S. Chandrasekhar

Bio: S. Chandrasekhar is an academic researcher from Raman Research Institute. The author has contributed to research in topics: Liquid crystal & Biaxial nematic. The author has an hindex of 31, co-authored 124 publications receiving 3368 citations. Previous affiliations of S. Chandrasekhar include Royal Institution & University of Mysore.

Schlieren Textures in Biaxial Nematic Liquid Crystals

Abstract: The optical textures exhibited by the mesophases of three compounds, all of which are reported to show the biaxial nematic phase, have been examined. The textures are of the usual nematic schlieren type, except that they consist entirely of disclinations of strength |s| = 1/2. It is suggested that the absence of disclinations of unit strength is diagnostic of biaxiality.

Theory of Birefringence of Nematic Liquid Crystals

Abstract: A theory of the birefringence of nematic liquid crystals is de- veloped taking into account the intermolecular potential energy arising from dipole-dipole, anisotropic dispersion, induction and repulsion inter- actions. The potential energy exhibits a dependence on molecular orientation and is expressible ae - (uo + u1 cost9 + uz cosat9 + u4 cos48 + u6 cosee + ...) where t9 is the angle which the long axis of the molecule makes with the uniaxial direction of the liquid crystal. The birefringence of the medium is evaluated in terms of the Boltzmann distribution of the oriented mole- cules. The theory explains the experimentally observed result that the temperature coefficient of the extraordumy index is large and negative whereas that of the ordinary index is small and positive. Analysis of the data on p-azoxyanisole and p-azoxyphenetole shows that dispersion and repulsion forces play a predominant role in determining the temperahre variation of the birefringence. Assuming that the molecular librations in the liquid crystal can be represented by a system of harmonic oscillators, the rn librational mnpli- tude is evaluated for p-azoxyaniaole from recent measurements of the ultrasonic velocity. The increase in the rn amplitude With temperature in the nematic range is found to be in good agreement with that obtained directly from the experimental data on birefringence.

The structure of bytownite (`body‐centred anorthite')

Abstract: Bytownite (a plagioclase feldspar with composition aboul An 80 Ab 20 ) closely resembles anorthite in its lattice dimensions and its diffracted intensities, except for the systematic absence of those wiih h + k odd ('c' and 'y' type). The deduction of a body-centred lattice (whence the previous name, 'body-centred anorthite') is here shown to be incorrect. Three-dimensional electron-density maps and difference maps show conspicuously elongated or doubled Ca/Na peaks and 'half-atom splitting' for other atoms. The results are explained in detail if bytownite has a primitive lattice and a structure very close to (but significantly different from) that of anorthite, and if small anti-phase domains are present with origins related by the vector ½(a + b + c). The evidence for this conclusion, and against other possible explanations of the observed facts, is discussed fully. Bond lengths and angles (tabulated in full) resemble those in anorthite, with some significant differences. Inequalities of bond lengths and angles within the same tetrahedron are real; an analysis of their resemblances and differences in corresponding tetrahedra in different feldspars suggeests an empirical approach to the study of the structural stress systems involved, and emphasizes the difference between the groups comprising microcline, reedmergnerite, and low albite on the one hand, and anorthite, bytownite, and high albite on the other. Ordering of Si/Al is nearly complete, on the same set of sites as in anorthite. At a closer approximation, a few Al-rich sites show significant differences in thier Si content, with extreme value of 0% and 30% against the average value of 13 ± 5% for the rest.

Paramagnetic nematic liquid crystals

Abstract: The paper reports new nematic liquid crystals that are paramagnetic.

Handbook of Optical Materials

Abstract: CRYSTALLINE MATERIALS Introduction Physical Properties Optical Properties Mechanical Properties Thermal Properties Magnetooptic Properties Electrooptic Properties Elastooptic Properties Nonlinear Optical Properties GLASSES Introduction Commercial Optical Glasses Specialty Optical Glasses Fused Silica Fluoride Glasses Chalcogenide Glasses Magnetooptic Properties Electrooptic Properties Elastooptic Properties Nonlinear Optical Properties Special Glasses POLYMERIC MATERIALS Optical Plastics Index of Refraction Nonlinear Optical Properties Thermal Properties Engineering Data METALS Physical Properties of Selected Metals Optical Properties Mechanical Properties Thermal Properties Mirror Substrate Materials LIQUIDS Introduction Water Physical Properties of Selected Liquids Index of Refraction Nonlinear Optical Properties Magnetooptic Properties Commercial Optical Liquids GASES Introduction Physical Properties of Selected Gases Index of Refraction Nonlinear Optical Properties Magnetooptic Properties Atomic Resonance Filters APPENDICES Safe Handling of Optical Materials Abbreviations, Acronyms, and Mineralogical or Common Names for Optical Materials Abbreviations for Methods of Preparing Optical Materials and Thin Films Fundamental Physical Constants Units and Conversion Factors

Dendron-Mediated Self-Assembly, Disassembly, and Self-Organization of Complex Systems

Abstract: Dendron-mediated self-assembly, disassembly, and self-organization of complex systems have been investigated. The most ideal building blocks would need to display shape persistence in solution and in the solid state, since only this feature provides access to the use of complementary methods of structural analysis. Most supramolecular dendrimers are chiral even when they are constructed from nonchiral building blocks and are equipped with mechanisms that amplify chirality. This poses additional challenges associated with the understanding of the structural origin of chirality in different supramolecular structures through combinations of structural analysis methods. While many supramolecular structures assembled from dendrimers and dendrons resemble some of the related morphologies generated from block-copolymers, they are much more complex and are not determined by the volume ratio between the dissimilar parts of the molecule.

Discotic Liquid Crystals: From Tailor-Made Synthesis to Plastic Electronics

Abstract: Most associate liquid crystals with their everyday use in laptop computers, mobile phones, digital cameras, and other electronic devices. However, in contrast to their rodlike (calamitic) counterparts, first described in 1907 by Vorlander, disklike (discotic, columnar) liquid crystals, which were discovered in 1977 by Chandrasekhar et al., offer further applications as a result of their orientation in the columnar mesophase, making them ideal candidates for molecular wires in various optical and electronic devices such as photocopiers, laser printers, photovoltaic cells, light-emitting diodes, field-effect transistors, and holographic data storage. Beginning with an overview of the various mesophases and characterization methods, this Review will focus on the major classes of columnar mesogens rather than presenting a library of columnar liquid crystals. Emphasis will be given to efficient synthetic procedures, and relevant mesomorphic and physical properties. Finally, some applications and perspectives in materials science and molecular electronics will be discussed.