Surface forces between mica surfaces confining inorganic nanoparticle dispersions and frictional properties

The normal forces between mica surfaces confining dispersions of ceria (CeO2) nanoparticles in decalin were measured using the surface forces apparatus. The nanoparticles (size ca. 6 nm), synthesized under supercritical conditions in a cubic shape, were coated with decanoic acid. A repulsion force appeared at a distance of 50–80 nm for the first compression, whereas the range was reduced in the subsequent approaches. This indicated that the nanoparticles were rearranged on the mica surface by compression from a disordered initial adsorption pattern. Resonance shear measurements were applied for the first time to a nanoparticle dispersion. The confined particle layers were shown to significantly reduce the friction compared to the mica–mica contact. Those results should contribute to the understanding of the assembly of nanoparticles into thin films under confinement and to the implementation of nanomaterials in tribological applications.