Adsorption of polyelectrolyte and nanoparticles at the silica-aqueous solution interface: Influence of the history of additions of the two components

The interfacial properties of a mixed system of low-charged cationic polyel ectrolyte and silica nanoparticles has been studied by means of ellipsometr y. Special attention was devoted to the effect that the order of addition o f the two components has on the adsorption behavior of the mixed system. Ad sorption on silica was in one case studied after simultaneous addition of t he components to the aqueous solution. The measured adsorption rates were t hen much slower than expected for a mass-transfer limited process. This beh avior signifies the presence of an electrosteric barrier arising due to pre adsorbed polymer-particle complexes. Interfacial layers containing particle s were at plateau conditions shown to be highly swollen, whereas the cation ic polymer in the particle-free systems adopted a more flat surface conform ation. The layer thickness was observed to monotonously increase with an in creasing presence of nanoparticles in solution, while the surface excess sh owed a maximum at intermediate values. The finding was rationalized by the competition between particles and the surface for polymer charges leading t o swelling and a decreased effective interaction between polymer and surfac e. In the other case studied, when polyelectrolyte and nanoparticles were a dded sequentially, a much more rapid concentration-dependent adsorption was observed. The kinetic adsorption barrier for nonassociated particles was c learly negligible compared with that for the polymer-particle complex. The surface excess did not exhibit an adsorption maximum as a function of added nanoparticles in this situation, indicating that the polymer layer to some degree is irreversibly anchored at the silica surface. Some implications o f the above findings for practical papermaking using multicomponent retenti on systems are put forward. (C) 2001 Academic Press.