, C. C. Almasan, Jim T. Gleeson, Oleg Lavrentovich Jul 2012

Elasticity Of Lyotropic Chromonic Liquid Crystals Probed By Director Reorientation In A Magnetic Field, Shuang Zhou, Yuriy A. Nastishin, M. M. Omelchenko, L. Tortora, V. G. Nazarenko, O. P. Boiko, T. Ostapenko, T. Hu, C. C. Almasan, Jim T. Gleeson, Oleg Lavrentovich

Chemical Physics Publications

Using a magnetic Frederiks transition technique, we measure the temperature and concentration dependences of splay K1, twistK2, and bend K3 elastic constants for the lyotropic chromonic liquid crystal sunset yellow formed through noncovalent reversible aggregation of organic molecules in water. K1 and K3 are comparable to each other and are an order of magnitude higher thanK2. At higher concentrations and lower temperatures, K1 and the ratios K1/K3 and K1/K2 increase, which is attributed to elongation of self-assembled lyotropic chromonic liquid crystal aggregates, a feature not ...


Highly Piezoelectric Biocompatible And Soft Composite Fibers, J. Morvan, E. Buyuktanir, John L. West, Antal Jakli Feb 2012

Highly Piezoelectric Biocompatible And Soft Composite Fibers, J. Morvan, E. Buyuktanir, John L. West, Antal Jakli

Chemical Physics Publications

We report the fabrication of highly piezoelectric biocompatible soft fibers containing barium titanate ferroelectric ceramic particles dispersed in electrospun poly lactic acid (PLA). These fibers form mats that have two orders of magnitude larger piezoelectric constant per weight than single crystal barium titanate films. We propose that the observed apparent piezoelectricity results from the electrospinning induced polar alignment of the ferroelectric particles that pole the fibers similar to ferroelectret polymer foams that are poled by corona discharge. Due to the biocompatibility of PLA that encases the ferroelectric particles, these mats can be used in biological applications such as bio-sensors, artificial ...


Large Flow Birefringence Of Nematogenic Bent-Core Liquid Crystals, C. Bailey, Katalin Fodor-Csorba, Rafael Verduzco, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli Dec 2009

Large Flow Birefringence Of Nematogenic Bent-Core Liquid Crystals, C. Bailey, Katalin Fodor-Csorba, Rafael Verduzco, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli

Chemical Physics Publications

We have found that bent-core liquid crystalline materials show exceptionally large intrinsic flow birefringence in their isotropic liquid phase. This effect is more than 100 times larger than typical values measured for low molecular weight liquid crystals. The specific flow birefringence (i.e., normalized by the flow viscosity) is an order of magnitude larger than in both side-chain polymeric as well as low molecular weight liquid crystals. We propose that this large enhancement for bent-core compounds may be attributed to nanoscale smecticlike clusters that persist above the nematic-isotropic transition temperature, and shear align under shear flow; however, this mechanism has ...


What Aligns Liquid Crystals On Solid Substrates? The Role Of Surface Roughness Anisotropy, Satyendra Kumar, Jae-Hoon Kim, Yushan Shi Feb 2005

What Aligns Liquid Crystals On Solid Substrates? The Role Of Surface Roughness Anisotropy, Satyendra Kumar, Jae-Hoon Kim, Yushan Shi

Physics Publications

The mechanism responsible for liquid crystal (LC) alignment on mechanically buffed or UV exposed polymer films is poorly understood. A comprehensive study of LC alignment on variously prepared substrates unequivocally shows that the anisotropy in the surface roughness of the substrate completely determines the direction of LC alignment. In all the cases studied, including those where an anchoring transition occurs with temperature, the LC director (re)aligns in the directions of low roughness.


Three-Dimensional Director Structures Of Defects In Grandjean-Cano Wedges Of Cholesteric Liquid Crystals Studied By Fluorescence Confocal Polarizing Microscopy, Ivan I. Smalyukh, Oleg Lavrentovich Nov 2002

Three-Dimensional Director Structures Of Defects In Grandjean-Cano Wedges Of Cholesteric Liquid Crystals Studied By Fluorescence Confocal Polarizing Microscopy, Ivan I. Smalyukh, Oleg Lavrentovich

Chemical Physics Publications

We use a nondestructive technique of fluorescence confocal polarizing microscopy to visualize three-dimensional director patterns of defects in Grandjean-Cano wedges filled with a cholesteric liquid crystal of pitch p=5 mum. Strong surface anchoring of the director causes a stable lattice of dislocations in the bulk. Optical slicing in the vertical cross sections of the wedges allows us to establish the detailed structure of dislocations and their kinks. Dislocations of Burgers vector b=p/2 are located in the thin part of the sample, very close to the bisector plane. Their cores are split into a pair of tau(-1 ...


Molecular-Motion Analysis Of E7 In Pdlcs As A Function Of Droplet Size Using Solid-State C-13 Nmr Relaxation Spectroscopy, Karen L. Buchert, Jack L. Koenig, Shi-Qing Wang, John L. West Jan 1993

Molecular-Motion Analysis Of E7 In Pdlcs As A Function Of Droplet Size Using Solid-State C-13 Nmr Relaxation Spectroscopy, Karen L. Buchert, Jack L. Koenig, Shi-Qing Wang, John L. West

Chemistry & Biochemistry Publications

13C NMR relaxation spectroscopy as applied to polymer-dispersed liquid crystals (PDLCs) provides a method for measuring the molecular motions of the liquid crystal molecules within droplets dispersed throughout the material's polymer matrix. Because liquid crystal molecular motion may play a major role in the switching phenomenon of PDLC materials from an opaque film to a clear film, both T 1 and T 1ρ relaxation experiments are used to measure molecular mobility of the liquid crystal as a function of droplet size for PDLC materials made of E7 and epoxy. The segmental molecular motions measured by T 1 ...