Effect of sodium polyacrylate on the properties of dilute and concentrated BaSO4 dispersions

Abstract

The adsorption of sodium polyacrylate on BaSO₄ particles has been studied and the adsorption characteristics have been related to the properties of both dilute and concentrated dispersions. The extent of particle aggregation has been monitored by turbidity or viscosity measurements for dilute and concentrated dispersions, respectively. For dilute dispersions, the results show that in the absence of electrolyte, aggregation is prevented when the extent of adsorption is much less than plateau coverage. The e.s.r. technique reveals that the polyanions are adsorbed in ‘trains’ under these conditions and, since the zeta potential is sufficiently high, charge stabilisation predominates. For concentrated dispersions the same mechanism is effective once a critical polymer concentration has been reached, this concentration being greater than that for dilute dispersions but still less than plateau coverage. This is possibly due to the requirement of a more uniform charge distribution. In the presence of electrolyte the amount of polymer necessary to bring about stabilisation corresponds closely to the amount of polymer adsorbed at the end of the high-affinity region of the adsorption isotherm for both dilute and concentrated dispersions. Under these conditions the adsorbed polymer adopts a more extended configuration with loops and tails protruding out into solution, thus enabling steric repulsive forces to come into operation.