Wetting of surfaces decorated by gas-phase synthesized silver nanoparticles: Effects of Ag adatoms, nanoparticle aging, and surface mobility

The wetting state of surfaces can be rendered to a highly hydrophobic state by the deposition of hydrophilic gas phase synthesized Ag nanoparticles (NPs). The aging of Ag NPs leads to an increase in their size, which is also associated with the presence of Ag adatoms on the surface between the NPs that have a strong effect on the wetting processes. Furthermore, surface airborne hydrocarbons were removed by UV-ozone treatment, providing deeper insight into the apparent mobility of the NPs on different surfaces and their subsequent ripening and aging. In addition, the UV-ozone treatment revealed the presence of adatoms during the magnetron sputtering process. This surface treatment lowers the initial contact angle of the substrates and facilitates the mobility of Ag NPs and adatoms on the surface of substrates. Adatoms co-deposited on clean high surface energy substrates will nucleate on Ag NPs that will remain closely spherical and preserve the pinning effect due to the water nanomeniscus. If the adatoms are co-deposited on a UV-ozone cleaned low surface energy substrate, their mobility is restricted, and they will nucleate in two-dimensional islands and/or nanoclusters on the surface instead of connecting to existing Ag NPs. This growth results in a rough surface without overhangs, where the wetting state is reversed from hydrophobic to hydrophilic. Finally, different material surfaces of transmission electron microscopy grids revealed strong differences in the sticking coefficient for the Ag NPs, suggesting another factor that can strongly affect their wetting properties.