Two-point microrheology of inhomogeneous soft materials

We demonstrate a novel method for measuring the microrheology of soft visco elastic media, based on cross correlating the thermal motion of pairs of em bedded tracer particles. The method does not depend on the exact nature of the coupling between the tracers and the medium, and yields accurate rheolo gical data for highly inhomogeneous materials. We demonstrate the accuracy of this method with a guar solution, for which other microscopic methods fa il due to thr polymer's mesoscopic inhomogeneity. Measurements in an F-acti n solution suggest conventional microrheology measurements may not reflect the true bulk behavior.