Faceted particles embedded in a nematic liquid crystal matrix: Textures, stability and filament formation

Abstract

Two dimensional texture simulations, based on the Landau-de Gennes equations of nematodynamics in the absence of flow, were carried out for nematics with embedded faceted binary and multiple particles using temperature, size, and density as topological control variables. The stable modes obtained from kinetic simulations are summarized in texture phase diagrams in terms of temperature, particle separation and particle size. The key novelty in 2D faceted particles is the presence of corners that are sources/sinks of disclination lines or active corner defects. Under close corner-to-corner proximity, disclination lines form inter-or intra-particle links, while under larger distances, surface defects decorate the corners. This generic geometric behaviour is modulated by temperature since the line tension of disclinations decreases with increasing temperature. The characteristic texture diagrams show that for nanoparticles, increasing particle separation results in a disclination mode sequence of linked particles, cross-linked particles, and intra-particle disclinations. For colloidal particles, increasing size results in a mode sequence of linked particles and isolated particles with corner defects. For intermediate particle size, a continuous evolution of the phase diagrams from the former to the latter is demonstrated. At low temperatures, increasing interparticle distances leads to a defect breakage at a critical value independent of particle size. Multimer particle assemblies form stable filaments via a corner-to-corner interparticle disclination linkage mechanism. The stability of the multimers to bending is characterized using curvature as a topological control variable. As stretchingdriven instabilities in binary particles give rise to surface defects modes, bending-driven instabilities give rise also to multi-particle rings with corner decorated surface defects. The integrated texture phase diagrams, topological transitions, tension and bending-driven instabilities demonstrate the potential functionality of faceted particle liquid crystal nanocomposites.

Edge pinning and transformation of defect lines induced by faceted colloidal rings in nematic liquid crystals

“…The sharp change of the orientation of the faces of the square cross section of a colloidal ring with respect to n 0 introduces incompatible boundary conditions, thus diminishing the nematic degree of order at the particle edges [9,23,36,37,38]. This incompatibility of director orientations in the LC bulk can be resolved via deformations where the director n(r) rotates by θ = π/2 around the edge, resulting in a surface defect line of a strength k = 1/4 that we will call a structures is equal to zero in both n(r) configurations, consistent with the predictions of topological theorems for the defects induced by genus-one colloidal surfaces [28].…”

Repulsion–attraction switching of nematic colloids formed by liquid crystal dispersions of polygonal prisms

“…2,[21][22][23][24][25][26][27][28] However, n(r)-deformations and topological defects around faceted colloidal particles with sharp edges were shown to be more diverse and complex. [29][30][31][32][33][34][35] Changing the propagation of defect lines at the edges of faceted colloidal particles can induce not only achiral director structures but also the ones with chiral symmetry of n(r) of the ensuing LC colloids. 16,25,30,31 In this article, we realise low-symmetry achiral and chiral n(r)-dressed colloids in the nematic liquid crystals using polygonal concave and convex prisms with sharp edges.…”

Elastic and hydrodynamic torques on a colloidal disk within a nematic liquid crystal

“…While the vast majority of research on inclusions in liquid crystals has concerned spherical particles, several studies have revealed new phenomena that emerge with nonspherical particles [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. For example, Lapointe and coworkers have found that equilateral polygonal platelets assemble in a nematic via either dipolar or quadrupolar forces depending on the number of polygon sides and that the elastic forces on cylindrical inclusions can be used to position the particles with high precision [7,12].…”