Cusps, spouts and microfiber synthesis with microfluidics

Abstract

We produced jets of two immiscible liquids in a standard microfluidic flow focusing geometry, using semi-dilute aqueous polymer solutions as the external phase and immiscible liquids, oil or photocurable polymers as the internal one. We map out the different flow regimes on a “phase diagram”. Two new flow regimes – oscillatory jet and spout – are observed, as a result of the non-Newtonian behavior of the external phase. In the spout regime, cusp-shaped interfaces form at the junction, emitting extremely small round jets (spouts), with diameters ranging between 1.2 and 7 μm, i.e. an order of magnitude smaller than the microchannel cross-sectional dimensions. These spouts are found to be stable over remarkably long distances. We analyze the properties of the cusps and the spouts in some detail. The system can be utilized to synthesize fibers of micrometric sizes: the fibers we obtained, under different flow conditions, have diameters ranging between 1.8 and 14 μm and lengths ranging between 0.5 mm and 2 centimeters.