Preparation of Carbon Nanosheets Modified with Hydrophilic Molecules and the Corresponding Research on Influence Factors of Hydration Lubrication

Traditionnal oil-based lubricants play significant role in interaction systems of heavy duty machaniery, which has propelled the rapid development of industrial age. Nevertheless, with the increasing demand in environmental friendiness of materials, as well as the continuous enrichment of lubrication systems in using scenarios, safe, envirornmentally-friendly and inexpennsive water-based lubriants is inexorably occupying more and more important position, in which the water-based lubricant additives compose a vital part. In this paper, carbon nanosheets abound with doped N atoms were fabricated by means of carbonizing coordination polymers, based on which mussel-inspired “sticky” poly-dopamine was taken as intermediary, creating environment for hydrophilic molecules with electropositive, electronegative, zwitterionic groups covalently anchored into the surface of carbon nanosheets via Michael addition reaction. Thus three water-based lubricant additives were obtained to investigate their tribological performance and accordingly dig out the water-based lubrication mechanism as well as influence factors via various physicochemical characterizations. It was found in experiments that all the modifications were able to enhance the anti-frcition and anti-wear performance of hybrid lubricity efficiently due to the stronger hydration ability of charged groups, among which the carbon nanosheets modified with electronegative acrylate sulfonates (SPMA-PCNS) exhibited the most enhancement effect, the outstanding superiority in tribological performance of which could be attributed to two aspects: on the one hand, SPMA possessed the highest acitivity of Michael addition reaction, resulting in the most grafting amount, which brought sufficient hydration and the thicker hydration layer acted on better effect on boundary lubrication, on the other hand, the surface of SPMA-PCNS presented to be eletronegative, which was conducive to the adsorption and tribo-reaction between the additives and tribo-pairs, and hence a robust protective tribo-film was able to form. Further analysis into wear scar revealed that SPMA-PCNS was capable of reacting with steel substrate during friction under the action of friction heat and mechanical force, as a consequence, a tribo-film composed of carbon nitride, iron sulfide and iron oxides was formed, which played a synergistic effects with the boundary lubrication layer by hydartion to protect the surface of tribo-pairs, meanwhile, reduce the friction and wear efficiently. This research provided a feasible idea in preparation and modification of water-based lubricant nanoadditives, in the meanwhile, it revealled the potential influence factors of water-based lubrication, which contributed to the design of lubricant additives with high performance and the understanding of lubrication mechanism respectively.