Solution and adsorption properties of hydrophobically associating water-soluble polyacrylamides

The behavior in aqueous solution and at a solid/liquid interface of an associating hydrophilic/hydrophobic copolymer of acrylamide and alkyl methacrylate has been studied. A comparison between the behavior of hydrophobically associating and of non-associating polymers termed HAPAM and PAM, respectively of the same molecular weight indicates the role played by the hydrophobic moieties. Viscosity measurements in solution show the behavior expected of HAPAM compared to PAM i.e. a smaller intrinsic viscosity measured in the dilute regime and a larger viscosity in the semi-dilute regime. At the water/mineral interface, adsorption isotherms for HAPAM show an unusual shape, characterized by the absence of a plateau region and a continual increase in the adsorbed amount with polymer concentration in the bulk. The enhancement of polymer chain interactions in solution and the increase in the adsorbed amount on a mineral surface are observed within the same polymer concentration range. This particular adsorption shape can be explained by the formation of multiple layers through hydrophobic associations, the adsorbed layers being formed in part by some chains that are not directly in contact with the surface. The influence of KCl concentration has been studied. Modification of the polymer solution rheological properties and of the adsorbed amount of polymer leads to a strengthening of hydrophobic interactions in the presence of KCl.