High lubricity and electrical responsiveness of solvent-free ionic SiO2 nanofluids

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 6; no. 6; pp. 2817 - 2827
• Main Authors: Guo, Yuexia, Zhang, Ligang, Zhang, Ga, Wang, Daoai, Wang, Tingmei, Wang, Qihua
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 2018
• Subjects: adsorption; Boundary lubrication; canopy; Coefficient of friction; Electric contacts; electric field; Electric potential; Fluidity; Friction; Friction reduction; Inorganic materials; lubricants; Lubricants & lubrication; Lubrication; Lubricity; mixing; Nanofluids; Nanoparticles; oils; Polyethylene glycol; Silica; Silicon dioxide; Solvents; Synthesis; Tethering; Unloading
• ISSN: 2050-7488; 2050-7496; 2050-7496
• DOI: 10.1039/c7ta09649f

Solvent-free ionic nanofluids with a core–shell structure were successively synthesized via functionalizing silica nanoparticles with a charged corona and ionically tethering with oligomeric chains as a canopy. It was demonstrated that the as-synthesized nanofluids were endowed with outstanding dispersion stability and fluidity. Importantly, when used as a lubricant and additive, the nanofluids showed excellent friction-reducing and antiwear properties. That is, blending even a small fraction of nanofluids into polyethylene glycol base oil dramatically reduced the friction and wear of a steel–steel contact. Depending on the specific shell structures, the lubricity of the nanofluids exhibited a responsive characteristic to electrical potential. The friction coefficients can be adjusted by loading or unloading the external power and changing the direction of the electrical potential. Formation of a unique double electric layer consisting of both organic and inorganic materials during the friction was proposed, which can be essential for yielding robust lubrication of the adsorption film. Moreover, a nanostructured tribofilm comprising a significant fraction of silica and tribo-chemical products of the organic layers was identified, and it was believed to be significant in improving the boundary lubrication performance.