Mucus-inspired functionalized ionic liquid/carnauba wax composite polyurethane with friction-driven underwater multi-lubrication

Achieving stable and long-lasting low friction and extended lifespan for polymeric components in underwater mechanical systems remains challenging. Inspired by the low friction and efficient lubrication provided by the mucus secreted on fish skin, this study fabricated the bioinspired functionalized ionic liquid/carnauba wax (IL-SiO₂/CW) reinforced polyurethane composites (PUCW-ILs) and investigated its properties. The results demonstrate that PUCW-1.5ILs, with a 1.5 wt.% addition ratio, achieved stable and persistent low friction and wear performance: an average coefficient of friction as low as 0.07 and an average wear loss of 0.006 g at 0.5 MPa (decreased 81% and 84.2% compared to PU respectively). This superior performance stems from the enhanced shear resistance of the matrix by IL-SiO₂, the formation of stable lubricating and transfer films at the interface by both CW and IL-SiO₂ and the hydration effect of IL-SiO₂.