The critical divergence of the shear viscosity of a colloid polymer mixture is experimentally found to be as strong as the divergence of the correlation length. This is in contrast with the divergence of the viscosity in atomic and molecular sytems, which is known to be very weak. The different behavior of the shear viscosity of Brownian systems and molecular systems is believed to be due to the long ranged character of the hydrodynamic interactions between the Brownian particles, a type of interaction absent in molecular systems.

• Received 19 August 1996

DOI:https://doi.org/10.1103/PhysRevLett.77.5304