Thermal Variation of the Optical Anisotropy of Some Homologues of Smectic Compounds

Abstract

From the available birefringence data in the smectic-A phase of di-n-alkyl 4,4′-azoxy-α-methyl cinnamates the optical anisotropies of eleven members of the homologous series are calculated for different temperatures. It emerges that the optical anisotropy decreases with increase of temperature. From an analysis of the data, it is concluded that the net variation of the optical anisotropy with temperature is the sum total of the variations arising from the rotations of the methylenes of the end chains and the fluctuations in the orientation of the rigid portion of the molecules with respect to the normal to the smectic layers. The paper also presents results with regard to the coefficient of volume expansion in the smectic phase calculated from the thermal variation of the mean electric susceptibilities of the different homologues.