Pressure-driven reentrant phenomena in liquid crystals: the role of inverse layer spacing

Abstract

The occurrence of pressure-driven reentrant phenomena observed in high-pressure experimental studies in some achiral mesogenic materials has been explained using a thermodynamic model based on Landau–de Gennes theory. In this approach, the free-energy is expanded in terms of nematic, smectic A order parameters and the couplings (cubic and biquadratic) between them. The basic theme here is that the ‘inverse layer spacing’, which mimics an order parameter, becomes coupled to the nematic and smectic A order parameters. Secondly, in addition to the order parameter couplings the N–S_A metastable temperature (which appears due to elimination of inverse layer spacing from the free-energy density expression) becomes pressure dependent. The occurrence of a pressure-driven reentrant nematic phase is explained in terms of these three pressure-dependent parameters. They all show smooth but rapid variation at the critical pressure beyond which nematic reentrance appears.

Keywords:

• liquid crystals
• reentrant phenomena
• phase transitions
• Landau–de Gennes theory

Acknowledgements

Financial support from DST, New Delhi is gratefully acknowledged. One of us (Amit Srivastava) is grateful to CSIR, New Delhi for a Senior Research Fellowship.