Ferroelectric polysiloxane liquid crystals with ‘de vries’-type smectic a* -smectic c* transitions

We report preliminary results of optical and small angle X-ray scattering (SAXS) experiments on the smectic A*2smectic C* transition in two ferroelectric liquid crystalline polysiloxanes. Although the optical tilt angle in the SmC* phases reaches values up to 30‡, temperature-dependent SAXS measurements clearly reveal that the smectic layer spacing is basically conserved during the A*–C* transition as well as in the subsequent C* phase. Connected with the A*–C* transition we further observed a significant increase in bire- fringence, hence reflecting an increase of orientational order. The practical absence of layer shrinkage and the enhanced orientational ordering are consistent with the de Vries diffuse cone model of smectic A2smectic C transitions.