Liquid-crystalline transitions in homologous p-phenylenes and their mixtures. Part 3.—Relation of orientation-dependent interactions to optical anisotropies

Abstract

The theory of anisotropic dispersion interactions between rod-like particles has been adapted to estimation of the temperature T^* that characterizes the intensity of these interactions through use of the relationship [graphic omitted], where Δα is the anisotropy of the polarizability, provided by depolarized Rayleigh scattering measurements, reported here, on dilute solutions of the lower homologues of the poly(p-phenylene) series; is the mean polarizability available from the refractive index, E_s is the total intermolecular energy per segment, which may be obtained from the equation of state or from the latent heat of vaporization, [graphic omitted] is the reduced volume and σ is a numerical parameter estimated according to theory, with account of geometric constraints, to be ca. 0.05. With ascent of the homologous series, Δα/ increases, and likewise T^* calculated according to this relationship. Values of T^* thus obtained for p-quaterphenyl and p-quinquephenyl are in approximate agreement with those deduced from the transition temperatures of these prototype nematogens in the preceding paper. The lattice theory (Flory and Ronca) that takes account of both the asymmetry of shape of rod-like particles and the orientation dependence of the forces operating between them gains substantial support from these results.