TEXTURES IN HEXATIC FILMS OF NONCHIRAL LIQUID-CRYSTALS - SYMMETRY-BREAKING AND MODULATED PHASES

Novel modulated textures, such as stripes and multiarmed star defects, have been observed in freely suspended films of nonchiral liquid crystals just below the smectic-C to hexatic phase transition. Detailed studies using depolarized reflection microscopy suggest that the stripes are locally chiral surface splay domains of the smectic-L phase, a tilted hexatic not previously identified in thermotropic liquid crystals. Line defects which form additional domain walls in the hexatic lattice lead to characteristic modulations of the basic one-dimensional stripe pattern. Inside thick circular islands, for example, stripes form circumferentially and the lines form centered 12-armed stars, resulting in a regular arrangement of hexatic domains in the form of a brick wall pattern. The observation that line defects which are not pinned at the film boundaries always form closed loops supports a model of the stripe pattern based on local chiral symmetry breaking.