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

Abstract

Self-assembly of colloidal particles due to elastic interactions in nematic liquid crystals promises tunable composite materials and can be guided by exploiting surface functionalization, geometric shape and topology, though these means of controlling self-assembly remain limited. Here, we realize low-symmetry achiral and chiral elastic colloids in the nematic liquid crystals using colloidal polygonal concave and convex prisms. We show that the controlled pinning of disclinations at the prisms edges alters the symmetry of director distortions around the prisms and their orientation with respect to the far-field director. The controlled localization of the disclinations at the prism's edges significantly influences anisotropy of the diffusion properties of prisms dispersed in liquid crystals and allows one to modify their self-assembly. We show that elastic interactions between polygonal prisms can be switched between repulsive and attractive just by controlled re-pinning the disclinations at different edges using laser tweezers. Our findings demonstrate that elastic interactions between colloidal particles dispersed in nematic liquid crystals are sensitive to the topologically equivalent but geometrically rich controlled configurations of the particle-induced defects.

Mesoscopic Approach to Nematic Fluids

“…Similar results were observed when using colloidal pyramidal cones and octahedrons made from thin nanofoil, which are physical analogues of mathematical surfaces with boundaries and induce no defects when flat [117]. Also switching between repulsion and attraction through re-pinning the disclinations at different edges of polygonal prism using laser tweezers has been demonstrated [118].…”

High-order elastic multipoles as colloidal atoms

“…1). However, similar multipolar director distortions can be also achieved using colloidal objects with complex shapes obtained by means of photolithography [18,21,51] and two-photon-polymerization [52,53]. On the other hand, the concept of controlling surface anchoring on spherical constituents of composite colloidal objects that we present here can be extended to patchy particles [7][8][9]54], where different patches can exhibit different boundary conditions, and particles with controlled surface topography [43], surface charging [55] and chemical functionalization [15].…”

“…This approach can be effectively extended to other potential strategies of designing elastic multipoles discussed above, as well as supplemented by adding magnetic and electrostatic interactions [56][57][58]. Since the colloidal objects can have different compositions, including constituents made of noble metals [57], magnetic materials [42,43,57,58], semiconductor nanoparticles [55,56] and dielectric objects [17,18,21,24,31,[51][52][53] (with means of defining boundary conditions for director on such colloidal objects already demonstrates [17,18,21,24,31,42,43,[51][52][53][54][55][56][57][58][59]), we envisage that properties of the ensuing colloidal composite metamaterials can be pre-engineered by expanding the above described design toolkit to account for collective behavior of such assemblies enriched by plasmonic resonances [32][33][34], plasmonexciton interactions [60,61], etc.…”

Interactions between pentagonal truncated pyramids with homeotropic anchoring in a nematic liquid crystal

“…Furthermore, an energy level crossing is observed by the superposition of both repulsive and attractive free energy branches. Experimentally, we can switch between repulsive and attractive states by applying laser tweezers that rearrange the disclinations at the edges [32]. In Fig.…”

“…The strong binding energy between the blocks results in their stability against external perturbations, this allows the PTP lattices to be considered as candidates for usage in colloidal photonic and electro-optic applications [31]. The rearrangement of the disclination lines at the edges of the polygonal prisms alters the symmetry of director orientation around the colloids and the nature of elastic interactions in the colloidal structures [32]. The self-tiling of the pentagonal truncated pyramids with homeotropic anchoring can also form quasi-crystalline Penrose patterns in contrast to that formed in case of pentagonal platelets with planar anchoring.…”