Nanoscale Clustering in Bent Core Nematic Liquid Crystals and Liquid Crystal Polymers

Bent-core liquid crystals (LCs) have a kinked, or bent, molecular shape in contrast to the more common calamitic, or rod-like, LCs (see Figure). Due to their bent molecular shape, bent-core LCs form locally polar clusters, which result in novel LC phases and potentially useful properties such as ferroelectricity. Polymeric bent-core LCs are of particular interest because they can be incorpoated into functional devices and lead to new nanostructured soft materials with confined bent-core LCs. In this work, we investigate the synthesis, nanoscale structure, and physical properties of a variety of bent-core LCs and polymeric bent-core LCs. Small-angle x-ray scattering reveals the presence of biaxial, locally polar clusters over a wide temperature range in the nematic phase for all materials studied, including pure bent-core LCs, swollen liquid crystal elastomers (LCEs) swollen with bent-core LCs, and bent-core side-group LC polymers. The presence of locally polar clusters can account for the unexpected physical properties in nematic bent-core LCs, such as enhanced flexoelectricity. Direct flexoelectric measurements on pure bent-core LCs and swollen LCEs show that nematic bent-core materials have a flexoelectric coupling three orders orders of magnitude larger than calamitic LCs. Nematic clusters in bent-core LCs represent an unexpected and potentially useful phenomenon for building responsive LC devices.