Kathleen StebeUniversity of Pennsylvania, Chemical Engineering
Colloidal particles are often directed to assemble by applying external fields to steer them into well-defined structures at given locations. We are developing alternative strategies based on fields that arise when a colloid is placed within soft matter to form an inclusion that generates a potential field. For example, a particle adsorbed on a fluid interface can distort that interface to satisfy its wetting boundary conditions. The distortion has an associated energy field given by the product of its interfacial area and the surface tension. Fields generated by neighboring particles interact to drive assembly; preferred orientations for anisotropic objects emerge. Interface curvature couples to the particle’s capillary energy. By molding the interface to impose well defined curvature fields, we drive microparticles along pre-determined paths to well defined locations with deterministic energies. This example captures the emergent nature of the interactions, and their potential importance in schemes to make reconfigurable materials, since interfaces and their associated capillary energy landscapes can be readily reconfigured. We explore analogies in other reconfigurable soft matter systems. Liquid crystals are one important host medium. Particles immersed in liquid crystals distort the director field to elicit an elastic energy response. Preferred paths and locations for assembly can be defined by molding the director field and its associated defect structures. Particles adhered to lipid bilayer vesicles are another system in which such fields can be generated and exploited. These example systems have important analogies and pronounced differences which we seek to understand and exploit.
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