Optical signals of uniaxial and biaxial cholesteric lyotropic phases

Abstract

Lyotropic cholesteric liquid crystalline phases were prepared by doping the ternary mixture of potassium laurate (KL)/decanol (DeOH)/ deuterium oxide (D2O) with brucine sulphate, in two different concentrations. Using the variation of the average color in a heating cycle, with and without the insertion of compensator a gypsum plate (1 λ), in the light path, the optical signal of the cholesteric phases ChD-(ChC+) was confirmed as being negative(positive). When the biaxial cholesteric phase (ChB) is between two uniaxial phases (ChD-ChB-ChD) or (ChD-ChB-ChC), the sign of the ChB phase depends on the uniaxial phase in its vicinity. In the case (ChD--ChB--ChD-), the phase ChB has a negative optical signal (ChB-) across the domain. However, if the ChB phase is between uniaxial cholesteric phases of opposite optical signals, it cannot have just one signal, but must have a change at some point in the biaxial domain showing (ChD--ChB--ChB+-ChC+) phase sequence.