Alumina interaction with AMPS-PEG random copolymer: II. Stability and rheological behavior

A study has been undertaken concerning the interaction of copolymers of acrylamido-sulfonic acid sodium salt and polyethyleneglycolmethacrylate (AMPS-X) with alumina particles. Electrokinetic analysis indicated that adsorption of the copolymer is accompanied by a shift in the isoelectric point (IEP) towards acid pH values. Above a certain concentration, of the order of 0.8 wt.%, the absolute value of the zeta potential |ξ| reaches a saturation plateau. The higher the fraction of ionic groups in the polymer, the higher the plateau level. The rheological behaviour is greatly affected in the presence of added polymer; the viscosity of the alumina suspension decreases and reaches an optimum, which is all the lower as the fraction of the ionic groups is higher. Adding AMPS-X copolymer increases the stability of the suspension via electrostatic effects, but also via steric effects induced by the polyethyleneglycol (PEG) segments. The steric contribution to the stabilisation process is relatively small, probably due to the short length of the PEG chain.