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 γ . Thus, this thinning of η was related to the weak distortion of the particle distribution. Furthermore, the thermodynamic stress σT estimated from the I(q) profile under the shear increased only weakly with increasing γ , and the corresponding viscosity ηT (=σT/ γ ) was close to the η data. These results strongly suggested that the thinning of the MS suspension reflected the nonlinearity of σT.