Coagulant mediation of interfacial forces between anionic surfaces

The distance dependent interaction forces between a model clay filler surface, mica, and a model silica microparticle were measured as a function of coagulant treatment chemistries under acidic conditions. Poly(aluminumchloride) and poly(dialyldimethylammonium chloride) coagulants were added at concentrations ranging from 0.5-100 ppm at pH=4.5. At low coagulant dosages, an increase in the attractive forces via a patch charge compensation mechanism was observed. At higher coagulant dosages, charge reversal at the mica-silica interface was evidenced by repulsive interaction forces. The formation of coagulant-poly(anion) complexes on the silica surface yielded a compressible film with repulsive interaction forces observed between the polyelectrolyte complex and mica. Adhesion force measurements were qualitatively consistent with the interpretation of the approach curve data. The experiments and results are discussed with an emphasis on papermaking applications.