Lotus effect in wetting and self-cleaning

Effects of flow-induced electromagnetic field and surface roughness on antifouling activity of phenolic compounds

Microbial fouling involves the physicochemical interactions between microorganisms and solid surfaces. An electromagnetic field (EMF) may change the diffusion rates of microbial cells and the electrical double layer around the cells and contacting surfaces. In the current study, polycardanol exhibiting antibiofouling activity was modified with ferromagnetic iron oxide (IO) to investigate the EMF effects on bacterial adhesion. When there was a flow of electrolyte that contained bacterial cells, flow-induced EMF was generated according to Faraday's principle. It was observed that the IO-ionic solution (IS)-modified surfaces, with an induced current of 44, 53, 66 nA, showed decreases in the adhesion of bacteria cells more than the unmodified (polycardanol) and IO-nanoparticles-modified ones. In addition to the EMF effects, the nano-scale uniform roughness of the modified surfaces appeared to play an important role in the reduction of cell adhesion. The results demonstrated that the IOIS-modified surface (3.2 × 10-6 mM IO) had the highest antibiofouling activity.

Ultrathin zigzag-surface copper nanowire assembled hierarchical microspheres to enhance oxygen reduction catalysis

Ultrathin catalysts predominantly expose surface active atoms to deliver promising applications in oxygen reduction reactions (ORRs). However, they are commonly synthesized at high reaction temperatures, with tedious chemical routes involved. Herein, we report a low temperature (273 K) electric field driven route to synthesize zigzag-surface ultrathin copper nanowires. Interestingly, the ultrathin copper nanowires assemble into three-dimensional microspheres, which exhibit hydrophobic-aerophilic features, eventually resulting in good ORR activities. The aerophilicity and hydrophobicity of copper nanowires are related to their Cu2O active sites and hierarchical protuberances, respectively. Our findings open a new door to grow ultrathin catalysts for new energy storage systems.

Dislodgement of Hydrogen Bubbles in Microchannels with Embedded Pillars: An Analytical, Experimental, and Numerical Study

Microchannels with integrated pillars have enhanced the production capabilities and performance of various applications due to their high surface-to-volume ratio. However, emerging gas bubbles can become trapped, potentially limiting the functionality or efficiency of the device when scaled down to the low-micrometer scale. Understanding the conditions required to dislodge these bubbles is thus critical for optimizing microfluidic devices with complex physical behaviors. Here an analytical model is presented that outlines the dislodgment conditions and driving forces for such gas-liquid flows. These terms are derived from the gas-liquid interface properties, geometry, and processing parameters. As the density of the pillar arrangement is scaled down, the resistance to bubble dislodgment typically increases. Nevertheless, the bubble is compelled to dislodge at lower pressure loads when critical volumes are reached. This newly discovered effect is particularly noticeable in densely packed arrays and can be explained by the interplay of increased surface tension, geometrical restrictions, and volume-preserving forces. The analytical terms and effects are validated through novel experimental and numerical methods tailored for microchannels in the low-micrometer scale, showing strong agreement.

Bio-Inspired Functional Materials for Environmental Applications

With the global population expected to reach 9.7 billion by 2050, there is an urgent need for advanced materials that can address existing and developing environmental issues. Many current synthesis processes are environmentally unfriendly and often lack control over size, shape, and phase of resulting materials. Based on knowledge from biological synthesis and assembly processes, as well as their resulting functions (e.g., photosynthesis, self-healing, anti-fouling, etc.), researchers are now beginning to leverage these biological blueprints to advance bio-inspired pathways for functional materials for water treatment, air purification and sensing. The result has been the development of novel materials that demonstrate enhanced performance and address sustainability. Here, an overview of the progress and potential of bio-inspired methods toward functional materials for environmental applications is provided. The challenges and opportunities for this rapidly expanding field and aim to provide a valuable resource for researchers and engineers interested in developing sustainable and efficient processes and technologies is discussed.

Bionic Surfaces for Fog Collection: A Comprehensive Review of Natural Organisms and Bioinspired Strategies

Water scarcity has become a critical global threat, particularly in arid and underdeveloped regions. However, certain insects and plants have evolved the capability to obtain water from fog under these arid conditions. Bionic fog collection, characterized by passive harvesting, minimal energy requirements, and low maintenance costs, has proven to be an efficient method for water harvesting, offering a sustainable water source. This review introduces two superwettable surfaces, namely, superhydrophilic and superhydrophobic surfaces, detailing their preparation methods and applications in fog collection. The fog collection mechanisms of three typical natural organisms, Namib Desert beetles, spider silk, and cactus, along with their bionic surfaces for fog collection devices, are discussed. Additionally, other biological surfaces exhibiting fog transport properties are presented. The main challenges regarding the fabrication and application of bionic fog collection are summarized. Furthermore, we firmly believe that environmentally friendly, low-cost, and stable fog collection materials or devices hold promising prospects for future applications.

Application of the Lattice-Boltzmann method to wetting on anisotropic textured surfaces: Characterization of the liquid-solid interface

HYPOTHESIS

To understand the relationship between topography and wetting, it is not enough to study the contact angle. Indeed, the liquid-solid interface plays an important role in wetting. However, data such as the total triple line length, the wetting area and the anchoring depth are inaccessible or difficult to obtain experimentally. This work proposes to overcome the experimental limitations by using a numerical approach to characterize the wetting behavior on textured surfaces.

METHODS

The wetting behavior of an anisotropic textured surface was compared for both experimental and numerical approaches. The experimental wetting is characterized by sessile drop experiments. The simulations were performed by applying the pseudo-potential Lattice-Boltzmann method. The numerical approach was then used to predict the wetting behavior of different materials.

FINDINGS

The simulations capture both the wetting state and the contact angle, in accordance with the experimental observation. Without making any assumptions about the interfacial shape and anchoring, the simulation allows to characterize the liquid-solid interface by quantifying the total length of the triple line and the wetting area. Simultaneously, the simulations enable the characterization of impregnation within textures for complex mixed regimes.

Recyclable Superhydrophobic Surface Prepared via Electrospinning and Electrospraying Using Waste Polyethylene Terephthalate for Self-Cleaning Applications

Superhydrophobic surfaces, i.e., surfaces with a water contact angle (WCA) ≥ 150°, have gained much attention as they are multifunctional surfaces with features such as self-cleaning, which can be useful in various applications such as those requiring waterproof and/or protective films. In this study, we prepared a solution from recycled polyethylene terephthalate (PET) and fabricated a superhydrophobic surface using electrospinning and electrospraying processes. We observed that the fabricated geometry varies depending on the solution conditions, and based on this, we fabricated a hierarchical structure. From the results, the optimized structure exhibited a very high WCA (>156.6°). Additionally, our investigation into the self-cleaning functionality and solar panel efficiency of the fabricated surface revealed promising prospects for the production of superhydrophobic surfaces utilizing recycled PET, with potential applications as protective films for solar panels. Consequently, this research contributes significantly to the advancement of environmentally friendly processes and the progress of recycling technology.

Unleashing the Power of Artificial Intelligence in Materials Design

The integration of artificial intelligence (AI) algorithms in materials design is revolutionizing the field of materials engineering thanks to their power to predict material properties, design de novo materials with enhanced features, and discover new mechanisms beyond intuition. In addition, they can be used to infer complex design principles and identify high-quality candidates more rapidly than trial-and-error experimentation. From this perspective, herein we describe how these tools can enable the acceleration and enrichment of each stage of the discovery cycle of novel materials with optimized properties. We begin by outlining the state-of-the-art AI models in materials design, including machine learning (ML), deep learning, and materials informatics tools. These methodologies enable the extraction of meaningful information from vast amounts of data, enabling researchers to uncover complex correlations and patterns within material properties, structures, and compositions. Next, a comprehensive overview of AI-driven materials design is provided and its potential future prospects are highlighted. By leveraging such AI algorithms, researchers can efficiently search and analyze databases containing a wide range of material properties, enabling the identification of promising candidates for specific applications. This capability has profound implications across various industries, from drug development to energy storage, where materials performance is crucial. Ultimately, AI-based approaches are poised to revolutionize our understanding and design of materials, ushering in a new era of accelerated innovation and advancement.

One-Step Multifunctionalization of Flax Fabrics for Simultaneous Flame-Retardant and Hydro-Oleophobic Properties Using Radiation-Induced Graft Polymerization

This study concerns the one-step radiografting of flax fabrics with phosphonated and fluorinated polymer chains using (meth)acrylic monomers: dimethyl(methacryloxy)methyl phosphonate (MAPC1), 2-(perfluorobutyl)ethyl methacrylate (M4), 1H,1H,2H,2H-perfluorooctyl acrylate (AC6) and 1H,1H,2H,2H-perfluorodecyl methacrylate (M8). The multifunctionalization of flax fabrics using a pre-irradiation procedure at 20 and 100 kGy allows simultaneously providing them with flame retardancy and hydro- and oleophobicity properties. The successful grafting of flax fibers is first confirmed by FTIR spectroscopy. The morphology of the treated fabrics, the regioselectivity of grafting and the distribution of the fluorine and phosphorus elements are assessed by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (SEM-EDX). The flame retardancy is evaluated using pyrolysis combustion flow calorimetry (PCFC) and cone calorimetry. The hydro- and oleophobicity and water repellency of the treated fabrics is established by contact angle and sliding angle measurements, respectively. The grafting treatment of flax irradiated at 100 KGy, using M8 and MAPC1 monomers (50:50) for 24 h, allows achieving fluorine and phosphorus contents of 8.04 wt% and 0.77 wt%, respectively. The modified fabrics display excellent hydro-oleophobic and flame-retardant properties with water and diiodomethane contact angles of 151° and 131°, respectively, and a large decrease in peak of heat release rate (pHRR) compared to pristine flax (from 230 W/g to 53 W/g). Relevant results are also obtained for M4 and AC6 monomers in combination with MAPC1. For the flame retardancy feature, the presence of fluorinated groups does not disturb the effect of phosphorus.

Optimization of the wetting-drying characteristics of hydrophobic metal organic frameworks via crystallite size: The role of hydrogen bonding between intruded and bulk liquid

HYPOTHESIS

The behavior of Heterogeneous Lyophobic Systems (HLSs) comprised of a lyophobic porous material and a corresponding non-wetting liquid is affected by a variety of different structural parameters of the porous material. Dependence on exogenic properties such as crystallite size is desirable for system tuning as they are much more facilely modified. We explore the dependence of intrusion pressure and intruded volume on crystallite size, testing the hypothesis that the connection between internal cavities and bulk water facilitates intrusion via hydrogen bonding, a phenomenon that is magnified in smaller crystallites with a larger surface/volume ratio.

EXPERIMENTS

Water intrusion/extrusion pressures and intrusion volume were experimentally measured for ZIF-8 samples of various crystallite sizes and compared to previously reported values. Alongside the practical research, molecular dynamics simulations and stochastic modeling were performed to illustrate the effect of crystallite size on the properties of the HLSs and uncover the important role of hydrogen bonding within this phenomenon.

FINDINGS

A reduction in crystallite size led to a significant decrease of intrusion and extrusion pressures below 100 nm. Simulations indicate that this behavior is due to a greater number of cages being in proximity to bulk water for smaller crystallites, allowing cross-cage hydrogen bonds to stabilize the intruded state and lower the threshold pressure of intrusion and extrusion. This is accompanied by a reduction in the overall intruded volume. Simulations demonstrate that this phenomenon is linked to ZIF-8 surface half-cages exposed to water being occupied by water due to non-trivial termination of the crystallites, even at atmospheric pressure.

Modified Electrospun Membranes Using Different Nanomaterials for Membrane Distillation

Obtaining fresh drinking water is a challenge directly related to the change in agricultural, industrial, and societal demands and pressure. Therefore, the sustainable treatment of saline water to get clean water is a major requirement for human survival. In this review, we have detailed the use of electrospun nanofiber-based membranes (ENMs) for water reclamation improvements with respect to physical and chemical modifications. Although membrane distillation (MD) has been considered a low-cost water reclamation process, especially with the availability of low-grade waste heat sources, significant improvements are still required in terms of preparing efficient membranes with enhanced water flux, anti-fouling, and anti-scaling characteristics. In particular, different types of nanomaterials have been explored as guest molecules for electrospinning with different polymers. Nanomaterials such as metallic organic frameworks (MOFs), zeolites, dioxides, carbon nanotubes (CNTs), etc., have opened unprecedented perspectives for the implementation of the MD process. The integration of nanofillers gives appropriate characteristics to the MD membranes by changing their chemical and physical properties, which significantly enhances energy efficiency without impacting the economic costs. Here, we provide a comprehensive overview of the state-of-the-art status, the opportunities, open challenges, and pitfalls of the emerging field of modified ENMs using different nanomaterials for desalination applications.

Wetting Effect on Patterned Substrates

A droplet deposited on a solid substrate leads to the wetting phenomenon. A natural observation is the lotus effect, known for its superhydrophobicity. This special feature is engendered by the structured microstructure of the lotus leaf, namely, surface heterogeneity, as explained by the quintessential Cassie-Wenzel theory (CWT). In this work, recent designs of functional substrates are overviewed based on the CWT via manipulating the contact area between the liquid and the solid substrate as well as the intrinsic Young's contact angle. Moreover, the limitation of the CWT is discussed. When the droplet size is comparable to the surface heterogeneity, anisotropic wetting morphology often appears, which is beyond the scope of the Cassie-Wenzel work. In this case, several recent studies addressing the anisotropic wetting effect on chemically and mechanically patterned substrates are elucidated. Surface designs for anisotropic wetting morphologies are summarized with respect to the shape and the arrangement of the surface heterogeneity, the droplet volume, the deposition position of the droplet, as well as the mean curvature of the surface heterogeneity. A thermodynamic interpretation for the wetting effect and the corresponding open questions are presented at the end.

A critical review on robust self-cleaning properties of lotus leaf

The robust self-cleaning of a lotus leaf is the most classic and powerful phenomenon in nature, whose hybrid papillae and biological wax guarantee its functions. The stability of the lotus leaf surface function is determined by its overall structural design, and is also the fundamental reason for its long-term survival in the natural environment. In fact, the durability of lotus leaf surface function is facilitated by the coordination of many factors which is why it is challenging to be investigated using bionic technology. In this review, we comprehensively examined the synergistic effects of flexible characteristics, surface topography, hollow interlayers, leaf shape, and bent petioles on the structural stability of the lotus leaf surface. The key significance of these factors is in transferring the stress and strain on the surface downwards, reducing the load on the surface, improving the durability of the self-cleaning function, and ultimately ensuring respiration and photosynthesis of leaves in the natural environment. This comprehensive scrutiny offers a novel classical bionic scheme for enhancing the structural stability of a surface, which has potential for applications in deepwater self-cleaning, anti-drag, anti-icing, thermal insulation, and mechanical enhancement of membranes and buildings.

Dynamics of Droplets Impacting on Aerogel, Liquid Infused, and Liquid-Like Solid Surfaces

Droplets impacting superhydrophobic surfaces have been extensively studied due to their compelling scientific insights and important industrial applications. In these cases, the commonly reported impact regime was that of complete rebound. This impact regime strongly depends on the nature of the superhydrophobic surface. Here, we report the dynamics of droplets impacting three hydrophobic slippery surfaces, which have fundamental differences in normal liquid adhesion and lateral static and kinetic liquid friction. For an air cushion-like (super)hydrophobic solid surface (Aerogel) with low adhesion and low static and low kinetic friction, complete rebound can start at a very low Weber (We) number (∼1). For slippery liquid-infused porous (SLIP) surfaces with high adhesion and low static and low kinetic friction, complete rebound only occurs at a much higher We number (>5). For a slippery omniphobic covalently attached liquid-like (SOCAL) solid surface, with high adhesion and low static friction similar to SLIPS but higher kinetic friction, complete rebound was not observed, even for a We as high as 200. Furthermore, the droplet ejection volume after impacting the Aerogel surface is 100% across the whole range of We numbers tested compared to other surfaces. In contrast, droplet ejection for SLIPs was only observed consistently when the We was above 5-10. For SOCAL, 100% (or near 100%) ejection volume was not observed even at the highest We number tested here (∼200). This suggests that droplets impacting our (super)hydrophobic Aerogel and SLIPS lose less kinetic energy. These insights into the differences between normal adhesion and lateral friction properties can be used to inform the selection of surface properties to achieve the most desirable droplet impact characteristics to fulfill a wide range of applications, such as deicing, inkjet printing, and microelectronics.

Fabrication of Robust Waterborne Superamphiphobic Coatings with Antifouling, Heat Insulation, and Anticorrosion

Water-based superamphiphobic coatings that are environmentally friendly have attracted tremendous attention recently, but their performances are severely limited by dispersibility and mechanical durability. Herein, a dispersion of poly(tetrafluoroethylene)/SiO₂@cetyltrimethoxysilane&sodium silicate-modified aluminum tripolyphosphate (PTFE/SiO₂@CTMS&Na₂SiO₃-ATP) superamphiphobic coatings was formed by mechanical dispersion of poly(tetrafluoroethylene) emulsion (PTFE), modified silica emulsion (SiO₂@CTMS), sodium silicate (Na₂SiO₃), and modified aluminum tripolyphosphate (modified ATP). The four kinds of emulsions were mixed together to effectively solve the dispersity of waterborne superamphiphobic coatings. Robust waterborne superamphiphobic coatings were successfully obtained by one-step spraying and curing at 310 °C for 15 min, showing strong adhesive ability (grade 1 according to the GB/T9286), high hardness (6H), superior antifouling performance, excellent impact resistance, high-temperature resistance (<415 °C), anticorrosion (immersion of strong acid and alkali for 120 h), and heat insulation. Remarkably, the prepared coating surface showed superior wear resistance, which can undergo more than 140 abrasion cycles. Moreover, the composite coating with 35.53 wt % SiO₂@CTMS possesses superamphiphobic properties, with contact angles of 160 and 156° toward water and glycerol, respectively. The preparation method of superamphiphobic coatings may be expected to present a strategy for the preparation of multifunctional waterborne superamphiphobic coatings with excellent properties and a simple method.

Effect of dust and methods of cleaning on the performance of solar PV module for different climate regions: Comprehensive review

Recent achievement and progress in solar PV play a significant role in controlling climate change. This study reviewed comprehensively electrical characteristics, life cycle of dust, optical characteristics, and different cleaning techniques related to the effect of dust on the performance of PV modules throughout different climate regions of the world. The power maximum power point (MPP) and curve of PV module under the effect of irradiance and temperature were presented. The effect of dust (shading) on the electrical efficiency of PV module was discussed based on soft, partial, and complete (soiling) shading. The physical properties of dust around the globe such as PM₁₀ concentration, dust loading (mgm^-2), and fine dust particles concentration were covered and discussed. Reasons behind the accumulation of dust based on, location and installation factors, dust type, and environmental factors. Environmental reasons causing dust and dust removal in accordance with the life cycle of dust was covered in detail. All the reasons that cause the generation, accumulation and removal of dust during its life cycle were explained. All forces responsible for the adhesion phase of the dust life cycle were presented. The effect of dust on PV module transmittance and electrical parameters module were discussed in detail based on physical properties of the dust at its location and installation conditions. Self-cleaning super hydrophobic surfaces based on methods such as solvents, vapor-assisted coating, powder coating, and polymerization were discussed. All cleaning technologies, including self-cleaning technologies, based on the material coating used, and the manufacturing of PV cells was compared. The future prospective for PV technologies and cleaning methods were also covered.

Spontaneous Movement of a Droplet on a Conical Substrate: Theoretical Analysis of the Driving Force

Experiments and simulations have shown that a droplet can move spontaneously and directionally on a conical substrate. The driving force originating from the gradient of curvatures is revealed as the self-propulsion mechanism. Theoretical analysis of the driving force is highly desirable; currently, most of them are based on a perturbative theory with assuming a weakly curved substrate. However, this assumption is valid only when the size of the droplet is far smaller than the curvature radius of the substrate. In this paper, we derive a more accurate analytical model for describing the driving force by exploring the geometric characteristics of a spherical droplet on a cylindrical substrate. In contrast to the perturbative solution, our model is valid under a much weaker condition, i.e., the contact region between the droplet and the substrate is small compared with the curvature radius of the substrate. Therefore, we show that for superhydrophobic surfaces, the derived analytical model is applicable even if the droplet is very close to the apex of a conical substrate. Our approach opens an avenue for studying the behavior of droplets on the tip of the conical substrate theoretically and could also provide guidance for the experimental design of curved surfaces to control the directional motion of droplets.

Deterioration of graffiti spray paints applied on granite after a decade of natural environment

Graffiti spray paints are commonly used in contemporaneous mural paintings in public spaces, contributing to the transformation of sites and urban life. These outdoor artworks are now beginning to show different deterioration forms, such as physical-mechanical alteration (loss of material and cohesion, etc.) and chromatic changes. However, the deterioration has not been formally characterized, and the influence of the paint composition and underlying substrate are not known. In this study, three non-metallic (red, blue and black) alkyd graffiti spray paints and one metallic (silver) polyethylene graffiti spray paint were applied to two granite stones with different mineralogy and texture and exposed to a natural urban-marine environment near Vigo (NW Spain) for one decade (2010-2020). Physical changes were evaluated by stereomicroscopy, colour spectrophotometry, measurements of gloss, surface roughness and static contact angle, and peeling test. Mineralogical changes were determined by x-ray diffraction and molecular changes by Fourier transform infrared spectroscopy. Moreover, micromorphological and chemical characterization of the surfaces was conducted by scanning electron microscopy. Physical-mechanical changes, such as craquelure and paint loss, depended on the texture of the granite. More specifically, paint on the granite with the finest grain size showed most intense cracking and loss of material. Chemical changes, which were not related to the granite substrate, were most intense in the red and silver paint coatings. In the red paint, loss of binder was accompanied by an intense fading of the colour (due to titanium dioxide relative enrichment), while in the silver paint coating, chemical changes occurred in both the organic binder and aluminium particles, thus darkening the colour. Fewer chemical changes were observed in the blue and black paints. Physical and chemical changes detected in these paints were not correlated.

Ag-enriched TiO2 nanocoating apposite for self-sanitizing/ self-sterilizing/ self-disinfecting of glass surfaces

The excellent strategy to mitigate the spread of the COVID-19 pandemic is to inhibit the transmission of the SARS-CoV-2. Since fomites are one of the vital routes of coronaviral transmission, disinfecting of fomites play a pivotal role in curbing its survival on the contaminated surfaces. Available commercial disinfectants cannot keep the contaminated surfaces sanitized all the time. Self-disinfecting ability of Ag-enriched TiO₂ nanocoating due to its superb photocatalytic efficiency can effectively reduce infections caused by spread of pathogens at public places. Anatase Ag-TiO₂ nanocoatings synthesized by sol-gel process at 0.5, 1.5, and 2.5% enriching concentrations were casted on glass substrates by spin-coating technique and subsequently annealed at 650 °C. The morphological shape, crystallographic structure, light absorbance, photo-luminosity, vibrational modes, and functional groups of Ag-TiO₂ nanocoating on glass surface were studied by FE-SEM, GIXRD, UV-Visible, Photoluminescence, Raman, and FTIR spectroscopy. The developed anatase Ag-TiO₂ nanocoatings manifested to improve photocatalytic disinfecting performance due to the achieved small crystallite size of 10.5-19.2 nm, diminished band gap energy of 2.56-2.60 eV, elevated surface area of 0.802-1.470 ×10⁵ cm²/g, and enhanced light absorbance. Among the enriched specimens, 0.5% Ag-TiO₂ nanocoatings predicted an overall exalted functionality compared to pristine one.

Gracia L, Amor JI, Borro M, Hernández-Gascón B. Demoulding process assessment of elastomers in micro-textured moulds

Background: Micro-texturing is an increasingly used technique that aims at improving the functional behaviour of components during their useful life, and it is applied in different industrial manufacturing processes for different purposes, such as reducing friction on dynamic rubber seals for pneumatic equipment, among others. Micro-texturing is produced on polymer components by transfer from the mould and might critically increase the adhesion and friction between the moulded rubber part with the mould, provoking issues during demoulding, both on the mould itself and on the rubber part. The mould design, the coating release agent applied to the mould surface, and the operational parameters of the moulding/demoulding process, are fundamental aspects to avoid problems and guarantee a correct texture transfer during the demoulding process. Methods: In this work, the lack of knowledge about demoulding processes was addressed with an in-house test rig and a robust experimental procedure to measure demoulding forces (DFs) as well as the final quality of the moulded part, between thermoset polymers and moulds. After the characterization of several Sol-Gel coating formulations (inorganic; hybrid) the influence of several parameters was analysed experimentally, i.e.: Sol-Gel efficiency, texture effects, pattern geometry, roughness and material compound. Results: The results obtained from the experimental studies revealed that texture depth is the most critical geometrical parameter, showing high scatter among the selected compounds. Finally, the experimental results were used to compute a model through reduced order modelling (ROM) technique for the prediction of DFs. Conclusions: The characterization of DFs in a laboratory, with a specific device operated by a universal testing machine (UTM), provided valuable information that allows a fast and optimized introduction of texturing in rubber components. Selection of a novel Sol-Gel coating and the use of the ROM technique contributed to speed up implementation for mass production.

Calcium Carbonate@silica Composite with Superhydrophobic Properties

In this paper, spherical calcium carbonate particles were prepared by using CaCl₂ aqueous solution + NH₃·H₂O + polyoxyethylene octyl phenol ether-10 (OP-10) + n-butyl alcohol + cyclohexane inverse micro emulsion system. Then, nanoscale spherical silica was deposited on the surface of micron calcium carbonate by Stöber method to form the composite material. Scanning electron microscope (SEM), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) were used to characterize the morphology and structure of the composite material. It is found that the surface of the composite material has a micro-nano complex structure similar to the surface of a “lotus leaf”, making the composite material show hydrophobicity. The contact angle of the cubic calcium carbonate, spherical calcium carbonate and CaCO₃@SiO₂ composite material were measured. They were 51.6°, 73.5°, and 76.8°, respectively. After modification with stearic acid, the contact angle of cubic and spherical CaCO₃ were 127.1° and 136.1°, respectively, while the contact angle of CaCO₃@SiO₂ composite was 151.3°. These results showed that CaCO₃@SiO₂ composite had good superhydrophobicity, and the influence of material roughness on its hydrophobicity was investigated using the Cassie model theory.

Are telechelic polysiloxanes better than hemi-telechelic for self-cleaning applications?

HYPOTHESIS

Polysiloxanes are becoming new trend in self-cleaning (oil- and water-repellent) applications due to their low-cost and environmentally friendly nature. Lower phase separation of polysiloxanes in coating matrix is critical to obtain excellent self-cleaning properties. We hypothesize that telechelic polysiloxanes can bind to coating matrix at both ends and thus will suppress phase separation of polysiloxane as compared to hemi-telechelic analog and thus will offer excellent self-cleaning properties.

EXPERIMENT

Eight PDMS additives were prepared via the free-radical polymerization of telechelic and hemi-telechelic methacryloxypropyl-based PDMS precursors with methylmethacrylate (MMA) and glycidylmethacrylate (GMA). The compositions of the prepared polysiloxane additives were optimized to obtain excellent self-cleaning performance.

FINDINGS

Our breakthrough development confirms that telechelic polysiloxanes (PDMS-T) incorporated into epoxy-based anti-smudge coatings outperform hemi-telechelic polysiloxanes (PDMS-HT) by offering excellent repellency against difficult to repel liquids. These breakthrough findings will vertically advance Science and innovations in the self-cleaning field by offering robust guidelines for choosing suitable polysiloxane for self-cleaning applications.

Influences of Stent Design on In-Stent Restenosis and Major Cardiac Outcomes: A Scoping Review and Meta-Analysis

Thanks to the developments in implantable biomaterial technologies, invasive operating procedures, and widespread applications especially in vascular disease treatment, a milestone for interventional surgery was achieved with the introduction of vascular stents. Despite vascular stents providing a solution for embolisms, this technology includes various challenges, such as mechanical, electro-chemical complications, or in-stent restenosis (ISR) risks with long-term usage. Therefore, further development of biomaterial technologies is vital to overcome such risks and problems. For this purpose, recent research has focused mainly on the applications of surface modification techniques on biomaterials and vascular stents to increase their hemocompatibility. ISR risk has been reduced with the development and prevalent usage of the art technology stent designs of drug-eluting and biodegradable stents. Nevertheless, their problems have not been overcome completely. Furthermore, patients using drug-eluting stents are faced with further clinical challenges. Therefore, the bare metal stent, which is the first form of the vascular stent technology and includes the highest ISR risk, is still in common usage for vascular treatment applications. For this reason, further research is necessary to solve the remaining vital problems. In this scoping review, stent-based major cardiac events including ISR are analyzed depending on different designs and material selection in stent manufacturing. Recent and novel approaches to overcome such challenges are stated in detail.

Drops Sliding on Non-SLIPS Structures

Inspired by a plant leaf, a slippery liquid-infused porous surface (SLIPS) exhibits attractive nonwetting and self-cleaning abilities. However, rigorous requirements for the infused liquid layer and its inevitable loss limit its practical use. Here, we propose a model structure defined as a non-SLIPS by introducing solid nanostructures covered with a discontinuous lubricant film. This non-SLIPS tuned by solid wettability achieves the excellent self-cleaning feature with a small sliding angle comparable to the counterpart of a typical SLIPS. This sliding angle α* can be further reduced to a saturated plateau by a slight enhancement of hydrophobicity of the solid nanostructures. Interestingly, the sliding velocity remains almost constant for all of these non-SLIPS samples at a given tilt angle, independent of solid wettability. We formulate the slippery mechanism by defining an energy barrier responsible for the sliding initiation on the non-SLIPS. This energy barrier of the non-SLIPS is correlated, with a qualitative agreement, to the molecular adsorption on the solid nanostructures. The antibiological contamination is confirmed for this non-SLIPS, indicating its excellent self-cleaning ability. The findings suggest that the new surfaces, even with the gradual depletion of the infused oil layer, exhibit the nondegradation of the self-cleaning performance.

Hydrophobic Mesoporous Silica Particles Modified With Nonfluorinated Alkyl Silanes

This work reports the preparation of hydrophobic mesoporous silica particles (MSPs) modified with nonfluorinated alkyl silanes. Alkyl silanes were grafted onto the surface of the MSPs as a function of the length of nonfluorinated alkyl chains such as propyltriethoxysilane (C₃), octyltriethoxysilane (C₈), dodecyltriethoxysilane (C₁₂), and octadecyltriethoxysilane (C₁₈). Moreover, the grafting of the different alkyl silanes onto the surface of MSPs to make them hydrophobic was demonstrated using different conditions such as by changing the pH (0, 4, 6, 8, and 13), solvent type (protic and aprotic), concentration of silanes (0, 0.12, 0.24, 0.36, 0.48, and 0.60 M), reaction time (1, 2, 3, and 4 days), and reaction temperature (25 and 40 °C). The contact angles of the alkyl silane-modified MSPs were increased as a function of the alkyl chain lengths in the order of C₁₈ > C₁₂ > C₈ > C₃, and the contact angle of C₁₈-modified MSPs was 4 times wider than that of unmodified MSPs. The unmodified MSPs had a contact angle of 25.3°, but C₁₈-modified MSPs had a contact angle of 102.1°. Furthermore, the hydrophobicity of the nonfluorinated alkyl silane-modified MSPs was also demonstrated by the adsorption of a hydrophobic lecithin compound, which showed the increase of lecithin adsorption as a function of the alkyl chain lengths. The cross-linking ratios of the modified silanes on the MSPs were confirmed by solid-state ²⁹Si-MAS nuclear magnetic resonance (NMR) measurement. Consequently, the hydrophobic modification on MSPs using nonfluorinated alkyl silanes was best preferred in a protic solvent, with a reaction time of ∼24 h at 25 °C and at a high concentration of silanes.

Stimuli-responsive surfaces for switchable wettability and adhesion

Diverse unique surfaces exist in nature, e.g. lotus leaf, rose petal and rice leaf. They show similar contact angles but different adhesion properties. According to the different wettability and adhesion characteristics, this review reclassifies different contact states of droplets on surfaces. Inspired by the biological surfaces, smart artificial surfaces have been developed which respond to external stimuli and consequently switch between different states. Responsive surfaces driven by various stimuli, e.g. stretching, magnetic, photo, electric, temperature, humidity and pH, are discussed. Studies reporting on either atmospheric or underwater environments are discussed. The application of tailoring surface wettability and adhesion includes microfluidics/droplet manipulation, liquid transport and harvesting, water energy harvesting and flexible smart devices. Particular attention is placed on the horizontal comparison of smart surfaces with the same stimuli. Finally, the current challenges and future prospects in this field are also identified.

How to Achieve a Monostable Cassie State on a Micropillar-Arrayed Superhydrophobic Surface

Superhydrophobic surfaces with a monostable Cassie state possess numerous interesting applications in many fields, such as microfluidics, oil-water separation, drag reduction, self-cleaning, heat dissipation, and so on. How to guarantee a monostable Cassie state of a superhydrophobic surface is still an interesting problem. In this paper, considering the influence of external interferences that may induce the possible wettability transition, the whole wetting process of a droplet on a trapezoidal micropillar-arrayed superhydrophobic surface is divided into six possible stages. Both the Gibbs-free energy in each stage and the energy barrier between adjacent stages are obtained and analyzed theoretically. It is interesting to find that the finally stable wettability of a trapezoidal micropillar-arrayed superhydrophobic surface significantly depends on the apparent contact angle of the lateral surface of a single micropillar, which can be divided into three regions from 0 to 180°, corresponding to the Wenzel state, metastable Cassie state, and monostable Cassie state. Furthermore, the size of each region is explicitly related to and can be well-tuned by the geometry of microstructures. Such a wettability classification is well verified by a number of existing experimental results and our numerical simulations. As a relatively general case, such a trapezoidal micropillar-arrayed superhydrophobic surface can also be conveniently degenerated to the triangular or rectangular micropillar-arrayed surface. All the results should be useful for the precise design of functional surfaces of different wettabilities.

Functional Superhydrophobic Surfaces with Spatially Programmable Adhesion

A superhydrophobic surface that has controllable adhesion and is characterized by the lotus and petal effects is a powerful tool for the manipulation of liquid droplets. Such a surface has considerable potential in many domains, such as biomedicine, enhanced Raman scattering, and smart surfaces. There have been many attempts to fabricate superhydrophobic films; however, most of the fabricated films had uniform adhesion over their area. A patterned superhydrophobic surface with spatially controllable adhesion allows for increased functions in the context of droplet manipulation. In this study, we proposed a method based on liquid-crystal/polymer phase separation and local photopolymerization to realize a superhydrophobic surface with spatially varying adhesion. Materials and topographic structures were analyzed to understand their adhesion mechanisms. Two patterned surfaces with varying adhesion were fabricated from a superhydrophobic material to function as droplet guides and droplet collectors. Due to their easy fabrication and high functionality, superhydrophobic surfaces have high potential for being used in the fabrication of smart liquid-droplet-controlling surfaces for practical applications.

Passive Anti-Icing and Active Electrothermal Deicing System Based on an Ultraflexible Carbon Nanowire (CNW)/PDMS Biomimetic Nanocomposite with a Superhydrophobic Microcolumn Surface

The icephobicity property of multifunctional surfaces has been widely studied due to their potential application in the aerospace field. Herein, a controllable CNW/PDMS biomimetic nanocomposite film with a superhydrophobic surface is fabricated. The microcolumns are etched on the surface of the biomimetic nanocomposite to provide superhydrophobicity. Two defense strategies of biomimetic nanocomposites are proposed while passive anti-icing and active electrothermal deicing behaviors of the biomimetic nanocomposite are experimentally studied. It is found that the initial nucleation time of a single water droplet is delayed by 353.3 s on the superhydrophobic surface relative to the hydrophilic surface. The adhesion strength increases with the increase of surface roughness. The heating uniformity on the biomimetic nanocomposite surface was validated by infrared thermography technology. The ice layer is completely melted within 150 s under 40 V voltage captured by a noncontact infrared camera. The proposed strategy was validated by the characterization of the passive anti-icing and active electrothermal deicing property from biomimetic nanocomposites with superhydrophobic microstructure surfaces. Research results show that the two lines of defense collaborative work for an icephobicity system were able to keep biomimetic nanocomposite surfaces ice-free under test conditions.

Vacuum-Free Fabrication Strategies for Nanostructure-Embedded Ultrathin Substrate in Flexible Polymer Solar Cells

In this paper, we discuss a method for fabricating an ultrathin polymer substrate with one-dimensional nanograting patterns to improve the power conversion efficiency (PCE) of ultrathin polymer solar cells (PSCs) and suppress the dependence on the incident angle of light. Because the fabricating process of the ultrathin polymer substrate was carried out using a solution process, it can be manufactured in a large area, and the PCE of the patterned ultrathin substrate-based PSC is improved by 8.9% compared to the non-patterned device. In addition, triple-patterned ultrathin PSCs incorporating the same nanograting pattern as the substrate were fabricated in the electron transport (ZnO) layer and the photoactive layer (PBDTTT-OFT and PC71BM mixture (ratio-1: 1.5)) to achieve PCE of 10.26%. Thanks to the nanograting pattern introduced in the substrate, ZnO layer, and photoactive layer, it was possible to minimize the PCE change according to the incident angle of light. Moreover, we performed 1000 cycles of compression/relaxation tests to evaluate the mechanical properties of the triple-patterned ultrathin PSCs, after which the PCE remained at 71% of the initial PCE.

Structural design and environmental applications of electrospun nanofibers

Nanofibers have attracted extensive attention and been applied in various fields due to their high aspect ratio, high specific surface area, flexibility, structural abundance, etc. The electrospinning method is one of the most promising and effective ways to produce nanofibers. The electrospun nanofibers-based films and membranes have already been demonstrated to possess small pore sizes, larges specific surface area, and can be grafted with different functionalities to adapt to various purposes. The environmental applications of nanofibers are one of the essential application fields, and great achievements have been made in this field. To well summarize the development of nanofibers and their environmental applications, we review the nanofiber fabrication methods, advanced fiber structures, and their applications in the field of air filtration, heavy metal removal, and self-cleaning surface. We hope this review and summary can provide readers a comprehensive understanding of the structural design and environmental applications of electrospun nanofibers.

Biomimetic Nanomembranes: An Overview

Nanomembranes are the principal building block of basically all living organisms, and without them life as we know it would not be possible. Yet in spite of their ubiquity, for a long time their artificial counterparts have mostly been overlooked in mainstream microsystem and nanosystem technologies, being a niche topic at best, instead of holding their rightful position as one of the basic structures in such systems. Synthetic biomimetic nanomembranes are essential in a vast number of seemingly disparate fields, including separation science and technology, sensing technology, environmental protection, renewable energy, process industry, life sciences and biomedicine. In this study, we review the possibilities for the synthesis of inorganic, organic and hybrid nanomembranes mimicking and in some way surpassing living structures, consider their main properties of interest, give a short overview of possible pathways for their enhancement through multifunctionalization, and summarize some of their numerous applications reported to date, with a focus on recent findings. It is our aim to stress the role of functionalized synthetic biomimetic nanomembranes within the context of modern nanoscience and nanotechnologies. We hope to highlight the importance of the topic, as well as to stress its great applicability potentials in many facets of human life.

Effect of surface interactions on the settlement of particles on a sinusoidally corrugated substrate

Naturally-occurring surface topographies abound in nature and endow diverse properties, i.e., superhydrophobicity, adhesion, anti-fouling, self-cleaning, anti-glare, anti-bacterial, and many others. Researchers have attempted to replicate such topographies to create human-made surfaces with desired functionalities. For example, combining the surface topography with judicial chemical composition could provide an effective, non-toxic solution to combat non-specific biofouling. A systematic look at the effect of geometry, modulus, and chemistry on adhesion is warranted. In this work, we use a model system that comprises silica (SiO_x) beads interacting with a substrate made of a commercial polydimethylsiloxane kit (PDMS, Sylgard 184) featuring a sinusoidal topography. To examine the impact of interactions on particle settlement, we functionalize the surfaces of both the PDMS substrate and the SiO_x beads with polyacrylic acid (PAA) and polyethyleneimine (PEI), respectively. We also use the PDMS commercial kit coated with liquid glass (LG) to study the effect of the substrate modulus on particle settlement. Substrates with a higher aspect ratio (i.e., amplitude/periodicity) encourage adsorption of particles along the sides of the channel compared with substrates with lower aspect ratio. We employ colloidal probe microscopy to demonstrate the effect of interaction between the substrate and the particle. The interplay among the surface modulus, geometry, and interactions between the surface and the particle governs particle settlement on sinusoidally-corrugated substrates.

The interplay among the surface modulus, geometry, and interactions between the surface and the particle governs particle settlement on sinusoidally-corrugated substrates.

SiO2@TiO2 Composite Synthesis and Its Hydrophobic Applications: A Review

Titanium dioxide is well known for its photocatalytic properties and low toxicity, meanwhile, silicone dioxide exhibits hydrophobic and hydrophilic properties and thermal stability. The union of these two materials offers a composite material with a wide range of applications that relate directly to the combined properties. The SiO2-TiO2 composite has been synthesized through physical methods and chemical methods and, with adequate conditions, morphology, crystallinity, boundaries between SiO2-TiO2, among other properties, can be controlled. Thus, the applications of this composite are wide for surface applications, being primarily used as powder or coating. However, the available research information on this kind of composite material is still novel, therefore research in this field is still needed in order to clarify all the physical and chemical properties of the material. This review aims to encompass the available methods of synthesis of SiO2-TiO2 composite with modifiers or dopants, the application and known chemical and physical properties in surfaces such as glass, mortar and textile, including aspects for the development of this material.

Inhibition of biofilm formation by rough shark skin-patterned surfaces

In this study, we investigate the microscale structure of shark skin denticles at abdomen (A) and fin (F) locations, analyze the roughness and wetting properties related to their microstructures, and evaluate the effect of the surface properties on early bacterial attachment and biofilm formation. Microstructural analysis by scanning electron microscopy and confocal laser scanning microscopy confirmed the length (A: 165-180 μm vs. F: 145-165 μm), width (A: 86-100 μm vs. F: 64-70 μm), height (A: 10.5-13.5 μm vs. F: 6.2-8.8 μm), and density (A: 110-130 denticles/mm²vs. F: 80-130 denticles/mm²) of the denticles. The results showed that the roughness and hydrophobicity properties were affected with slight differences in the microscale architecture. The denticles with a larger width, higher ridge, and denser overlap provided a rougher and more hydrophobic surface. The microscale structure not only affected surface properties but also the biological attachment process. The microscale topography of shark skin slightly promoted bacterial attachment at an early stage, but prevented bacteria from developing biofilms. This systematic investigation provides insights into the effects of the surface topography of shark skin on its anti-fouling mechanism, which will enable the future development of various products related to human activity, such as healthcare products, underwater devices and applications, and water treatment applications.

Wetting and recovery of nano-patterned surfaces beyond the classical picture

Hydrophobic (nano)textured surfaces, also known as superhydrophobic surfaces, have a wide range of technological applications, including in the self-cleaning, anti-moisture, anti-icing, anti-fogging and friction/drag reduction fields, and many more. The accidental complete wetting of surface textures, which destroys superhydrophobicity, and the opposite process of recovery are two crucial processes that can prevent or enable the technological applications mentioned before. Understanding these processes is key to designing surfaces with tailored wetting and recovery properties. However, recent experiments have suggested that the currently available theories are insufficient for describing the observed phenomena. In this work we offer a dynamic picture of these processes beyond the state of the art showing that the key ingredient determining the experimental behavior is the inertia of the liquid in the wetting and dewetting processes, which is neglected in microscopic and macroscopic quasi-static theories inspired by the classical nucleation theory. The present findings are also important for other related phenomena, such as heterogeneous cavitation, where vapor/gas bubbles form at surface asperities, condensation, dynamics of the triple line, micelle formation, etc.

On the Droplet Size and Application of Wettability Analysis for the Development of Ink and Printing Substrates

For the printing industry to grow and for companies in the field to remain competitive, there is a drive toward enhancing research and development so that costs of inks and substrates can be minimized. This paper details one of the first studies into the importance of liquid droplet size for applying wettability science to the development of inks and substrates using a newly developed picoliter droplet dispensing system (PDDS). Differences between using microliter, μL (0.2-5 μL), and picoliter, pL (15-380 pL), droplets for wettability analysis is considered, showing the importance of using pL droplets within the development of inks and substrates for printing applications. This is due to differences in contact angle being up to 40° when comparing results from pL- and μL-sized water-based droplets. Wetting, absorption, and evaporation behavior of different droplet sizes are also discussed with specific consideration to the use of wettability science for ink development and the development of inkjet printing substrates. A newly developed commercially available water-based blue ink and a commercially available water-based black ink are studied using pL experimentation to show how pL-sized droplets for inkjet wettability analysis is the optimum volume range to ensure optimized inkjet printing analysis and development.

Ultrafast Laser Surface Texturing: A Sustainable Tool to Modify Wettability Properties of Marble

Conservation strategies to reduce the degradation of stone caused by the action of water are focusing on increasing the hydrophobicity of the surface by imitating existing solutions in nature (lotus leafs and others). These are mainly based on the existence of hierarchical roughness with micro- and nanoscale structures. In the case of marble, research has focused on protective coatings that sometimes are dangerous for the health and the environment, and with undesirable effects such as color changes or reduction of water vapor permeability of the stone. Laser texturing, however, is an environmentally friendly technique, because no chemicals or toxic waste are added and, moreover, it can process nearly all types of materials. It has been used to change the surface texture of metals and other materials on a micro or even nanometric scale, to meet a specific functional requirement, such as hydrophobicity. The objective of this work was to analyze the feasibility of this technique to provide hydrophobic properties to a marble surface without appreciable changes in its appearance. Therefore, an analysis of the irradiation parameters with ultra-short-pulse laser was performed. Preliminary results demonstrate the ability of this technique to provide hydrophobic character the marble (contact angles well above 90 ∘ ). Besides, the analysis of the treated surfaces in terms of roughness, color and gloss indicates that changes in the appearance of the surface are minimal when properly selecting the process parameters.

Impact of Perfluoro and Alkylphosphonic Self-Assembled Monolayers on Tribological and Antimicrobial Properties of Ti-DLC Coatings

The diamond-like carbon (DLC) coatings containing 1.6%, 5.3% and 9.4 at.% of Ti deposited by the radio frequency plasma enhanced chemical vapor deposition (RF PECVD) method on the silicon substrate were modified by n-decylphosphonic acid (DP) and 1H, 1H, 2H and 2H-perfluorodecylphosphonic acid (PFDP). The presence of perfluoro and alkylphosphonic self-assembled monolayers prepared by the liquid phase deposition (LPD) technique was confirmed by Fourier transform infrared spectroscopy (FTIR). It was shown that DP and PFDP monolayers on the surface of titanium incorporated diamond-like carbon (Ti-DLC) coatings had a huge influence on their wettability, friction properties, stability under phosphate- and tris-buffered saline solutions and on antimicrobial activity. It was also found that the dispersive component of surface free energy (SFE) had a significant influence on the value of the friction coefficient and the percentage value of the growth inhibition of bacteria. The dispersive component of SFE caused a reduction in the growth of bacteria and the friction coefficient in mili- and nano-newton load range. Additionally, both self-assembled monolayers prepared on Ti-DLC coatings strongly reduced bacterial activity by up to 95% compared to the control sample.