A monosurfactant-stabilized dual-responsive and versatile emulsion lubricant

Emulsions consisting of lubricating base oil and water have extensive applications in the fields of metalworking and heavy-duty machinery. Due to the compositional complexity that confines an effective recycling of emulsion constituents and the frequent use of toxic, non-biodegradable mineral base oil, an industrial emulsion lubricant is usually easy to produce severe environmental burdens and health issues. Here we report a dual-responsive and versatile lubricating emulsion solely consisting of water, an eco-friendly ester base oil and a synthetic cationic emulsifier. Taking advantage of the inclusion of azobenzene moiety, [CeCl3Br]- anion and methylimidazole head-group, the surfactant can not only undergo tribochemical reactions to function as a lubricant additive to achieve very low interfacial friction, but also endow the resulting emulsion efficient anticorrosion, antibiosis and both light-and magneto-responsiveness. Based on a reversibly photo-triggered variation in the hydrophobicity of surfactant, an on-demand separation and recycling of emulsion component followed by a nearly one order of magnitude conversion in the friction can be realized. Together with its magneto-controlled migration and adaptivity to high normal loads, we envision that the emulsion lubricant may find potential applications in a broad range of industrial systems requiring lubrication and heat dissipation as well as smart devices needing control over the friction between two contacting surfaces.

Automated summary

This study presents a dual-responsive and versatile lubricating emulsion composed solely of water, eco-friendly ester base oil, and synthetic cationic emulsifier. The emulsion exhibits efficient anticorrosion, antibiosis, and light-and magneto-responsiveness, thanks to the unique surfactant with azobenzene moiety, [CeCl3Br]- anion, and methylimidazole head-group. By exploiting the reversible photo-triggered hydrophobicity of the surfactant, an on-demand separation and recycling of emulsion components can be achieved, accompanied by a significant reduction in friction. Additionally, the emulsion lubricant demonstrates magnetically controlled migration and adaptivity to high normal loads, making it promising for applications in various industrial systems and smart devices.