The effects of adsorbed layers and solution polymer on the viscosity of dispersions containing associative polymers

Abstract

Associative polymers adsorb on polymer lattices via hydrophobic interactions to generate dense layers that increase the hydrodynamic size of the particles but also reduce the polymer concentration in solution, thereby decreasing the continuum viscosity. The telechelic polymers employed in this work adsorb at low concentrations with both hydrophobes on the surface but at the concentrations of general interest have one hydrophobe free to couple with micelles in solution and adsorbed layers on other particles. Detailed measurements of adsorption and the steady shear viscosity of the dispersions provide consistent quantitative support for this scenario. The adsorbed amounts and layer thicknesses of hydrophobically modified poly(ethylene oxides) on poly (methylmethacrylate) particles suggest a dense layer of moderately stretched chains in very dilute dispersions. At higher concentrations, adsorption increases the intrinsic viscosity [eta], by an amount consistent with the measured layer thickness, and the Huggins coefficient k(h). The former indicates strong coupling with the associated solution, equivalent to a no slip boundary condition. The value of kh exceeds that for hard spheres implying direct coupling between adsorbed layers,of interacting particles. Thus the observed enhancement of the dispersion viscosity arises from the high viscosity of the polymer solution, the increased hydrodynamic volume of the particles, and direct interactions between adsorbed layers. (C) 1998 The Society of Rheology.