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

We have studied by optical means recently synthesized benzoate ester series exhibiting SmCA*, SmCFI*, SmC* and SmCalpha* phases. We have made pitch me asurements on SmCA* and SmC* phases, using the Grandjean-Cano method, and o ptical period measurements on the SmCalpha* phase, on free surface drops. T he results are in good agreement with the pitch and optical period evolutio ns we previously described for other compounds-especially those of a thiobe nzoate series. We have also shown that one of the structural models propose d in the literature is in agreement with our experimental results, and have established a qualitative relation between optical period measurements, th e azimuthal difference between two successive layers, and the helical pitch . We present results for several benzoate compounds, using a new classifica tion of the observed behaviours.