Exploring dynamics of polymerlike wormlike micelles in high shear flow*

Wormlike micelle solutions entangle and flow like polymers, yet micelles can break and reform. Stress may influence breakage dynamics and the microscopic behavior of these fluids at high stress is not understood. We explore this behavior in pressure-driven microchannel flow. Velocity profiles are measured with high resolution using holographic 3D microparticle tracking velocimetry, to determine the relationship of stress and shear rate. As reported by others, this relationship depends on wall stress and channel dimensions and suggests diffusive processes whose rate depends on channel dimension. We therefore are measuring the local solution concentration with fluorescence microscopy, to explore molecular diffusion. We compare our velocity and concentration profiles to theoretical models that include a diffusive term in the stress balance, which becomes relevant at small channel dimensions.