Micro-rheological investigation of dextran solutions using diffusing wave spectroscopy

Diffusing-wave-spectroscopy-based micro-rheology was used to measure the rheological behaviour of dextran solutions of concentration up to 40%. Three dextrans of different molecular weights, namely 2×105, 5×105 and 2×106 Daltons, were studied. It was found that these solutions were mainly viscous, with the loss modulus G″ higher than the elastic modulus G′. However, at high frequencies and for high dextran concentrations, a crossover between G′ and G″ was observed. A plot of the specific viscosity ηsp as a function of the dextran concentration showed two critical concentrations c* and c**. For cc**, ηsp∼c3.8. These results were in very good agreement with those found in the literature.