Shear viscosity of a near-critical binary system analyzed with variable-temperature atomic force microscopy

Variation in shear viscous drag in a near-critical binary mixture was measured between a hydrophilic probe sphere and a hydrophilic substrate down to a distance range comparable to or smaller than the correlation length ξ using a magnetic excitation method of atomic force microscopy at temperatures T=Tc−∆T with ∆T varying from 0.1 to 0.7 K. As the temperature approached the Tc, the increase in the drag coefficient toward the zero distance was observed to be less pronounced in the distance range below ca. 100 nm. The data was discussed as arising from suppression in a concentration gradient in the intersurface region due to the overlap of the affected layers on similar surfaces.