Nanoparticle patterning in a microfluidic drop induced by surface acoustic waves

We demonstrate complex nonlinear pattern formation dynamics associated with standing wave vibrations induced along a piezoelectric substrate on which a small drop of colloidal suspension is placed. Interfacial colloidal islands which self-assemble due to surface acceleration and capillarity are subsequently erased once fluid streaming becomes significant at higher powers. Due to a peculiar instability, the system cycles between colloidal island assembly when streaming ceases and erasure when streaming resumes.