An inorganic–organic hybrid CQDs@PVP lubricant additive:Achieving low friction and wear in PEG and water

High-temperature lubrication has always been a hot topic in the lubricant and grease industry,and is also an essential concern in the high-end equipment sector to be addressed.Carbon quantum dots(CQDs)are an emerging material widely applied in the field of lubrication,owing to their exceptional lubricity and high load-bearing capacity.However,the vulnerability of CQDs to oxidation in air and reduced stability dramatically restrict their high-temperature application capability.In this study,a nanocomposite of amphiphilic polyvinyl pyrrolidone(PVP)homopolymer with excellent lubricating properties and thermal stability,which is hydrogen bonded to CQDs(CQDs@PVP),was designed to achieve low friction and wear of lubricants at high temperatures.The CQDs@PVP are consistently dispersed in both PEG400 and water,and exhibit superior lubricity compared to unmodified CQDs at high temperatures(ranging from 200‒150°C and 90‒50°C).Meanwhile,the dense carbon film on the wear surface and the chemically reactive film of iron compounds directly contribute to the enhanced lubrication performance.These analytical results demonstrate the powerful candidacy of CQDs@PVP as a lubrication additive and promote future high-temperature applications of CQDs in industrial production.

Tribological study of two ammonium chloride-decanoic acid deep eutectic solvents(DESs)as high-performance lubricants

Deep eutectic solvents(DESs)are acknowledged as a novel class of functional liquid.DESs share similar physical properties with ionic liquids(ILs)and have the potential to be a novel class of lubricants.In this study,two DESs,namely tetrabutylammonium chloride-decanoic acid DES(C4-DES)and methyl tricaprylmethylammonium chloride-decanoic acid DES(C8-DES),were synthesized,and their physico-chemical properties and tribological performances were evaluated.Post-analysis of the rubbing surfaces used multiple techniques to gain insights into the lubrication mechanisms.Results show that the coefficient of friction(COF)and wear were reduced by approximately 29%and 91%for the C4-DES,and 36%and 94%for the C8-DES,compared to an ester base oil.The friction reduction behavior of the DESs is attributed to the monolayer adsorption of the polar group in the decanoic acid(DEAC),whose effectiveness is affected by the component of the ammonium salts in the DESs and the operating temperatures.In addition to the adsorbed film,worn surface analysis revealed that an ultra-thin tribochemical film with a thickness of 3–7 nm was formed on the surfaces lubricated with the C8-DES.The composition of the film was studied,and the lubrication mechanisms of the two DESs were discussed.