DYNAMIC-RESPONSE OF A HELICOIDAL CHOLESTERIC PHASE TO AN APPLIED FIELD

It is shown that the transient response of a helicoidal phase cholesteric liquid crystal to an applied field described by a step function is governed by two relaxation constants. The shorter one characterizes the local rotation of the director field and the longer the change in the overall twist angle between the bounding surfaces. For typical thermotropic liquid crystals, the ratio between these two time constants is of the order of 10(4), the shorter time being tens of microseconds and the longer a few seconds. It is suggested that these results are general and can be used to interpret recent studies of the dynamic response of cubically ordered cholesteric blue phases.