Liquid crystals are unique materials that exhibit properties of both liquids and crystals, making them interesting for research and applications, where they are often exposed to external electric or magnetic fields. Their behavior becomes even more complex in confined systems, where surface effects become increasingly important.
In this thesis, we perform molecular dynamics simulations using the LAMMPS software to study the behavior of liquid crystals in confined geometries – thin layers and spherical droplets. Liquid crystal molecules are modeled as ellipsoids, and their interactions are described using the Gay-Berne potential. Selected boundary conditions are achieved by introducing a repulsive potential that includes an orientational term, allowing us to impose either homeotropic or planar anchoring in addition to confinement.
This allows us to observe the influence of boundary conditions on the phase transition between isotropic and nematic phases in layers and droplets. We show that ordering boundary conditions increase the transition temperature, while disordering ones keep it constant or decrease it slightly, and that this effect is more pronounced in smaller systems. In layers, we also study the anchoring transition and attempt to relate anchoring strength to the potential parameters.
In droplets, we are additionally interested in topological defects: for homeotropic boundary conditions, we obtain a ring disclination in the center, and for planar boundary conditions, we observe two disclinations at the poles. Finally, we describe how the defect shapes change when an external (either magnetic or electric) field is applied, which imposes a preferred molecular orientation along the field.
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