Curvature-Driven Fluxes of Colloids
Chemical and Biomolecular Engineering Theatre
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There are important fields, intrinsic to soft matter, which we can exploit to direct colloidal assembly. The central idea is this: When a colloid is placed in a soft matter host, the colloid deforms the host, with some energetic consequence. If the host is a fluid interface, changes in interface area and particle wetting energies define the energetic consequence. If the host is a nematic liquid crystal, elastic energy costs owing to deformations of the director field play this role. If the host is a lipid bilayer membrane, costs associated with bending and tension emerge. In each of these examples, by molding the soft matter host within well-defined boundaries, we can define global energy fields that drive colloids along well defined paths to sites for preferred assembly. We demonstrate this concept at fluid interfaces by molding their curvatures, in nematic liquid crystals by molding their director fields, and on lipid bilayer membranes by dictating their tension and shape. In the limit of small distortions, each of these systems can be discussed as analogies to electrostatic multipoles interacting with external fields. The value and limitations of these analogies are explored. Strategies are developed to drive colloids into complex structures; here, particle-particle interactions, particle-field interactions, and issues of trapped vs equilibrated structures are key. Approaches to actuate or reconfigure these structures are discussed.