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Full-Text Articles in Physics
Novel Surface State In A Class Of Incommensurate Systems, A. E. Jacobs, D. Mukamel, David W. Allender
Novel Surface State In A Class Of Incommensurate Systems, A. E. Jacobs, D. Mukamel, David W. Allender
David W Allender
We study the Landau model of the class of incommensurate systems with a scalar order parameter where the modulated phase is driven by a gradient-squared term with negative coefficient. For example, theoretical studies of cholesteric liquid crystals in a field (electric or magnetic) suggest that such an modulated phase should exist at high chirality. The bulk phase diagram in the presence of a bulk external field which couples linearly to the order parameter exhibits a modulated phase inside a loop in the temperature-field plane, and a homogeneous phase outside. On analyzing the same model for a semi-infinite system, we find …
Effect Of Mosaicity In X-Ray Studies Of Critical Behavior At The Nematic To Smectic-A Transition, Andrew Primak, Michael Fisch, Satyendra Kumar
Effect Of Mosaicity In X-Ray Studies Of Critical Behavior At The Nematic To Smectic-A Transition, Andrew Primak, Michael Fisch, Satyendra Kumar
Satyendra Kumar
Previous studies of critical behavior at the nematic to smectic-A transition by high-resolution x-ray scattering were performed using low magnetic fields of 0.1-0.8 T. In those studies, the transverse resolution was limited by the sample mosaicity which complicated data analysis. In order to understand the effect of sample mosaicity on the measured values of critical exponents, the divergence of the smectic order correlation lengths xi(parallel to,perpendicular to) and susceptibility sigma(o) was studied in a magnetic field ranging from 0.25 to 5 T. The use of high (5 T) field reduced the sample mosaicity and improved the effective transverse resolution by …
Absence Of The Incommensurate Smectic-A Phase In Db7ocn+8ocb Mixtures, Satyendra Kumar, Li Chien, V. Surendranath
Absence Of The Incommensurate Smectic-A Phase In Db7ocn+8ocb Mixtures, Satyendra Kumar, Li Chien, V. Surendranath
Satyendra Kumar
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.
Critical Behavior At The Nematic To Lamellar Phase Transitions: A Synchrotron X-Ray Scattering Study, S. T. Shin, J. D. Brock, Mark Sutton, J. D. Lister, Satyendra Kumar
Critical Behavior At The Nematic To Lamellar Phase Transitions: A Synchrotron X-Ray Scattering Study, S. T. Shin, J. D. Brock, Mark Sutton, J. D. Lister, Satyendra Kumar
Satyendra Kumar
The nematic (N) to lamellar (Lα) phase transition in binary mixtures of cesium-perfluoro-octanoate (CsPFO) and water has been studied by high-resolution synchrotron x-ray scattering at 46.6 weight % CsPFO. The longitudinal correlation length ξ∥ and the susceptibility σ associated with the lamellar phase fluctuations in the N phase, measured over three decades of reduced temperature, diverge with critical exponents ν∥=0.86±0.04 and γ=1.37±0.11, respectively. These results show that the N to Lα phase transition is quantitatively similar to the N to smectic-A phase transition of thermotropic liquid crystals with a wider nematic range.
High Resolution X-Ray Diffraction Study Of Smectic Polymorphism And Fluctuations In A Mixture Of Octyl- And Decyl-Oxyphenyl Nitrobenzoyloxy Benzoate, Yushan Shi, George Nounesis, Carl W. Garland, Satyendra Kumar
High Resolution X-Ray Diffraction Study Of Smectic Polymorphism And Fluctuations In A Mixture Of Octyl- And Decyl-Oxyphenyl Nitrobenzoyloxy Benzoate, Yushan Shi, George Nounesis, Carl W. Garland, Satyendra Kumar
Satyendra Kumar
Reentrant nematic phases and smectic antiphases occur as intermediate states between two one-dimensionally ordered frustrated smectic phases, characterized by two competing and, in general, incommensurate smectic density waves. Using high-resolution x-ray diffraction, we have examined the evolution of the two density waves as a function of temperature in all phases of a mixture of polar liquid crystals octyl-and decyl-oxyphenyl nitrobenzoyloxy benzoate (47.4 mol% DB8ONO2+52.6% DB10ONO2). This mixture exhibits at temperatures below 127 degrees C the liquid-crystal phase sequence: smectic-A(d), reentrant nematic phases N-d and N-1, smectic-A(1), tilted antiphase (C) over tilde, smectic-A(2), and smectic-C-2 phases. Detailed investigations of several order-disorder …
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
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
David W Allender
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 simulating H-2-NMR line …