Evidence for three typical behaviours of the helicity in the SmC_alpha* phase from recent benzoate ester series

Abstract

We have studied by optical means recently synthesized benzoate ester series exhibiting SmC_A*, SmC_FI*, SmC* and SmC_alpha* phases. We have made pitch measurements on SmC_A* and SmC* phases, using the Grandjean-Cano method, and optical period measurements on the SmC_alpha* phase, on free surface drops. The results are in good agreement with the pitch and optical period evolutions we previously described for other compounds - especially those of a thiobenzoate series. We have also shown that one of the structural models proposed in the literature is in agreement with our experimental results, and have established a qualitative relation between optical period measurements, the azimuthal difference between two successive layers, and the helical pitch. We present results for several benzoate compounds, using a new classification of the observed behaviours.