THE USE OF A TIME-RESOLVED RAMAN MICROPROBE TO STUDY THE ELECTRIC-FIELD-INDUCED FREEDERICKSZ TRANSITION IN THE ALKYL CYANOBIPHENYL HOMOLOGS

The bond selectivity of the Raman technique is exploited with a time r esolved Raman microprobe to determine the effective splay viscosity co efficients and elastic constants in the nematic phase of the 4-n-alkyl -4-cyanobiphenyl homologues 5, 6, 7 and 8CB. The Raman effect, using t he signal associated with the core and the flexible alkyl chains, was used to probe the Freedericksz transition in the limit of small deform ations. The data for the cores show good agreement with data published elsewhere. Odd-even effects were found and, in the case of 8CB, pretr ansitional effects due to the lower temperature S(A) phase were observ ed. The viscosity data for the flexible alkyl chains, at a reduced tem perature of 3-degrees-C, yield values for the apparent viscosity coeff icients that are approximately half that of their respective rigid cor es. This is considered to be indicative of the influence of the molecu lar flexibility on the effective director field. The data illustrate t he usefulness of the technique for studying microscopic volumes of mul ticomponent systems.