Anisotropic nanoparticles immersed in a nematic liquid crystal: Defect structures and potentials of mean force

Abstract

We report results for the potential of mean force (PMF) and the defect structures that arise when spherocylindrical nanoparticles are immersed in a nematic liquid crystal. Using a dynamic field theory for the tensor order parameter Q of the liquid crystal, we analyzed configurations, including one, two, and three elongated particles, with strong homeotropic anchoring at their surfaces. For systems with one nanoparticle, the most stable configuration is achieved when the spherocylinder is placed with its long axis perpendicular to the far-field director, for which the defect structure consists of an elongated Saturn ring. For systems with two or three nanoparticles with their long axes placed perpendicular to the far-field director, at small separations the defect structures consist of incomplete Saturn rings fused with new disclination rings orthogonal to the original ones, in analogy to results previously observed for spherical nanoparticles. The shape of these orthogonal rings depends on the nanoparticles' configuration, i.e., triangular, linear, or parallel with respect to their long axis. A comparison of the PMFs indicates that the latter configuration is the most stable. The stability of the different arrays depends on whether orthogonal disclination rings form or not, their size, and the curvature effects in the interparticle regions. Our results suggest that the one-elastic-constant approximation is valid for the considered systems; similar results were obtained when a three-constant expression is used to represent the elastic free energy. The attractive interactions between the elongated particles were compared to those observed for spheres of similar diameters. Similar interparticle energies were observed for linear arrays; in contrast, parallel and triangular arrays of spherocylinders yielded interactions that were up to 3.4 times stronger than those observed for spherical particles.

Liquid-crystal mediated nanoparticle interactions and gel formation

“…Rather than expelling the colloidal particles from the nematic completely, the system minimized free energy by driving colloids toward each other. [20][21][22][23][24][25][26][27][28][29][30][31][32] For degenerate planar anchoring, this results chaining of particles at 30…”

Elastic response of a nematic liquid crystal to an immersed nanowire

“…Monte Carlo simulations were performed on rods of infinite length [24]. Also, there is work on soft two-dimensional cylinders using lattice Boltzmann [25] and FEM simulations on hard cylinders [26]. All these works used homeotropic anchoring which leads to saturn ring-like defects along and around the cylinder.…”

Colloidal nematostatics

“…Depending on the size and nature of colloids, these systems can be very different. The recent development of the field has been inspired mostly by a great diversity of a few-and many-body ordering phenomena in microemulsions with micrometer and submicrometer size colloids [4][5][6][7][11][12][13][14][15][16][17][18]. However, there is also an important class of nematic nanoemulsions with molecular size colloids (dopants) and supramolecular size colloids.…”