EFFECT OF SHEAR-FLOW ON POLYMER DESORPTION AND LATEX DISPERSION STABILITY IN THE PRESENCE OF ADSORBED POLYMER

Poly(ethylene oxide) (PEO) and poly(vinyl alcohol) (PVA) molecules were adsorbed on polystyrene (PS) latex as stabilizing agents for the latex dispersion. The effect of shear flow on the desorption of the adsorbed polymer and the flocculation of the latex were investigated by measuring the hydrodynamic layer thickness of the adsorbed polymer and the average particle diameter of the latex with photon correlation spectroscopy (PCS), respectively. For PEO molecules with molecular weights of 100 000 and 900 000, shear flow caused the layer thickness of the adsorbed polymer to decrease rapidly in the early stage and then approach a steady-state value. The average particle diameter showed little change for a short period followed by a rapid increase during the flocculation. The shear rate and molecular weight affected negligibly the layer thickness but considerably the average particle diameter. On the other hand, the layer thickness of the adsorbed polymer showed a small reduction only at a higher shear rate for PVA of molecular weight 15 000. The flocculation behavior was similar to the case of PEO molecules. For PVA with molecular weight 49 000, there was no change of the layer thickness but a slight increase of the average particle diameter after a long shearing time. It was assumed that PVA molecules had a higher resistance to the shear-induced desorption than PEO molecules because of the strong hydrophobic interaction of residual acetate groups in PVA with the surface of PS latex. The shear-induced desorption influenced strongly the flocculation of the latex stabilized with adsorbed polymer.