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.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.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.

In order to improve battery performance by tuning battery separator membranes, this work reports on porous poly(vinylidene fluoride-co-trifluoroethylene) - P(VDF-TrFE)- membranes with surface pillar microstructures. Separators with tailored pillar diameter, height and bulk thickness were fabricated by template patterning and computer simulations, allowing to evaluate the effect of the pillar microstructure characteristics on battery performance. It is shown that the different pillar microstructures of the separators affect the uptake value (150–325%), ionic conductivity value (0.8–1.6 mS·cm⁻¹) and discharge capacity of the lithium ion batteries (LIB) when compared with the separator without pillars. The experimental charge-discharge behavior demonstrates that the pillar parameters affect battery performance and the best microstructure leading to 80 mAh·g⁻¹ at 2C. Battery performance can be thus optimized by adjusting pillar diameter, height and bulk thickness of the separators keeping its volume constant, as demonstrated also by the simulation results. The parameter with most influence in battery performance is the bulk thickness of the separator, allowing to obtain a maximum discharge capacity value of 117.8 mAh·g⁻¹ at 90C for a thickness of 0.01 mm. Thus, this work shows that the optimization of the pillar microstructure of the separator membranes allows increasing the capacity towards a new generation of high-performance LIBs.

The droplets ejected from an infected host during expiratory events can get deposited as fomites on everyday use surfaces. Recognizing that these fomites can be a secondary route for disease transmission, exploring the deposition pattern of such sessile respiratory droplets on daily-use substrates thus becomes crucial.The used surrogate respiratory fluid is composed of a water-based salt-protein solution, and its precipitation dynamics is studied on four different substrates (glass, ceramic, steel, and PET). For tracking the final deposition of viruses in these droplets, 100 nm virus emulating particles (VEP) are used and their distribution in dried-out patterns is identified using fluorescence and SEM imaging techniques.The final precipitation pattern and VEP deposition strongly depend on the interfacial transport processes, edge evaporation, and crystallization dynamics. A constant contact radius mode of evaporation with a mixture of capillary and Marangoni flows results in spatio-temporally varying edge deposits. Dendritic and cruciform-shaped crystals are majorly seen in all substrates except on steel, where regular cubical crystals are formed. The VEP deposition is higher near the three-phase contact line and crystal surfaces. The results showed the role of interfacial processes in determining the initiation of fomite-type infection pathways in the context of COVID-19.

Due to the good electrical, optical, magnetic, catalytic properties, transition metal nanoparticles (TMNPs) have been becoming more and more interesting in the fileds of environment, material, biomedicine, catalysis, and so on. Here, tannic acid (TA) is used as a green and efficient stabilizer to fabricate all kinds of TMNPs including AuNPs, AgNPs, CuNPs and PdNPs. These TMNPs possess small sizes ranging from 1 nm to 6 nm, which is conducive to several catalytic reactions in aqueous solution, such as 4-nitrophenol (4-NP) reduction, CuAAC reactions and Suzuki–Miyaura coupling reactions. AuNPs and PdNPs are found to have distinctly higher catalytic activities than AgNPs and CuNPs in the 4-NP reduction process. Especially, PdNPs show the highest catalytic activities with TOF up to 7200 h⁻¹ in the 4-NP reduction. Furthermore, PdNPs also exhibit satisfying catalytic performance in the Suzuki–Miyaura coupling process, and CuNPs are catalytically active in the copper-catalyzed azide alkyne cycloaddition (CuAAC) reactions. The applicability and generality of PdNPs and CuNPs are respectively confirmed via the reaction between different substrates in the Suzuki–Miyaura coupling reactions and the CuAAC reactions. This work present a simple, fast, green and efficient strategy to synthesize TMNPs for multiple catalysis.

Light-controlling of surface characteristics in polymeric coatings has been a significant research area because of its potential application in development of smart surfaces. Wettability of light-responsive polymeric coatings based on spiropyran photochromic compound could be tuned by light irradiation. This is mainly because of spiropyran isomerization between the hydrophobic and hydrophilic states.Light-responsive latex nanoparticles containing spiropyran moieties were synthesized by semi-continuous emulsion copolymerization of acrylate monomers, which have different chain flexibility depending on the copolymer composition. Photochromic properties of spiropyran in stimuli-responsive latex nanoparticles displayed dependence of photochromism intensity and its kinetics to flexibility of the polymer chains in addition to the polarity of media. Photoswitchable surface wettability of the spiropyran-containing acrylic copolymer coatings was investigated, where the photo-responsive coatings were prepared by solution casting and electrospinning methods.The photoswitchable coatings prepared by solution casting and electrospinning methods showed significant differences in their physical characteristics and especially surface wettability. The polymeric coatings displayed water droplet contact angles in the range of 60-93°, which could reversibly be switched to 55-86° upon UV light (365 nm) illumination as a result of isomerization of the hydrophobic spiro form to the zwitterionic merocyanine form. The nanofibrous coatings prepared by electrospinning method displayed higher contact angles in the range of 120-136°, which was switched to 78-105° upon UV light irradiation. The developed photo-responsive coatings displayed highly-efficient photoswitching between the two hydrophobic and hydrophilic states as a response to UV and visible light irradiation. The photoswitchable nanofibrous coatings displayed ultrahydrophobic characteristics, where the colored water droplets were stable on their surface and could easily be adsorbed by a cellulosic tissue. In summary, the photoswitchable nanofibrous coatings could be applied for design and development of ultrahydrophobic materials with the ability of photo-controlling of surface wettability by light irradiation with tunable intensity.

As the applications of supramolecular assemblies are ultimately inscribed in their nanostructures, strategies that can precisely fabricate and regulate supramolecular architectures from small molecules are of great importance. Herein, in this research multiple modulations of supramolecular assembled structures of a natural triterpenoid-tailored bipyridinium amphiphile, 1-[2-(methyl glycyrrhetate)-2-oxoethyl]-[4,4′]bipyridinium bromide (MGBP), have been achieved by adjusting solvents or counterions. Depending on the polarity of solvents, MGBP assembled into nanofibers, helices, pentagon and hexagon microsheets, respectively. Moreover, the nanofibers in methanol/water can transform into ribbons, robust fibers and fiber bundles by addition of counterions with different ionic sizes and valences. This work presents a simple and feasible methodology to modulate assembly structures of a natural triterpenoid-based amphiphile, which may expand the application of natural products in supramolecular materials.

Solar driven interfacial evaporation has received extensive attention as a very promising desalination technique to solve the fresh water shortage crisis. However, salt-fouling and poor stability during long-term solar desalination seriously hinder applications of solar evaporators. In addition, most of the reported evaporators rely on expensive materials and complex preparation processes. Here, we report facile preparation of polydimethylsiloxane/carbon nanotubes (PDMS/CNTs) modified melamine solar evaporators for efficient steam generation and desalination. The elastic solar evaporators feature (i) macroporous network with rough skeleton owing to phase separation of PDMS, high solar absorbance (99%) and excellent photothermal performance, low thermal conductivity (0.032 W m⁻¹ K⁻¹), and (iii) unique wettability (hydrophobic upper surface and hydrophilic lower part). Consequently, the evaporators have an evaporation rate of 1.44 kg m⁻² h⁻¹ and a solar-to-vapor conversion efficiency of 84% for solar evaporation of deionized water under 1 sun illumination. Interestingly, the evaporators show similar solar evaporation performance for saline water compared to deionized water. Moreover, the evaporators show excellent salt-resistance and stability during long-term continuous solar desalination owing to rapid water replenishment in the evaporators. The evaporators may find practical applications in solar desalination because of the merits of the evaporators and the simple preparation method.

The design and preparation of metal-organic frameworks (MOFs) as self-sacrificed precursors/templates has been considered as a promising strategy in recent years for fabricating metal/carbon electrocatalysts with intriguing architectures and outstanding properties. However, the serious aggregation during the calcination and the poor electron conductivity are still obstacles for these electrocatalysts which need to be urgently solved. Herein, an in situ confinement pyrolysis protocol is reported to transform ZIF-67 nanocrystals on hollow carbon spheres (HCS) to cobalt and nitrogen-enriched carbon shell, resulting in the formation of hierarchical HCS@Co/NC. This is the first study of electrochemistry for HCS decorated with MOFs or MOFs derivatives. In the structure, metallic Co nanoparticles (NPs) and N species are strongly anchored and dispersed in the network of nanocarbon shell, which not only affords a boosting conductivity but also greatly alleviates the aggregation of active sites. Meanwhile, the unique structure with hollow feature provides an effective pathway for mass transport and shortens the transmission path of electrons. Thanks to the advantages of structure and composition, the HCS@Co/NC catalyst exhibits a superb performance of oxygen reduction reaction, which outperforms the commercial Pt/C benchmark.

Although some groundbreaking work has proved the feasibility of non-contact Marangoni propulsion generated by combination of the superhydrophobicity and photothermal effect, there are still challenges including the strong interfacial adhesion, multifunctional structural design and superior durability. In this paper, a simple two-step spraying method is used to prepare superhydrophobic and multi-functional fluorinated acidified carbon nanotubes (F-ACNTs)/Fe₃O₄ nanoparticles/polydimethylsiloxane (PDMS) coatings. The introduction of Fe₃O₄ nanoparticles and F-ACNTs not merely improve the surface roughness but also endow the coating with the outstanding magnetic property and photothermal conversion performance. The PDMS can reduce the surface energy and also improve the interfacial adhesion between the nanofillers and the substrate (the filter paper). The superhydrophobicity can be maintained when the material experiences abrasion, near-infrared (NIR) light irradiation and acid treatment, exhibiting outstanding durability. The highly stable superhydrophobic coating introduces a thin layer of air to decrease the drag force between the filter paper and the water surface, and can be used for controlled self-propelled light-driven motion and magnetic-driven motion. The movement can be manipulated by adjusting the direction of the incident NIR light and magnetic field. In particular, the superhydrophobic and superoleophilic coating based actuators can be easily driven to the oil-contaminated area on the water surface by using a magnet for high efficiency oil removal. This work provides a simple and universal strategy for developing intelligent and multi-responsive actuators possessing promising applications in various fields such as environmental protection, micro-robots and biomedicine.

With the ever-increasing demands for energy resources, the exploration of high energy density hybrid supercapacitors is urgently required. Herein, an effective hydrothermal strategy is demonstrated to construct advanced cathode of nickel carbonate hydroxide (NCH) ultrathin nanosheets anchored nitrogen-doped carbon quantum dots (NCQDs) for hybrid supercapacitors. It is revealed that the NCQDs are evenly deposited on the surface of NCH nanosheets, which provide abundant active sites for NCH nanosheets and endow them improved electrochemical characteristics. The NCH/NCQDs nanosheets deliver a decent electrochemical capacity of 727C g⁻¹ at 1 A g⁻¹ with ameliorative rate capability and cyclic stability. In addition, a hybrid supercapacitor device with an impressive energy density (49.1 Wh kg⁻¹ at 700.3 W kg⁻¹) and stable cycling property (87.5% after 8000 cycles) is fabricated by employing NCH/NCQDs nanosheets and p-phenylenediamine functionalized reduced graphene oxide (PRGO) as cathode and anode. These results indicate the great potential of NCH/NCQDs nanosheets for renewable energy storage.