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Geometry, Confinement and Directed Motion of Colloids in Nematic Liquid Crystals

Speaker: Kate Stebe, University of Pennsylvania
Series: CBE Departmental Seminars
Location: Elgin Room (E-Quad A224)
Date/Time: Wednesday, December 5, 2018, 4:00 p.m. - 5:00 p.m.

The ability to dictate the trajectories and docking sites of colloidal objects has far-reaching implications in fields ranging from reconfigurable materials to intelligent systems. diverse approaches have been developed in the literature, ranging from the use of external fields or of active colloids near structured boundaries. Here, we exploit confined nematic liquid crystals (NLCs) near undulating boundaries to embed energy landscapes. Related concepts have been widely explored for NLCs that create defects that can trap colloids, thereby impeding our ability to reconfigure structures. To avoid such trapping, we design a director field that, in the absence of the colloids, is defect-free, but features regions of bend and splay that can be sensed by colloids placed within the domain. This NLC director field gently guides colloid motion. We show that a simple boundary of alternating hills and wells embeds energetic cues that dictate particle paths and multi-stable equilibrium loci. Furthermore, we demonstrate remarkable control over the defect structure associated with the colloid, a significant outcome, since such defects attract surfactants and nanoparticles. Since the field is related to NLC orientation, the interactions are reconfigurable, either by reorientation of the NLC under applied fields, or by reconfiguration of the boundary shape. This means of directing colloid motion is readily combined with other fields to afford additional control with promise in reconfigurable systems and in microrobotics applications.