Layer Curvature and Optical Activity in Bent Core Liquid Crystalline Phases
Loren E Hough
University of Colorado, Boulder
The B4 and Dark Conglomerate are smectic (layered) liquid crystalline phases formed by bent-core molecules that have both significant optical activity and very short inter-layer correlation length. Using freeze fracture transmission electron microscopy to visualize the local layer structure, we show that the Dark Conglomerate is a thermotropic analogue of the lyotropic sponge phase, and that the B4 phase is a unique variant of the twist grain boundary phase where the smectic layers rotate about a helix axis. Both phases are characterized by significant saddle splay curvature. We show that the observed optical activity is a consequence of the achiral symmetry breaking seen in bent-core liquid crystals. This optical activity can also be seen in the well ordered B2 phase, although the optical texture is typically dominated by the birefringence.