Time-resolved FT-IR study of ferroelectric liquid crystals with SiO obliquely evaporated alignment layers

Abstract

Time-resolved FT-IR spectroscopy was performed to monitor the behaviour of ferroelectric liquid crystals on a microsecond time scale. A bookshelf geometry was obtained by alignment with SiO obliquely evaporated layers in a CaF₂ cell with 2 μm gap. Six kinds of FLC mixtures were examined, all of which were three-component systems consisting of chiral molecules of 5 wt% and two kinds of phenyl pyrimidine molecules of 47·5 wt% each. All IR spectra were dominated by vibrational modes from the phenyl pyrimidines. Typical vibrational modes from core and alkyl chain parts are selected in order to compare the movement of the alkyl chain as a function of the chiral components. A novel parameter α = (intensity of largest peak at 2925 cm^?1/intensity of smallest peak at 2925 cm^?1)/(intensity of largest peak at 1432 cm^?1/intensity of smallest peak at 1432 cm^?1) for evaluating the alkyl chain movement is introduced. It was found that the length of the rigid or flexible parts of the chiral molecules and the parameter α are correlated. Moreover, relations between the cone angle and α and between the rise time and α were found.