Molecular flexibility and orientational statistics in liquid crystals: Raman study of 7-CB and 8-OCB

Abstract

The Raman depolarization ratios of the –C[equivalent]N vibrational band of 7-CB and 8-OCB have been measured in the aligned liquid crystal and isotropic phases. The temperature dependence of the absolute orientational order parameters <P2> and <P4> have been evaluated for the mesophases of both compounds. A comparison of their <P4> values in the nematic phase with those determined by Miyano for 5-CB suggests that molecular flexibility is an importnant factor that serves to lower <P4> well below the predictions of mean field theories.