CONTINUOUS FERROELECTRIC SWITCHING IN TWISTED SMECTIC C-ASTERISK LIQUID-CRYSTALS

We report on the uniform alignment and continuous ferroelectric switch ing of a twisted smectic C liquid crystals (LCs). In contrast to surf ace stabilized ferroelectric LCs, a twisted smectic C (Sm C*) structu re exhibits essentially no threshold field and produces intrinsic gray scales. For constructing such a twisted structure, the symmetry in mo lecular tilt with respect to the rubbing axis is externally imposed by the surface forces. The symmetry required for producing a uniformly t wisted structure is that the twist angle between two rubbing axes on t he substrates must be exactly twice of the molecular tilt. One importa nt parameter is the existence of the smectic A state in the phase sequ ence, which facilitates to the uniform growth of the smectic layers. W e perform numerical simulations to obtain the director profiles and th e resultant electro-optic modulation as a function of the electric fie ld in the twisted Sm C structure. It is found that the experimental d ata agree well with the numerical results.