Vapor sorption in self-assembled gold nanoparticle/dendrimer films studied by specular neutron reflectometry

In the present work, specular neutron reflectometry was used to study the sorption of D2O and perdeuterated toluene in self-assembled Au nanoparticle/poly(amidoamine) composite films. The method provides information about analyte-induced film swelling and analyte distribution profiles across the films. Our data suggest that film swelling upon exposure to the analytes is negligible within the resolution of the method. Strong differences are observed between the distribution profiles of D2O and toluene-d(8). Water penetrates into the film with an exponentially decaying concentration profile. In contrast, toluene-d(8) forms a thin "wetting" layer on top of the film, while the bulk of the film remains essentially analyte free. These results are explained by taking into account the chemical structure of the dendritic polymer used for film preparation.