  The common rules of classical nonequilibrium thermodynamics do not allow an
Onsager coefficient like the viscosity to depend on the shear rate. Such a
dependence is experimentally well documented, however. In this paper it is
shown, using nonequilibrium thermodynamics alone, how it is possible that the
effective viscosity coefficient of an isotropic colloidal system depends on
both the shear rate and the frequency.
