What Are ThresholdLess AntiFerroelectric (TLAF) LCs?–Disordered SmC*-Like Phase with qT = 1/2 in a Wide Temperature Range

Abstract

In the MC881-MC452 binary mixture system developed by MGC, the near-IR Bragg reflection peak is observed in a wide temperature range from 80°C down to room temperature or lower for a narrow concentration region between 54.99 and 57.50 wt.%; the phase responsible for this near-IR Bragg reflection peak can be identified as disordered SmC*-like phase with qT = 1/2 – hereafter designated as SmC*D(1/2) – which has the TLAF property in the bulk. Four intriguing mechanisms are operative: (1) The critical concentration exists, above which the free energy of SmC*A never becomes lower than that of SmC*; (2) The disclination-assisted thermal linkages assure the thermal equilibrium between ferroelectric and antiferroelectric orderings; (3) The long-range interlayer interactions in the quasi-molecular model stabilize the qT=1/2 state in a wide temperature range; and (4) A ferroelectric hexatic phase exists on the low temperature side of SmC*A and the frustration between them stabilizes another qT=1/2 state which may coalesce into the ordinary one in the intermediate concentration region. In this way coalesced SmC*D(1/2) emerges stably. Because of the disclination-assisted thermal linkages, SmC*D(1/2) must be disordered and soft with respect to the tilting directions and senses of the in-layer directors even in the bulk; electric-field-induced switching is expected to occur layer by layer but not cooperatively and hence shows the TLAF property.