Bioinspired multi-crosslinking and solid–liquid composite lubricating MXene/PVA hydrogel based on salting out effect

Due to the unique synergistic lubrication mechanisms, solid–liquid composite lubrication has received widespread attention in tribology. However, the cumbersome preparation process and solid–liquid separated service conditions limit its practical application. Inspired by the phenomenon of cell dehydration in electrolyte solutions, a simple salting out method is employed to develop multi-crosslinked and salted out MXene/polyvinyl alcohol (PVA) (MS-MP) hydrogels that can release water controllably for achieving solid–liquid composite lubrication in a single material. In this work, zinc ions (Zn2+) with both multi-crosslinking effect and salting out effect are incorporated into MXene/PVA hydrogels. These effects not only induce the formation of crystalline domains and the strengthening of network structure of hydrogels, but also release the water in hydrogels to realize the solid–liquid composite lubrication. Furthermore, the structure and tribological properties of MS-MP hydrogels can be regulated by adjusting the salting out degree, resulting in the acquisition of a structurally stable hydrogel with exceptional load-bearing capacity and superior lubrication performance. In brief, this work provides a novel and simple strategy for the fabrication of solid–liquid composite lubricating hydrogels, which shows great potential in fabricating liquid-containing lubrication materials.