Determining concentration depth profiles of thin foam films with neutral impact collision ion scattering spectroscopy

Adsorption of ionic surfactants at the air-water interface: The gap between theory and experiment

We review the experimental and theoretical results for the adsorption and structure of ionic surfactants at the air-liquid interface. The results show that ionic surfactants form thick adsorption layers at the interfacial region. We also review several adsorption models for ionic surfactants, which become increasingly complex as they capture the many features of adsorption layers. However, the adsorption layer structures determined by experiments and the structures predicted by models do not match because most models assume very thin adsorption layers. We show the discrepancies between measured and predicted surface properties and provide several explanations. We conclude that the mismatch in the adsorption layer structure provided by experiments and the structure provided by adsorption models is the main reason for the discrepancies in the surface excess and the surface potential.

New insights into the structure of PAMAM dendrimer/gold nanoparticle nanocomposites

In this work, we have employed a suite of complementary analytical techniques to shed light on the nanocomposite structures formed during gold nanoparticles (AuNPs) synthesis in the presence of poly(amidoamine) (PAMAM) dendrimers. Nanocomposites of AuNPs and either fourth or eighth generation amine-terminated PAMAM dendrimers (G4 or G8) were prepared. The size distributions of AuNPs and the nanocomposites were determined by transmission electron microscopy. Atomic force microscopy phase imaging and neutral impact collision ion scattering spectroscopy (NICISS) were utilized for the first time to investigate and compare nanocomposite structures formed from G4 and G8. Our results suggest that G4 stabilized the AuNP by capping the AuNP particle surface but that a certain fraction of the gold surface was still barely covered. In contrast, the metal nanoparticle surface was completely covered by G8. In addition, NICISS results provided evidence that nanocomposites deformed when being deposited directly onto a substrate.