Adsorption and surface-induced precipitation of poly(acrylic acid) on calcite revealed with atomic force microscopy

Adsorption of high-molecular mass poly(acrylic acid) (PAA) was investigated at the water–calcite interface by atomic force microscopy (AFM). The adsorption process was studied for different PAA concentrations in the presence of calcium and sodium ions at pH 9. Three principal adsorption regimes were identified. At low PAA concentrations around 0.1 mg/L, the adsorbed layer is composed of individual globules consisting of about 100 molecules. At concentrations around 1 mg/L, individual adsorbed molecules are observed. At concentrations above 10 mg/L, the adsorbed film consists of individual globular clusters containing about 1000 molecules. At even higher concentrations, irregular networks form at the surface by aggregation of these clusters. The layers formed at low concentrations are stable upon washing with water of the same pH. The layers formed at higher concentrations are unstable upon washing, and they transform into extended networks.