This work aims at a better understanding of the interaction between a polycationic quaternary amine polymer (F25) and three different clay minerals: montmorillonite, illite, and kaolinite. For this, adsorption isotherms of F25 on the clay surfaces were measured together with the evolution of the CEC along the isotherm, which revealed that cation exchange plays an important role in the adsorption process. These first results were confirmed by XRD measurements on dried powders that are evidence in the case of montmorillonite of the presence of polymer in the interlayer spaces. In addition, the evolution of the short range structure of clay minerals suspensions on polymer adsorption was followed by WAXS experiments. Polymer intercalation was observed while the structure of the resulting stacking appeared to change slightly along the polymer adsorption isotherm. Diffuse reflectance infrared measurements revealed that significant conformational changes Occur on polymer adsorption onto montmorillonite surfaces. Furthermore, adsorption above the CEC is observed which involves a charge reversal of clay mineral Surfaces, the zero charge being reached for an adsorbed amount corresponding to the CEC. Finally, flocculation was discussed compared to adsorption amounts and zeta potential measurements, confirming that Optimum flocculation concentration is reached for noncharged particles. (C) 2009 Elsevier Inc. All rights reserved.