Rheology of polymer solutions using colloidal-probe atomic force microscopy

International audienceWe use colloidal-probe atomic force microscope (AFM) to study the rheological behavior of polymer solutionsconfined between two surfaces: the surface of a sphere and a flat surface on which the fluid is deposited.Measurements of the hydrodynamic force exerted on the sphere by the flowing liquid allowed retrieving theviscosity of the solution for different distances between the sphere and the flat surface. This method has beenexperimentally tested for Newtonian fluids for which the viscosity does not vary versus the gap dimensions. Onthe other hand, for non-Newtonian fluids, such as the large molecular weight polymer solutions used here, themeasured viscosity depends on the gap height D between the flat surface and the sphere. The decrease of theviscosity versus gap height is similar to previously observed variations in colloidal suspensions. Depletion ofpolymers in the gap region due to the high shear rates involved is a possible cause for such a variation