Isotropic–nematic phase transitions in confined mesogenic fluids. The role of substrate anchoring

Abstract

The anchoring of rodlike liquid-crystalline molecules at solid surfaces plays an important role in the design of novel nanotechnological devices such as, for example, biosensors. In this work we investigate the impact of various anchoring scenarios on the isotropic–nematic phase transition of weakly anisometric, prolate mesogens confined to a mesoscopic slit-pore. We employ isostress ensemble Monte Carlo simulations in which the isotropic–nematic transition is driven by applying an external stress in the direction parallel to the substrate plane. The fluid–fluid interaction is described by a Lennard-Jones potential with an orientation-dependent attractive term. Our simulations show that different anchoring scenarios may shift the isotropic–nematic phase transition considerably. We locate this transition through response functions such as an isostress heat capacity, isothermal compressibility, and the Maier–Saupe order parameter. Our results suggest that for the present model system the isotropic–nematic transition is likely to be continuous. For the planar anchoring scenario we observe the formation of a new layer of fluid molecules during a structural transformation preceding the isotropic–nematic transition.