Steady streaming rheology for non-Newtonian fluids

Microfluidic rheometry of complex fluids has received much attention in the last decade and methods are in place to measure shear viscosity, extensional viscosity, and more recently, relaxation time. In this work, we discuss an experimental study on the use of steady streaming for rheology of dilute viscoelastic liquids. An oscillatory flow field is setup in a microfluidic channel using an electroacoustic transducer over a range of frequencies (≤ 1 kHz). The resulting steady streaming flow around a cylindrical post is observed using stroboscopic and high-speed imaging of passive tracer particles on an inverted microscope. The velocity fields are acquired through particle tracking velocimetry methods and the effect of elasticity is quantified by a systematic comparison with a Newtonian liquid as a function of excitation frequency and non-dimensional oscillation amplitude.