Absolute Measurement Of Laminar Shear Rate Using Photon Correlation Spectroscopy

An absolute measurement of the components of the shear rate tensor $\mathcal{S}$ in a fluid can be found by measuring the photon correlation function of light scattered from particles in the fluid. Previous methods of measuring $\mathcal{S}$ involve reading the velocity at various points and extrapolating the shear, which can be time consuming and is limited in its ability to examine small spatial scale or short time events. Previous work in Photon Correlation Spectroscopy has involved only approximate solutions, requiring free parameters to be scaled by a known case, or different cases, such as 2-D flows, but here we present a treatment that provides quantitative results directly and without calibration for full 3-D flow. We demonstrate this treatment experimentally with a cone and plate rheometer.