The interaction of polyelectrolyte-surfactant with interfaces plays a very important role in many technological fields, including cosmetics, food science or drug delivery. This has stimulated the research trying to shed light on the most fundamental aspects governing the adsorption processes and the equilibration of the interfacial layers. The current knowledge of the physico-chemistry of polyelectrolyte-surfactant systems has evidenced that in most of the cases, the association process of polyelectrolyte and surfactant molecules in the bulk is guided by non-equilibrium effects, even though the control of the mixing protocol allows obtaining reproducible aggregates (kinetically trapped-aggregates), with these non-equilibrium effects impacting decisively on their interfacial properties of polyelelectrolyte-surfactant systems. Therefore, the understanding of the interfacial processes involving polyelectrolyte-surfactant mixtures makes necessary the analysis of the association phenomena occurring in the bulk, i.e. the formation of the so-called polyelectrolyte-surfactant complexes, and their impact on the equilibration of the interface.
This work addresses the main physico-chemical aspects related to the formation of polyelectrolyte-surfactant layers at fluid interfaces, combining a careful examination of the equilibrium and rheological properties of the interfacial films with the structural and compositional information obtained using neutron reflectometry. Furthermore, the assembly of the mixtures will be correlated to the bulk association processes trying to provide a comprehensive picture describing the interfacial behavior of polyelectrolyte-surfactant mixtures at fluid interface. This requires the study of combinations of different polycations (poly(diallyldimethylammonium chloride) and chitosan) with surfactant bearing different charge (neutral, anionic and zwitterionic). Thus, it will be possible to obtain a whole perspective of the role of the association processes on the structure and properties of the interfacial layers.