Versatile Pickering emulsion gel lubricants stabilized by cooperative interfacial graphene oxide-polymer assemblies.

Although a large number of water- and oil-based gel lubricants have found extensive potential applications in industrial and biomedical fields, developing new-type emulsion-based gel lubricants that may effectively integrate their characteristics and preponderances remains a significant challenge. Here a water-in-oil Pickering emulsion gel lubricant that is able to combine the high colloidal stability of traditional Pickering emulsions, the good swelling and corrosion resistance of oil-based gel lubricants, and the high cooling capacity of water-based gel lubricants prepared from a binary mixture of aqueous graphene oxide (GO) dispersion and diamino-functionalized polydimethylsiloxane oil solution in a broad concentration, pH, and water volume fraction range is reported. It can provide favourable lubrication for the Si3N4/steel and Si3N4/silicone tribopairs either in air or under water owing to the formation of a sturdy adsorbed oil film and ball-bearing actions of the GO particles. It can also be printed into various colourful 2D and 3D geometries upon direct extrusion into water, thanks to its water-in-oil nature and inherent shear-thinning and thixotropic properties, which further shows good prospects in underwater operations and artificial biomimetic organs. Our study may provide new insights into the design and preparation of novel semi-solid materials for diverse industrial, engineering, and biomedical applications.

The Improved Antiwear and Anticorrosion Properties of Epoxy Resin with Metal-Organic Framework ZIF-8 Containing Lubrication Oil.

Zeolitic imidazolate framework-8 (ZIF-8) was fabricated as a lubrication container to encapsulate lubrication oil, which was added to epoxy resin (EP) as a filler to get the self-lubricating ZIF-8/EP composites coating. The antiwear and anticorrosion peculiarities of EP can be significantly improved by the encapsulation method. The antiwear peculiarities of EP were evaluated by the macroscopic ball-disk friction tests with the 9Cr18 steel ball as the counterface material. The result demonstrates that the coefficient of friction (COF) and wear rate of the self-lubricating ZIF-8/EP composites were reduced by 82.1% and 93.5% compared with that of the pure EP, respectively. Importantly, the ZIF-8/EP composite shows anticorrosion performance in the artificial seawater (ASW). The constant phase element and effective capacitance of the coating containing ZIF-8 fillers are lower than that of the non-containing coating. In addition, the diameter of the capacitive arc and the impedance modulus of the coating containing ZIF-8 + YR1800 are higher than those of the coating non-containing, which proved that the corrosion resistance of the EP is improved by the ZIF-8 + YR1800.

Lattice distortion-enhanced superlubricity of (Mo, X)S2 (X = Al, Ti, Cr and V) with moiré superlattice.

Two-dimensional (2D) materials with the advantage of low interlayer shear strain are ultilized as lubricants in aerospace and precision manufacturing. Moiré superlattices (MSL), with attractive physical properties of electronic structures, interlayer hybridization and atomic forces, have been widely investigated in superlubricity, which is caused by elimination of interlayer lock-in by incommensurate atomic reconstruction. Although the foundations of superlubricity and the development of 2D lubricants via vanishing friction have been investigated, it is still important to comprehensively reveal the influence of MSL on the interlayer van der Waals (vdW) interactions of 2D lubricants. Here, the contributions of lattice distortions of solute-doped twisted bilayers (Mo, X)S2 (X = Al, Ti, V and Cr) to superlubricity are comprehensively investigated by high-throughput modelling and DFT-D2 calculations. It is revealed that the lattice distortion not only breaks the interlayer balance of repulsion and van der Waals interactions but also yields layer corrugation. These layer-corrugation-induced changes of the interlayer interactions and spacing distances are utilized to optimize lubricity, which matches with the experimental friction coefficients in the order of (Mo, Al)S2 > (Mo, Cr)S2 > MoS2 >(Mo, V)S2 >(Mo, Ti)S2. The evolutions of the band structures show an exponential relationship of the band edge width and layer deformations, paving a path to accelerate the development of advanced superlubricity materials via lattice distortions.

Dependence of Friction and Wear on the Microstructures of WS2 Films under a Simulated Space Environment.

Atomic oxygen (AO) has an important influence on the performance of solid lubricating materials applied in space. The tribological behaviors of both sputtered WS2 films without and with a dense layer were mainly investigated under the ex situ AO irradiation condition. AO irradiation results in the worse tribological property for the WS2 film without a dense layer. On the contrary, it is surprising that the WS2 film with the dense layer exhibits a lower friction coefficient after irradiation, which is different from the reported results that the solid lubricating films always increased the friction and wear because the surfaces of the films were oxidized by AO. Meanwhile, it is found that the generated W oxides contributes to the partial surface of the wear track becoming smooth because of the shear and slip of crystal planes for WS2 crystals on the surface of the dense layer. Eventually, the lubricating mechanisms of the irradiated WS2 films are also revealed via correlating the friction and wear characteristics of the films.

Tailoring the Tribocorrosion and Antifouling Performance of (Cr, Cu)-GLC Coatings for Marine Application.

Doped graphite-like coating (GLC) has aroused great interest as one of the most promising protective materials in marine applications. However, there is a lack of systematic research on the tribocorrosion and antifouling performance of doped GLC coatings in harsh marine environments. Herein, a multifunctional (Cr, Cu)-GLC coating with combined antifouling and tribocorrosion properties was prepared via a magnetron sputtering method. The experimental results indicate that the resultant coatings changed from a dense structure to a loose columnar structure with the increment of Cr and Cu doping amount. At the same time, the hardness of the coating gradually decreases, but the contact angle between coating and seawater gradually increases. The algae adhesion test reveal that the algae density on the surface of the (Cr, Cu)-GLC coating decreases from about 565 to 70/mm2 as the amount of doping increased. However, on the contrary, the friction coefficient of the coating under OCP condition increases from 0.06 to about 0.35. Overall, the mild doped (Cr, Cu)-GLC coating exhibits the best comprehensive properties, combining antifouling and tribocorrosion properties. The corresponded mechanisms are discussed in terms of the coating microstructure, antifouling, and tribocorrosion behavior.

Formation of bcc and fcc during the coalescence of free and supported Fe and Ni clusters.

The formation of bcc and fcc during the coalescence of free and supported Fe and Ni clusters has been studied by molecular dynamics simulation using an embedded atom method. Structural evolution of the clusters, coalesced under varying temperature, Ni content and substrate conditions, was explored by interatomic energy, snapshots, pair distribution functions and bond order parameters. The results show that the formation of bcc and fcc is strongly related to Ni content, substrate and coalescence temperature. Free clusters coalesced at 1200 K form bcc at lower Ni contents with fcc forming at higher Ni concentrations and no observable coexistence of bcc and fcc. Differences in coalescence at 1000 K result from the coexistence of bcc and fcc within the Ni range of 50-70%. Free clusters supported on disordered Ni substrates were shown to transform from spherical morphology to islands of supported clusters with preferred epitaxial orientation. The Ni content required to form bcc and fcc coexistence on supported clusters at 1000 K decreased to 30-50% Ni. Free clusters possessing bcc and fcc generally stacked along the bcc (110) and fcc (111) facets, whereas supported clusters stacked along the (111) bcc and (100) fcc planes. Structural transformation was induced by clusters containing greater numbers of atoms. Spread over the substrate enhanced interatomic energy, order substrates affect the epitaxial growth direction and increase the melting points of the supported clusters. This study can be used to predict the nature of fcc and bcc formation in Fe-Ni films.