Molar mass selectivity in the adsorption of polyacrylates on calcite

Aqueous solutions of polyacrylates, with a wide molar mass distribution, ha ve been equilibrated with aqueous dispersions of calcium carbonate particle s. In mixtures with excess polyacrylates, it is found that only a fraction of the original collection of macromolecules adsorbs on the mineral surface s. The adsorbed macromolecules have been recovered, and their molar mass di stribution has been measured using size exclusion chromatography (SEC). It is found that a narrow fraction with intermediate molar mass is preferentia lly adsorbed. This selection results from a kinetic process where these mac romolecules are the first to bind to the surface. Smaller macromolecules do not bind at all and larger ones could bind, but are repelled by the macrom olecules that arrived first at the surface. (C) 2000 Elsevier Science B.V. All rights reserved.