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Full-Text Articles in Physics
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 …
Shape-Persistent V-Shaped Mesogens-Formation Of Nematic Phases With Biaxial Order, Matthias Lehmann, Shin-Woong Kang, Christiane Köhn, Sönke Haseloh, Ute Kolb, Dieter Schollmeyer, Qingbing Wang, Satyendra Kumar
Shape-Persistent V-Shaped Mesogens-Formation Of Nematic Phases With Biaxial Order, Matthias Lehmann, Shin-Woong Kang, Christiane Köhn, Sönke Haseloh, Ute Kolb, Dieter Schollmeyer, Qingbing Wang, Satyendra Kumar
Satyendra Kumar
A homologous series of shape-persistent V-shaped molecules has been designed to form the biaxial nematic phase. Phenyleneethynylene moieties are attached to a bent fluorenone unit to create an apex angle of about 90°, which is determined from the single crystal structure. Two mesogens, one symmetric and another unsymmetric, have been synthesized by attaching a cyano group to one or both of the peripheral phenyl units, respectively. These groups introduce local dipoles essential for the formation of the nematic phases. The tendency to form a crystalline phase is reduced by laterally substituted hexyloxy chains which allow the nematic phase to be …
Novel Examples Of Achiral Bent-Core Azo Compounds Exhibiting B1 And Anticlinic-Antiferroelectric B2 Mesophases, Veena Prasad, Shin-Woong Kang, Satyendra Kumar
Novel Examples Of Achiral Bent-Core Azo Compounds Exhibiting B1 And Anticlinic-Antiferroelectric B2 Mesophases, Veena Prasad, Shin-Woong Kang, Satyendra Kumar
Satyendra Kumar
The first examples of achiral bent-core molecules consisting of an azo linkage and five aromatic rings exhibiting bent-core mesophases are reported. They exhibit B1 and B2 phases as identified by optical microscopy, differential scanning calorimetry, X-ray diffraction, and electro-optical techniques. The B2 phase of these materials is identified to be the anticlinic–antiferroelectric, SmCAPA phase. The mesophases of these compounds have relatively low transition temperatures and wide temperature ranges. The observation of bent-core phases in azo compounds assumes significance from the fact that the introduction of the –NN– linkage adds a new dimension, namely photochromism, to this field.