Migration and Orientation of Cylindrical Particles by Curvature Induced Capillary Interactions

The directed assembly of particles by capillary interactions using curvature to steer and orient particles is explored. Specifically, we study capillary assembly of right cylindrical microparticles at curved interfaces. Theory predicts that particles should orient on curved surfaces and migrate to regions of high local curvature. To explore these ideas, we fill lithographically-defined vessels with water, and place them beneath hexadecane layers to create oil-water interfaces which present known curvature fields. Particles ‘adsorb' at the air-oil interface from the oil phase. Upon attaching to the interface, the particles align and migrate along curvature gradients to high curvature regions. Particles trajectory and orientation are recorded using high speed video microscopy. Curvature of the interface is measured by interferometric methods. The trajectories and orientations are compared to theory.