Density functional theory study of the nematic-isotropic transition in an hybrid cell

TL;DR

This study uses Density Functional Theory to explore how nematic-isotropic phase transitions in liquid crystals are affected by confinement in hybrid cells with antagonistic wall interactions, revealing conditions where transitions are suppressed or become continuous.

Contribution

It provides a detailed analysis of capillary transition suppression and the emergence of interface-like states in hybrid cells, identifying mechanisms for transition disappearance.

Findings

Capillary transition can be suppressed by opposing wall interactions.

Interface-like states enable continuous transformation between phases.

Two mechanisms for transition disappearance are identified.

Abstract

We have employed the Density Functional Theory formalism to investigate the nematic-isotropic capillary transitions of a nematogen confined by walls that favor antagonist orientations to the liquid crystal molecules (hybrid cell). We analyse the behavior of the capillary transition as a function of the fluid-substrate interactions and the pore width. In addition to the usual capillary transition between isotropic-like to nematic-like states, we find that this transition can be suppressed when one substrate is wet by the isotropic phase and the other by the nematic phase. Under this condition the system presents interface-like states which allow to continuously transform the nematic-like phase to the isotropic-like phase without undergoing a phase transition. Two different mechanisms for the disappearance of the capillary transition are identified. When the director of the nematic-like state is homogeneously planar-anchored with respect to the substrates, the capillary transition ends up in a critical point. This scenario is analogous to the observed in Ising models when confined in slit pores with opposing surface fields which have critical wetting transitions. When the nematic-like state has a linearly distorted director field, the capillary transition continuously transforms in a transition between two nematic-like states.