POLARIZATION FREDERIKS TRANSITION IN SMC-ASTERISK LIQUID-CRYSTAL FILMS

A new Frederiks transition is predicted for freely suspended SmC liqu id-crystal films. Frederiks transitions in nematic liquid crystals are the result of the competition between two orientational effects. One coming from the orientation of the director field at the boundary and one from the orientational effect due to an external electrical or mag netic field acting on the bulk orientation of the director field via t he magnetic or dielectric susceptibility anisotropy. Here we discuss t he consequences of the additional ferroelectric torques. A new branch for the splay Frederiks transition due to the presence of the spontane ous polarization in SmC liquid-crystal films is predicted, and it is pointed out that on this new branch a transition from supercritical to subcritical bifurcation behaviour can occur.