Papers by Satyendra Kumar
Liquid Crystals Today, 2003
The nematic to smectic-A (NA) phase transition would appear to be the simplest example of a freez... more The nematic to smectic-A (NA) phase transition would appear to be the simplest example of a freezing transition in nature. However, it has proven to be one of the most challenging problems of liquid crystal science and equilibrium statistical mechanics. One quantitative method to study this transition, that yields high quality data of almost transparent interpretation, has been X-ray measurements of the divergence of smectic order correlations as the SmA phase is approached from the nematic side. However, even data from these experiments have proved difficult to interpret because of the imperfect magnetic alignment or ''mosaic spread'' of the nematic phase. This mosaic spread limits the experimental transverse resolution and hence affects the data very close to the transition. Previous studies employed magnetic fields of y0.1-0.8 T. The use of a high (5 T) field, in the work we recently completed, improved the effective transverse resolution by almost two orders of magnitude allowing us to obtain results essentially free of mosaic spread. The generally used technique for removing this effect has now been tested. The high field results shed new light on this transition and reveal a new and proper way to apply the mosaicity correction.
Physical Review E, 2002
X-ray diffraction from Anodisc membrane filters is measured and analyzed. The patterns are consis... more X-ray diffraction from Anodisc membrane filters is measured and analyzed. The patterns are consistent with pores of constant diameter and a Gaussian distribution of pore-pore spacing. The mean distance between pores, measured using x rays is 0.37 m compared to 0.32 m calculated from the nominal density of pores/cm 2. The results may be modeled both in terms of the convolution of a structure factor of the pores with the resolution function, and by modeling the source as a collection of incoherent sources with an ideal monochromator crystal. The incoherent source analysis provides an explanation for the common observation that the resolution function in many x-ray spectrometers is better fit to a sum of Lorentzians, rather than a single Lorentzian.
Journal of Materials Chemistry C, 2013
We report the synthesis and characterization of a series of board-like ("sanidic") compounds with... more We report the synthesis and characterization of a series of board-like ("sanidic") compounds with dibenzo[fg,op]naphthacene cores. The compounds exhibit good self-assembly into one-dimensional beltlike structures, and also smectic liquid crystal phases typical of rodlike molecules, but with important differences ascribed to their board-like shapes.
Phys. Chem. Chem. Phys., 2015
Relaxation rate of the chevron angle, α becomes about ten times faster at strains exceeding 0.7 t... more Relaxation rate of the chevron angle, α becomes about ten times faster at strains exceeding 0.7 than at low strains.
Physical Review Letters, 1993
Results of a high-resolution x-ray reflectivity study of growth morphology and ordering of thin l... more Results of a high-resolution x-ray reflectivity study of growth morphology and ordering of thin liquidcrystal films on flat glass substrate are reported. An adsorbed bilayer of crystalline order, under three dimensional clusters, was found to persist well beyond the nematic to isotropic transition. This adsorbed layer appears to be related to the surface memory effects in liquid-crystal devices. The morphology of these films can be described by the Stranski-Krastanov growth mode.
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Papers by Satyendra Kumar