Ferroelectric liquid crystals

2014 A general symmetry argument is presented, and experiments on newly synthesized p-decyloxybenzylidene p’-amino 2-methyl butyl cinnamate are described, demonstrating that chiral smectic C and H liquid crystals are ferroelectric. Some of the properties of this new class of ferroelectrics are discussed. In spite of speculation on the possibility of ferroelectric liquid crystalline phases [1], there has never been a compelling fundamental reason for, or experimental demonstration of the existence of ferroelectricity in these systems. In this letter we show by symmetry that smectic C and H liquid crystals composed of chiral molecules must have a spontaneous polarization. The synthesis of a new material exhibiting these phases is reported, and experiments are described which determine the existence and approximate magnitude of the spontaneous polarization. Some of the unusual properties of these fluid ferroelectrics are discussed. In a smectic C liquid crystal, rod-like molecules are arranged in layers, with the long molecular axes parallel to one another and tilted at an angle 0 from the layer normal. Each layer is a two-dimensional liquid. In the smectic H phase (also called tilted B), the molecular layers are crystalline; there remains some question about the degree of correlation of the lattices on different layers. These properties are well established by x-ray [2] and optical studies [3]. _ Both these phases have monoclinic symmetry, the point group for which contains only a two-fold rotation axis parallel to the layers and normal to the long molecular axis, a reflection plane normal to the two-fold axis, and a center of inversion. However, if the phase is composed of chiral molecules (not (*) Alfred P. Sloan Foundation Research Fellow. Present address, Division of Engineering and Applied Physics, Harvard University, Cambridge, Massachusetts, U.S.A. 02138. (**) Laboratoire associe au CNRS. superposable on their mirror image) then the mirror plane and the center of inversion are eliminated. The remaining single two-fold axis allows the existence of a permanent dipole moment parallel to this