Viscoelasticity and generalized Stokes-Einstein relations of colloidal dispersions

BANCHIO, A. J.; NÄGELE, G.; BERGENHOLTZ, J.

JOURNAL OF CHEMICAL PHYSICS

Año: 1999 vol. 111 p. 8721 - 8721

0021-9606

The linear viscoelastic and diffusional properties of colloidal model dispersions are investigated andpossible relations between the ~dynamic! shear viscosity and various diffusion coefficients areanalyzed. Results are presented for hard sphere and charge-stabilized dispersions with long-rangescreened Coulomb interactions. Calculations of the dynamic long-time properties are based on a(rescaled) mode coupling theory (MCT). For hard sphere suspensions a simple hydrodynamicrescaling of the MCT results is proposed which leads to good agreement between the theory andexperimental data and Brownian dynamics simulation results. The rescaled MCT predicts that thezero-shear limiting viscosity of hard sphere dispersions obeys nearly quantitative generalizedStokes?Einstein (GSE) relations both with regard to the long-time self-diffusion coefficient and thelong-time collective diffusion coefficient measured at the principal peak of the static structure factor.In contrast, the MCT predicts that the same GSEs are violated in the case of dispersions of highlycharged particles. The corresponding short-time GSEs are found to be partially violated both forcharged and uncharged colloidal spheres. A frequency dependent GSE, relating the elastic storageand viscous loss moduli to the particle mean squared displacement, is also investigated, Accordingto MCT, this GSE holds fairly well for concentrated hard spheres, but not for charge-stabilizedsystems. Remarkably good agreement is obtained, however, with regard to the frequencydependence of the Laplace-transformed reduced shear stress relaxation function and theLaplace-transformed reduced time-dependent self-diffusion coefficient for both charged anduncharged particle dispersions.