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Superlubricity is an ideal lubrication state where friction nearly vanishes between contact interfaces. It has become one of the most important research topics and approaches owing to its significance in reducing energy consumption and preventing device failures. As an efficient and universal lubricating principle capable of achieving superlubricity, rolling lubrication has attracted widespread attention in recent years. In this review, the theoretical concept of rolling lubrication and the experimental research progress of spherical/scroll structures are summarized. The review focuses on the possibility of achieving rolling lubrication using spherical/scroll structures (such as spherical fullerenes, carbon nanotubes, and formed and constructed spherical/scroll structures). The challenges in achieving rolling lubrication are summarized, and the possibility of molecular rolling lubrication, as well as its potential applications in superlubrication, are discussed. [ABSTRACT FROM AUTHOR]

Ferroaluminate cement is widely used in marine engineering applications owing to the remarkable durability and strength of its main hydrate, Al(Fe)–ettringite. The structure and performance of Al(Fe)–ettringite still require extensive exploration. An Al(Fe)–ettringite molecular model containing different Fe contents (0%, 25%, 50%, and 75%) was developed via Materials Studio. Radial distribution functions, time-correlated functions, and mean square displacement were used to analyze the structure of Al(Fe)–ettringite, after which Al(Fe)– ettringite was prepared using a coprecipitation method. The hydration of Al(Fe)–ye'elimite, the nanoindentation testing, and compressive strength of four ettringite types were assessed to facilitate a comparison with the simulation results. Increasing the Fe content resulted in increased lattice size and density. Fe atoms mainly reacted with Ohs atoms to form Fe–Ohs bonds, resulting in an increased Fe–Ohs bond length, with the Fe atom density resulting in volume expansion and increased density in Al(Fe)–ettringite. At 25% Fe content, the number of Hw–Ow hydrogen bonds in Al(Fe)–ettringite was 1166.14, the MSD value was 1.53 Å2, and the water molecules diffused the fastest. The improved macromechanical properties obtained by adding Fe atoms demonstrate that Fe atom substitution can enhance the ettringite structure. The experimental results validated the simulation results. [ABSTRACT FROM AUTHOR]

Permafrost active layer soils are harsh environments with thaw/freeze cycles and sub-zero temperatures, harboring diverse microorganisms. However, the distribution patterns, assembly mechanism, and driving forces of soil microeukaryotes in permafrost remain largely unknown. In this study, we investigated microeukaryotes in permafrost active layer across the Qinghai-Tibet Plateau (QTP) using 18S rRNA gene sequencing. The results showed that the microbial eukaryotic communities were dominated by Nematozoa, Ciliophora, Ascomycota, Cercozoa, Arthropoda, and Basidiomycota in terms of relative abundance and operational taxonomic unit (OTU) richness. Nematozoa had the highest relative abundance, while Ciliophora had the highest OTU richness. These phyla had strong interactions between each other. Their alpha diversity and community structure were differently influenced by the factors associated to location, climate, and soil properties, particularly the soil properties. Significant but weak distance-decay relationships with different slopes were established for the communities of these dominant phyla, except for Basidiomycota. According to the null model, community assemblies of Nematozoa and Cercozoa were dominated by heterogeneous selection, Ciliophora and Ascomycota were dominated by dispersal limitation, while Arthropoda and Basidiomycota were highly dominated by non-dominant processes. The assembly mechanisms can be jointly explained by biotic interactions, organism treats, and environmental influences. Modules in the co-occurrence network of the microeukaryotes were composed by members from different taxonomic groups. These modules also had interactions and responded to different environmental factors, within which, soil properties had strong influences on these modules. The results suggested the importance of biological interactions and soil properties in structuring microbial eukaryotic communities in permafrost active layer soil across the QTP. [ABSTRACT FROM AUTHOR]

This study demonstrates that magnetron-sputtered NbSe2 film can be used as a lubricant for space current-carrying sliding contact, which accommodates both metal-like conductivity and MoS2-like lubricity. Deposition at low pressure and low energy is performed to avoid the generation of the interference phase of NbSe3. The composition, microstructure, and properties of the NbSe2 films are further tailored by controlling the sputtering current. At an appropriate current, the film changed from amorphous to crystalline, maintained a dense structure, and exhibited excellent comprehensive properties. Compared to the currently available electrical contact lubricating materials, the NbSe2 film exhibits a significant advantage under the combined vacuum and current-carrying conditions. The friction coefficient decreases from 0.25 to 0.02, the wear life increases more than seven times, and the electric noise reduces approximately 50%. [ABSTRACT FROM AUTHOR]

Recent studies have reported that adding nanoparticles to graphene enables macroscale superlubricity to be achieved. This study focuses on the role of nanoparticles in achieving superlubricity. First, because graphene nanoscrolls can be formed with nanoparticles as seeds under shear force, the applied load (or shear force) is adjusted to manipulate the formation of graphene nanoscrolls and to reveal the relationship between graphene-nanoscroll formation and superlubricating performance. Second, the load-carrying role of spherical nano-SiO2 particles during the friction process is verified by comparison with an elaborately designed fullerene that possesses a hollow-structured graphene nanoscroll. Results indicate that the incorporated nano-SiO2 particles have two roles in promoting the formation of graphene nanoscrolls and exhibiting load-carrying capacity to support macroscale forces for achieving macroscale superlubricity. Finally, macroscale superlubricity (friction coefficient: 0.006–0.008) can be achieved under a properly tuned applied load (2.0 N) using a simple material system in which a graphene/nano-SiO2 particle composite coating slides against a steel counterpart ball without a decorated diamond-like carbon film. The approach described in this study could be of significance in engineering. [ABSTRACT FROM AUTHOR]

The solid lubricant MoS2 demonstrates excellent lubricating properties, but it spontaneously oxidizes and absorbs moisture in air, and thus results in poor wear resistance and short wear-life. In this study, the additive g-C3N4 (CN) was successfully combined with MoS2 via hydrothermal synthesis as a solid lubricant for the first time. Meanwhile, a low friction coefficient (COF, μ = 0.031) and ultra-long wear-life of CN/MoS2 compared to pure MoS2 in air were demonstrated. The functional groups and good crystallinity of the lubricant material were characterized via Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). The formed valence states in CN/MoS2 were analyzed via X-ray photoelectron spectroscopy (XPS). The characterized results of the scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) show the morphology and interior crystal phase structure of CN/MoS2. From the cross-section analysis, the presence of iron oxide nanoparticles lubricating film is synergistic with CN/MoS2 film during the friction process, resulting in its ultra-long wear-life. In particular, the friction mechanism of interlayer sliding friction combined with energy storage friction was analyzed and proposed. [ABSTRACT FROM AUTHOR]

The reinforcing effect of graphene oxide (GO) and its derivatives for polymer matrices highly depends on their dispersion therein. Thus, a facile method was developed to enhance the dispersibility of GO via compounding with γ-methacryloxypropyltrimethoxysilane (GO–KH570). The interfacial interactions between GO and KH570, as well as the surface morphology, chemical composition and polarity, were investigated by molecular dynamics simulation combined with experimental methods. Findings indicate that KH570 can successfully graft onto the surface of GO nanosheets via the covalent bonding, and the polarity of the as-obtained GO–KH570 can be tuned by adjusting the dosage of KH570. Besides, the GO–KH570 was further used as the filler to improve performances of polyimide (PI) matrix. After using this GO–KH570 composite, the PI-based coating was endowed with excellent wear resistance and corrosion resistance properties. Particularly, PI/GO–KH570-2 coating with a GO–KH570-2 dosage of 0.5 wt% exhibits much higher hardness, showing promising potential as the candidate high-performance coating in aerospace and marine industries. [ABSTRACT FROM AUTHOR]

POSS-doped organic-inorganic nanocomposites (POSS referring to polyhedral oligomeric silsesquioxane) as a new generation of high-performance materials are of special significance, since they simultaneously possess the high rigidity and stability of inorganic species as well as the desired flexibility, ductility and processability of polymer species. Thus, octa(3-amino propyl) POSS (amino-functionalized POSS, denoted as NH2-POSS) was incorporated into polyamide-imide (denoted as PAI) to obtain a series of NH2-POSS/PAI hybrid composites. The molecular structures of NH2-POSS and NH2-POSS/PAI hybrid composites were analyzed by Fourier transform infrared spectrometry and X-ray diffraction. The impact of NH2-POSS on the thermal stability and mechanical properties of PAI as well as the tribological properties of PAI/PTFE-based (PTFE referring to polytetrafluoroethylene) bonded solid lubricant coatings was investigated. Findings indicate that the introduction of a proper amount of NH2-POSS leads to an increase in the glass transition temperature (Tg) as well as hydrophobicity and microhardness of PAI. Besides, NH2-POSS contributes to reducing the friction coefficient and wear rate of PAI/PTFE-bonded solid lubricant coatings. Particularly, the introduction of 7% (mass fraction) of NH2-POSS leads to a decrease in the wear rate of PAI/PTFE-bonded solid lubricant coating by about 50%. This could be attributed to the increase in the load-bearing capacity and decrease in the surface energy of the polymer matrix coatings upon the addition of NH2-POSS. [ABSTRACT FROM AUTHOR]

As high-efficiency nanofiller for resin systems, surface functionalization of graphene oxide (GO) by introducing macromolecules has attracted enormous scientific interest. Current research on GO-based nanocomposites mainly focuses on its strong interfacial interactions with polymer matrix, but the different adsorption states of the macromolecules on the surface of GO sheets can also severely affect its reinforcement effect. Herein we concentrated on the two generally modified methods and grafted GO sheets with polyacrylamide (PAM) via facile physical adsorbing and chemical grafting routes so as to afford PAM-1, PAM-2, and PAM-3. Both the transformation procedures and the detailed interaction mechanism of products are investigated by molecular dynamic simulation combining with experiments. Besides, the PAM-modified GO nanosheets are employed as the nanofillers to improve the mechanical properties of polyimide (PI) matrix. The mechanical properties of the prepared PI-based nanocomposite films are significantly enhanced by incorporation of a small amount of chemical grafting nanosheets PAM-3 without any surface modification. In particular, compared with pure PI matrix, the addition of 0.2 wt% PAM-3 in PI can result in 78.9% increase in tensile stress and 22.4% increase in elongation at break. This article provides theoretical guidance for the choice of synthesis methods for nanofillers with high comprehensive performances. [ABSTRACT FROM AUTHOR]

A series of hydrogenated amorphous carbon (a-C:H) films doped with molybdenum disulfide (MoS 2) were deposited by medium frequency unbalanced magnetron sputtering with mixed Ar/CH 4 gases of different volume ratios as the source gases. The effects of Ar/CH 4 ratio on morphology, microstructure, mechanical, and tribological properties of the MoS 2/a-C:H composite films were investigated. Results show that the content of MoS 2 in the as-deposited films decreases with the decreasing Ar/CH 4 ratio, and the highest Ar/CH 4 ratio favors the formation of nanostructured films. Besides, the hardness and internal stress of the composite films first decrease and then increase with decreasing Ar/CH 4 ratio. Furthermore, the film deposited at the highest Ar/CH 4 ratio exhibits excellent antiwear ability in all test environments and shows promising potential as a solid lubricating film in aviation and space industries. [ABSTRACT FROM AUTHOR]

A series of graphite-like carbon films with a titanium concentration of about 3.0 at.% were successfully deposited on silicon wafer substrates using an unbalanced magnetron sputtering system with different bias voltages. The microstructure, surface morphology, and properties of the titanium-containing graphite-like carbon films were subsequently studied using different characterization techniques. The results show that the resulting titanium-containing graphite-like carbon films are completely dominated by sp sites and that these films have moderate hardness, low internal stress, and superior tribological properties with low friction and a high load-bearing capacity. The hardness ( H), elastic modulus ( E), H/ E, H/ E, and internal stress of the titanium-containing graphite-like carbon films initially increase with increasing bias voltage, only to be followed by a decrease with further increases in the bias voltage. Tribologically, the studied carbon film shows a slight increase in friction with increasing bias voltage, while the wear rate initially decreases, followed by an obvious increase. The tribological properties of the studied titanium-containing graphite-like carbon films are greatly improved under the liquid paraffin-lubricated condition, achieving extremely low friction (~0.045) and wear (~10 mm/Nm). The effect of bias voltage on the microstructure and properties of the titanium-containing graphite-like carbon films is discussed in detail. [ABSTRACT FROM AUTHOR]

Four types of graphite-like carbon (GLC) films were deposited on different substrates (Ti6Al4V, WC-27CrNi) with a different interlayer (TiC/Ti, TiC/Ti/TiN) using an unbalanced magnetron sputtering system. The effect of substrate and interlayer on the microstructure and properties of the studied GLC films was then investigated using different characterization techniques. The results show that both the substrate and interlayer had an obvious influence on the tribological properties of the studied GLC films even though there was no significant structural difference between these films. Specifically, a substrate with a high hardness was propitious to achieving superior tribological behaviors for carbon film even with a different interlayer. However, the interlayer had a distinct influence on the tribological properties of the carbon film deposited on different substrates, and this effect varied with the hardness property of the substrate. For a hard substrate, the wear rate and wear life were similar irrespective of the interlayer. For a soft substrate, the addition of a TiN interlayer improved the wear life sevenfold compared to the film with only a TiC/Ti interlayer, but the wear rate for a film with and without a TiN interlayer was approximately the same. The obvious discrepancy between wear life and wear rate for a carbon film deposited on soft substrate was closely related with the film adhesion strength and plastic deformation of the substrate materials. Based on these results, it can be concluded that the wear life is a better parameter than wear rate in terms of characterization of the wear resistance of carbon film once the applied load causes the plastic deformation of the substrate. [ABSTRACT FROM AUTHOR]