On the viscosity and shear modulus of strongly interacting colloids

The authors have studied the viscosity of dilute suspensions of strongly interacting monodispersed colloidal particles. Theoretically one finds that the viscosity can be calculated from the infinite frequency shear modulus times a Maxwellian relaxation time G^infinity tau , where G^infinity is obtained from the interactions and tau depends on the interparticle spacing but is independent of the interactions over the physically interesting range. Experimentally it is found that this relation holds quantitatively when G is identified with the shear modulus extrapolated from measurements on colloidal crystals, and when tau is taken as a 'Lindemann time'-the time for a particle to diffuse approximately ¹/₁₀ of the distance to a near neighbour-a similar value results from the calculations. Thus for the Brownian dynamics of colloids it is possible to completely determine the viscosity of the melted state from measurements of the solid.