Spread films of synthetic polyelectrolyte-surfactant complexes: Dilational viscoelasticity and effect on water evaporation

Data are presented on the dynamic surface properties of films formed from sodium polystyrenesulfonate-dodecyltrimethylammonium bromide (PSS-DTAB) and poly(diallyldimethylammonium chloride)-sodium dodecyl sulfate (PDADMAC-SDS) complexes by the spreading of the above substances onto a water surface from their concentrated solutions. These films are shown to be stable up to surface pressures of 20 mN/m (PSS-DTAB) and 37 mN/m (PDADMAC-SDS). In the latter case, when the limiting surface pressure is reached, microaggregates are formed in the surface layer along with the film dissolution. The surface films in question markedly decelerate water evaporation, and this phenomenon cannot be explained in terms of the classical Goddard model of the structure of films prepared from polyelectrolyte-surfactant complexes and, at the same time, is in good agreement with a recently proposed model that takes into account hydrophobic interactions.