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.

Keywords:

• ferroelectric liquid crystals
• antiferroelectric phase
• dielectric properties
• lactate group
• TGBA phase

Acknowledgements

This work was supported by Research Project AVOZ 10100520, Projects No. IAA100100710 from Grant Agency of the Academy of Sciences of the Czech Republic, Czech‐Polish bilateral collaboration program No.8 (2006‐2007) under the Ministry of Education, Youth and Sports of the Czech Republic. The X‐ray diffraction measurements were accomplished at the Structural Research Laboratory, Chemistry Department, University of Warsaw, Poland, which has been established with financial support from European Regional Development Found, project no: WKP 1/1.4.3./1/2004/72/72/165/2005/U.