Modulated Crystalline-B Phases in Liquid Crystals

Abstract

Detailed x-ray scattering studies of the modulated phases of 4-n-heptyloxybenzylidene-4-n-heptylaniline (7O.7) are reported. In addition to the previously identified one-dimensional modulation that appears at the transition from the crystalline-B (CrB) phase with AB AB stacking to the CrB phase with orthorhombic stacking, there are two other modulation structures each of which contains two noncolinear modulations. The modulations are explained in terms of a phenomenological model in which domains are separated by walls for which the intralayer packing is identical to the lower-temperature crystalline-G phase. This model yields the measured values for both the modulation wave vector and the lattice distortion.