Temperature Sensitive Helical Pitches and Wall Anchoring Effects in Homogeneous Monodomains of Ferroelectric Sm C* Liquid Crystals, nOBAMBC (n=6-10)

Abstract

2-methylbutyl p-(p-n-alkoxybenzylidencamino) cinnamates were synthesized and their helical pitches in the Sm C^* phase were measured by optical microscopic and/or diffraction methods. After the phase transition from Sm A to Sm C^*, the pitches increase steeply within 0.5°C, attain relatively broad maxima, and then gradually decrease in all the nOBAMBC investigated, except for HpOBAMBC (n=7) whose pitch shows some anomalies at low temperatures. The “odd-even effect” is clearly observed in the dependence of the maximum pitch on the alkoxy chain length. The dependence of the helical pitch on cell thickness has also been studied. During the steep increase, the wall anchoring effect is not observed when the cell is at least thicker than 100 µm; at lower temperatures, however, the pitch depends on the thickness even when the cell is as thick as 200 µm or more. Finally, the observed temperature variation of the pitch is compared with the Landau-type phenomenological theories so far proposed.