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

Abstract

The Raman depolarization ratios of the –C≡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.