Nematic topological defects positionally controlled by geometry and external fields

Abstract

Using a Landau-de Gennes approach, we study the impact of confinement topology, geometry and external fields on the spatial positioning of nematic topological defects (TDs). In quasi two-dimensional systems we demonstrate that a confinement-enforced total topological charge of m > 1/2 decays into elementary TDs bearing a charge of m = 1/2. These assemble close to the bounding substrate to enable essentially bulk-like uniform nematic ordering in the central part of a system. This effect is reminiscent of the Faraday cavity phenomenon in electrostatics. We observe that in certain confinement geometries, varying the correlation length size of the order parameter could trigger a global rotation of an assembly of TDs. Finally, we show that an external electric field could be used to drag the boojum fingertip towards the interior of the confinement cell. Assemblies of TDs could be exploited as traps for appropriate nanoparticles, opening several opportunities for the development of functional nanodevices.109

Qualitatively and Quantitatively Different Configurations of Nematic–Nanoparticle Mixtures

“…Such cases promote phase separation [ 64 ], which one tends to avoid if homogeneous LC + NP mixtures are of interest. Note that the case shown is reminiscent [ 65 ] of the Faraday cavity effect. In the latter case, charges introduced to a 3D metal body rearrange at the outer surface in such a way that the electric field within the body equals zero to minimise the electric field energy within the body.…”

In Situ Measurements of Elastic Constants In Liquid Crystalline Droplets

“…The study of liquid crystals confined to microscopic cavities demonstrates growing interest for the last decades, both from the fundamental point of view [1][2][3][4][5] and applications [6][7][8][9][10] , including sensors [11][12][13] , display technologies 14 , biological applications 15,16 and other [17][18][19] . The direct connection between topological defects in particle physics and liquid crystals allows using liquid crystals as convenient systems for studies of several fundamental problems [20][21][22] . Last decade, the most intriguing discoveries shift from nematic to cholesteric liquid crystals (CLC).…”