ADSORPTION OF MODEL ASSOCIATIVE POLYMERS ON MONODISPERSE POLYSTYRENE LATEX

Adsorption isotherms of model nonionic associative polymers on monodisperse polystyrene latexes were measured using a modified serum replacement technique to elucidate the relationships among colloidal stability, latex rheology, and the adsorption behavior of model associative polymers. The model associative polymers' structures consist of linear water-soluble poly(oxyethylene) backbones of molecular weights 51,000-100,400 that have been capped with hydroxyl, dodecyl, or hexadecyl end-groups. A minimum amount of associative polymer is required to flocculate the dispersion by bridging; a certain degree of networking among the associative polymers is needed to span the interparticle distance. The degree of flocculation depends on molecular weight and passes through a maximum at a molecular weight near 50,000-80,000 because the driving force for networking decreases, and the length of associative polymer backbone increases, as the molecular weight increases. Restabilization of the latex occurs at larger concentrations of associative polymer, and a homogeneous network of associative polymer and latex particles forms. The molecular areas of adsorption calculated from adsorption isotherms are large, on the order of 2000-20,000 Å2/molecule, and suggest that this restabilization coincides with full coverage of the particle surface by associative polymer. The dependence of the molecular areas of adsorption and the stability of the latex on particle size, hydrophobe length, and associative polymer molecular weight suggest that the polymer conformation on the surface probably consists of loops and trains, with one of the hydrophobic end-groups firmly anchoring the associative polymer and one hydrophobic end-group extending out into the dispersion medium. © 1992.