A Review of Cholesteric Blue Phases

Abstract

Blue phases (BP) challenge our understanding of phase transitions since they exhibit three dimensional translational order yet occur between phases of higher symmetry: the cholesteric phase which has translational order in only one dimension and the isotropic phase (or the amorphous blue fog phase) which has no translational order at all. Materials exhibiting blue phases are necessarily chiral; that is to say, on a microscopic scale they lack reflection symmetry. In liquid crystal systems, a macroscopic expression of this microscopic property is often a helicoidal structure. For example, in cholesteric liquid crystals the director, or the direction along which the long axis of the molecules tends to align, rotates with a constant pitch along a single direction, the z axis, say, this structural feature distinguishes the z direction from the other two directions and a cholesteric liquid crystal is optically anisotropic. In addition, cholesterics are optically active: the plane of polarization of light rotates as it travels along the cholesteric twist axis but is unchanged traveling in directions perpendicular to it. Blue phases share the optical activity of cholesteric liquid crystals but they are optically isotropic.KeywordsLiquid CrystalIsotropic PhaseColloidal CrystalCholesteric Liquid CrystalIsotropic LiquidThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.