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Agriculture faces pressing challenges of heat stress and water scarcity due to climate change. While mulching is a common solution, traditional mulching materials lack sub-ambient cooling capabilities and biodegradability, resulting in elevated soil temperature, increased moisture evaporation, exacerbated global agricultural heat-water crisis, and soil microplastics pollution. Herein, we have developed a biodegradable and biocompatible ethyl-cellulose radiative cooling mulch with a solar reflectance and thermal emissivity of 97% and 0.93, respectively, to provide zero-energy cooling for soil surfaces. Field tests have demonstrated that the radiative cooling mulch significantly reduces soil moisture evaporation by 60% through cooling soil surfaces, while also improves plant growth by 30% through reducing crop leaf temperature and increasing sunlight exposure for photosynthesis in hot days. Moreover, global heat-water nexus simulations show that the mulch increases soil moisture preservation by over 80% and alleviates agricultural water scarcity by over 60% in arid regions during hot seasons. The work offers an eco-friendly and feasible pathway to foster sustainable agriculture by alleviating heat stress and water scarcity in the context of global warming.

Rapid shedding of microdroplets enhances the performance of self-cleaning, anti-icing, water-harvesting, and condensation heat-transfer surfaces. Coalescence-induced droplet jumping represents one of the most efficient microdroplet shedding approaches and is fundamentally limited by weak fluid-substrate dynamics, resulting in a departure velocity smaller than 0.3

A microfluidic system was created to fabricate polydimethylsiloxane (PDMS) microspheres, whose shape, surface smoothness, and size were controlled. Resulting from their excellent optical properties and elasticity prepared by the apparatus, each PDMS microsphere could act as a microlens and separate imaging unit. The focal length of the microlens was simply tuned by the forces posed on the beads. For the microlens array (MLA) application, it was constructed simply through the assembly of the monodisperse PDMS beads.

As a functional decorative material on the surface of printing and packaging, coating plays the role of increasing gloss, wear resistance, and antifouling. It has broad application prospects in high-end printed materials such as posters, art reproductions, and maps. In this paper, dodecafluoroheptyl methacrylate was used as the fluorine-containing monomer, which was used to modify the epoxy resin and introduce fluoride first. Under the action of polymerization inhibitor and catalyst, the epoxy resin was further modified by ring opening, esterification, and neutralization with acrylic acid, maleic anhydride, and organic base as raw materials. Additionally, a fluorine-containing coating with hydrophobic and oleophobic properties was obtained finally. The effects of fluorine modification of epoxy resin and synthetic polymer were characterized by infrared spectrometer and photoelectron spectroscopy. The results showed that fluorine monomer could be successfully grafted to the molecular body of epoxy resin, and fluorine had been introduced into the surface of the polymer film. Using the contact angle tester, combined with the performance parameters such as grafting rate, thermal stability, adhesion, and gloss, the effects of the amount of fluorine monomer on the properties of the synthetic coating were discussed. The results showed that the hydrophobic and oleophobic properties of the copolymer film surface were closely related to the amount of fluorine monomer. When the molar ratio of the epoxy group to dodecafluoroheptyl methacrylate was 26:1, the mass fraction of fluorine on the film surface was 18.09%, and the contact angles of water and ethylene glycol were 121.8° and 78.2° respectively. At the same time, the printability of self-made hydrophobic and oleophobic coating was tested in this paper. The liquid repellency of inkjet printing before and after glazing and the influence of the coating on the optical properties of printed images were discussed and studied too. The results showed that the coating synthesized by the experiment was suitable for inkjet printing. It had improved the printing quality performance and the functional modification on the surface of inkjet printings, such as liquid repellency, gloss, and color reproduction.

Patterned surfaces combining hydrophobic and hydrophilic properties show great promise in moisture condensation; however, a comprehensive understanding of the multiscale interfacial behavior and the further controlling method is still lacking. In this paper, we studied the moisture condensation on a hybrid superhydrophobic-hydrophilic surface with hierarchical structures from micro- to nanoscale. For the first time, we demonstrated the effects of wettability difference and microstructure size on the final condensation efficiency. By optimizing the wettability difference, sub-millimeter pattern width, and microstructure size, maximum 90% enhancement of the condensation rate was achieved as compared with the superhydrophobic surface at a subcooling of 13 K. We also demonstrated the enhanced condensation mechanism by a detailed analysis of the condensation process. Our work proposed effective and systematical methods for controlling and optimizing moisture condensation on the patterned surfaces and shed light on application integration of such promising functional surfaces.

The dewetting phenomenon of a liquid film in the presence of a surfactant exists in various natural, industrial, and biomedical processes but still remains mysterious in some specific scenarios. Here, we investigate the dewetting behavior of water films initiated by surfactant-laden droplet impact and show that the maximum dewetting diameter can even reach more than 50 times that of the droplet size. We identify the S-type variation of the dewetting area and demonstrate its correlation to the dynamic surface tension reduction. From a viewpoint of energy conversion, we attribute the dewetting to the released surface energy caused by the surfactant addition and establish a linear relation between the maximum dewetting and the surfactant concentration in the film, i.e., dmax2 ∝ cfilm, which agrees well with the experiments. These results may advance the physics of liquid film dewetting triggered by surfactant injection, which shall further guide practical applications.

Hypothesis Due to the complex hydrodynamics of droplet impact on ridged superhydrophobic surfaces, quantitative droplet spreading characteristics are unrevealed, limiting the practical applications of ridged superhydrophobic surfaces. During droplet impacting, the size ratio (the ratio of the ridge diameter to the droplet diameter) is an important factor that affects droplet spreading dynamics. Experiments We fabricated ridged superhydrophobic surfaces with size ratios ranging from zero to one, and conduct water droplet impact experiments on these surfaces at varied Weber numbers. Aided by the numerical simulations and theoretical analysis, we illustrate the droplet spreading dynamics and reveal the law on the maximum axial spreading coefficient. Finds The results show that the droplet spreading and retraction dynamics on ridged superhydrophobic surfaces are significantly asymmetric in the axial and spanwise directions. Focusing on the maximum axial spreading coefficient, we find it decreases first and then increases with increasing size ratios, indicating the existence of the critical size ratio. The maximum axial spreading coefficient can be reduced by 25-40% at the critical size ratio compared with that on flat surfaces. To predict the maximum axial spreading coefficient, two theoretical models are proposed respectively for size ratios smaller and larger than the critical size ratio.

Wind-dispersal of seeds is a remarkable strategy in nature, enlightening the construction of microfliers for environmental monitoring. However, the flight of these microfliers is greatly affected by climatic conditions, especially in rainy days, they suffer serious raindrop impact. Here, a hierarchical superhydrophobic surface is fabricated and a novel strategy is demonstrated that the superhydrophobic coating can enhance spreading while reduce contact time and impact force of raindrops, all of which are beneficial for the rotating microfliers. When the surface rotating speed exceeds a critical value, the effect of centrifugal force becomes considerable so that the droplet spreading is enhanced. The rotating superhydrophobic surface can rotate an impacting droplet by the tangential drag force from the air boundary layer, and the rotation of the droplet generates a negative pressure zone inside it, reducing the contact time by more than 30%. The impact force by the droplet on the rotating superhydrophobic surface also has a remarkable reduction of 53% compared to that on unprocessed hydrophilic surfaces, which helps maintain the flight stability of the microfliers. This work pioneers in revealing the droplet impact effect on rotating microflier surfaces and demonstrates the effectiveness of protecting microfliers with superhydrophobic coatings, which shall guide the manufacture and flight of microfliers in rainy conditions.

The evolution of xylan-rich hemicelluloses (XH) aggregation behaviors in the presence of alkaline lignins (AL) under a wide range of pH values and NaCl concentration were investigated via dynamic light scattering and turbidity measurements. XH isolated from wheat straw contain a xylose backbone with arabinose side chains and a small amount of phenol groups. XH tend to aggregate in solution due to their low ratio of arabinose to xylose and hydrophobic phenol groups. AL interact with XH through the phenol groups bonded to the hemicellulose main chain to form an AL-XH complex. As the pH value decreases, the particle size and turbidity of AL, XH and their bonded complex all increase. The size of the AL-XH complex agglomerate is greater than the size of a XH at the same pH value, which indicates that the self-assembly of lignin molecules initiate the aggregation of XH. The particle size and turbidity of XH and AL-XH complexes increase as the XH concentration increase. At low pH values, e.g., 6.0, the particle size of the AL-XH complex more obviously increases compared to the XH particles. The size and turbidity of the AL, XH, and AL-XH complex agglomerates increased as the NaCl concentration increased.

Water-borne polyurethane/acrylate (WPUA) emulsion was prepared through emulsion polymerization between vinyl terminated waterborne polyurethane (WPU) and methyl methacrylate (MMA) in this research. Thermogravimetric Analysis (TGA), transmission electron microscopy (TEM), contact angle analysis, and particle size distribution analysis were employed to investigate the performance of the prepared emulsion and coatings with various content of MMA content. The results demonstrated that the thermal resistance, water resistance, and hardness of the prepared WPUA coatings were enhanced by the introduction of the MMA monomer. The contact angle (CA) and particle size of WPUA emulsion increased with the increase of MMA content. Meanwhile, the water-borne inkjet printing ink was prepared using WPUA emulsion as binder resin, and the printing test result showed that the prepared inkjet ink has good printability and color rendering, indicating that WPUA emulsion has great application prospects in the field of inkjet printing.

Superhydrophobic surfaces have shown great application prospects due to their excellent water repellency in many applications involving fluid–surface interactions. As a ubiquitous fluid–surface interaction phenomenon, droplet impacting dynamics has a crucial effect on the application of superhydrophobic surfaces. In this Perspective, we summarize the basic process of droplet impacting on superhydrophobic surfaces and introduce the two most concerned parameters that describe the droplet impacting dynamics, i.e., the maximum spreading coefficient and the contact time. We then review two improvement strategies for superhydrophobic surfaces: one is to construct macrostructures and the other is to set wettability patterns on the surface. The former strategy shows great potential in reducing the droplet contact time, and the latter one can accurately regulate the behavior of impacting droplets. The motion of superhydrophobic surfaces also changes the droplet impacting dynamics due to the additional aerodynamic effect or energy input, which arouses attention recently. However, only the individual influence of each factor (e.g., macrostructures, wettability patterns, or surface motion) on the droplet impacting dynamics has been focused in literature, so we write this Perspective to emphasize the importance and urgency of studying the coupled effects of these three factors.

In this work, inkjet printing of porous graphene/silver composite with low temperature vapor phase reduction was studied. Silver precursor and graphene oxide (GO) with a low weight ratio were used as ink for inkjet printing into a film. After vapor phase reduction, the inserted silver nanoparticles between reduced graphene oxide (RGO) layers acted as physical separators to prevent agglomeration of the RGO and reduce the Van Der Waals force between graphene sheets. The fabricated RGO/Ag electrode presented a high electrical conductivity of 2.9 × 105 S/m, and could keep stable after multiple bending. Meanwhile, the reducing agent vapor entered the interior of the RGO during the vapor reducing process, which generated porous channels in the RGO/Ag electrode. The porous channels could facilitate the penetration of the electrolyte into the graphene/silver electrode, resulting in a good electrochemical performance with a specific capacitance of 60.6 mF/cm2 at a scan rate of 5 mV/s, which greatly improves the property compared with the previous reports.

As an environmentally friendly coating, waterborne coatings have broad application prospects in paper packaging products in food and medicine. In this paper, a waterborne coating is synthesized from epoxy resin, polypropylene glycol diglycidyl ether, acrylic acid, trimellitic anhydride, maleic anhydride, and organic amine by three steps: ring opening reaction, esterification reaction, and neutralization reaction. Using viscosity, particle size, thermal stability, adhesion, and friction resistance as performance evaluation factors, the effects of the ratios of epoxy resin and polypropylene glycol diglycidyl ether in the polymerization system on the performance of synthetic waterborne coatings were discussed. Taking water solubility, water absorption, and water resistance as performance evaluation factors, the effects of the amount of ratio of anhydride groups to hydroxyl groups in the epoxy acrylic resin, which were produced in the second step of the reaction, were considered on the performance of synthetic waterborne coatings. The experimental results showed that when the molar ratio of the epoxy group in the epoxy resin and polypropylene glycol diglycidyl ether was about 1:1, and the molar ratio of anhydride in maleic anhydride to hydroxyl in the epoxy acrylic resin generated in the second step of reaction was about 0.9:1, the performance of the prepared waterborne coatings was comprehensively better. At the same time, the applicability of self-made waterborne coatings was tested. The results showed that when the coating amount was about 3.60 g/m2, the properties of the packaging base paper were greatly improved with respect to air resistance, oxygen resistance, oil resistance, and color reproducibility.

Superhydrophobic surfaces decorated with macrostructures have attracted extensive attention due to their excellent performance of reducing the contact time of impacting droplets. In many practical applications, the surface is not perpendicular to the droplet impact direction, but the impacting dynamics in such scenarios still remain mysterious. Here, we experimentally investigate the dynamics of droplet impact on inclined ridged superhydrophobic surfaces and reveal the effect of

A series of ether-bond free polybenzimidazole (PBI) bearing pendant imidazolium groups (HIm-PBI and PIm-PBI) are synthesized via a low cost preparation process under mild reaction conditions. HIm-P...

There is significant interest in preparing packaging film from sustainable polysaccharides, especially hemicellulose (HC). Hemicellulose isolated from wheat straw tends to aggregate into dissolved particles in aqueous solutions and to form poor films. When methylcellulose (MC) was added into the HC solution, HC and MC formed a HC-MC complex. With increased MC content, the size of the HC-MC complex decreased, and its surface charge increased at the same time. When 35 wt% MC was added into the HC, a continuous HC-MC film formed in the layer structure. The HC-MC film with 75 wt% MC showed a more compact layer structure compared with other films. The tensile strengths of the HC-MC film increased with the MC addition. When MC was added to 75 wt%, the tensile strengths of the HC-MC film reached their maximum values, which were higher than that of MC film. This high film strength suggested these HC-MC composite films have potential applications in packaging material.

The direction control of self-propelled jumping of droplets has great significance for efficient chip cooling, anti-icing and self-cleaning. The transport mechanism of guided self-propelled jumping needs to be further explored since it is different in many ways from the extensively-studied vertical jumping of coalescing droplets on surfaces without a surface energy gradient. In this work, the VOF method was used to simulate the guided self-propelled jumping of droplets on superhydrophobic, wettability gradient surfaces. The effects of the surface energy gradient and the initial droplet arrangement on the jumping velocity and energy conversion efficiency are investigated. The results show that the jumping direction is tilted to the side with a smaller contact angle, rather than being perpendicular to the surface, due to the uneven force distribution along the three-phase line. In addition, the surface energy gradient reduces the droplet symmetry resulting in a lower energy conversion efficiency.

In the present work, a series of poly(phenylene oxide) (PPO) based uncross-linked and cross-linked anion exchange membranes (AEMs) with bis-imidazolium cations were synthesized and characterized. Compared with cross-linked AEMs, uncross-linked membranes with similar ion exchange capacities showed a much higher water uptake and swelling degree. Cross-linked membranes showed vastly improved alkaline stability, oxidation stability and mechanical properties compared with uncross-linked membranes due to the effective cross-linked structure, and a well-developed hydrophilic/hydrophobic phase separated morphology was observed for cross-linked membranes by atomic force microscopy (AFM). A single cell with a cross-linked membrane (Cross-Im-PPO-75) showed a maximum power density of 212.45 mW cm−2. Considering the enhanced alkaline stability and mechanical properties, the cross-linked PPO membranes with bis-imidazolium cations are promising AEM materials for alkaline exchange membrane fuel cells.

Droplet splitting is a fascinating interfacial phenomenon, which shows great potential in applications such as fluid dispending and liquid spraying. Splitting behaviors of droplet impact on structured superhydrophobic surfaces are highly transient and complex, but the underlying mechanism is far from clear. Here, we report the splitting dynamics on ridged superhydrophobic surfaces through experimental and theoretical investigations. As the Weber number increases, three splitting modes appear in sequence: non-splitting, departure splitting, and contact splitting. Based on the movement of the liquid film behavior on the ridge along the axial direction, the splitting time consists of durations of three stages: axial spreading, axial retraction, and oscillation retraction, and it decreases with the increasing Weber number. A theoretical model is further established to predict the splitting time, where the law of the axial spreading and retraction is revealed. Splitting dynamics can be regulated by the geometric shape of the ridge. Droplet splitting is inhibited on the rectangular ridge, while the splitting time and contact time are effectively reduced on the semi-cylindrical and triangular ridges. This work is expected to provide fundamental support for diverse applications related to droplet splitting and offer guidance for the design of superhydrophobic surfaces.

International audience; Seawater desalination is vital to our modern civilization. Here, we report that the carbon honeycomb (CHC) has an outstanding water permeability and salt rejection in the seawater desalination, as revealed by molecular dynamics simulations. More than 92% of ions are rejected by CHC at applied pressures ranging from 50 to 250 MPa. CHC has a perfect salt rejection at pressures below 150Mpa.On increasing the applied pressure up to 150 MPa, the salt rejection reduces only to 92%. Pressure, temperature and temperature gradient are noted to play a significant role in modulating the water flux. The water flux increases with pressure and temperature. With the introduction of a temperature gradient of 3.5 K/nm, the seawater permeability increases by 33% as compared to room temperature. The water permeability of the carbon honeycomb is greater than other carbon materials and osmosis membranes including graphene (8.7 times) and graphyne (2.1 times). It indicates the significant potential of the carbon honeycomb for commercial application in water purification.

Direct-write printing, as a flexible and adjustable printing method, meets the requirements of graphene ink for printability, and has been widely used in the preparation of extraordinary electrode materials. Herein, the fabrication of three-dimensional graphene electrodes is completed by direct-write printing. The porous microstructure of graphene electrode can be controlled by freezing-casting method, which is uncomplicated, low-cost and can be mass produced. According to the performance test of the graphene electrode, the conductivity of the three-dimensional electrode is measured as 122.6 S/m, and the area capacitance is 30.2 mF/cm2. The porous graphene electrode has excellent electrochemical performance and can play a significant role in printed electronics, which paves the way for exploring high-performance equipment with extended functions.

In order to evaluate the printing effect of self-made on-demand ink-jet printing ink and to study its influencing factors, its printing suitability and the influence of different substrate on its performance were studied in this paper. The drying process of ink on different paper was tested by contact angle tester. The color reproduction performance of self-made ink and common ink-jet ink was compared by measuring the printing samples of ink on different substrates with spectrodensitometer. The experimental results showed that the absorption rate of ink on offset paper was the fastest compared with that of coated paper and photo paper, and the drying time of self-made ink on substrate was shorter than that of ordinary ink-jet ink, which was basically volatilized and permeated in 2–3 s on offset paper. In terms of color reproduction performance, two kinds of three primary color inks could reproduce the better color of the image on the coated paper. The color strength of the self-made three primary color inks on the offset paper and the coated paper was higher than that of the ordinary ink-jet ink and the color hue error was smaller, so the color reproduction performances on the paper were better.

An elaborated surface with a superhydrophilic area and a superhydrophobic area was fabricated by inkjet printing a water-soluble polymer template on a superhydrophilic layer. Titanate was used to generate the superhydrophilic layer with an in situ reaction. A water-soluble polymer template was inkjet printed on the facile fabricated superhydrophilic layer. Superhydrophobic treatment was carried out on the inkjet-printed surface with perfluorinated molecules. A superhydrophilic-superhydrophobic patterned surface (SSPS) was obtained by washing out the water-soluble polymer template. Various patterns of SSPS were fabricated with the different water-soluble polymer templates. Then, adhesion and deposition of water droplets were studied on the SSPS with the different wetting abilities on the surface. Meanwhile, a microreaction with a microfluidic chip was realized on the SSPS. In this work, systematic research on fabricating an SSPS based on a facile fabricated superhydrophilic layer with an inkjet-printed water-soluble polymer template is presented. It will have great potential for patterning materials, fabricating devices, and researching interfaces, such as microdroplet self-removal, analyte enrichment, and liquid-liquid interface reaction.

The dynamics of droplets impacting on solid surfaces are directly related to a variety of engineering applications. As some industrial processes have been refined to the nanoscale, research interest in nanodroplets impact is growing. In this work, molecular dynamics (MD) is employed to investigate the impact processes of nanodroplets on superhydrophobic surfaces decorated with triangular nanoridges. We confirm that the decorated nanoridges can significantly promote the bouncing performance of nanodroplets, including enlarging the bounce domain, reducing the contact time, and enhancing the bounce velocity. We identify five distinct bounce modes for nanodroplets on the nanoridged surfaces, and the variation laws of contact time and bounce velocity of nanodroplets are determined by the characteristics of these bounce modes. Configuration of nanoridges can influence the variation laws of contact time and bounce velocity through changing the bounce modes of nanodroplets. The restitution coefficient can be piecewise fitted as the power functions of the impact Weber number of nanodroplets, regardless of the droplet diameters and ridge configurations. This work elucidates the characteristics and mechanism of nanodroplets impacting on the nanoridged surfaces, which is conducive to the design of nanostructured surfaces for related applications.

Although a superhydrophobic surface could realize rapid rebounding (i.e., short contact time) of an orthogonal impacting droplet, the rebounding along the original impacting route may limit its engineering application; in contrast, the directional transportation seems to be more promising. Here, we achieve directional transportation of a droplet impacting a wettability-controlled surface. When the droplet eccentrically impacts on the boundary between the superhydrophobic part and the hydrophilic part, it undergoes spreading, retracting, departure, throwing, and breaking up stages, and finally bounces off directionally. The directional transportation distance could even reach more than ten times the droplet size, considered the adhesion length (i.e., covering length on the hydrophilic part by the droplet at the maximum spreading) is optimized. However, there is a critical adhesion length, above which the directional transportation does not occur. To be more generalized, the adhesion length is de-dimensionalized by the maximum spreading radius, and the results show that as the dimensionless adhesion length increases, the transportation distance first increases and then decreases to zero. Under the present impacting conditions, the optimal dimensionless adhesion length corresponding to the maximum transportation distance is near 0.4, and the critical dimensionless adhesion length is about 0.7. These results provide a fundamental understanding of droplet directional transportation and could be useful for related engineering applications.

The metal pattern plays a crucial role in various optoelectronic devices. However, fabrication of high-resolution metal patterns has serious problems including complicated techniques and high cost. Herein, an inkjet printed water-soluble sacrificial layer was proposed to fabricate a high-resolution metal pattern. The water-soluble sacrificial layer was inkjet printed on a polyethylene glycol terephthalate (PET) surface, and then the printed surface was deposited with a metal layer by evaporating deposition. When the deposited surface was rinsed by water, the metal layer deposited on the water-soluble sacrificial layer could be removed. Various high-resolution metal patterns were prepared, which could be used in electroluminescent displays, strain sensors, and 3D switches. This facile method could be a promising approach for fabricating high-resolution metal patterns.

Droplet jumping phenomenon widely exists in the fields of self-cleaning, antifrosting, and heat transfer enhancement. Numerous studies have been reported on the static droplet jumping while the rolling droplet jumping still remains unnoticed even though it is very common in practice. Here, we used the volume of fluid (VOF) method to simulate the droplet jumping induced by coalescence of a rolling droplet and a stationary one with corresponding experiments conducted to validate the correctness of the simulation model. The departure velocity of the jumping droplet was the main concerned here. The results show that when the center velocity of the rolling droplet (V0 = ωR, where ω is the angular velocity of the rolling droplet and R is the droplet radius) is fixed, the vertical departure velocity satisfies a power law which can be expressed as Vz,depar = aRb. When the droplet radius is fixed, the vertical departure velocity first decreases and then increases if the center velocity exceeds a critical value. Interestingly, the critical center velocity is demonstrated to be approximately 0.76 times the capillary-inertial velocity, corresponding to a constant Weber number of 0.58. Different from the vertical departure velocity, the horizontal departure velocity is basically proportional to the center velocity of the rolling droplet. These results deepen the understanding of the droplet jumping physics, which shall further promote related applications in engineering fields.

Supercapacitors are widely used in wearable electronic devices because of high power density, fast charge-discharge speed, and extremely long cycle life. However, low energy density is one of its shortcomings. In order to improve the energy density, in this paper, a flexible substrate having the micro-structure surface was fabricated by inkjet printing, which increased the specific surface of the electrode. Then the micro-structure surface was modified by plasma and promoted the deposition of graphene oxide(GO)/silver nitrate(AgNO3) solution on the micro-structure surface. For the micro-structure electrode prepared after vapor phase reduction of hydrated hydrazine, the area specific capacitance could reach 120 mF/cm2 at the scanning rate of 0.05 v/s, which increased the specific capacitance.