Effect of micro-nano hierarchical structure on lubrication mechanism in carbon/urea soft-nanocomposites

Soft-nanocomposites not only preserve the tunable sol-gel phase transition of gel lubricants, but also further enhance their tribological performance. However, the complex micro-nano hierarchical structures of soft-nanocomposites make it difficult to clearly understand their structure-performance relationship. In this paper, soft-nanocomposites composed of fibrous self-assembled urea-based gelators (TO, formed by the reaction of TDI with octadecylamine), oleic acid-modified graphene oxide (GO/OA), and carbon nanotubes with different aspect ratios were designed and prepared. The results reveal that the fiber-interpenetrated micro-nano structure, formed by carbon nanotubes and TO, exhibits superior anti-wear performance, with the synergistic effect further enhanced by higher carbon nanotube aspect ratios. Furthermore, lamellar-stacked soft-nanocomposites (GO/OA-TD) were prepared by integrating GO/OA with lamellar urea-based gelators (TD, formed by the reaction of TDI with dodecylamine). Under a load of 392 N and a rotational speed of 1200 rpm, the GO/OA-TD achieved a 34.5% reduction in the coefficient of friction and a 44.8% decrease in wear scar diameter compared with pristine TD, showing significantly better synergistic lubrication than the dimensionally mismatched lamellar-fiber structure (GO/OA-TO). This demonstrates that dimensional matching between nanomaterials and gelator networks is likely a major contributing factor to synergistic lubrication, providing new insights for the rational design of high-performance soft-nanocomposite lubricants.