(482e) Microbubble Streaming Flows in Viscoelastic Fluids: Flow Patterns Induced By a Square Wave

Microbubble streaming is a phenomenon where vortex flows are induced by an oscillating micro-sized bubble. We have studied steady microstreaming induced by a semi-cylindrical oscillating bubble trapped in a side channel attached to a microchannel. Experiments have been performed to study the effect of viscoelasticity on the flow pattern, which shows a different trend than in Newtonian fluids. We found that the flow pattern is changed at a certain frequency depending on the concentration and the molecular weight of a polymer solution. We also found that the transition frequency becomes much lower in oscillation by a square wave than by a sin wave. We will discuss a possible microfluidic application of the square wave bubble streaming to measurement of relaxation time for dilute polymer solutions.