In-Situ Growth of Hydrogel Lubrication Film on Self-Adhesive Silicon Elastomer Surface and Its Performance

Reversible and convenient bonding underwater between hydrogel lubrication film and substrate is one of the challenges in the field of tribology. In this study, the lubrication film was combined with the silicone rubber to prepare hydrogel-lubricated silicone rubber with reversible wet adhesion. Polydimethylsiloxane (PDMS) with low degree of crosslink was used as an underwater adhesion material, and the initiator benzophenone was buried on its surface/subsurface, then the hydrogel lubricating film Poly (acrylic acid-co-acrylamide) P(AA-co-AAm) was grown on the surface through surface photopolymerization. The interface structure of obtained hydrogel-lubricated silicone rubber was explored by field emission scanning electron microscope (FESEM). The effects of ratio of hydrogel monomers, concentration of crosslinking agent, and polymerization time on performance of films were explored. The ratio of curing agent in PDMS was adjusted to explore its effects on adhesion and tribological properties of films. The results showed that a densely connected structure formed between the interface of hydrogel and PDMS. As the content of acrylic acid increased, the friction coefficient showed a trend of first decrease and then increase. When the content of acrylamide was further reduced, the acrylic acid segment absorbed water easily and swelled, leading to the reduction of mechanical strength and increase of friction coefficient. When the molar ratio of acrylic acid to acrylamide was 1:1, the hydrogel exhibited excellent tribological properties and mechanical strength. When the content of the crosslinking agent increased, the mechanical properties of hydrogel was optimized, and it exhibited better lubrication property. In addition, the modulus of PDMS increased as the content of curing agent, while the friction coefficient showed the opposite trend.; when the mass ratio of PDMS silane prepolymer to curing agent was 30:1, PDMS had favorable mechanical properties, adhesion performance and low friction coefficient. The prepared hydrogel-lubricated silicone rubber made the hydrogel adhesive underwater and endowed the silicone rubber with excellent lubrication and anti-wear properties. PDMS substrate was worn severely in the sliding direction after the friction test, its surface was damaged and there were obvious pits. In contrast, the hydrogel film only produced very slight scratches. The wear scar of the hydrogel was investigated, and the results showed that after nearly 3 000 cycles, the surface layer of the hydrogel film did not change much, which proved that the hydrogel film had excellent resistance to abrasiveness compared to PDMS. After repeated adhesion tests, the hydrogel film still had excellent adhesion properties. In addition, the hydrogel-lubricated silicone rubber had different adhesion on two sides. PDMS side showed good adhesion to titanium alloy, PTFE, and ceramics underwater while the hydrophilic hydrogel layer had no adhesion to titanium alloys, ceramics, etc. underwater, and directly falls off the surface of the materials.