Boundary lubrication under harsh working conditions results in severe wear of water-lubricated bearing materials, e.g., the tail bearing in a ship. Inspired by cartilage lubrication, we prepare a smart hydrogel with balanced hydration and load-bearing properties through the construction of PVA-chitosan/sodium alginate double networks and the introduction of aramid nanofiber. The hydrogels are blended with UHMWPE into new bionic biphasic hydrogel-containing composites. The thorough assessments (chemical, thermal, surface, and bulk mechanical properties) of the hydrogels and the composites reveal that the high hydrophilicity of the hydrogel particles encapsulated in bulk UHMWPE facilitates water absorption leading to improved friction performance under boundary lubrication mode, e.g. at the startup. while the stripped hydrogel pits and induced micro-texture between friction interfaces as hydration layer play the role of separating the friction interface, effectively reducing the friction contact. Under 40 N load, the friction coefficient and wear rate of one composite are 28.7% and 14% lower than those of the plain UHMWPE, respectively. After soaking in seawater for 28 days and holding at 50℃ for 1 hour, the mechanical properties of the composite material are still better than plain UHMWPE. Altogether, the smart biphasic hydrogel-containing composites the intelligent biphasic hydrogel composites were able to improve the lubrication state according to operation conditions.

The application of antifouling paints to the surfaces of marine installations is the most economically efficient means for mitigating damage caused by marine biofouling in the shipping industry. However, conventional antifouling paints currently in widespread use can no longer meet the requirements of green antifouling. Although hydrogel coatings have made great progress in marine antifouling applications, current hydrogel coatings still suffer from construction difficulties and poor mechanical stability under wet conditions. In this paper, we innovatively exploit the phenomenon of the absorption of pyrogallol (PG) by large-molecular-weight polyvinylpyrrolidone (PVP), resulting in hydrophilic copolymer macromolecules, to propose a prepolymer-reactor rapid contact molding of sprayable hydrogel coatings. The PG/PVP copolymer produced microscopic reticular mimetic mussel adhesion protein (MAP) bioscaffolds via the chemical crosslinking of polyethyleneimine (PEI), contributed to the conversion of PG to PG-quinone upon the introduction of vanadium pentoxide particles, increased the hydrophobicity of the system and enhanced waterproof adhesion. The wet adhesion of the hydrogel coatings was measured up to 3.42 MPa via the micrometer scratch method, indicating that the prepared hydrogel coating had a stable adhesive force in a wet environment. The hydrogel coating was instantly molded on the surface of 304 stainless steel (SS) via two-step spraying. The swelling, friction, antifouling, and anticorrosion properties of the coatings were investigated along with the wet adhesion strength on the SS surfaces. The results showed that the hydrogel, after double cross-linking of PEI and V₂O₅, had a swelling rate within 30% and a low modulus along with stable lubricating properties. After the formation of the hydrogel coating, the inhibition rate of common bacteria and algae in the ocean reached more than 99%, and the electrochemical corrosion protection rate of SS reached 63.49%. This study provided ideas for improving the wet adhesion of hydrophilic marine antifouling coatings.

Polymers are widely used in bearing applications. In the case of water-lubricated stern tube bearings, thermoplastic polyurethane (TPU)-based composites are used due to their excellent wear resistance, corrosion resistance, and tunable mechanical properties. Their tribological performance, however, depends on operating conditions. In this work, TPU was blended with carbon fiber, graphene platelet, and ultra-high molecular weight polyethylene (UHMWPE). Friction tests of TPU based-composites against copper countersurface were carried out in water to mimic the actual operating conditions of the bearing. Most of the resulting contacts were in the boundary lubrication regime, in which friction was attributed to both contact mechanics of asperities as well as water lubrication. Our results show that the viscoelasticity of TPU has a considerable impact on its tribological performance. Water lubrication at 50 °C promotes the softening of polymer surface material during sliding, resulting in higher fluctuation in the coefficient of friction and wear loss. This is attributed to the reduced thermomechanical properties. In addition, Schallamach waviness is observed on worn surface. The tribological properties of TPU are significantly improved by the inclusion of carbon fiber, graphene platelet, and UHMWPE. The formation of graphene transfer-layers and UHMWPE transfer film reduces friction and wear loss, while the inclusion of carbon fiber enhances wear resistance due to improved mechanical properties and load bearing capacity.

Natural materials tend to exhibit excellent performance in the engineering field because of their structure and special functions. A natural red willow, called natural porous wood material (NPWM), was found, and wear tests were conducted to determine its potential as an oil-impregnated material by utilizing its special porous structure. Fluorination treatment was adopted to improve the NPWM properties for absorbing and storing lubricating oil. The different contributions of soaking and fluorination-soaking treatments on the tribological properties of NPWMs and their respective mechanism of effect were revealed. The results showed that the fluorination-soaking treatment helped absorb and store sufficient lubricating oil in the NPWM porous structure; therefore, more lubricating oil would be squeezed out and function as a tribol-film between contacting surfaces during the friction process, thus ultimately contributing to stable and smooth wear responses even under prolong friction. However, the formation of an oil-in-water emulsion, caused by the buoyancy effect, destroyed the oil films on the worn NPWM surface in a water environment, resulting in higher coefficients of friction (COFs) under water conditions than under dry friction, even after the fluorination-soaking treatment. The knowledge gained herein could not only verify the potential of NPWM as an excellent oil-impregnated material in the engineering field but also provide a new methodology for the design of artificial porous materials with stable and smooth friction processes.

Several soft tissues residing in the living body have excellent hydration lubrication properties and can provide effective protection during relative motion. In order to apply this advantage of soft matters in practical applications and try to avoid its disadvantage, such as swelling and weakening in water, a design strategy of a soft/hard double network (DN) hydrogel microsphere modified ultrahigh molecular weight polyethylene (UHMWPE) composite is proposed in this study. A series of microspheres of urea-formaldehyde (UF), polyacrylamide (PAAm) hydrogel, UF/PAAm double network, and their composites were prepared. The mechanical properties, swelling, wettability, friction properties, and the lubrication mechanisms of the composites were investigated. The results show that DN microspheres can have an excellent stability and provide hydration lubrication. The performance of 75 DN-1 composite was superior to others. This finding will provide a novel strategy for the development of water-lubricated materials and have wide application in engineering fields.