Phase transition between the cholesteric and twist grain boundary C phases

The upper critical temperature T-c2 for the phase transition between the cholesteric phase (N*) and the twist grain boundary C phase with the layer inclination tilted to the pitch axis (TGB(C1)) in thermotropic liquid crystals is determined by the mean field Chen-Lubensky approach. We show that the N*-TGB(C1) phase transition is split in two with the appearance of either the TGB(A) or the TGB(2q) phase in a narrow temperature interval below T-c2 The latter phase is novel in being superposed from two degenerate TGB(C1) phases with different (left and right) layers inclinations to the pitch axis.