Viscoelastic rheology of polymer solution probed by resonant thermal capillary fluctuation

We present a measurement of viscoelastic properties of polymer solutions using resonant thermal capillary fluctuations of the surface of a polymer solution droplet. The instantaneous deflection of a cantilever in contact with the drop surface allows for measuring the nanoscale thermal fluctuations of the interface. From the power spectral density of measured fluctuations, we determine the two components of the rheological (dynamic and elastic viscosity) response of the fluid. Our experimental results were compared with rheological measurements using a classical commercial rheometer. We find a good agreement between the two measurements. Our experiments allow to extend the range for dynamical measurements of rheological properties of the solutions up to 20 000 s-1. Furthermore, our method requires only a small volume of liquid (10 mu l) to measure the viscosity and is thus suitable for measurements on precious liquids.