Cobaltocenium-Based Metallo-polyampholyte for Friction Reduction and Antiwear via Hydration Lubrication

Water-based lubricants offer cost-effective, non-flammable, and environmentally friendly complements to conventional oil-based lubricant systems. However, their practical application is often limited by inadequate tribological performance. In this study, we present a cobaltocenium-based zwitterionic polymer (PGMA-Co+S-) as a high-performance additive for water-based lubrication. Tribological tests demonstrate that PGMA-Co+S- can achieve a reduction of the coefficient of friction from 0.343 to 0.167 (by up to 51%) and a decrease of the wear volume from 5.85 × 104 to 1.65 × 104 μm3 (by up to 72%) compared to pure water. The additive exhibits consistent lubricating performance under demanding conditions, including high load (20 N), high frequency (7 Hz), extended duration, and salinity environments. The outstanding lubrication and antiwear properties can be ascribed to a synergistic mechanism involving strong surface adsorption mediated by cobaltocenium groups and a high-capacity hydration layer enabled by sulfonate groups, which promotes the formation of a durable lubricating film with anticorrosion functionality. This work not only provides new insight for the design of zwitterionic polymer-based lubricant additives, but also provides potential candidate for high-efficient and sustainable water-based lubrication under severe operating conditions.