Adsorption of an amphoteric polymer on barium sulphate and its effect on colloid stability

Abstract

This paper describes the adsorption of an amphoteric polymer on BaSO4 crystals and demonstrates its ability to enhance greatly the colloid stability of BaSO4 dispersions. The adsorption capacity of BaSO4 increases with increasing ionic strength, with isotherms in both water and electrolyte showing shoulders following an initial high-affinity portion. Colloid stability increased sharply at polymer coverages higher than the end of the high-affinity portion of the adsorption isotherm. At saturation coverage the particles were unstable only between pH 4 and 5, which is also the pH range over which the polymer in solution precipitated. On increasing the ionic strength of the dispersion medium at pH 4.3 the polymer-covered crystals decreased their extent of flocculation. At pH values outside the range 4–5, the crystals with polymer at saturation coverage were stable in 3 mol dm–3 NaCl, which is far in excess of the critical coagulation concentration normally associated with charge-stabilised dispersions.