Tunable colloid trajectories in nematic liquid crystals near wavy walls

Abstract

The ability to dictate the motion of microscopic objects is an important challenge in fields ranging from materials science to biology. Field-directed assembly drives microparticles along paths defined by energy gradients. Nematic liquid crystals, consisting of rod-like molecules, provide new opportunities in this domain. Deviations of nematic liquid crystal molecules from uniform orientation cost elastic energy, and such deviations can be molded by bounding vessel shape. Here, by placing a wavy wall in a nematic liquid crystal, we impose alternating splay and bend distortions, and define a smoothly varying elastic energy field. A microparticle in this field displays a rich set of behaviors, as this system has multiple stable states, repulsive and attractive loci, and interaction strengths that can be tuned to allow reconfigurable states. Microparticles can transition between defect configurations, move along distinct paths, and select sites for preferred docking. Such tailored landscapes have promise in reconfigurable systems and in microrobotics applications.

Control of the Folding Dynamics of Self‐Reconfiguring Magnetic Microbots Using Liquid Crystallinity

“…Third, we found defects at corners of the native microcube (indicated by circles in Figure c), but a Saturn‐ring defect around DMOAP‐treated microcubes (indicated by an ellipsoid in Figure g). This LC organization is consistent with planar anchoring on nontreated surfaces and homeotropic anchoring on DMOAP‐treated surfaces (Figure a) . Together, the above observations reveal that the surfaces of nontreated microcubes (both SU‐8 and cobalt) impose planar anchoring of the LC, but DMOAP treatment provides a direct means by which the preferential orientation of LCs on the microcube surfaces are switched to a homeotropic anchoring.…”

“…The inferred surface alignments of n were confirmed by independent optical investigations on LCs supported on SU‐8 coated substrates (Figure S1, Supporting Information). We note here that the DMOAP treatment of silica and chromium was reported earlier to impose a homeotropic alignment, but DMOAP‐treated SU‐8 surfaces have not, to our knowledge, been previously reported.…”

Topological Defect Arrays in Nematic Liquid Crystals Assisted by Polymeric Pillar Arrays: Effect of the Geometry of Pillars

“…These small regions have many interesting properties. For example, distortions created in the vicinity of defects generate elastic interactions, which can be harnessed to drive colloidal assembly [1,[6][7][8]. Defects are also a way to "visualize" topological structures [9][10][11], such as disclination lines or loops, in real space.…”

Colloids in confined liquid crystals: a plot twist in the lock-and-key mechanism

“…Curved boundaries, corners and protrusions act as attractive or repulsive sites for colloidal particles in LCs, and thus they create elastic energy gradients that determine the colloids' trajectories and interactions [25][26][27][28][29] . Recently, we have applied these principles to spherical homeotropic particles in quasi 2-D geometry in proximity to a wavy wall 30,31 . The waviness of the wall introduces sites of high splay energy density at the convex hills and in the concave dales, and sites of high bend energy density at the inflection points.…”