Temperature dependence of the shear viscosity of sterically stabilised polymer colloids

Abstract

The steady shear viscosity of poly(methyl methacrylate) particles, sterically stabilised by terminally anchored polydimethylsiloxane and dispersed in n-hexadecane, have been measured as a function of shear rate, particle concentration and temperature. It was found that the dispersions were shear thinning, the degree of shear thinning, increasing with increasing particle concentration. For the least concentrated dispersion, φ= 0.079, the viscosity was found to decrease with increasing temperature. This occurs because the viscosity of the dispersion is dominated by the viscosity of the n-hexadecane. However, for particle concentrations with φ≳ 0.1 the viscosity was found to increase with increasing temperature. From a simple model it was concluded that colloidal interactions are not important in this particle-size and shear-rate regime and that hydrodynamic effects dominate the viscous response. It was found that the viscosity data could not be fitted to a hard-sphere hydrodynamic model for the dispersion. The model is thought to be unsatisfactory because the particles are stabilised by a ‘thick’ flexible steric barrier, which is likely to have a significant effect on the hydrodynamic and microstructural properties of the dispersion.