Thin Film-Formation Mechanisms of Aqueous Lubricant in Elastohydrodynamic Lubrication

Aqueous lubricants are increasingly used in industry due to their excellent cooling capability and to environmental considerations. However, the film forming mechanisms in high-pressure contacts, such as in EHL regime, differ from those, well-known, of classical piezoviscous oil lubricants. This work investigated the role of the molecular architecture of polyalkylene glycol (PAG) molecules dispersed in water, with co-solvent monopropylene glycol, on the film forming capability in elastohydrodynamic lubrication regime by means of in situ in-operando chemical distribution mapping of the contact. These mappings were based on infrared hyperspectral images. A specific focus was made on the analysis of the area absorbance ratio of the ether stretching band, characteristic of PAG polymer, and the O–H stretching band of continuous water media, in order to identify the relative contribution of the solvent and of the polymer additives. Linear and branched PAG molecules were used as well as mixtures of different molecular weight PAGs. The penetration capability of the polymers in the high-pressure zone of the contact under pure rolling conditions, was discussed in terms of molar mass, architecture and polarity.

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