Effect of temperature and electric field on 2D nematic colloidal crystals stabilised by vortex-like topological defects

Abstract

We report experimental studies on 2D colloidal crystals of dimers stabilized by vortex-like defects in planar nematic and π/2 twisted nematic cells. The dimers are prepared and self-assembled using a laser tweezer. We study the effect of temperature and electric field on the lattice parameters of the colloidal crystals. The lattice parameters vary with the temperature in the nematic phase and a discontinuous structural change is observed at the nematic to smectic-A phase transition. In the nematic phase, we observed a large change in the lattice parameters (≃30%) by applying an external electric field perpendicular to the plane of the 2D crystals. The idea and the active control of the lattice parameters could be useful for designing tunable colloidal crystals.

Orientation, elastic interaction and magnetic response of asymmetric colloids in a nematic liquid crystal

“…The colloids together with defects are known as elastic dipoles or quadrupoles, based on the similarity of the director fields with their electric counterparts 4 . In addition, other kinds of defects such as boojums 15,16 and vortex 17,18 are also observed in different anchoring and confinement conditions. Based on the interplay of elastic interaction and topological defects a variety of self-assembled structures such as chains 3 , two and three dimensional crystals 6,8 , entangled clusters 9,19 , knotted and linked colloids 19–22 are reported.…”

The fate of liquid crystal topological defects on chemically patterned surfaces during phase transitions

“…Only a few studies have revealed the gradual morphological transformation of topological defects during a phase transition. [20][21][22][23][24][25][26][27][28][29] The reorganization of LC molecules at the transition point to accommodate the changes in order is an intriguing phenomenon. Recent studies on topological defects appearing in LC spherical shells, [20][21][22][23] LC including colloidal particles, 24,25 LC thin films on multidirectional rubbed substrates, 26,27 and LCs at water-air interfaces 28,29 have identified the morphological changes across the N-SmA transition.…”

“…[20][21][22][23][24][25][26][27][28][29] The reorganization of LC molecules at the transition point to accommodate the changes in order is an intriguing phenomenon. Recent studies on topological defects appearing in LC spherical shells, [20][21][22][23] LC including colloidal particles, 24,25 LC thin films on multidirectional rubbed substrates, 26,27 and LCs at water-air interfaces 28,29 have identified the morphological changes across the N-SmA transition. The broken directional symmetry of the director n(r) in the N phase is extended to the broken positional symmetry along the n direction for the SmA phase with density modulation to generate equally spaced layers normal to n(r).…”

N−SmA−SmCphase transitions probed by a pair of elastically bound colloids

“…The surface anchoring of the SmA layers at the colloid's surface is not well defined, and understanding of the induced defects and equilibrium separation among the particles is incomplete. Very recently we have shown that the surface anchoring and defects in the SmA phase can be studied by dispersing the colloids in the nematic phase of a liquid crystal that exhibits N -SmA phase transition [29][30][31][32][33]. In the nematic phase the well-defined anchoring of the molecules on the particle's surface guides the layer orientation and elastic deformation in the SmA phase around the colloids when cooled across the N -SmA phase transition.…”