Unusual behavior of binary mixtures of ferroelectric and antiferroelectric liquid crystals with three chiral centers

Two binary mixtures have been studied of homologues from a series derived from 4-alkoxybiphenyl-4'-carboxylic acid with three chiral centers exhibiting ferroelectric (FE), antiferroelectric (AF) and tilted hexatic phases. One homologue exhibits a re-entrant SmC* (SmC*re) phase, which is miscible with the SmC* phase. The phase diagrams of the studied mixtures exhibit a close pocket of the SmC*A phase. The SmC*re phase is induced even in the mixtures composed from homologues without this phase. Dielectric spectroscopy reveals the Goldstone mode in both ferroelectric SmC* and the SmC*re phases, this mode being stronger when increasing concentration of the antiferroelectric homologue: In the SmC*A phase a relaxation mode is detected with the relaxation frequency three orders higher, which exhibits critical slowing down when approaching the SmC*re phase. This mode, which can be attributed to the anti-phase mode is responsible for the appearance of the SmC*re phase. In mixtures exhibiting the SmC*A phase a helix twist inversion occurs in the vicinity of the low temperature border of the AF phase.