Flow velocimetry measurements are made on a non-shear-banding wormlike micellar solutionwithin high-aspect-ratio rectilinear microchannels over a wide range of imposed steady flow rates.At the lowest and highest flow rates tested, Newtonian-like velocity profiles are measured.However, at intermediate flow rates the velocity field never stabilizes on the timescale of theexperiments (up to several hours). Here, spatiotemporally dependent ¿jets¿ of high velocity fluidare observed to fluctuate within regions of essentially stagnant fluid. The reason for this flowinstability remains undetermined, but it has significant consequences for many industrialapplications and also for microfluidic rheometry of complex fluids.
展开▼
