Directional Hydration Lubrication Underwater: Enabled by TA/PAAm Submicron Particles

Achieving durable hydration lubrication underwater is challenging due to interference from interfacial hydration layers. This study developed tannic acid/polyacrylamide (TA/PAAm) nanoparticles, synergistically combining TA's adhesive pyrogallol groups with PAAm's hydrophilic chains to enhance aqueous lubrication. Tests showed TA/PAAm suspensions improved copper/ultra-high molecular weight polyethylene tribo-pair wettability by 42% (contact angle reduction), lowered friction coefficients by 29%, and reduced wear volume by 56% versus water. Mechanistically, TA immobilizes nanoparticles onto surfaces via catechol-mediated adhesion to form a protective film, whereas PAAm disrupts the hydration layer via its hydrophilicity, establishing a hydrogen-bonded lubrication network and thereby enhancing lubrication performance. This strategy provides an environmentally friendly directional lubrication solution for marine applications such as water-lubricated bearings and subsea mechanical seals.