(477j) Modification of the Pinning Properties of Interfacially Trapped Colloidal Ellipsoids Using External Electric Fields

Interfacial assemblies involving anisotropic colloids, such as rods or ellipsoids, generally lack long-range order due to anisotropic capillary forces that drive interparticle attraction and the adoption of kinetically arrested disordered configurations at fluid interfaces. Modifying the interparticle forces, and thus the interfacial assembly, requires changing the materials involved in the pinning, creating fluid interface curvature, and/or introducing an external field to manipulate polarizable particles. In this talk we will show how external electric fields can be used to reversibly modify the pinning of polymer microparticles at fluid interfaces. Mirau interferometry will be used to measure the height profile of the fluid surrounding pinned colloids with ~nm precision and deduce the particle contact angle. Spherical and ellipsoidal colloids of varying size and aspect ratio will be examined in this analysis. Under static conditions, increasing the particle aspect ratio decreases the contact angle. Applied electric fields change the location of the particle relative to the fluid interface as well as how the fluid interface approaches the three-phase contact line with the particle surface. As the electric field strength increases, the contact angle increases for anisotropic particles. By controlling the contact angle with external fields, the interparticle capillary forces, and thus the final two-dimensional particle assembly, may be controlled in the future.