Phase transitions and topological defects in discotic liquid crystal droplets with planar anchoring: a Monte Carlo simulation study

A Monte Carlo simulation study of a Janus discotic liquid crystal droplet

The study of discotic liquid crystals (DLCs) under spherical confinement has gained considerable significance due to its relevance in the design and optimization of advanced materials with tailored properties. The unique characteristics of DLC fluids, coupled with confinement within a spherical Janus surface, offer a compelling avenue for exploring novel behaviors and emergent phenomena. In this study, Monte Carlo simulations within the NpT ensemble are employed to investigate the behavior of a DLC fluid confined by a spherical Janus surface. The Janus surface is characterized by distinct hemispheres, with one promoting homeotropic (face-on) anchoring and the other planar (edge-on) anchoring. Our analysis reveals the emergence of two topological defects: one exclusively on the edge-anchoring hemisphere and the other at the boundary of both anchorings. Each topological defect possessing a topological charge ofk= +1/2. We observe that as the temperature transitions the central region of the droplet into a nematic phase, a disclination line forms, linking the two surface defects. By investigating droplets of three different sizes, we confirm that the isotropic-nematic transition is first-order for the larger droplet studied. However, this transition becomes continuous under strong confinement conditions. In contrast, the nematic-columnar transition remains first order even for smaller systems.

Exploring the interplay of liquid crystal orientation and spherical elastic shell deformation in spatial confinement

The application of liquid crystal technology typically relies on the precise control of molecular orientation at a surface or interface. This control can be achieved through a combination of morphological and chemical methods. Consequently, variations in constrained boundary flexibility can result in a diverse range of phase behaviors. In this study, we delve into the self-assembly of liquid crystals within elastic spatial confinement by using the Gay-Berne model with the aid of molecular dynamics simulations. Our findings reveal that a spherical elastic shell promotes a more regular and orderly alignment of liquid crystals compared to a hard shell. Moreover, during the cooling process, the hard-shell confined system undergoes an isotropic-smectic phase transition. In contrast, the phase behavior within the spherical elastic shell closely mirrors the isotropic-nematic-smectic phase transition observed in bulk systems. This indicates that the orientational arrangement of liquid crystals and the deformations induced by a flexible interface engage in a competitive interplay during the self-assembly process. Importantly, we found that phase behavior could be manipulated by altering the flexibility of the confined boundaries. This insight offers a fresh perspective for the design of innovative materials, particularly in the realm of liquid crystal/polymer composites.