Temperature Dependence and Dispersion of the Rotatory Power of a Ferroelectric Liquid Crystal in the S_I* Phase

Abstract

High resolution rotatory power measurements have been carried out in the vicinity of the S_A-S_I* phase transition of 1-ethoxycarbonylethyl (S)-4-(4′-decyloxy-2′-hydroxybenzylidene)aminocinnamate (DOHBAECEC). A remarkable rotatory dispersion has been observed in the visible range, together with a decrease in light transmission due to the selective reflection phenomenon. This effect has allowed us to measure the helical pitch in the S_I* phase and, in conjunction with the optical activity, to obtain the temperature dependence of the tilt angle. This indirect method, which has been recently described in the literature, provides the tilt data on the unperturbed helicoidal phase and thus avoids the problems connected with the use of electric fields. The tilt results present a behaviour similar to the case of a S_A-S_C* transition and can be accounted for within the framework of a mean-field model.

Key Words:

• S_I* phase
• rotatory power measurements
• selective relection
• tilt