Electric field effect on phase transitions in liquid-crystalline blue-phase systems

The influence of an electric field on the phase-transition temperatures of cholesterogenic mixtures CB 15/M 18 exhibiting blue phases (BP) has been investigated. From temperature-voltage phase diagrams it can be seen that the transition temperature BP I/cholesteric depends on the field strength $E$, whereas that of BP II/cholesteric does not. The effect $\Delta T\left(E\right)\mathrm{}$ can be understood by means of the Kirkwood-Helfrich equation considering the nonlinear field dependence of the BP I permittivity.