Adsorption of linear and star-shaped poly(acrylic acid) to model surfaces formed by amphiphiles at the air/water interface

Abstract

Monolayers of dioctadecyldimethylammonium bromide (DODA) and an azobenzene containing ammonium amphiphile at the air/water interface have been used as model surfaces to study the polyelectrolyte adsorption. The influence of the polyelectrolyte architecture on the adsorption process was studied using linear and star-shaped poly(acrylic acid)s, which have been synthesized by atom transfer radical polymerization. The differences in the polyelectrolyte structure result in different structures of the polyelectrolyte-amphiphile-complex monolayer at the air/water interface. Compared to the amphiphiles on pure water the area per molecule is significantly enlarged for all polyelectrolyte complexes, the most for complex with the six-arm-star. Moreover, UV/ Vis-spectroscopical measurements indicate that chromophore aggregation is supressed by the complexation with poly(acrylic acid)s. The differences in monolayer properties between the pure amphiphile monolayer and the polyelectrolyte complexes monolayer can be employed for the in situ investigation of the adsorption of the polyelectrolyte to an already compressed amphiphile monolayer. Preliminary experiments were carried out by monitoring the change of the surface pressure during adsorption over time, and significant differences between linear and star-shaped poly(acrylic acid) were found. © Wiley-VCH Verlag GmbH, 2000.