Phase diagram of new lactic acid derivatives exhibiting ferro‐ and antiferroelectric phases

Abstract

Rich polymorphism has been found in a new series of lactic acid derivatives. The length of a non‐chiral n‐alkyl chain plays an important role in changing the sequence and temperature range of phases. Except for one homologue with the shortest chain, all compounds exhibit a rather wide antiferroelectric chiral smectic C (SmC*A) phase below the ferroelectric (SmC*) and paraelectric smectic A (SmA) phases. The spontaneous polarisation and tilt angle were measured in the SmC* and SmC*A phases. For several compounds, small‐angle X‐ray diffraction measurements provided information about layer spacing, d. Temperature dependences, d(T), exhibit a rather large jump at the SmC*–SmC*A phase transition, but no anomaly was observed in the temperature dependences of the tilt angle and spontaneous polarisation. For one compound studied, a TGBA phase was established on the basis of the planar sample and free‐standing film observation under a polarising optical microscope. For two compounds with the longest non‐chiral chain, a direct phase transition from isotropic to the SmC*A phase was observed. All materials studied by dielectric spectroscopy revealed soft and Goldstone modes in the respective SmA and SmC* phases and two high‐frequency modes in the SmC*A phase.