Trimethylolpropane trioleate–ethanolamine amphiphile-based emulsions with excellent Tribological performance for water-based lubrication

To address the critical bottlenecks of high dosage, poor load-bearing capacity, and limited temperature adaptability in traditional water-based lubricants, herein, a series of phosphorus‑sulfur‑nitrogen (P-S-N) ternary amphiphilic additives (PS-TMPTO-MEA, PS-TMPTO-DEA, PS-TMPTO-TEA) were synthesized via a three-step molecular modification strategy, which can form stable oil-in-water (O/W) emulsions for water-based lubrication. Structural characterizations by FT-IR, NMR, and TG confirm the successful preparation of target additives; among which PS-TMPTO-TEA exhibited superior thermal stability with an initial decomposition temperature up to 378.9 °C. At an ultralow dosage of 0.5 wt%, PS-TMPTO-TEA achieved excellent tribological performance, maintaining a stable friction coefficient of ~0.1 and a wear rate of 3.01 × 10 −9 mm 3 /N·m, corresponding to ~91% wear reduction compared with pure water, Although 1.5 wt% gives the minimum wear rate (1.76 × 10 −9 mm 3 /N·m), the optimal practical concentration of 0.5 wt% was selected for the comprehensive evaluations due to the balanced tribological performance and low-dosage advantage. It also demonstrated good load-bearing capacity over 50–300 N and stable performance at 30–50 °C. Compared with the commercial additive JP at the same dosage, PS-TMPTO-TEA showed a lower friction coefficient and less than half the wear rate, outperforming most reported water-based lubrication systems. The superior performance originated from a P-S-N synergistic film-forming effect, generating dense organic–inorganic composite tribochemical film at the friction interface to achieve effective friction reduction and anti-wear. This work offers a new route for the design of high-performance, low-dosage water-based lubricant additives with promising industrial application potential.