Chemical Engineering Seminar

In materials science, the control over the spatial arrangement of colloids in soft matter hosts implies control over a wide variety of materials properties, ranging from the system's rheology, its optics or its catalytic activity.  To direct particle assembly, colloids are often manipulated using external fields to steer them into well-defined structures at given locations.  We have been 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.  Such potential fields allow particles to interact with each other.  If the soft matter host is deformed in some way, the potential allows the particles to interact with the global system distortion.

One important example is a particle on a fluid interface.  The particle distorts that interface owing to 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.  The particle's capillary energy depends on the local interface curvature.  We explore this coupling in experiment and theory, and discuss results for disks, spheres and cylindrical microparticles in interfaces with curvature fields of varying complexity.  There are important analogies in other soft matter systems.  Particles in liquid crystals distort the director field and form defect structures that elicit an elastic energy response that can be used to define particle paths and sites for assembly.  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.