Showing papers by "S. Chandrasekhar published in 1972"
TL;DR: A liquid crystal is a state of aggregation that is intermediate between the crystalline solid and the isotropic liquid as mentioned in this paper, where the molecules must be highly geometrically anisotropic.
Abstract: The term “liquid crystal” signifies a state of aggregation that is intermediate between the crystalline solid and the isotropic liquid. A substance in this state is strongly anisotropic in some of its properties and yet exhibits a certain degree of fluidity, which in some cases may be comparable to that of an ordinary liquid. A large number of organic compounds are now known to form liquid crystals. An essential requirement for mesomorphism to occur is that the molecules must be highly geometrically anisotropic. The transition to the intermediate state may be brought about by purely thermal processes (thermotropic mesomorphism) o r by the action of solvents (lyotropic mesomorphism).
30 citations
TL;DR: In this article, the thermodynamic conditions of nematic stability are discussed on the basis of the molecular statistical theory of orientational order developed in previous papers, and theoretical calculations of the order parameter in the nematic phase and the volume change at the nematic-isotropic transition point are presented for 2-4 non-adienic acid, 2 -4undecadienistic acid, p-azoxyanisole, p -azoxyphenetole and anisaldazine.
Abstract: The thermodynamic conditions of nematic stability are discussed on the basis of the molecular statistical theory of orientational order developed in previous papers. Theoretical calculations of the order parameter in the nematic phase and the volume change at the nematic-isotropic transition point are presented for 2-4-nonadienic acid, 2-4-undecadienic acid, p-azoxyanisole, p-azoxyphenetole and anisaldazine. The significance of the results are discussed briefly.
30 citations
TL;DR: The theory of melting of molecular crystals developed in Parts I and II is extended to include short range orientational order, and the thermodynamic properties are evaluated by the quasi-chemical method, which is mathematically equivalent to Bethe's treatment.
Abstract: The theory of melting of molecular crystals developed in Parts I and II is extended to include short range orientational order. The thermodynamic properties are evaluated by the quasi-chemical method, which is mathematically equivalent to Bethe's treatment, and the theory is applied to liquid crystalline transitions. The interesting result is obtained that the nematic-isotropic transition is always first order, and that although the long range orientational order disappears suddenly at this transition point, a certain degree of short range orientational order persists in the isotropic phase. The specific heat exhibits both pre- and post-transition anomalies, in conformity with observations. The thermal expansion and isothermal compressibility show pre-transition anomalies but, contrary to experimental facts, no post-transition anomalies, indicating that even the quasi-chemical approach is not quite adequate for explaining all the properties.
21 citations
TL;DR: In this article, a relationship between curvature, elasticity and orientational order in nematic liquid crystals was derived based on the molecular statistical theory developed in Part I. Calculations show that the elastic moduli of p-azoxyphenetole should be greater than those of p -azoxyanisole, in quantitative agreement with the values reported by the Orsay Group.
Abstract: A relationship is derived between curvature, elasticity and orientational order in nematic liquid crystals on the basis of the molecular statistical theory developed in Part I. Calculations show that the elastic moduli of p-azoxyphenetole should be greater than those of p-azoxyanisole, in quantitative agreement with the values reported by the Orsay Group. The theoretical temperature variation of the elastic moduli is also in accord with the available data.
9 citations