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Full-Text Articles in Physics

Critical-Behavior At The Nematic To Smectic-A Transition In A Nonpolar Liquid-Crystal With Wide Nematic Range, Li Chen, J. D. Brock, J. Huang, Satyendra Kumar Oct 1991

Critical-Behavior At The Nematic To Smectic-A Transition In A Nonpolar Liquid-Crystal With Wide Nematic Range, Li Chen, J. D. Brock, J. Huang, Satyendra Kumar

Physics Publications

High-resolution x-ray scattering experiments to study the critical smectic-A fluctuations in the nematic phase have been performed on a mixture of two nonpolar, two-benzene-ring compounds. The ratio T(NA)/T(NI) (= 0.885) for this mixture is much smaller than for previously studied similar materials. The smectic correlation lengths parallel and perpendicular to the smectic-layer normal are found to diverge anisotropically with characteristic exponents-nu parallel-to = 0.75 +/- 0.03, nu perpendicular-to = 0.65 +/- 0.03, and the susceptibility with gamma = 1.24 +/- 0.05.


Determination Of The Liquid-Crystal Surface Elastic-Constant K24, David W. Allender, G. P. Crawford, J. W. Doane Sep 1991

Determination Of The Liquid-Crystal Surface Elastic-Constant K24, David W. Allender, G. P. Crawford, J. W. Doane

Physics Publications

Analysis of the Frank free energy for nematics confined to cylindrical regions indicates that the director pattern is dependent on the surface elastic constant K24 if there is weak normal anchoring and escape along the cylinder axis. Using deuterium nuclear-magnetic-resonance techniques on samples of submicrometer-size cavities in Nuclepore membranes, we report the first measurement of K24.


Finite Molecular Anchoring In The Escaped-Radial Nematic Configuration: A 2-H-Nmr Study, G. P. Crawford, David W. Allender, J. William Doane, M. Vilfan, I. Vilfan Aug 1991

Finite Molecular Anchoring In The Escaped-Radial Nematic Configuration: A 2-H-Nmr Study, G. P. Crawford, David W. Allender, J. William Doane, M. Vilfan, I. Vilfan

Physics Publications

The director-field configuration of a nematic liquid crystal confined to cylindrical cavities of polycarbonate Nuclepore membranes ranging from 0.3 to 0.05-mu-m in radius is determined using deuterium nuclear magnetic resonance (H-2 NMR). Spectral patterns from cavities of radius 0.3-mu-m reveal the escaped-radial configuration with singular point defects, but as the cylinder size is decreased, the elastic energy imposed by the curvature of the confining walls competes with the anchoring energy to tilt the directors away from their preferred perpendicular anchoring direction, preventing the expected transition to the planar-radial configuration. A surface fitting parameter is directly determined by ...


Absence Of The Incommensurate Smectic-A Phase In Db7ocn+8ocb Mixtures, Satyendra Kumar, Li Chien, V. Surendranath Jul 1991

Absence Of The Incommensurate Smectic-A Phase In Db7ocn+8ocb Mixtures, Satyendra Kumar, Li Chien, V. Surendranath

Physics Publications

The results of a high-resolution x-ray-diffraction study of the smectic phases in mixtures of DB7OCN and 8OCB show that the incommensurate smectic-Ai2 phase, previously reported in this mixture, is in fact a coexistence of the partially bilayer smectic-Ad and the bilayer smectic-A2phases at a first-order phase transition between them.


Nematic-Isotropic Phase-Transition In A Liquid-Crystal Droplet, S. Kralj, S. Zumer, David W. Allender Mar 1991

Nematic-Isotropic Phase-Transition In A Liquid-Crystal Droplet, S. Kralj, S. Zumer, David W. Allender

Physics Publications

Possible phases in a nematic liquid crystal confined to a spherical submicrometer droplet embedded in a solid polymer are analyzed in terms of a Landau-de Gennes theory. For a droplet with a radial structure we show that the strength of the nematic-polymer interfacial interaction affects the nematic-paranematic (partially ordered isotropic phase) phase transition and may in addition induce a boundary-layer nematic phase. This boundary layer phase exists only in a narrow (approximately 0.1 K) temperature interval above the nematic phase for a restricted range of interfacial interactions. Also in the radial structure the degree of ordering is suppressed close ...


Microcalorimetric Study Of Nematic-To-Neat-Soap And Nematic-To-Isotropic Phase Transitions In A Lyotropic Liquid Crystal, T. S. Shin, Satyendra Kumar Feb 1991

Microcalorimetric Study Of Nematic-To-Neat-Soap And Nematic-To-Isotropic Phase Transitions In A Lyotropic Liquid Crystal, T. S. Shin, Satyendra Kumar

Physics Publications

The results of specific-heat measurements at the nematic- (N) to-neat-soap (NS) and nematic-to-isotropic (I) phase transitions in binary mixtures of cesium-perfluoro-octanoate and water are reported. The ratio of specific-heat amplitudes above and below the N-NS transition, A+/A-, and the specific-heat exponent α remain ∼1.0 and ≤0.02, respectively, suggesting 3D XY-type behavior. At the first-order N-I transition, vanishing latent heat and coexistence range at low concentration indicate the existence of a Landau point.