Reverse micelles as nanocarriers for polar friction modifiers in non-polar oils: AOT-mediated solubilization and boundary film formation

Polar organic friction modifiers can form effective boundary-lubrication films, but their limited compatibility with non-polar oils restricts their delivery to sliding interfaces. In this study, LCC was selected as a model polar additive to evaluate the ability of AOT reverse micelles in n-dodecane to act as nanocarriers for oil-incompatible friction modifiers. Increasing the water-to-surfactant molar ratio, w, expanded the transparent solubilization range of the model additive and increased the hydrodynamic size of the reverse micellar aggregates. Neutron reflectometry showed that hydrated AOT aggregates formed an adsorbed layer at the FeO_x/oil interface, and incorporation of the model additive increased the fitted adsorbed-layer thickness from 3.05 to 3.43 nm under the same fixed-SLD fitting condition. Ball-on-disk tests showed lower friction after additive incorporation, and XPS detected chlorine-containing LCC-derived species on the worn surfaces, indicating that LCC was delivered to and retained at the sliding interface. Molecular dynamics simulations were used to observe the structural response of additive-loaded reverse micelles under high-pressure shear. These results support a reverse-micelle-assisted delivery mechanism in which hydrated AOT aggregates solubilize polar additives in the bulk oil, adsorb at the interface, and release additive-derived species under sliding.