Spatially resolved microrheology through a liquid/liquid interface.

We present a light-scattering technique for the measurement of the microrheological properties of viscoelastic liquids in small volumes over a large frequency range (on the order of eight decades). The accuracy of the method for model viscoelastic liquids (polyethylene oxide solutions in water) is demonstrated by comparing the results with conventional mechanical measurements of the loss and storage moduli. Then we show that the method can be used to measure variations in viscoelastic properties in a heterogeneous system by measuring the variation in the moduli with position (and time) across a liquid/liquid interface between a viscoelastic polymer solution and a Newtonian liquid.