Temperature hysteresis of the change in the cholesteric pitch and surface anchoring in thin planar layers

Abstract

Hysteresis of the temperature of jumps in the cholesteric pitch in planar layers of cholesteric liquid crystals (CLCs) has been observed in the temperature dependence of the optical transmission spectra measured in a 4.8 ¼ m thick specimen of a 60% chiral racemic mixture of CE6. The temperature difference for the pitch jumps during heating and cooling was equal to about 0.1°C near 40.3°C. No difference in the temperature of the pitch jumps during heating and cooling was observed for an 18 µm thick specimen. A theoretical description of this hysteresis is presented on the basis of a continuum theory of elasticity of CLCs that also takes account of the surface anchoring of the CLC. Different possible mechanisms leading to a change in the director configuration in the layer during a pitch jump and their correspondence to the jump mechanism and hysteresis which occur in the experimental specimens are discussed.