This study demonstrates a passive strategy for enhancing the output of liquid-solid triboelectric nanogenerators (L-S TENGs) using superhydrophobic meshes to induce microdroplet generation and regulate droplet charging. When a millimetric water droplet impinges on a superhydrophobic mesh, it fragments into microdroplets, leading to a substantial increase in the total liquid surface area. This surface-area amplification is directly correlated to the total droplet charge, which can be further tuned by selecting appropriate hydrophobic coating materials on the mesh. At an impact velocity of 2.58 m/s, the total liquid surface area increased by up to 4.06-fold, resulting in a 7.7-fold enhancement in total droplet charge compared with that in the no-mesh case. Consequently, the voltage output of the L-S TENG was significantly improved, reaching -0.329 V─more than an 11-fold increase relative to that generated by a single droplet without a mesh.

Droplet splashing during impact plays a critical role in diverse applications such as disease transmission, inkjet printing, spray cooling, fuel injection, and surface coating. Despite extensive studies, quantitatively characterizing splashing under high-speed impact remains challenging due to the extremely short timescales, small length scales, and complex interfacial instabilities involved. In this study, we develop a deep learning–based machine vision framework using the Segment Anything Model (SAM) to quantitatively analyze the kinematic characteristics of secondary droplets generated during impact. On superhydrophobic surfaces with varied micro–nano structures, we find that splashing behavior is governed by a combination of geometric parameters, including surface pitch, air fraction, and pillar diameter. In particular, surfaces with larger pitch tend to exhibit more pronounced splashing trends. These findings suggest that conventional roughness-based criteria alone are insufficient to predict splashing behavior and the detailed structural parameters must be considered. By enabling reproducible, frame-by-frame quantification of droplet ejection events, the proposed framework provides new insights into droplet–surface interactions and offers practical guidelines for the design of functional surfaces for splash control.

Force measurement and interface observation during droplet impact are essential for understanding droplet behavior in both scientific and industrial applications. However, achieving both backside optical transparency for interface observation and two-axis force measurement for quantifying shear-force effects has been challenging with conventional force-sensing methods using a single device. In this study, we propose a transparent two-axis force plate based on the sampling moir & eacute; (SM) method combined with a line-scan camera, which enables high-temporal-resolution force measurement while permitting optical observation beneath the impacted surface. The proposed device consists of a spring-supported, laser-cut glass plate with a periodic striped pattern and a prism-based optical system. A line-scan camera is employed to overcome the inherent tradeoff between spatial resolution and frame rate associated with area-scan cameras. By duplicating the pattern image using a prism and analyzing the resulting displacements via the SM method, in-plane and out-of-plane forces are independently measured from 1-D images. Calibration experiments confirm linear force-displacement characteristics, with force resolutions of F-x =0.39 mN and F-z =0.12 mN. Positional errors remained below 2% in-plane and 6% out-of-plane. The fabricated device exhibits a minimum resonant frequency of 656 Hz, which is sufficient to capture short-duration impact events. Finally, droplet impact experiments are conducted under both vertical and tilted conditions. Compared with the vertical configuration, the inclined condition demonstrates F-x values comparable in magnitude to F-z and a clear elongation of the droplet induced by shear forces. Overall, the proposed force plate provides a customizable platform for high-precision, high-speed force measurements in droplet dynamics.

The impact of liquid droplets on porous substrates governs a wide range of natural and industrial processes, from soil erosion and additive manufacturing to agricultural spraying and pathogen transmission. This review focuses on recent progress into two distinct types of porous substrates: deformable granular beds and thin porous membranes. On granular beds, interaction of liquid drop and particle gives rise to such rich phenomena as crater formation, liquid marble formation, and granule aggregation, as shaped by interplay of inertia, capillarity, viscous forces and substrate deformability. Thin porous membranes permit penetration of high-inertia liquid drop, thus exhibiting unconventional drop spreading and rebound behavior, and triggering post-penetration dynamics such as jet formation, microdroplet ejection, and spray generation. We examine the effects of viscosity, wettability, and non-Newtonian properties on these dynamics. By comparing these two classes of porous substrates, we highlight both common physical principles and system-specific behaviors. This unified perspective aims to guide future research and application of droplet-porous surface interactions in areas including inkjet printing, environmental remediation, and infection control.

The dynamic impact of liquid drops on rigid surfaces can be found in numerous practical applications, including spray cooling, inkjet printing, spray coating, airplane wings, and steam turbine blade. Notably, the post-impact dynamics can affect the robustness and durability of the impacted surfaces by causing erosion or degradation. This study experimentally and numerically investigates the impact forces on cylindrically curved superhydrophobic (C-SHPo) surfaces across a wide range of Weber number (We = 50 - 175) and cylinder diameter (3 - 20 mm). The results show two distinct peaks in the impact force: the one originating from the inertial impact of the drop and the other from the pressure rise during the retraction motion. Initial peak force increases with We owing to higher inertial effect, whereas the second peak force shows unexpected behavior on small C-SHPo surfaces: the second peak force increases with We first then it decreases again if We is greater than the certain Weber numbers. Based on the three-dimensional direct numerical simulation, it is found that the reduced contact area resulted from the detached and fingered parts of drop plays a major role in the reduced second peak force on small C-SHPo surfaces.

This paper proposes a method to measure the 2-axis force of a droplet collision when it is dropped on the slope surface. To calculate the 2-axis small impact force at the same time, a force plate using the sampling moire method with a line scan camera and a prism is employed. The sampling moire method can precisely calculate the pattern's in-of-plane displacement. Moreover, both in-plane and out-of-plane displacements of the pattern are detectable utilizing a prism. Additionally, a line scan camera can capture 10k images in one second with 4096 pixels width, which is sufficient for high precision and high-time resolution displacement measurement. In this report, line&space patterns are attached to a glass plate, which is supported by four springs. The applied 2-axis force is calculated by multiplying the analyzed displacement and spring constant. We fabricated and calibrated the force plate system. It was confirmed that the force resolutions were less than 4 mu N for the 2-axis. Finally, droplet collision experiments were conducted under several conditions. The force plate was able to measure impact force during oblique impact with 2-axis.

ABSTRACT Slippery surfaces that minimize contact line pinning and enable high droplet mobility have emerged as promising solutions for enhancing condensation and anti‐icing performance. Among them, lubricant‐infused surfaces (LIS) and liquid‐like surfaces (LLS) are two dominant design strategies that achieve dynamic liquid repellency via fundamentally different mechanisms. This review distills what works, why it works, and how to make it last. We clarify the distinct mechanisms: liquid–liquid interfacial transport in LIS versus tethered‐chain mobility in LLS and connect these to application‐level outcomes: stable dropwise condensation (including low‐surface‐tension fluids), low ice adhesion, and delayed frost propagation. We identify durability as the rate‐limiting barrier and clarify the primary failure pathways: lubricant loss in LIS (via cloaking, wetting‐ridge–mediated entrainment, and frost wicking) and molecular or structural degradation in LLS (including chain scission, entanglement, and interfacial heterogeneity). From these insights, we extract design rules for LIS and LLS: employing closed‐cell and hierarchical reservoirs to immobilize lubricants under shear; defining lubricant's property windows, such as viscosity and miscibility, that suppress cloaking while retaining mobility; and optimizing grafting‐density and molecular‐weight regimes to preserve LLS segmental dynamics while ensuring coverage. We further highlight emerging, application‐ready solutions, such as active and passive lubricant replenishment schemes, stimuli‐ and phase‐change–responsive systems, hybrid LIS/LLS stacks, and fluorine‐free chemistries. Finally, we outline critical future directions to ensure commercial success, focusing on overcoming economic barriers and meeting environmental regulations. Together, these insights provide a roadmap for engineering scalable, long‐lived slippery surfaces that translate interfacial physics into robust performance across next‐generation energy, water, and anti‐icing systems.

Superhydrophobic (SHPo) surfaces resist fouling by maintaining a gas layer, known as plastron; however, their stability underwater is often compromised by factors such as high hydrostatic pressure and gas diffusion. In this study, we developed an active anti-fouling SHPo surface with integrated electrolytic gas generation, enabling cyclic regeneration of the gas layer even under fouling conditions. The liquid-gas meniscus movement during gas replenishment was found to effectively detach adhered bacteria from the surface. The surface's ability to recover the gas layer was evaluated through cyclic relative reflectivity tests. Using Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) as biofouling agents, the results showed that the surface could restore reflectivity to over 80 % of the initial value after three gas depletion-regeneration cycles, even in foulant-rich environments. Cyclic plastron recovery experiment using a stained P. aeruginosa demonstrated a bacterial coverage reduction of over 80 % compared to non-regenerated SHPo surfaces, maintaining bacterial coverage area below 10 % after 12 and 24-hour exposures under static condition. Additionally, the improved antibiofouling efficiency (IAE) reached 92 %, significantly outperforming hydrophobic and hydrophilic surfaces. These findings confirm that the repeated gas layer regeneration on SHPo surfaces substantially enhances antibiofouling performance, providing a promising approach for mitigating fouling in various applications.

When a water drop is impinged upon a superhydrophobic surface with submillimetric surface structures, unconventional impact dynamics such as pancake-like bouncing and asymmetric drop spreading can occur. However, the fabrication of such surface structures often requires an unconventional fabrication approach, which is either time-consuming or costly. In this study, we propose a simple lithography-based approach to manufacture submillimetric cone-shaped pillars over a large area by taking advantage of a unique optical property of hydrogels: a change of refractive index after UV-curing. With an additional hydrophobic nanoparticle coating, we demonstrate that such structures can be used to reduce the contact time during drop impact and induce a drop rotation during rebound. Moreover, the flexibility of hydrogels enables the transfer of surface structures to non-planar substrates.

Recent studies on water-based pyroelectric generators (PEGs), which convert thermal energy to electrical energy, have focused on different operational modes like water evaporation, water stream, and droplet sliding. However, the development of sustainable, high-powered generators and comprehensive theoretical models has been limited. In response, our research introduces a droplet-based superhydrophobic pyroelectric generator (S-DPEG), exploiting the characteristics of lead magnesium niobate-lead titanate (PMN-0.3PT) coated with titanium dioxide nanoparticles. We analyzed power density by considering the phase transient temperature that maximizes the pyroelectric coefficient of PMN-0.3PT, testing various Weber numbers and droplet diameters within a moderate operating temperature range of 40°C to 80°C. Considering the dynamic characteristics of water droplet on superhydrophobic surfaces, we suggest a peak current model that can accurately predict the peak current within ~15% of error. Also, the maximum power density of 54.5 μW/cm2 at a droplet diameter of 3.6mm and a temperature of 80°C, a noteworthy improvement over 3 times higher than previous water-based PEGs. Our results enhance the understanding of the pyroelectric effect coupled with drop impact dynamics and outline novel strategies for designing high-performance water-based PEGs.

This study introduces a facile method for fabricating hydrophilic 3D-network hydrogels, integrating plasmonic gold nanoparticles to boost solar absorption, enhancing evaporation rates and solar efficiency to 1.6 kg m−2 h−1 and 77%, respectively.

While perfectly water-repellent surfaces, such as superhydrophobic surfaces, always repel water drops after contact, the drops can either stick to or bounce off lubricant-impregnated surfaces (LISs) depending on the impact conditions. This study investigates the rebound behavior of water drops on LIS, highlighting how this phenomenon significantly depends on both the viscosity of the lubricant and the obliqueness of the surface. Both the lubricant viscosity and surface obliqueness contribute to an increase in dissipation: an increase in lubricant viscosity directly increases the viscous force, and increased surface obliqueness causes the drop to slide on a viscous liquid, resulting in increased dissipation energy. Throughout the study, the dissipation energy attributed to sliding and inelastic collision is addressed. Additionally, we identify an intriguing rotational behavior of drops post-rebound. The direction of rotation varies with the viscosity of the LIS, impact velocity, and surface obliqueness. Numerical simulations demonstrate that this rotation direction is determined by the front and rear velocities of the drop, which is affected by the dynamic advancing and receding contact angles.

In converting a salinity difference to the electrical power by using an ion-selective membrane, achieving a high-power density necessitates both a high ion permeability and ion selectivity of the membrane. However, meeting these two requirements often leads to the conflicting tradeoff in the membrane properties. In this study, we introduce a new mechanistic approach to meeting both requirements by combining an ultra-thin (<100 nm thickness) graphene oxide-based membrane for a high permeability with an asymmetric access area for a high ion selectivity, forming a new type of ionic-diode nanofluidic system. With a graphene oxide/silk fibroin composite membrane, a large power density of 2 kW/m2 is achieved with 32% conversion efficiency under a 1000-fold salt concentration ratio. This approach can be utilized to overcome the low power density limitation with any ultra-thin membranes, and thereby it will provide a new route to utilize blue energy in a reliable and efficient way.

This study delves into the dynamics of generating microdroplets by impacting a droplet onto a micropore on superhydrophobic copper substrates. It identifies the necessary impact velocities for single microdroplet formation for each micropore and characterizes microdroplet size in relation to micropore diameter. The results underscore the significant role of viscosity, especially as the diameter of the micropore decreases. For micropores measuring 400 μm, an increase in viscosity up to 8 cP does not alter the critical impact velocities, while smaller diameters of 50 and 100 μm see a notable change in critical velocities with even minor increases in viscosity. Remarkably, the diameter of the microdroplet remains consistent regardless of changes in the liquid viscosity or impact velocity. This research showcases two practical uses of single microdroplets: printing on paper and fabricating microbeads. The insights gained from these findings pave the way for advancements in printing technology and microfabrication techniques.

The transport of ions in nanofluidic systems, specifically the rectified ion transport or the ionic diode phenomenon occurring in the presence of asymmetrical geometry and/or charge distribution, has drawn considerable attention due to its relevance in energy conversion and biosensing applications. However, previous numerical research has frequently overlooked the concurrent liquid flow within these systems, even though multiple experimental studies have highlighted intriguing flow patterns in ionic diode configurations. In the present study, we employ comprehensive numerical simulations to probe the influence of geometrical or charge asymmetry in a nanofluidic system on electroosmotic flow and ion transport. These simulations employ the Poisson–Nernst–Planck equation in conjunction with the Navier–Stokes equation. Our findings reveal that even when the current rectification trend is consistent between conical and straight nanopores, charge asymmetry and geometric asymmetry can generate significant variations in the rectification effects of electroosmotic flow. Furthermore, our research indicates that the direction of ion rectification and flow rectification can be independently manipulated by utilizing charge asymmetry in conjunction with geometric asymmetry, thereby facilitating advanced control of ions and flows within nanofluidic systems. Collectively, our findings contribute to a more profound understanding of the mechanisms underlying osmotic flow rectification and propose a novel approach for developing efficient ion and flow rectification systems.

Precise and controlled drug delivery is crucial in continuous infusion systems used for drug treatment, anesthesia, cancer chemotherapy, and pain management. Elastometric pumps are commonly utilized in continuous infusion systems for their ease of use and cost-effectiveness. However, the infusion accuracy is often compromised due to the fluctuating supply pressure of elastomeric pumps, requiring an additional flow regulator to stabilize the output flow rate. We, here, present a novel approach to passively control a flow rate even under the fluctuating pressure environment based on a channel deformation. The flow rate control is enabled by a flow regulator consisting of an open-end microchannel, a closed-end microchannel, and a flexible membrane in the middle. The pressure within an open-end microchannel decreases in the downstream direction, while the pressure within a closed-end microchannel remains equal to the input pressure, creating the pressure difference between the two channels. The membrane deforms in response to this pressure difference, allowing for adjustment of the output flow rate by decreasing the flow path area with the increase in the input pressure. It is found that this concept successfully works by maintaining a steady output flow rate over a target pressure range of 40–50 kPa. Fluid–structure interaction numerical simulations and theoretical analysis are used to explain the flow rate control mechanism of the device. The results show that the present approach offers a promising solution for achieving stable drug delivery in continuous drug infusion systems, addressing the limitations of conventional elastomeric pumps.

We experimentally confirmed the idea of mitigating (or delaying) the cavitation on the turbomachinery (rotating blades) by transforming the blade surface to be superhydrophilic, thereby the population of the cavitation nuclei is reduced near the surface. We focused on the changes in the cavitation incidence rate, amount of cavitation bubble, and bubble distribution on the superhydrophilic blade through the high-speed camera imaging, compared to the case with a regular (i.e., smooth) surface. With superhydrophilic blades, the cavitation incidence rate decreased significantly, indicating that fewer nuclei evolved into the actual cavitation bubbles. This is also associated with 8.6% delay of the critical rotational speed at which the cavitation process is almost completely established (incidence rate exceeds 80%), and the reduction in the total amount of cavitation bubbles was achieved as much as 18% (maximum 38% in the tested range of rotational Reynolds number). Additionally, the distribution of cavitation bubbles was generally pushed upstream, with fewer bubbles extending downstream, i.e., pushed away from the blade trailing edge. We believe the present results are promising enough to spur the follow-up investigation for the in-depth analysis and practical application toward the robust cavitation control without the substantial modulation of the geometry.

Recently, membrane-based power generation from salinity difference has been in the spotlight as a blue energy harvesting, but achieving a high power density and conversion efficiency still remains as a major challenge in this approach. Instead of developing new membranes, regulating the thermal condition within the membrane has been proposed as a way to enhance the power generation by several numerical studies, but this concept has rarely been explored through the systematic experimental studies due to the difficulty of imposing a controlled temperature gradient within the membrane. In this work, we experimentally and systematically study how the temperature difference can influence osmotic power generation using a commercial polycarbonate membrane and demonstrate that even when a thermal gradient is negligibly small within the nanoporous membrane, it is still possible to achieve a significant enhancement of the power generation. We propose that the effective ion concentration at the interfacial region between the reservoir and the membrane varies with the direction of the imposed temperature difference, such that the opposite direction of salinity and temperature differences can lead up to 5.3 times power enhancement as a result of the increase of the effective ion concentration ratio across the membrane. As an example of practical applications, we apply our findings to a floating type nanogenerator by incorporating a solar absorber to generate the temperature difference spontaneously under solar radiation conditions, and the results with the nanogenerator show that the power generation is indeed enhanced under both simulated and actual solar radiation conditions. We believe that our approach can be applied to any nanoporous membrane regardless of its thermal property, and therefore would provide a practical path to the power enhancement of reverse electrodialysis systems.

1 The range of the vertical axes of Fig. 10 is incorrect, and the new figure with corrected range is shown below

We developed asymmetric capillary wicks composed of slanted microposts using inclined photolithography. Then we investigated the effects of inclination angle and wicking direction on the capillary and the heat transfer performances. The working fluid accelerates when it flows in the slope direction of the structure (forward direction, FD) and decelerates when it flows in the opposite slope direction (rear direction, RD). We applied the scaling law to the capillary rise experiment data to verify that the inclination angle and the wicking direction affect the capillary performance. The capillary performance parameter was improved by up to ∼39% with FD case and decreased by 21.3% with RD. The heat transfer performance test showed that the wick-CHF (the enhanced critical heat flux due to the formation of the wick) of the asymmetric FD case was increased by 43.3% compared to symmetric ones while maintaining the heat transfer coefficient. This work shows that asymmetric evaporator wicks can enhance the critical heat flux without sacrificing the heat transfer coefficient, which can help develop high-performance thermal management solutions.