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.

Density, Dielectric and X-ray Studies of Smectic A-Smectic A Transitions

Abstract: We report here the results of detailed density, dielectric and x-ray studies on three systems exhibiting different types of Smectic A-Smectic A transitions. It is found that although the layer spacing shows marked changes at the transitions, the corresponding density changes are extremely small. In every case studied, the dielectric anisotropy shows a pronounced decrease on going over to the lower temperature smectic A phase. This decrease can be correlated with the structural changes.

Phase Transitions of Nematic Main-Chain Polyesters Under High Pressure

Abstract: Abstract. The nematic-isotropic (NI) and crystalnematic (KN) transition temperatures were measured from atmospheric pressure to 1 kbar for a homologous series of thermotropic polyesters based on regularly alternating 2,2'-dimethylazoxybenzene mesogen and alkanedicarboxylic acid spacer. The values of (dP/dT) for the NI transitions show an odd-even alternation with n, consistent with the previously reported alternation of TNI and (ΔH)NI. The characteristic temperature T* calculated for n = odd is approximately 300 K, similar to the values for noncybotactic nematics. On the other hand, for n =even, T* could not be reliably calculated, perhaps due to the existence of cybotactic ordering. At the KN transition there is no such clear alternation in (dP/dT). The specific volume changes (ΔV)KN at melting are very small and comparable in magnitude with (ΔV)NI. They are much smaller than the corresponding values for low molar mass liquid crystals and conventional polymers. This suggests that the crystals of...

An experimental method of correcting for extinction in crystals

Abstract: This paper deals with an experimental method of correcting for extinction errors by the use of polarised X-rays. It involve an accurate study of the variation of the integrated reflection with angle of polarisation. The theory and limits of applicability are discussed in detail. It is shown experimentally that the method is feasible when intensity measurements are made with high precision. The principal merit of the technique is that it accounts in certain circumstances for both primary and secondary extinction simultaneously in a crystal of any shape.

A redetermination of the rotatory dispersion of sodium chlorate

Abstract: SODIUM chlorate is the best known exarnple of a crystal belonging to the cubic system exhibiting optical activity. As an aqueous solutiorl of it does not display such activity, it is clear that the optical rotatory power is a consequence of the crystal structure which belongs to the space group T4-p213. Precise data regarding the rotatory power and its variation with wave-length are obviously needed a s a starting point for any theoretical discussion of the optical behaviour of the crystal in relation to its structure. Determinations have been made in the visible region of the spectrum by Sohncke (1878), Voigt (1908), Perucca (1919) and also by Ramaseshan (1948). Measurements extending far into to the ultra-violet were first made by Guye (1889) and later by Rose (1909), both of whom have obtained values of the rotation from 7200 A.U. to 2500 A.U. Though it is known that sodium chlorate transmits light upto nearly 2200 A.U., it appears that no one has since pursued the measurements farther into the ultra-violet. The data obtained by Guye and Rose, which are the most extensive, have been presented in Table I. From the data it can be seen that in the visible region Biot's Law is approximately valid, but as we proceed into the ultra-violet, the rotatory power increases at a much slower rate than is required by Biot's Law.

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.