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Full-Text Articles in Physics
Distance Of Closest Approach Of Two Arbitrary Hard Ellipses In Two Dimensions, Xiaoyu Zheng, Peter Palffy-Muhoray
Distance Of Closest Approach Of Two Arbitrary Hard Ellipses In Two Dimensions, Xiaoyu Zheng, Peter Palffy-Muhoray
Peter Palffy-Muhoray
The distance of closest approach of hard particles is a key parameter of their interaction and plays an important role in the resulting phase behavior. For nonspherical particles, the distance of closest approach depends on orientation, and its calculation is surprisingly difficult. Although overlap criteria have been developed for use in computer simulations [ Vieillard-Baron J. Chem. Phys. 56 4729 (1972); Perram and Wertheim J. Comput. Phys. 58 409 (1985)], no analytic solutions have been obtained for the distance of closest approach of ellipsoids in three dimensions, or, until now, for ellipses in two dimensions. We have derived an analytic …
Nematic Biaxiality In A Bent-Core Material, Hyungguen Yoon, Shin-Woong Kang, Ronald Y. Dong, Alberto Marini, Kattera A. Suresh, Mohan Srinivasarao, Satyendra Kumar
Nematic Biaxiality In A Bent-Core Material, Hyungguen Yoon, Shin-Woong Kang, Ronald Y. Dong, Alberto Marini, Kattera A. Suresh, Mohan Srinivasarao, Satyendra Kumar
Satyendra Kumar
The results of a recent investigation of the nematic biaxiality in a bent-core mesogen (A131) are in apparent disagreement with earlier claims. Samples of mesogen A131 used in the two studies were investigated with polarized optical microscopy, conoscopy, carbon-13 NMR, and crossover frequency measurements. The results demonstrate that textural changes associated with the growth of biaxial nematic order appear at similar to 149 degrees C. The Maltese cross observed in the conoscopic figure gradually splits into two isogyres at lower temperatures indicating phase biaxiality. Presence of the uniaxial to biaxial nematic phase transition is further confirmed by temperature trends of …
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.
Biaxial Nematic Phase In Bent-Core Thermotropic Mesogens, Bharat R. Acharya, Andrew Primak, Satyendra Kumar
Biaxial Nematic Phase In Bent-Core Thermotropic Mesogens, Bharat R. Acharya, Andrew Primak, Satyendra Kumar
Satyendra Kumar
A biaxial nematic phase had been predicted with D2h symmetry, wherein the mesogen’s long and short transverse axes are simultaneously aligned along the two orthogonal, primary and secondary directors, n and m, respectively. The unique low-angle x-ray diffraction patterns in the nematic phases exhibited by three rigid bent-core mesogens clearly reveal their biaxiality. The results of x-ray diffraction can be readily reproduced by ab initio calculations that explicitly include the bent-core shape in the form factor and assume short-range positional correlations.
Viscoelasticity, Dielectric Anisotropy, And Birefringence In The Nematic Phase Of Three Four-Ring Bent-Core Liquid Crystals With An L-Shaped Molecular Frame, Nejmettin Acvi, Volodymyr Borshch, Dipika Debnath Sarkar, Rahul Deb, Gude Venkatesh, Taras Turiv, Sergij V. Shiyanovskii, Nandiraju V. S. Rao, Oleg Lavrentovich
Viscoelasticity, Dielectric Anisotropy, And Birefringence In The Nematic Phase Of Three Four-Ring Bent-Core Liquid Crystals With An L-Shaped Molecular Frame, Nejmettin Acvi, Volodymyr Borshch, Dipika Debnath Sarkar, Rahul Deb, Gude Venkatesh, Taras Turiv, Sergij V. Shiyanovskii, Nandiraju V. S. Rao, Oleg Lavrentovich
Oleg Lavrentovich
Molecular shape is an important factor in determining the material properties of thermotropic liquid crystals (LCs). We synthesized and investigated several LC compounds formed by asymmetrically bent molecules with a rigid four-ring core in the shape of the letter 'L'. We measured the temperature dependencies of dielectric permittivities, birefringence, splay K-1 and bend K-3 elastic constants, splay viscosity eta(splay) and flow viscosities eta(parallel to) and eta(perpendicular to). The bend-splay anisotropy delta K-31 - K-3 - K-1 is negative, similar to the case of nematic LCs formed by symmetrically bent molecules of V-shape. The dielectric anisotropy Delta epsilon and birefringence are …
Search For Biaxiality In A Shape-Persistent Bent-Core Nematic Liquid Crystal, Young-Ki Kim, Madhabi Majumdar, Bohdan I. Senyuk, Luana Tortora, Jens Seltmann, Matthias Lehmann, Antal Jakli, Jim T. Gleeson, Oleg Lavrentovich, Samuel Sprunt
Search For Biaxiality In A Shape-Persistent Bent-Core Nematic Liquid Crystal, Young-Ki Kim, Madhabi Majumdar, Bohdan I. Senyuk, Luana Tortora, Jens Seltmann, Matthias Lehmann, Antal Jakli, Jim T. Gleeson, Oleg Lavrentovich, Samuel Sprunt
Antal Jakli
Using a range of optical techniques, we have probed the nature of orientational order in a thermotropic bent-core liquid crystal, which features a shape-persistent molecular architecture designed to promote a biaxial nematic phase. In the upper range of the nematic phase (enantiotropic regime), dynamic light scattering reveals strong fluctuations attributable to the biaxial order parameter, in addition to the usual uniaxial director modes. Assuming a Landau-type expansion of the orientational free energy, we estimate the correlation length associated with these fluctuations to be similar to 100 nm. At lower temperatures, and mainly in the monotropic regime of the nematic, we …
Calorimetric Study Of Nematic Prewetting, Xuewu Liu, David W. Allender, D. Finotello
Calorimetric Study Of Nematic Prewetting, Xuewu Liu, David W. Allender, D. Finotello
David W Allender
We report specific-heat measurements for a series of liquid crystals imbedded in a porous cylindrical geometry. Above the nematic-to-isotropic transition and dependent on nematic width (or chain length), the specific heat shows a small peak. In analogy to known ellipsometry results, the peak is believed to be the signature of a nematic prewetting transition.