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Reconfiguration of nematic disclinations in plane-parallel confinements
Saša Harkai, Charles Rosenblatt, Samo Kralj, 2023, original scientific article

Abstract: We study numerically the reconfiguration process of colliding |m|=1/2 strength disclinations in an achiral nematic liquid crystal (NLC). A Landau–de Gennes approach in terms of tensor nematic-order parameters is used. Initially, different pairs {m1,m2} of parallel wedge disclination lines connecting opposite substrates confining the NLC in a plane-parallel cell of a thickness h are imposed: {1/2,1/2}, {−1/2,−1/2} and {−1/2,1/2}. The collisions are imposed by the relative rotation of the azimuthal angle θ of the substrates that strongly pin the defect end points. Pairs {1/2,1/2} and {−1/2,−1/2} “rewire” at the critical angle θ(1)c=3π/4 in all cases studied. On the other hand, two qualitatively different scenarios are observed for {−1/2,1/2}. In the thinner film regime ℎ<ℎc, the disclinations rewire at θ(2)c=5π/4. The rewiring process is mediated by an additional chargeless loop nucleated in the middle of the cell. In the regime ℎ>ℎc, the colliding disclinations at θ(2)c reconfigure into boojum-like twist disclinations.
Keywords: liquid crystals, topological defects, disclinations, reconfiguration
Published in DKUM: 28.03.2024; Views: 126; Downloads: 7
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Finite size effects in soft matter under an electric field stimulus
Saša Harkai, 2016, master's thesis

Abstract: In this thesis, we study the effect of an external electric field on the properties of glass forming liquids. We present the properties relevant and important for understanding the phenomenon, such as the transition temperature and the temperature dependence of viscosity. We create a numerical model and use a method called molecular dynamics with the Lennard-Jones potential and an added external field as the interatomic potential to simulate molecular motion within a glass forming liquid. We implement analysis methods to calculate properties such as the radial distribution function, static structure factor, diffusion coefficient, non-Gaussian parameter, and relaxation time. We use the implemented methods to evaluate the molecular behaviour of the simulation and compare the results with theoretical predictions.
Keywords: finite size, glass transition, diffusion constant, dynamic heterogeneity, electric field
Published in DKUM: 21.09.2016; Views: 1447; Downloads: 117
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Difuzijsko omejena agregacija
Saša Harkai, 2014, undergraduate thesis

Abstract: V diplomskem seminarju obravnavamo difuzijsko omejeno agregacijo. Predstavimo matematični model, s katerim generiramo agregate, ki jih karakteriziramo s parametri, kot so število delcev, temperatura, velikost delcev, razdalja med robom in agregatom ter jakost zunanjega polja. Prikažemo vpliv različnih parametrov na kvalitativne lastnosti agregatov s poudarkom na fraktalni strukturi.
Keywords: difuzijsko omejena agregacija, model brez mreže, Brownovo gibanje, fraktal, fraktalna dimenzija
Published in DKUM: 22.10.2014; Views: 3899; Downloads: 232
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