Cusps and spouts in microfluidic systems

By injecting mineral oil (inner phase) and polymer solutions (outer phase), in a microfluidic flow focusing geometry, we observed the formation of cusps. These cusps undergo a transition from a steady state, to a thin cylindrical spout (oil in polymer). These oil spouts, do not touch the walls, and are surprisingly stable (they do not break into droplets). We study the nature of the cusp-spout transition, and find it is of first order. By taking advantage of the stability of the jet, we expect to synthesize micro-wires with this approach.