HYDRODYNAMIC INTERACTION OF PARTICLES WITH GRAFTED POLYMER BRUSHES AND APPLICATIONS TO RHEOLOGY OF COLLOIDAL DISPERSIONS

We calculate the lubrication force that acts in the normal direction b etween spherical surfaces bearing grafted polymer brushes and immersed in a viscous fluid. Brinkman's equation is employed to describe the f low in the brushes. For noncompressed brushes we include a slip approx imation that applies to poorly permeable brushes of arbitrary density profile. For the step-function profile we present an analytical repres entation of the force valid for any separation. For compressed brushes we assume the density to increase homogeneously through the gap depen ding only on the local separation and derive an integral representatio n for the force along with analytical approximations valid up to rathe r strong compression. Our results generalize earlier estimates, provid ing convenient representations for analyses of hydrodynamic interactio n between polymerically stabilized colloidal particles. As the simples t application we calculate the viscosity of a non-Brownian suspension of such particles for comparison with the. measured high-shear viscosi ty for polymerically stabilized lattices.