ALTERNATING-CURRENT-FIELD INDUCED CHOLESTERIC-NEMATIC PHASE TRANSITIONS

In order to determine whether interaction between the permanent or the induced molecular dipole moments of a cholesteric liquid crystal and an applied electric field is responsible for inducing a transition to a nematic phase, ac-field measurements were performed. In a mixture of cholesteryl chloride and cholesteryl myristate, phase transitions can be induced by an ac field of a frequency up to a threshold value fDt; fDt is approximately equal to the relaxation frequency for rotation of cholesteryl chloride molecules around a short molecular axis which has recently been determined by dielectric measurements. A relation between the rms field and fDt is derived and experimentally verified. The absence of ferroelectric ordering in the induced and aligned nematic phase is demonstrated.