Xiang Gao

Superhydrophobic surfaces can reduce underwater skin-friction drag by sustaining a lubricating plastron at the solid–liquid interface. Their practical use, however, is limited by plastron collapse under elevated hydrostatic pressure. Inspired by the micro/nanotopography of springtail cuticles, we constructed a molecular dynamics model of a superhydrophobic surface with mushroom-shaped re-entrant microstructures (MSRM) that markedly improves pressure resistance and drag-reduction performance. The Cassie-to-Wenzel transition was identified from abrupt changes in the solid–liquid interfacial interaction energy. The critical plastron-collapse pressure increased nearly linearly with the projected microstructure area fraction, whereas enhanced hydrophobicity raised both the critical pressure and the critical contact angle. Within the parameter range examined, projected area fraction exerted a substantially stronger influence on plastron stability than surface wettability. A theoretical model was developed to describe the combined effects of projected area fraction, wettability, and characteristic size on the plastron-collapse pressure. Among the morphologies considered, the MSRM surface exhibited the highest initial Cassie-state critical pressure and the largest slip velocity, demonstrating favorable overall plastron stability and drag-reduction performance. The T-shaped microstructure exhibited two successive wetting thresholds associated with its upper and lower cap edges, suggesting a route toward multilevel pinning designs. These findings will provide a molecular-scale basis for the design of durable superhydrophobic drag-reducing surfaces.

Buckling instability in carbon nanotubes (CNTs) represents a major limitation for their structural reliability in nanoelectromechanical systems. In this work, we use molecular dynamics (MD) simulations to uncover a novel mechanism for enhancing bending-induced buckling resistance in CNTs: filling the nanotube with water. We systematically investigate the effect of water-filled and structural dimensions on the bending and buckling behavior of CNTs, and reveal that although the initial bending stiffness remains essentially unchanged by water filling, the onset of bending-induced buckling under transverse load is markedly delayed. For example, for a (10,10) CNT of length ~174 Å, the critical bending-buckling load increases by ~75% when water-filled compared to the empty tube, demonstrating a substantial improvement in structural stability. The enhancementoriginates from fluid–structure coupling, whereby van der Waals interactions between the confined water and the CNT wall, together with deformation-induced reorganization of the confined water structure, constrain wall deformation and postpone instability. Additionally, we find strong size-dependent behavior: smaller-diameter CNTs experience more pronounced buckling-delay (delays of ~121%, 101%, 75%, 67% and 21% for diameters of 8.14 Å, 10.85 Å, 13.56 Å, 16.27 Å and 20.34 Å, respectively), Structural slenderness further modulates the instability behavior:although longer CNTs exhibit lower absolute bending stability, water filling induces progressively larger buckling delays of ~56%, 75%, and 90% for tube lengths of 144 Å, 174 Å, and 204 Å, respectively. These findings highlight a previously unexplored water-filling effect on bending-induced buckling, providing a mechanistic basis for tuning the mechanical stability of CNT-based nanostructures and offering guidance for the design of flexible nanoelectromechanical and integrated nanoscale systems.

The nanoscale electrical double layer (EDL) governs macroscopic phenomena such as ion adsorption and reaction kinetics, serving as a fundamental determinant in diverse applications ranging from sensing, and catalysis, to energy storage. While classical EDL models primarily describe conductive interfaces, most naturally occurring EDLs form at non-conductive surfaces in liquid environment, where characterization remains fundamentally challenging due to the constraints of conventional techniques. Here, we present a triboelectric nanogenerator (TENG)-based triboelectric charge transfer probe that utilizes the intrinsic solid-liquid contact electrification (CE) process to operando monitor the formation and evolution of the EDL at non-conductive interfaces. This bias-free and electrode-independent approach enables direct probing of interfacial charge dynamics fundamentally inaccessible to conventional electrochemical approaches constrained by conductive substrate dependencies and external potential requirements. This method also reveals distinct EDL behaviors, particularly in electrolytes with asymmetric ion sizes at concentrations exceeding 10^-1M and at non-conductive interfaces. Its fundamental mechanism and measurement precision were rigorously validated via atomic force microscopy, Kelvin probe force microscopy, surface-enhanced Raman spectroscopy, and molecular dynamics simulations, establishing a robust analytical platform and theoretical basis for EDL studies. This work introduces a CE-based methodology for direct triboelectric charge characterization on dielectric surfaces, overcoming conventional conductive substrate limitations. By integrating classical EDL theory with triboelectric frameworks, we establish models resolving interfacial charge dynamics across diverse solid-liquid interfaces, including high ionic strength regimes. It confirms material-agnostic applicability. This paradigm simultaneously advances fundamental EDL mechanisms and enables programmable charge manipulation for next-generation iontronic power, sensing, and neuromorphic devices.

Superhydrophobic conical surfaces exhibit significant potential in microfluidic manipulation and interfacial engineering due to their unique wettability and geometric constraints. However, previous studies have focused on steady-state bubble transport capacity on cone surfaces, overlooking the critical role of bubble morphology evolution in dynamic performance. Herein, a fluorinated silica nanoparticle suspension was synthesized and applied via spray-coating technology onto additively manufactured conical substrates, achieving simultaneous superhydrophobicity (water contact angle >150°) and exceptional bubble adhesion characteristics. Four stages of bubble transport on these surfaces were identified: (1) bubble-cone contact, (2) deformation and spreading, (3) maximum deformation and transition, and (4) stable transportation. A comparative analysis of bubble transport morphology across conical surfaces reveals that the transition stages 2 and 3, marked by maximum deformation and interfacial instability, play a pivotal role in determining overall transport efficiency. These observations were validated by COMSOL simulations, which showed consistent deformation times and revealed how bubble morphology influences migration velocity and pressure distribution. Notably, the double-cone structure enhanced transport efficiency by 62% over the single-cone design by simultaneously suppressing vertical bubble deformation and enhancing interfacial fluidity during the transition stages. Increasing the surface contact angle can enhance bubble transport velocity, whereas an increase in fluid viscosity slightly reduces the velocity. Simulations also show that cone arrangement strongly affects bubble transport, with vertical double-cones fastest and 30° configurations slowest. These findings offer practical insights for optimizing microfluidic devices and bubble collection systems, such as gas–liquid separators or microreactors, requiring precise hydrodynamic control.

Oceans, which cover more than 70% of Earth’s surface, are home to vast biological and mineral resources. Deep-sea exploration encounters significant challenges due to harsh environmental factors, including low temperatures, high pressure, and complex hydrodynamic forces. These constraints have led to the widespread use of underwater robots as essential tools for deep-sea resource exploration and exploitation. Conventional underwater robots, whether rigid with fixed stiffness or fully flexible, fail to achieve the propulsion efficiency observed in biological fish. To overcome this limitation, researchers have developed adjustable stiffness mechanisms for robotic fish designs. This innovation strikes a balance between structural rigidity for stability and flexible adaptability to dynamic environments. By dynamically adjusting localized stiffness, these bio-inspired robots can alter their mechanical properties in real time. This capability improves propulsion efficiency, energy utilization, and resilience to external disturbances during operation. This paper begins by reviewing the evolution of underwater robots, from fixed-stiffness systems to adjustable-stiffness designs. Next, existing methods for stiffness adjustment are categorized into two approaches: offline component replacement and online real-time adaptation. The principles, implementation strategies, and comparative advantages of each approach are then analyzed. Finally, we identify the current challenges in adjustable-stiffness underwater robotics and propose future directions, such as advancements in intelligent sensing, autonomous stiffness adaptation, and enhanced performance in extreme environments.

The capture and utilization of underwater fuel bubbles such as methane can alleviate the greenhouse effect, solve the global energy crisis, and possibly improve the endurance of underwater equipment. However, previous research routinely failed to achieve the integrated process of continuous adsorption, transportation, and collection of bubbles limited by the trade-off between the bubble adhesion and transport efficiency dependent on interfacial pinning, tremendously hindering the direct capture and utilization of underwater fuel bubbles. To break through this bottleneck, a magnetic-guided conical arrayed surface (CAS) associated with a laser etching technique is fabricated conveniently to realize superhydrophobicity. The bubbles on laser-etched CAS have higher adhesiveness and low-pinning transport compared with those on the nonlaser-etched surface. Intriguingly, the gas film adsorbed within the CAS seems to be a gas channel, which accelerates the bubble coalescence and fast spreading to eventually realize the integration of transport, coalescence, and collection. The dynamic behaviors of bubble adsorption, transportation, and coalescence on CAS are probed to reveal the mechanism of the gas film-generating process within conical arrays. Furthermore, a novel underwater bubble-collecting device with multiangled CAS is proposed to achieve multidirectional capture, highly efficient transportation, and collection of rising bubbles. The results advance our understanding of dynamic behaviors of bubbles at solid-liquid interfaces and facilitate design and manufacturing of an apparatus for bubble collection.

As a two-phase hybrid material, liquid-filled carbon nanotubes (CNTs) provide a great opportunity to design dexterous flexible nano-manipulator actuated by electric field. Here, we report a group of saline solution-filled CNTs with the end constraint can realize 360° all-round bending in a suitable electric field. The molecular dynamics (MD) simulation results show that saline solution-filled CNTs can be bent under the axial-lateral compound electric field, whereas the bending deflection increases with the increase of salinity, CNTs length and electric intensity. The deformation mechanism of saline solution-filled CNTs under the electric field is clarified by exploring the movement and distribution of salt ions in CNTs under the axial electric field. Moreover, based on the bending deformation characteristics of saline solution-filled CNTs, the MD simulations for the two-finger and four-finger nano grippers grasping diamond balls are carried out to demonstrate the micromanipulation functions of saline solution-filled CNTs. The findings will provide an important theoretical basis for the design and application of micromanipulation devices based on low dimensional carbon materials.

In recent years, a novel electro-hydraulic integrated self-powered brake system for aircraft has been proposed. A modular “self-powered device” is installed near the wheel to recover the rotational kinetic energy when the wheel lands and convert it into hydraulic energy for braking. The energy conversion device is the compact high-power-weight ratio energy harvesting mechanism, which needs to be designed in the extremely narrow internal space of the wheel. At the same time to ensure high reliability, high strength, high power weight ratio, difficult, and wheel brake disc internal temperature reaches 600 °C above, this to the design of the can take institutions are challenges. In this paper, the high strength compact high power-weight ratio energy conversion device as the research goal, through new principles, new structure, new materials, new technology, new methods and other means of the energy taking mechanism design and development, and finally achieve the strength, stiffness, reliability, life of the energy conversion device to meet the requirements of the system.