Oriented Assembly of Anisotropic Particles by Capillary Interactions

Recent advances in micro- and nanoscale science exploit self-assembly to create ordered structures from micro- and nano-scale objects. The ability to dictate the orientation of an object, or to force an object to assemble in registry with other particles remain important goals in the field. We study capillary interactions that drive oriented assembly of anisotropically shaped objects. Capillary interactions between particles drive particle assembly at fluid interfaces. The particles distort the interface, creating excess surface area. Excess area decreases as particles approach each other, creating attraction. Anisotropically shaped particles create excess areas that are non-uniformly distributed around the particle's center of mass. Local regions of concentrated excess area develop that drive oriented assembly. We use a force balance to develop relationships between particle aspect ratio and regions of concentrated excess area that drive orientation and assembly. These arguments are supported in experiment. Short-range capillary interactions have been predicted to promote alignment of particle faces. Based on this concept, particles with complex end faces that align with end-to-end registry are created.