Comparing macrorheology and one- and two-point microrheology in wormlike micelle solutions

We present here a comparison between three rheological techniques to verify a recently developed optical microrheology technique. As a model viscoelastic fluid we have used wormlike micelle solutions which are well-characterized Maxwell fluids. Using the same samples, we have measured the viscoelastic response function using macroscopic rheology as well as one-particle and two-particle microrheology. With all three techniques we have obtained frequency-dependent complex shear moduli over large and overlapping frequency ranges. Excellent agreement of the results from all three techniqes was observed. This was expected given that characteristic length scales of the solution, such as persistence length and mesh size, were significantly smaller than the probe particle size. Our results provide a much needed quantitative verification of microrheology on a simple model system.