Adsorption of an amphoteric polymer on silica and its effect on dispersion stability

Abstract

The adsorption of an amphoteric polymer from aqueous solution onto silica particles has been studied. The polymer adsorption capacity increased considerably in the presence of electrolyte and the adsorbed polymer configuration was shown to be predominantly flat for adsorption from pure water at pH 6.5, but to be very extended for adsorption from 0.5 mole dm −3 NaC1 or in the presence of surfactants (10 −2 mole dm −3). The stability of the dispersions has been monitored under various conditions such that in water at pH 6.5 they were found to be stable at all polymer concentrations, while in 0.5 mole dm −3 NaC1 (at pH 6.5) the polymer needed to be present to a surface coverage corresponding to the end of the high affinity region of the adsorption isotherm before stability was attained. In the absence of electrolyte and at saturation coverage, the dispersions flocculated at about pH 3.3, which corresponds to the point of zero charge for the polymer coated particles and also between pH 3.9 and 4.8 where the polymer itself precipitated from solution.