The rheological behavior and microstructure of shear-thinning suspensions of core-shell structured carboxylated latex particles were examined. The steady shear viscosity of the suspension increased with increasing dissociation of the carboxyl groups or increasing particle concentration, however the critical shear stress sigma(c) and inter-particle distance xi of the microstructure did not change. With increasing particle diameter, sigma(c) increased and decreased. These results were consistent with a Brownian hard sphere model, in which competition exists between the bulk mass transfer due to the applied field and diffusion of the particles. We confirmed that Ore depends on, Lis expressed by sigma(c), = 3k/4 pi xi(3). This relationship is consistent with the dynamics of it Brownian hard sphere model with particle diameter. Thus the dynamics of shear-thinning Suspensions of core-shell particles can be explained by a Brownian thermodynamic model. (c) 2005 Elsevier Inc. All rights reserved.