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.