Rheo-SANS study of an aqueous suspension of poly (methyl methacrylate-co-styrene) particle

For an aqueous suspension of poly (methyl methacrylate-co-styrene) (MS) particles, viscosity η and small-angle neutron scattering (SANS) intensity I(q) were measured under steady shear. The MS particles had partially screened surface charges. In the quiescent state, the particle distribution detected through the I(q) profile was isotropic and essentially liquid-like but also exhibited a weak, local order. Under steady shear, this distribution was distorted just moderately, and the η strongly decreased with increasing shear rate γ̇. Thus, this thinning of η was related to the weak distortion of the particle distribution. Furthermore, the thermodynamic stress σ_T estimated from the I(q) profile under the shear increased only weakly with increasing γ̇, and the corresponding viscosity η_T (=σ_T/γ̇) was close to the η data. These results strongly suggested that the thinning of the MS suspension reflected the nonlinearity of σ_T.