Abstract
In liquid crystal applications, boundary conditions are essential to ensuring suitable bulk molecular orientation and a deterministic response to external fields. Be it confinement to a droplet or a shell, a glass plate, or an interface with air or another liquid, proper surface alignment must be ensured—mechanically by rubbing, by chemical treatment that adds a layer of aligning molecules, by using photoalignment or even by leaving the surface untreated, using the intrinsic properties of the substrate itself. The anchoring can be classified as unidirectional (perpendicular homeotropic, or at oblique angles), or degenerate (planar or pre-tilted). However, if both substances at the interface are anisotropic, more diverse behaviour is expected. Here, we present a numerical simulation of a nematic droplet in a nematic host, and investigate behaviour of the director field and defects at the interface for different interfacial couplings. Finally, we compare the simulations to experimental images of discotic droplets in a calamitic nematic host.
Highlights
Liquid crystals are most known for their use in displays, but in recent years they are emerging as promising materials in photonics and lasing [1]
Orientation of the molecules at the surface is one of the contributions that affects equilibrium orientation within the liquid crystal. This contribution is especially important in more complex geometries, like in liquid crystal droplets, as prescribing orientation at surfaces may create a variety of topological defects
An equilibrium state in nematic droplets depends on the type of the surface anchoring, droplet size, and in the case of the chiral nematic on the chirality parameter N, measuring the number of π-turns per droplet diameter [3,13]
Summary
Liquid crystals are most known for their use in displays, but in recent years they are emerging as promising materials in photonics and lasing [1]. Systems with two anisotropic materials in contact remain a harder challenge and so both experimental and theoretical studies of such mixtures are rare. A few such systems emerged in active lyotropic-thermotropic mixtures, where the activity induced motion of defects in the thermotropic phase [6,7]. Orientation of the molecules at the surface is one of the contributions that affects equilibrium orientation within the liquid crystal. This contribution is especially important in more complex geometries, like in liquid crystal droplets, as prescribing orientation at surfaces may create a variety of topological defects. There are plenty of studies of relations between the preferred orientation at the surface and the corresponding structures inside or around droplets in nematic and cholesteric mixtures [4,8,9,10,11,12,13,14]
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