<title>Lifshitz point in ferroelectric liquid crystals</title>

Abstract

Ferroelectric liquid crystals (FLCs) find many applications in display devices, waveguide switching and optical computing. These applications exploit the electrically alignable polarization of FLCs in the Smectic C* (SmC*) phase. In the absence of an electrical field, the SmC* phase exhibits helical modulation of the polarization vector resulting in no net bulk polarization. Pitch length and polarization properties of the phase are associated with the tilted structure and chirality of FLCs. Fundamentally, these physical properties constitute secondary order parameters of the SmA-SmC* (AC*) phase transitions. In this paper, we report a unique and startling ACC* multicritical point in mixtures of chiral DOBAMBC (p-(n- decyloxybenzylidene)-p-amino-(2-methyl-butyl) cinnamate and archiral 10O.8 (4- decyloxybenzylidene-4' octylaniline) where the SmA, C, and C* (ACC* point) phases meet. Studies of the phase diagram, tilt angle ((theta) ), polarization (P) and helix pitch (p) reveal an ACC* Lifshitz point that can be described in terms of the extended Landau theory. Specifically, the T<SUB>AC*</SUB> and maximum polarization (P<SUB>m</SUB>) exhibit quadratic composition dependence while the helical pitch length (p equals 2(pi) /q) varies linearly. Both q and P<SUB>m</SUB> vanish discontinuously at the C-C* phase boundary revealing its first order nature. Significantly, the composition dependence (x) of P<SUB>m</SUB> and (theta) can be explained using percolation and thermodynamic scaling theories, respectively.