The molecular configuration and dynamic response behavior of liquids under low-dimensional confinement deviate substantially from those in the bulk state. However, even in the simplest systems composed of hydrocarbon molecules confined by atomically smooth and inert surfaces, the migration pattern and frictional shear response of confined molecules remain unclear. Here, we demonstrated a pressure-modulated, discontinuous superlubricity phenomenon exhibited by alkanol molecular films confined within nanogeometries formed by atomically thin two-dimensional materials. This segmented superlubricity arose from a pressure-induced phase transition process of the alkanol film, during which the molecules spontaneously migrated and reconfigured into an ordered, hierarchically structured, polycrystalline molecular arrangement within the confined nanogeometry. Combined sum-frequency generation and molecular dynamics simulations revealed that a non-covalent hydrogen-bond network among alkanol molecules stabilized the highly ordered structure of the solid-phase molecular film. These findings underscore the critical role of ordered hierarchical reconfiguration in enabling superlubricity in low-dimensional nanoconfined molecular systems, providing decisive insights into the phase behavior and molecular origin of friction in nanoconfined liquid flow.

Hydration lubrication provides a significant paradigm for reducing friction at rubbing interfaces, with widespread relevance in engineering and human health. Although the frictional energy dissipation behind hydration lubrication is largely attributed to the shear between hydration layers, the influence of ionic distribution within the confined hydration layer remains unclear. Here, we show that ionic distribution critically modulates the frictional behavior through controlling the shear plane. By systematically tuning the surface charging of sliding interfaces, continuous control was achieved over the friction coefficient—from a superlubricity state under negative charging to a high-friction state under positive charging. Surface characterization and numerical analyses confirm that the contact zone is flattened and the hydration layer remains nanometers thick during sliding, with the tuning process governed by physical interactions. Molecular dynamics simulations reveal that surface charging modulates the spatial distribution of hydrated ions in the confined hydration layer, leading to asymmetric ion compositions across the shear plane. This asymmetry reshapes the energy barrier encountered during sliding, thereby altering the friction behavior significantly. Our results further elucidate the energy dissipation mechanism of electrotunable hydration lubrication and establish a theoretical framework for understanding the macroscopic modulation of interfacial friction.

Surface drag reduction is of crucial importance in enhancing fluid mechanical efficiency and reducing energy consumption. Microgroove structures inspired by shark skin have shown promising potential for reducing turbulence drag. However, further investigation is required into their systematic parameter optimization and universal characterization parameters. The present study selects five typical microgroove configurations: isosceles triangle (V), ellipse (U), rectangle (I), trapezoid (T), and right triangle (R). Employing computational fluid dynamics simulations in combination with genetic algorithms, the study optimizes geometric parameters with drag reduction rate as the objective. It is proposed that three new dimensionless parameters for characterizing drag reduction be introduced: hydraulic diameter (HD+), periodic hydraulic diameter (PHD+), and modified periodic hydraulic diameter (MPHD+). Compared with the commonly used dimensionless cross-sectional scale (L+), these novel parameters achieve a maximum reduction of approximately 27% in the coefficient of variation within the optimal drag reduction range, thereby demonstrating superior consistency in characterization. The study further generates cloud maps of drag reduction performance for the five grooves and validates the optimization results through circulating-water-tunnel experiments. The simulation captures the same trend of drag reduction as the experiments. The microgroove structures effectively suppress near-wall turbulence pulsations, optimize the wall shear stress distribution, alter near-wall vortex patterns, and reduce turbulent dissipation, thereby achieving drag reduction. The present research provides theoretical foundations and engineering references for the design and performance prediction of microgroove drag reduction surfaces.

Intracellular bacterial infections caused by methicillin-resistant Staphylococcus aureus (MRSA) pose serious threat to human health due to immune evasion and antibiotic resistance. Here, a new integrated drug delivery system (DDS) based on hollow mesoporous silica nanoparticles (HMSNs) with cascade-targeting, acidic/NIR dual responsive, photothermal antibacterial and immune modulation activities is reported. Mannose was grafted onto HMSNs through Schiff-base bond, resulting in Man-HMSNs. IR780 and curcumin (Cur) were coloaded into ManHMSNs which resulted in the integrated drug delivery system, IR780/Cur@Man-HMSNs. The nanoparticles are specifically recognized and internalized by macrophages via mannose receptor recognition. Crucially, the acidic phagolysosome microenvironment triggers Schiff base cleavage to expose primary amine groups, achieving surface charge reversal from negative to positive that simultaneously promotes intracellular bacterial targeting through electrostatic adhesion and cargo release a cascade-targeting mechanism distinguishing this work from conventional HMSN platforms. Under NIR irradiation, photothermal and photodynamic effects directly eradicate intracellular MRSA while accelerating drug release. Cur enhances immune modulation by upregulating the M1/ M2 polarization, which further promotes antibacterial capacity. In vitro, IR780/Cur@Man-HMSNs exhibits 92% MRSA biofilm eradication efficiency under acidic conditions. In vivo, it reduces the total bacterial burden to 2.45 log10 CFU and achieves efficient intracellular MRSA elimination. IR780/Cur@Man-HMSNs show better intracellular bacteria elimination efficiency both in vitro and in vivo, compared with those of free IR780/Cur and individual IR780 or Cur loaded DDS. Therefore, the photothermal antibacterial and immune regulation integrated nanosystems with cascade targeting and acidic/NIR dual responsive properties provides a new method for treating intracellular bacterial infections.

Underwater fuel cell systems, with their high energy density and zero-emission characteristics, are attracting increasing attention as a highly promising power source. To address the technical requirements of oxygen supply and oxygen concentration under typical operating conditions of a hydrogen-air fuel cell adapted in underwater environments, this paper proposes an oxygen-nitrogen ejector-based cathodic recirculation system. The study begins with the design method of the oxygen-nitrogen ejector, providing theoretical guidance for structural design optimization. Then, the designed ejector is fabricated using Monel 400 alloy, exhibiting inherent resistance to combustion and explosion risks even under high-pressure operating conditions. An experimental test bench is constructed to validate the design ejector. Experimental results confirm that the designed ejector achieves an entrainment ratio greater than one across all typical operating conditions, fulfilling the required performance criterion. The oxygen concentration at the fuel cell stack inlet exhibits an approximately linear increasing trend with rising power output, gradually increasing from 28.25% to 47.96%, satisfying the requirement that oxygen concentration remains above 25% and below 50%. Considering the diverse operating conditions faced by underwater fuel cell systems, the effect of varying operating conditions on ejector performance is also investigated. The results show that the ejector-based cathodic recirculation approach exhibits good performance characteristics under variable operating conditions of underwater fuel cells.

Recent advances in the field of tribology have increasingly focused on superlubricity tribolayers due to their exceptional properties. Despite burgeoning interest, a comprehensive synthesis of research in this area remains elusive. This article aims to bridge this gap by providing a detailed overview of the latest findings on superlubricity tribolayers, with a particular emphasis on their mechanisms across carbon-based, layered-material-based, and polymer-based systems. Initially, we explore the essential characteristics, classifications, and formation processes of tribolayers within the context of superlubricity, summarizing the factors that influence their development. We proceed to assess advancements in carbon-based materials, including diamond-like carbon, graphite-like, polymer-like, and nanostructured tribolayers. The role of layered-material additives such as graphene-related materials, two-dimensional transition metal dichalcogenides (TMDs), hexagonal boron nitride (h-BN), and MXene in the formation of superlubricity tribolayers is also examined. Furthermore, the evolution of polymer-based superlubricity tribolayers is analyzed. We conclude by delineating future research trajectories in superlubricity tribolayers, underscoring potential applications and the integration challenges in engineering practices. This review illuminates the scientific principles and technical approaches essential for achieving ultra-low friction in each type of superlubricity tribolayer. Additionally, we present current challenges and propose future directions to foster the practical application and development of superlubricity tribolayers.

Macroscopic solid-liquid synergistic superlubricity based on two-dimensional (2D) materials and liquid molecules integrates the low interlayer shear strength of 2D materials with advantages of liquid superlubricity, significantly reducing friction and wear in industrial applications. However, the low load-bearing capacity of single 2D material and the unclear synergistic superlubricity mechanism severely constrain the design of long-lasting superlubricity systems. Herein, through innovatively introducing van der Waals interaction-induced molybdenum carbide/molybdenum disulfide (Mo2CTx/MoS2) heterojunction as additives in ethylene glycol (EG), this Mo2CTx/MoS2-EG superlubricity system exhibits an ultralow friction coefficient of 0.0044, an extremely low wear rate of 8.17 × 10-10 mm3•N-1•m-1, and an ultralong lubrication life of 432 000 cycles (equal to 2160 m). Meanwhile, the maximum average contact pressure reaches 711.9 MPa. The in-situ formed special tribofilms enriched with heterojunction and homojunction nanosheets effectively reduce the shear strength under boundary lubrication. Notably, the ultralow shear strength at the Mo2C-O/EG solid-liquid interface and the unique pressure-responsive lubrication properties of EG molecules which leads to the formation of short-range-ordered structures are also crucial for achieving superlubricity. This study provides a new perspective for designing novel solid-liquid synergistic superlubricity systems by utilizing heterojunction nanomaterial and has great potential for application in industrial lubrication.

Achieving stable superlubricity of diamond-like carbon (DLC) films in air at elevated temperatures remains a critical challenge due to thermally driven hydrogen loss and oxidation-induced structural degradation. In this work, we demonstrate that silicon-doped hydrogenated amorphous carbon (a-C:H:Si) films exhibit robust superlubricity (μ ≈ 0.002) at 300 °C in atmospheric air. In situ Raman and fourier transform infrared spectroscopy (FTIR) analyses reveal that oxygen accelerates hydrogen desorption, generating active dangling bonds that facilitate thermomechanical-induced graphitization during sliding. Simultaneously, silicon reacts with oxygen to form a SiOx interfacial layer that stabilizes the high-sp2 tribofilm and prevents excessive structural collapse at elevated temperatures. Transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) results confirm the formation of a transferable tribofilm consisting of graphite-like layers and carbon-onion nanostructures, which provides a low-shear sliding interface. This work identifies the synergistic role of oxygen-driven graphitization and SiOx-mediated structural locking in enabling high-temperature superlubricity, offering a general strategy for designing solid lubrication coatings for extreme environments.

Sustainable lubrication of biomedical hydrogels with high stability is important for their application in dry eye disease (DED) treatment but remains a challenge. We report a novel strategy to achieve sustainable superlubricity under ocular conditions on the basis of the degradation of a thermosensitive P-C(n)PEG (polyethylene glycol (PEG)) hydrogel. First, by adjusting the composition and chemical structure of the P-C(n)PEG complex, its aqueous solution undergoes an adaptive sol-gel transition at 25.1 degrees C during heating, resulting in a gel state upon injection onto the ocular surface (35 degrees C). In addition, the P-C(n)PEG hydrogel obtained at 35 degrees C also shows superior performance, such as shear resistance, high transmittance (> 80%), rapid swelling, self-healing, and Ca2+ responsiveness, making it suitable for ocular applications. In the tear environment of DED patients with high reactive oxygen species (ROS) content, the P-C(n)PEG hydrogel degrades within 6 days through the breakage of crosslinking sites. The degradation solution of each day presents ultralow coefficients of friction (COFs) under ocular conditions through the hydration effect. Finally, the excellent biocompatibility of the hydrogel demonstrates its potential for ocular applications. This study systematically discusses the mechanism of sustainable degradation-induced superlubricity of P-C(n)PEG hydrogels, introducing a novel and promising strategy for DED treatment.

Solid–liquid interfaces are ubiquitous in nature and engineering, and their frictional behavior remains a key factor limiting performance gains in surface engineering. However, conventional tribology has largely focused on the effect of macroscopic variables such as surface topography, which do not account for the microscopic essence of ultra-low-friction phenomena at the nanoscale. Recently, the role of quantum-scale excitations, such as electrons and phonons, in micro-/nanoscale solid–liquid friction has been increasingly emphasized. By using in situ detection techniques such as terahertz time-domain spectroscopy and non-contact atomic force microscopy, the quantum-scale friction has been observed. Its essence stems from the energy and momentum transfer induced by fluctuations in liquid charge density or electron or phonon excitations within solids. However, limited capabilities in simultaneously probing multiple physical quantities at sub-nanometer and femtosecond resolutions hinder a comprehensive understanding of the quantum origins and applications of solid–liquid interfacial friction. This review synthesizes the cutting-edge theories and experimental advances in quantum-scale solid–liquid friction and proposes a potential breakthrough path based on deep integration of simulation and experiment to address core gaps, including incomplete theoretical frameworks and constrained detection capabilities. Despite multidimensional challenges, quantum-scale friction research demonstrates substantial potential for transformative technologies, such as low-power nanofluidic devices, high-efficiency energy storage, intelligent drug delivery, and super-lubrication materials, underscoring its significance for the convergence of interfacial science, quantum mechanics, and micro/nanofluidics.

Abstract Friction is a key determinant governing energy dissipation at solid–water interfaces, but the interfacial friction mechanism remains poorly understood. Herein, we systematically investigated water slip in MoS2/(WS2, hBN, and graphene) van der Waals heterostructures (vdWHs) with MoS2 as the top layer. The water slip length increases from 9.6 nm on MoS2/WS2 to 12.8 nm on MoS2/hBN and reaches 36.7 nm on MoS2/graphene based on atomic force microscopy. Photoluminescence and Raman spectroscopy reveal charge transfer from vdWHs to water that strongly correlates with the water slip length. Simulations indicate that electron transfer from MoS2/WS2 to water enhances charge density at vdWHs–water interfaces, hindering water slip. In contrast, slight hole injection from MoS2/(hBN and graphene) into water reduces the residual interfacial charge, promoting water slip. Our findings elucidate friction mechanisms from the perspective of interfacial electronic friction, providing novel insights into energy transfer at vdWHs–water interfaces and a foundation for the design of advanced nanofluidic devices.

Superlubricity refers to the state in which friction and wear almost disappear in the interface. Phase transition structural superlubricity (PTSS) is the superlubricity state achieved in liquid-solid interface by contact stress inducing liquid-solid phase transition of the lubricating medium. However, thus far, the maximum Hertz contact stress of PTSS currently realized is only approximately 600 MPa. In this study, PTSS with Hertz contact stress up to 1.313 GPa was achieved at the liquid-solid interface by constructing in situ heterojunction between the solid phase 1-dodecanol molecular layer and the graphene crystalline boundary tribofilm. By covalently modifying graphene with polydopamine, the adsorption capacity of graphene and SiC substrate was significantly enhanced, leading to the growth of crystalline boundary tribofilm with a thickness of 180 similar to 200 nm. In addition, when the contact stress is greater than 137 MPa, 1-dodecanol will undergo liquid-solid phase transformation phenomenon. Solid phase 1-dodecanol molecules self-assemble to form a herringbone-like configuration by forming hydrogen bonds between the hydroxyl groups. These insights provide a novel method for realizing structural superlubricity and bridge the realms of solid superlubricity and liquid superlubricity.

Reducing friction has been a human pursuit for centuries, and is especially important for the development of nanotechnology. Nowadays, with the atomic-level understanding of friction, it is possible to reduce friction by modulating the configuration and motion of interfacial atoms. However, how to further reduce friction by modulating the interfacial electronic properties is still unclear. Here we show a strategy to achieve friction and wear reduction through inducing dynamic electronic density redistribution via alternating electric current. The friction force between conductive Ir AFM tip and graphene on Ni substrate can be reduced to 1/4 under 1 kHz alternating current, and maintain for more than 70,000 s under 9.1 GPa contact pressure without any obvious wear. An electronic-level friction model (PTT-E model) is presented to unravel and quantify the tuning effect, showing that the alternating current induced dynamic electron density redistribution is the key to friction reduction. This work proposes a feasible and robust method to reduce friction and wear in nanomechanical devices, and advances the understanding and predicting of electronic contribution in friction tuning.

van der Waals heterostructures stacked by transition metal dichalcogenides and graphene provide a new opportunity for exploring superlubricity. However, the further reduction of friction is limited by the unavoidable charge transfer in the heterostructures. The dynamics of charge transfer occur at picosecond time scale, which cannot be detected by traditional friction instruments, making the friction mechanism of charge transfer unclear. Here, we investigate friction-induced charge transfer in WS2/graphene heterostructures with ultrafast friction energy dissipation detecting technique. The observed friction exhibits a strong linear relationship with the dissipation rate of interlayer charge transfer. By modulating the band structure of heterostructures, the dissipation rate of interlayer charge transfer can be efficiently tuned from 0.72 to 0.17 ps−1, resulting in a ~ 35% reduction in friction. This work gives the direct explanation of friction-induced charge transfer, which enables the high-performance micro-electro-mechanical systems and new insight into the origin of friction from the perspective of ultrafast electron dynamics.

Friction is the central cause for about 1/3 of the primary energy dissipation, severely impacting the performance limits of micro and nanoscale mechanical devices. Especially in two-dimensional semiconductor devices, electronic friction energy dissipation becomes particularly pronounced. However, the dynamic mechanisms underlying electronic friction energy dissipation remain unclear due to the ultrafast timescales of electronic behavior. Here, the ultrafast dynamics of electronic friction energy dissipation in monolayer WS2 is observed using femtosecond transient absorption spectroscopy. We find that friction exhibits a significant enhancement as the rate of electron energy dissipation increases. It is experimentally found to be closely related to the generation of atomic defects at the sliding interfaces. These defects capture electrons in picoseconds and provide a new energy dissipation channel, resulting in increased friction. This study reveals the dynamics of electronic friction energy dissipation, which is vital to understand the origin of friction and improve the performance of micro and nanoscale devices.

Hydrated ions can achieve exceptional hydration lubrication through their adsorption onto oppositely charged surfaces. Similarly, the charge characteristics of polyelectrolytes are expected to significantly impact the hydration lubrication performance of polyelectrolyte-modified materials through the adsorption of counterions with surrounding hydration layers of different strength. To verify this hypothesis, a comprehensive polyelectrolyte-embedded modification on ultra-high molecular weight polyethylene (UHMWPE) employing polyanionic, polyzwitterionic, and polycationic brushes was performed for the construction of modified materials with diverse surface charge characteristics. Subsequently, the polyelectrolyte-modified UHMWPE were subjected to systematic investigations to understand the effect of polyelectrolyte charges on the surface hydration and lubrication performance under varying electrolyte conditions, including concentration and types of counterions. All polyelectrolyte-modified UHMWPE displayed more effective hydration lubrication with increasing ion concentrations, showcasing the contribution of hydrated counterions in the load-bearing and friction reduction of charged polyelectrolytes. A vertical comparison among different polyelectrolytes revealed that, polyanionic poly(3-sulfopropyl methacrylate potassium) (PSPMK), characteristic of the highest surface charge density, exhibited the strongest hydration lubrication that enables macroscale superlubricity. At the same time, a horizontal comparison of varying counterions in the solutions within each polyelectrolyte-modified UHMWPE displayed a sequence of hydration lubrication performance with more strongly hydrated ions resulting in lower friction and wear. These findings elucidate the impact of polyelectrolyte charge characteristics on hydration lubrication, highlighting the combined influence of ion adsorption density, determined by intrinsic surface potential, and the ionic hydration strength of surrounding counterions in determining the overall hydration lubrication performance of modified UHMWPE.

Novel intelligent lubricating materials and surfaces exhibit on-demand responsiveness and adaptability. The biomimetic self-regulating mechanism empowers in-service tribo-pairs with the autonomy to sense external environmental stimuli and adaptively modulate interfacial lubrication states. Such capabilities provide a groundbreaking solution for the "online sensing-decision-execution" intelligent transformation of advanced equipment in aerospace and defense sectors. Concurrently, the AI-driven intelligent inverse design of lubricating materials has revolutionized the traditional trial-and-error paradigm, enabling highly efficient and demand-responsive customization of lubrication for mechanical interfaces. This innovation provides a novel pathway for establishing a scientific framework for high-performance and high-reliability lubrication materials and surface systems capable of addressing diverse complex operational conditions. The intelligent evolution of lubricating materials and surfaces is progressively redefining the research paradigms in mechanical interface science, potentially unlocking breakthrough opportunities to advance frontier tribological theories and technologies. This paper discusses current research on self-lubricating, self-repairing, and self-diagnosing intelligent lubricating materials and surfaces, the frontier progress of AI-accelerated inverse design, and their future development trends, taking intelligent lubricating materials and surfaces and their AI paradigms as the pointcut. Currently, self-lubricating tribo-pairs that are environmentally robust and operationally adaptable use solid lubricating materials as the matrix, with liquid or solid-liquid-coupled lubricants as the dispersed phase. Effectively enhancing the interfacial lubrication performance can be achieved by releasing trace liquid lubricants to form fluid or boundary films. Two primary approaches are used for incorporating liquid lubricants into a tribo-pair matrix: porous-based self-storing and lubricating strategies and capsule-based self-storing and lubricating strategies. The development of capsule-based self-storage and lubrication techniques makes it a novel solid superlubrication method after carbon-based superlubrication and two-dimensional material superlubrication. This method enables macroscopic superlubrication at temperatures between 0 and 250 degrees C. Although intelligent capsule-based self-storing and lubricating technologies can significantly reduce friction and wear on tribo-pair surfaces, material degradation and surface damage are inevitable during prolonged service. It is important to promptly repair wear and damage to improve the wear resistance and service life of tribo-pair materials. Intelligent surface healing technologies for tribo-pairs can be broadly categorized into extrinsic and intrinsic types. Extrinsic repair typically employs stimulus-responsive materials (for example, microcapsules or microvascular networks) to encapsulate active repair agents that are autonomously released upon external stimulus-induced damage, thereby facilitating physicochemical reactions for localized repair. Intrinsic repair leverages the reversible reorganization of dynamic covalent bonds (for example, Diels-Alder (DA) bonds, acylhydrazone bonds, and disulfide bonds) or non-covalent interactions (for example, hydrogen bonds, metal-ligand coordination, and host-guest interactions) to enable autonomous damage repair. Moreover, excessive wear on tribo-pair surfaces generates clearance, and its enlargement exacerbates vibration during equipment operation and reduces service life. Thus, it is imperative to endow tribo-pairs with self-diagnostic capabilities for real-time monitoring of wear locations and damage severity, enabling intelligent lifecycle management and predictive maintenance of equipment. Three approaches are the primary focus of the current intelligent self-diagnostic technologies: dye-based chromatic detection, electrical signal diagnostics, and optical signal diagnostics. The latest paradigm in the research and development of lubricating materials and surfaces, driven by AI, is the fourth paradigm after empirical, theoretical, and computational science paradigms. The primary technical approach involves employing machine-learning models to establish potential mapping relationships between the properties (such as composition and structure) of lubricant materials and surfaces and their lubrication performance. This enables prediction of the lubrication performance of new materials and surfaces. Furthermore, by integrating optimization algorithms or deep-reinforcement-learning techniques, global optimization within the high-dimensional nonlinear design space of lubricant materials and surfaces can be achieved rapidly, thereby facilitating the efficient inverse design of materials and surfaces with target attributes. This transformative research paradigm is expected to decipher the lubrication and friction reduction mechanisms at mechanical interfaces, overcome the efficiency limitations of traditional trial-and-error iterative methods, and ultimately realize demand-driven customization of lubricant materials and surface designs.

Controlling exciton transport in van der Waals heterostructures opens new pathways for exploring quantum phenomena and advancing optoelectronic devices. Previous studies have primarily focused on bilayer structures, where exciton transport is governed by limited electronic hybridization between layers. Extending to trilayers promises greater freedom in tuning electronic hybridization and enabling richer exciton transport phenomena, yet this area remains largely unexplored. Here, we demonstrate tunable and robust exciton transport in fully hybridized WS2/MoSe2/WS2 trilayers. Unlike the monotonic behavior observed in bilayer systems, trilayers exhibit symmetry-driven exciton transport that can be modulated using external electric fields and remains stable up to 165 K. This distinctive transport mechanism originates from hybridization-driven transitions among different excitonic phases-quadrupolar, hybrid dipolar, and interlayer excitons. These transitions can also be triggered by adjusting the exciton density, resulting in abrupt changes in both transport characteristics and exciton lifetimes. Our findings provide essential insights into exciton transport mechanisms in multilayer heterostructures and highlight electronic hybridization as a key design principle for next-generation quantum optoelectronics.