Carbon films have been considered suitable to be applied in water lubrication since they exhibit excellent friction-reducing and wear resistance, chemical inertness, etc. However, the basic understanding of tribological behaviors of carbon-based films under water lubrication still needs to be explored. In the present work, carbon films with different nanostructures were prepared by the electron cyclotron resonance (ECR) plasma nano-surface manufacturing system, and micro-textures with different sizes were prepared on the surface of carbon films by plasma etching. The influence of nanostructure and surface texture on the tribological properties of carbon films was investigated. The results show that different nanostructured carbon films can obtain lower friction coefficients and longer wear life under water lubrication than under dry condition. Due to low surface roughness, high hardness, and compact structure, the tribological properties of amorphous carbon (a-C) films under water lubrication are much better than those of graphene sheet-embedded carbon (GSEC) films. The prepared surface texture has a negative effect on the hard a-C film, but it can make the soft GSEC film generate soft wear debris at the initial stage. With the action of water, the soft wear debris is bonded on the surface of the contacting ball to form a silt-like transfer film, which increases the wear life by nearly three orders of magnitude. These results extend the basic understanding of the tribological behavior of carbon film under water lubrication, which is crucial in both fundamental and applied science.

Switchable adhesives have attracted widespread attention due to their strong reusability and adaptability to operate stably in complex environments. However, the simple fabrication of adhesive structures and reliable control of adhesion remain challenging. Here, we developed a neodymium iron boron/polydimethylsiloxane (NdFeB/PDMS) magnetic composite with optimal mechanical and magnetic performance. Then we fabricated lamellar structures and setal arrays using a molding and magnetic field-induced process, imitating the multi-level adhesion system of gecko feet. The lamellar can be deformed under the action of a magnetic field to control the adhesion, and the setal array is used to enhance adhesion and provide self-cleanability to the adhering surface. Switchable adhesion was realized by applying an external magnetic field, where the maximum adhesion strength was 5.1 kPa, and the switchable range was within 40%. Through finite element analysis simulations and experimental verification, it was proved that the adhesion force variation was ascribed to the magnetic field-induced surface deformation. Finally, we installed the adhesive on the end of the robotic arm, realizing the transfer of the target object. This work provides a simple method to fabricate a gecko-like surface and a practical strategy to realize switchable adhesion, which sheds light on broad application potential in production lines, medical products, and more.