Dynamics of jumpwise temperature pitch variations in planar cholesteric layers for a finite strength of surface anchoring

Abstract

The dynamics of pitch jumps in cholesteric layers with a finite surface anchoring strength under variations in temperature is investigated theoretically. General expressions are presented that connect the dynamics of pitch jumps with the parameters that determine the process, such as the viscosity, the specific form of the anchoring potential, and the dimensionless parameter S _d = K ₂₂/Wd, where W is the depth of the anchoring potential, K ₂₂ is the twist elastic modulus, and d is the layer thickness. It is found that the shape of the anchoring potential significantly influences the temporal behavior of the cholesteric helix in the process of a pitch jump. To illustrate this revealed dependence of the pitch jump dynamics on the shape and strength of the anchoring potential, the problem was investigated for two different models of the surface anchoring potential for a jump mechanism in connection with the director at the surface slipping over the barrier of the anchoring potential. Calculations for the unwinding (winding) of the helix in the process of the jump were performed to investigate the case of infinitely strong anchoring on one surface and finite anchoring on the other, which is important in applications. The results show that an experimental investigation of the dynamics of the pitch jumps will make it possible to distinguish different shapes of the finite strength anchoring potential and, in particular, it will provide a means for determining whether the well-known Rapini-Papoular anchoring potential is the best suited potential relevant to the dynamics of pitch jumps in cholesteric layers with a finite surface anchoring strength. The optimal conditions for experimental observation of these phenomena are briefly considered.