ON THE SEEMINGLY ANTIFERROELECTRIC BEHAVIOUR OF CERTAIN FERROELECTRIC LIQUID CRYSTALS

Double current peak, double hysteresis loop and even in some sense three electro-optic states, the main characteristics of the antiferroelectric liquid crystal phase. are found also in the ferroelectric smectic C* phase. observed so far on several liquid crystal materials possessing a C*-N* phase sequence. In the observed cases, the confining surfaces bring about a pronounced monostable surface anchoring of the liquid crystal molecules forcing the layers to be broken in two alternating directions, corresponding to the equivalent surface directions of positive and negative molecular tilt relative to the layer normal. The resulting striped texture is very reminiscent of certain domain patterns in solid ferroelectrics. The seemingly anomalous electric switching behaviour of this C* texture mimics an antiferroelectirc and may thus easily lead to an incorrect designation of the phase if not supplemented by other identification methods. Hysteresis shape and switching current peaks are thus by themselves insufficient for distinguishing between ferroelectric and antiferroelectric liquid crystals.