The role of additives in liquid superlubricity is regarded as a crucial element of the running-in process due to their role in reducing friction. Nevertheless, there has been minor investigation into rheological changes that occur during the process. This paper presents an examination of the evolution of film thickness over time and its subsequent behavior. The primary experiments were performed on an optical ball-on-disk tribometer, with the ability to control the percentage of slip. The film thickness was evaluated by optical interferometry and its rheological behavior was subsequently researched by rotational rheometer and viscometer. It was discovered that the primary contribution to the reduction in friction during running-in is better contact separation caused by the evaporation of water. However, the global behavior of the solution was found to have been changed by formation of a convoluted compound and probably by adsorption to contact surfaces. It causes a behavior that is more complex than that predicted by common elastohydrodynamic equations, but may result in a reduction of friction due to an increased separating layer.

Macroscale rolling/sliding conditions are in the superlubricity, a little-studied topic so far. The purpose of this paper is to examine the formation of elastohydrodynamic lubrication (EHL) films by water-based lubricants (glycerol and polyethylene glycol (PEG)), providing superlubricous friction. Experiments were carried out on an optical ball-on-disc tribometer under rolling/sliding conditions. The film thickness was measured by the thin film colorimetric interferometry, and the viscosity of liquids was measured by rotational and high-pressure falling body viscometers. The results show that tribochemical reactions are not the mandatory reason for friction to reach the superlubricity level when using the water-based lubricants. The studied liquids themselves are almost Newtonian. With the addition of water, the signs of shear thinning behavior disappear even more. Suitable conditions for this type of lubricant can be predicted using the known Hamrock–Dowson equations. An anomaly in the thickness of the lubricants was observed as an abrupt change at certain conditions. The more PEG there is in the lubricant, the higher the thickness at the beginning of the jump.