INFLUENCE OF SILOXANE GROUPS ON THE PROPERTIES OF SOME SULFINATE FERROELECTRIC LIQUID-CRYSTALS DERIVATIVES

We present the electro-optic characterisation of two ferroelectric org anosiloxane liquid crystals differing from the length of the siloxane group attached to the chiral mesogen. A compared study of the electro- optic properties of both siloxane-based materials with their homolog h aving no siloxane group is presented. It is observed that the:presence of the siloxane moiety strongly contributes to the enhancement of the ferroelectric temperature range, the increase of the spontaneous pola risation and of the tilt angle, without having much effect on the rota tional viscosity. A stabilisation of the ferroelectric phases is thus achieved. The analysis of the experimental results reveals that the si loxane groups strongly contribute to the decrease of the orientational fluctuations of the transverse dipole moments, thus increasing the yi eld factor, f, of the spontaneous polarization. The dilution effect of the transverse dipole moment on the spontaneous polarisation is less important, when compared to the effect of the increase of the anisotro pic distribution of the transverse dipole moments.