Liquid Crystal Mediated Interactions Between Nanoparticles in a Nematic Phase

Abstract

A continuum theory is used to study the interactions between nanoparticles suspended in nematic liquid crystals. The free energy functional that describes the system is minimized using an Euler-Lagrange approach and an unsymmetric radial basis function method. It is shown that nanoparticle liquid-crystal mediated interactions can be controlled over a large range of magnitudes through changes of the anchoring energy and the particle diameter. The results presented in this work serve to reconcile past discrepancies between theoretical predictions and experimental observations, and suggest intriguing possibilities for directed nanoparticle self-assembly in liquid crystalline media.

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…”

“…23,24 For nondegenerate planar or homeotropic anchoring, pairs of particles will tend to also assemble linearly, with a minimum in free energy at a pair orientation parallel to the nematic director. 22 For the case of Saturnring defects, higher order coordinations can occur, 21,29,33 and the combined overlap of these leads to kinetic arrest. 13 In each of these cases, the formation of a colloidal network is inherently coupled to the isotropic-nematic transition.…”

“…Previous investigations 21,27,44,45 of nanoparticle interactions have focused primarily on the strong anchoring limit, valid for micron-sized particles, but inappropriate for simulations of nanoparticles, where binding of mesogens is expected to be much weaker due to curvature considerations. 22,46 To this end, we investigate how one might utilize various surface anchorings, and the pre-nematic wetting layers they induce, in order to assemble nanoparticles within the isotropic phase, using coarse-grained molecular simulations. Studies which have accounted for variable anchorings 22,47 used continuum models, unable to resolve any molecular details which may be of importance in nanoparticle interactions.…”

“…22,46 To this end, we investigate how one might utilize various surface anchorings, and the pre-nematic wetting layers they induce, in order to assemble nanoparticles within the isotropic phase, using coarse-grained molecular simulations. Studies which have accounted for variable anchorings 22,47 used continuum models, unable to resolve any molecular details which may be of importance in nanoparticle interactions. A previous investigation including such molecular detail 20 focused on homeotropic interactions in the strong coupling limit, finding a weak attraction (≈k B T) between two nanoparticles in the isotropic phase, with a deep minimum (≈10k B T) within the nematic phase.…”

Anisotropic shift of surface plasmon resonance of gold nanoparticles doped in nematic liquid crystal

“…The active research in this direction has been focused on the analysis and control of the interaction between LC molecules and gold nanoparticles (GNP) at nanoscale dimension. Some mathematical models have been presented to understand the alignment of LC molecular director around nanomaterials in the form of Saturn rings, hedgehogs, and boojams [4][5][6][7][8][9][10][11][12][13][14][15][16][17]. The inclusion of GNPs in nematic LC can create some stable defects with possible integral strength ± 1 or ± ½ depending on the interaction of LC with GNPs.…”