The paper deals with the correlation between the internal structure and dynamics of polyelectrolyte multilayers on one hand and their functional properties on the other hand. It considers different concepts of multilayer formation like driving forces, adsorption kinetics, mode of growth and stability aspects. A further focus is the control of internal structure and dynamics which is of high impact with respect to the design of stimuli-responsive material.

The present review is a topical survey of the disjoining pressure in thin liquid foam and emulsion films from both the experimental and the theoretical points of view. Section 2 deals with the latest research work on experimental techniques with which the disjoining pressure Π in foam, emulsion, and pseudo-emulsion films can be measured. Although a lot of techniques are available, the question of the origin of the charges at the water/air and the water/oil interfaces of films, which are stabilized by non-ionic surfactants, has not yet been answered. We address this question in section 3, reviewing the latest relevant literature. The relevance of structural forces for the disjoining pressure is outlined in section 4, which focuses on films which are stabilized by surfactant/polyelectrolyte mixtures.

The influence of ionic strength and polymer charge density on the multilayer formation of strong polyelectrolytes is investigated by X-ray reflectivity. To a first approximation the adsorption behavior as a function of the degree of charge, f, is binary:  For f ≤ 50% the films are one order of magnitude thinner than those for f ≥ 75%. This is due to a threshold of charge overcompensation after each adsorption step which seems to be at f between 50% and 75%. Above the charge reversal limit the thickness and the surface roughness increase with decreasing polymer charge. Below a charge density of 50% the film thickness cannot be changed by salt additive whereas the film thickness increases with c NaCl 1/2 above a degree of charge of 75%. The density of all investigated films is quite similar.

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The swelling behavior of layer-by-layer assemblies of poly(styrenesulfonate) sodium salt (PSS) and poly(allylamine hydrochloride) (PAH) with various number of layers were investigated. The data presented in this paper suggest that swelling and deswelling are completely reversible and reproducible. At 99% relative humidity, a pronounced “odd−even effect” in the swollen thickness is observed depending on the type of polyelectrolyte in the outermost layer. Contact angle measurements confirmed that the PSS surface is more hydrophilic than the PAH surface. The “odd−even effect” indicates that water has to be pressed out of the multilayer when PAH is adsorbed onto the PSS surface of the multilayer and that again more water penetrates into the multilayer on adsorption of the next PSS layer. It was also found that the relative amount of swelling with respect to the total film thickness decreases with increasing number of layers. This is an indication that the loosely packed outer layers are more sensitive to environmental humidity and consequently swell in a significantly more pronounced way than the inner ones closer to the substrate.

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