The synergistic effect of different types of solid particles in liquid lubricants is of great interest. In this work, g-C₃N₄ nanosheets were initially prepared using a calcination method and then as-prepared, and h-BN were used as lubricating additives to the white oil. A comparison between the mixed additives and the single g-C₃N₄ or h-BN additives revealed that the base oil with the addition of g-C₃N₄ and h-BN showed the best lubricating properties. The results show a 12.3% reduction in friction coefficient, resulting in a 68.6% reduction in wear rate compared to the white oil when filled with 0.5 wt% g-C₃N₄ and h-BN (1:1 by weight). Moreover, the addition of g-C₃N₄ and h-BN improves the high-temperature lubrication properties of the white oil. However, the friction coefficient and wear rate increase with increasing oil temperature. The large contact area between g-C₃N₄ and its sliding counterpart and the strong adhesive force between h-BN and its sliding counterpart improve the film formation efficiency, leading to enhanced tribological properties under oil lubrication conditions.

Hybrids of fluorinated graphite/MoS₂ (FGr@MoS₂) were prepared via a hydrothermal method and used as lubricating additives to take full advantage of the synergy between FGr and MoS₂ in carbon-fiber-reinforced polymer (CFRP). The results show a 21.6% reduction in the friction coefficient compared to the neat sample when the CFRP was filled with 1.2 wt.% FGr@MoS₂ hybrids. The addition of 1.5 wt.% FGr@MoS₂ resulted in a 60.9% reduction in the wear rate compared to neat CFRP. For the 1.2 wt.% FGr@MoS₂-reinforced CFRP, the friction coefficient maintained a relatively steady value of approximately 0.46 at various temperatures, indicating frictional stability. However, the wear rate increased by 13.95% at 60 °C compared to that at room temperature. The interfacial bonding force between the FGr@MoS₂ hybrid and the matrix, as well as the adhesive force with the surface of the counterpart ball, is improved, caused by the heterostructure of FGr@MoS₂, resulting in enhanced mechanical properties and formation efficiency as well as the transfer film on the surface of the counterpart ball. The results suggest that an FGr@MoS₂ micro-nano structure is a promising additive to be applied in polymer tribology.

The polymer water-lubricated bearing is widely used in marine transmission systems, and the tribological properties can be improved by addition of inorganic nano-fillers. The aim of this study is to investigate the effect of SCFs and temperature on the water-lubricating properties of high-density polyethylene (HDPE) composites. HDPE composites reinforced by varying content of short carbon fibers (SCFs) were fabricated via twin-screw extrusion and injection molding techniques to study the hardness and surface wettability of those composites. The tribological properties under water-lubricated conditions were investigated through a pin-on-disk reciprocating tribometer under different temperatures. The results showed that the increase in hardness of HDPE composites reached maximum to 42.9% after adding 25 wt % SCFs. The contact angle also increased with the increase in SCFs content and reached a maximum of 95.2° as the amount of SCFs increased to 20 wt %. The incorporation of SCFs increased the wear resistance and lubricating property of HDPE composites at different temperatures. The HDPE composite containing 20 wt % SCFs showed the lowest friction coefficient of 0.076 at 40 °C, and the wear track depth reached a maximum of 36.3 mm at 60 °C. Based on the surface wetting property and wear analysis, potential effect mechanisms of fillers and temperature were discussed. The knowledge from this study is useful for designing the anti-wear water-lubricated polymer bearing.

The epoxy nanocomposites reinforced by MoS₂ nanosheets and aligned multi-walled carbon nanotubes (MWCNTs) were fabricated by DC electric field inducement. The epoxy nanocomposites achieved improvement in the tribological properties with the addition of randomly dispersed MoS₂ and MWCNTs compared to the pure epoxy. Furthermore, the epoxy nanocomposites exhibit anisotropic tribological and mechanical properties when the MWCNTs are aligned in the composites. The tribological properties of epoxy nanocomposites containing 1 wt% MoS₂ and aligned 1.2 wt% MWCNTs achieved the maximum improvement when the sliding direction is perpendicular to the axial direction of MWCNTs. Compared to random MoS₂ nanosheets and random MWCNTs reinforced epoxy nanocomposites, the friction coefficient and wear rate of random MoS₂ and aligned MWCNTs reinforced epoxy nanocomposites decreased by 11.3 and 66.7% under a load of 5 N, respectively. The increased thermal conductivity and mechanical properties, higher surface content of nanoparticles, as well as unique alignment mode of MWCNTs are considered to be the main reasons for the improvement of tribological properties of epoxy nanocomposites.

Soft grippers have attracted great interest in the soft robotics research field. Due to their lack of deformability and control over compliance, it can be challenging for them to pick up objects that are too large or too small in size. In particular, compliant objects are vulnerable to the large grasping force. Therefore, it is crucial to be able to adjust the stiffness of the gripper materials. In this study, a soft gripper consisting of three artificial fingers is reported on. Each of the artificial fingers is made of a tri-layer polymer structure. An exterior layer, made of an ecoflex–graphene composite is embedded with electric wires as a heating source, by applying direct-current potential. The Joule heat not only allows for deformation of the exterior layer, but also transfers heat to the middle layer of the thermoplastic polyurethane (TPU) elastomer. As a result, the stiffness of the TPU layer can be adjusted using electro-thermal heating. Meanwhile, the third layer consists of a polydimethylsiloxane replica as a supporting layer with a gecko-inspired dry adhesive structure. By applying voltage through electric wires, the artificial fingers can bend and, thus, the soft gripper can hold the objects, with the help of the dry adhesive layer. Finally, objects like a shuttlecock, tennis ball and a glass beaker, can be picked up by the soft gripper. This research may provide an insight for the design and fabrication of soft robotic manipulators.

The incorporation of various types of fillers is critical to enhancing the starved oil lubrication performance of PEEK matrix composites. In this work, PEEK composites reinforced with h-BN and SCFs were fabricated via a hot-pressing method, and the friction and wear behaviors under dry sliding and starved oil lubrication were systematically investigated. Surface oil wettability and Vickers hardness were characterized, and tribological tests were conducted on a ball-on-disk reciprocating tribometer. Worn surface topography and wear mechanisms were elucidated through laser scanning confocal microscopy and scanning electron microscopy. The results show that h-BN effectively reduces the friction coefficient through its solid lubrication effect, while SCFs significantly improve the hardness and load-bearing capacity of the PEEK matrix. Under dry sliding conditions, the PEEK composite containing h-BN and SCFs achieves the lowest wear rate of 10.3 × 10⁻⁵ mm³/(N·m), which is 74.6% lower than that of pure PEEK, indicating a synergistic anti-wear effect. Under starved oil lubrication, PEEK/h-BN maintains the smoothest and lowest friction, and the presence of SCFs further improves wear resistance of PEEK composites despite a slight increase in friction. In addition, the fillers’ incorporation reduces the surface oil wettability of the PEEK composites; the dominant wear mechanism hence transforms from severe adhesive wear and plastic deformation in pure PEEK to mild abrasive wear.