Investigation on the adsorption mechanism and model of didodecyldimethylammonium bromide on ZnO nanoparticles at the oil/water interface.

• The ZnO NPs could further reduce the IFT in the mixed surfactants/NPs system. • DDAB molecules could adsorb on ZnO NPs and tend to form hemimicelles. • The modified NPs prefer synergizing with surfactants to further reduce the IFT. • DDAB adsorption processes with and without ZnO NPs are controlled by the DKC model. We systemically evaluated the effects of the additional ZnO nanoparticles (NPs) on the interfacial activity of the cationic surfactant didodecyldimethylammonium bromide (DDAB) with two hydrophobic chains by the interfacial tension (IFT) measurement and emulsification experiments. The addition of ZnO NPs greatly improved the interfacial activity of the mixed ZnO/DDAB system at the oil/water interface. The zeta potential and fluorescence spectra of the mixed ZnO/DDAB dispersions were investigated to explore the adsorption behavior of DDAB molecules on ZnO NP surfaces. The IFT between a homologous series of n-alkanes and DDAB aqueous solutions in the absence and presence of ZnO NPs was measured to explore the mechanism of the further IFT reduction caused by the additional ZnO NPs. The dynamic IFT data were fitted with two different models. The results indicated that the DDAB adsorption processes in the absence and presence of ZnO NPs were controlled by the mixed diffusion-kinetic controlled model. [ABSTRACT FROM AUTHOR]