20.500.12556/RUL-173701 Simulacije molekularne dinamike ograjenih tekočih kristalov Molecular dynamics simulations of confined liquid crystals Tekoči kristali so posebni anizotropni materiali, ki imajo lastnosti tako tekočin kot kristalov, zaradi česar so zanimivi za raziskave in aplikacije, v katerih so pogosto izpostavljeni zunanjemu električnemu ali magnetnemu polju. Njihovo obnašanje postane še bolj kompleksno v ograjenih sistemih, kjer postanejo pomembni tudi površinski efekti. V magistrskem delu s pomočjo simulacij molekularne dinamike, izvedenih v programu LAMMPS, raziskujemo obnašanje tekočih kristalov v ograjenih geometrijah – tankih plasteh in sferičnih kapljicah. Tekočekristalne molekule modeliramo z elipsoidi in interakcije med njimi z Gay-Berneovim potencialom. Izbrane robne pogoje dosežemo z uvedbo odbojnega potenciala, ki vsebuje orientacijski člen, kar omogoča, da lahko poleg ograditve izberemo homeotropno ali planarno sidranje. Na ta način opazujemo vpliv robnih pogojev na fazni prehod med izotropno in nematsko fazo v plasteh in kapljicah. Pri tem pokažemo, da urejajoči robni pogoji temperaturo faznega prehoda zvišajo, razurejajoči pa jo ohranijo ali rahlo znižajo, ta učinek pa je bolj izrazit v manjših sistemih. V plasteh raziskujemo še prehod sidranja in poskusimo povezati jakost sidranja s parametri potenciala. V kapljicah nas dodatno zanima pojav topoloških defektov. V primeru, ko imamo homeotropne robne pogoje, v središču dobimo obročasto disklinacijo in v primeru planarnih robnih pogojev dve disklinaciji na polih. Na koncu opišemo še, kako se oblika defektov spreminja, ko sistem izpostavimo zunanjemu (bodisi magnetnemu bodisi električnemu) polju, ki vsiljuje preferenčno orientacijo molekul vzdolž polja. 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. tekoči kristali molekularna dinamika ograjeni sistemi Gay-Berneov potencial tanke plasti sferične kapljice liquid crystals molecular dynamics confined systems Gay-Berne potential thin layers spherical droplets true false false Slovenski jezik Angleški jezik Magistrsko delo/naloga 2025-09-20 08:15:05 2025-09-20 08:15:10 2025-10-11 03:42:11 0000-00-00 00:00:00 2025 0 0 0000-00-00 NiDoloceno NiDoloceno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 154099 251443715 19019.pdf 19019.pdf 1 AEB539D6769160B4DC2CA5C2B18D7C28 20726f0938bf62c6d317cc113894e453eb2936d04b601c81831ee2242c352ba4 fc703c1d-95e8-11f0-9328-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=218351 Fakulteta za matematiko in fiziko 0 0 0