Adsorción de polielectrolitos de baja densidad de carga sobre superficies sólidas y fuerzas de interacción superficial

Abstract

Polymer adsorption in aqueous media and related interactions forces play an important role in many industrial applications that involve aggregation, flocculation, coagulation or colloidal particles dispersion phenomena. In this study X-Ray photoelectron spectroscopy and ellipsometry are employed to investigate the adsorption of low-charge-density cationic polyelectrolytes on negatively-charged surfaces (mica and silica). Additionally, the interferometric surface force apparatus is used to evaluate the interaction forces between polyelectrolyte-covered surfaces.It is demonstrated that in the case of polyelectrolytes of high molecular weight and low charge density, the adsorption mechanism is limited by steric factors with the effect of surface charge (or surface potential) being secondary. Aditionally, it is established that an increase of the ionic strength of the medium produces desorption of the polyelectrolyte with a simultaneous increase in the thickness of the adsorbed layer. This latter effect is frequently explained by the increase of the adsorbed amount. However, the occurrence of this phenomenon in the present case is explained by the reduction of polyelectrolyte-surface affinity and the fact that the adsorbed polyelectrolyte swells at the solid/liquid interface. Finally, the conformation of the adsorbed polyelectrolyte is discussed as well as its effect in the development of interparticle forces.