Pressure variation of reentrant transition temperature in liquid crystals
Department of Physics, Banaras Hindu University, Varanasi, 221005, India
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Published online: 7 March 2007
High pressure experimental studies show that in certain mesogenic materials, the nematic-smectic A (N-Sm A) transition temperature TAN exhibits nonlinear pressure dependence. As a consequence, the material shows reentrant phenomena that is a phase sequence nematic — smectic A — reentrant nematic appears. The characteristic features of this phenomenon have been addressed here within the framework of Landau-de-Gennes theory, where the coupling between nematic and smectic A order parameters (γ, λeff) plays an important role. The cubic coupling γ is chosen to be negative in order to form Sm A phase whereas the biquadratic coupling λeff is made large and positive to obtain reentrant behaviour. In the present work, we incorporate the pressure dependence in the theory through γ and λeff which justifies the experimental pressure dependence in the reentrant transition temperature . The pressure dependence of γ and λeff are employed in the calculation of excess specific heat capacity near the reentrant transition. The computed heat capacity shows strong pressure dependence near the reentrant transition which can be confirmed from high pressure measurement.
PACS: 05.70.Fh Phase transitions: general studies – / 64.70.Md Transitions in liquid crystals – / 61.30.-v Liquid crystals –
© EDP Sciences/Società Italiana di Fisica/Springer-Verlag, 2007