Structural changes in stimuli-responsive nanoparticle/dendrimer composite films upon vapor sorption

Au-nanoparticle/dendrimer composite films are stimuli-responsive materials with a potential application as highly sensitive chemiresistive sensors, since their conductance strongly changes upon sorption of chemical species from vapor phase. Here we report on the neutron reflectometry studies on such films exposed to water, methanol, and toluene vapors as external stimuli. Poly (amidoamine) (PAMAM) dendrimer third generation and poly (propylene imine) (PPI) dendrimer fourth generation were used to build up the films.The interaction between the film and the vapor is mainly governed by the chemical nature of the dendrimer component. Both AuPAMAM and AuPPI films have well expressed affinity to water. The more hydrophilic PAMAM adsorbs about 3 times more water than the more hydrophobic PPI. In contrast, the diffusion of toluene is limited to a thin region near the film/gas phase interface where a thin wetting layer of toluene is registered. Methanol as a solvent with transitional hydrophilicity shows intermediate behavior when interacting with the films.Since this work is largely based on neutron reflectometry we point out that this technique is outstanding in resolving fine details of film response to vapors which is important to understand the changes that occur in the vapors sensing process.