Kinetic effects in mixed polymer layers at particle/solution interfaces: non-equilibrium states of uncharged polymers

The interfacial processes controlling the structure of mixed adsorption layers of uncharged polymers at particle/solution interfaces were studied. Under equilibrium conditions for simultaneous competitive adsorption from ternary polymer solutions, preferential adsorption parameters for the polymers in pairs have been determined on negatively charged colloidal dispersions and used as a measure of the affinity for surface sites of chemically different polymer molecules. The spatial properties of the interfacial polymer layers after various contact times were investigated by photon correlation spectroscopy (PCS), laser Doppler-electrophoresis (LDE) and at low polymer dosages, by flocculation kinetic measurements. It was found that long-term kinetic effects have a marked effect on the structure of composite interfacial layers. At low surface coverages, competition for partially covered particle surfaces of suitable polymers may lead to the formation of extended mixed adsorption layers. Displacement from the interfaces of the less preferred polymer results in either increase or decrease in time of both the hydrodynamic and the electrophoretic thicknesses in the mixed layers. The non-equilibrium states of the adsorbed macromolecules, existing over much longer period in the mixed layers than in the individual polymer layers, closely correlate to the preferential affinity for surface sites of the competing macromolecules.