The strong influence of particle formation in colloidal polyelectrolyte/surfactant mixtures on the static and dynamic interfacial properties is presented. Mixtures of poly(ethylene imine) (PEI) and sodium dodecyl sulfate (SDS) were first studied using neutron reflectometry (NR) and ellipsometry at the expanding air/water interface of an overflowing cylinder. The formation of bulk aggregates has very different consequences on the dynamic interfacial properties depending on the polyelectrolyte charge density, as shown by the ellipsometry data in the figure. At low charge density (high pH), bulk aggregates deplete the solution of surface-active monomers and small complexes, yet the particles cannot adsorb to the dynamic liquid interface as a result of their slow diffusion. In contrast, at high charge density (low pH), bulk aggregates are transported to the surface by convection followed by their reorganization to spread transient thin patches of polymer and surfactant across the interface. The same mixtures were then studied using NR at the solid/liquid interface with solid surfaces located both above and below the bulk liquid. Very different interfacial properties at different surfaces of the same sample show that gravity plays a key role in the delivery of nanostructured particles into the adsorption layers. The diverse effects of bulk aggregation on the interfacial properties of PEI/SDS mixtures highlights a gap between our current understanding of polymer/surfactant mixtures at interfaces and their optimization under conditions used in processing and applications.

Effects of bulk aggregates on PEI/SDS adsorption layers at static and dynamic interfaces: Depletion vs. penetration vs. spreading

246th National Meeting (2013)

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