Designing Superoleophobic Surfaces

A general strategy to enhance surface hydrophobicity through modifying a rough-textured surface with weakly hydrophilic elemental sulfur

Lotus leaves usually get the superhydrophobicity from the presence of epicuticular wax on its multilevel micro- and nano-structured surface. It is known that the epicuticular wax is weakly hydrophilic with a contact angle of ∼ 74°, and inorganic elemental sulfur also has a weak hydrophilicity similar to the wax. Inspired by the waxy feature, here we first attempt a superhydrophobicity-harvested strategy by modifying a rough surface with weakly hydrophilic elemental sulfur. The superhydrophobicity of a series of materials including metal hydroxides, oxides, sulfides and chlorides, metals, and even hydrophilic organics, can be achieved by prefabricating their topographic textures combined with elemental sulfur surface modification. DFT calculation suggests that the presence of VS defects on the elemental sulfur coatings can make their rough surfaces have a stronger affinity for O22- than for H2O, which allows for the formation of O22--adsorbed layer on their surface, and thus imbues the hydrophobicity or superhydrophobicity. Our study offers a new and general approach to enhance the surface hydrophobicity via inorganic rather than low surface-energy organic modification.

New fluorine-free low surface energy surfactants and surfaces

Modification and control of surface properties, such as surface tension γ at air-liquid (AL) interfaces and surface energy at solid-liquid (SL) surfaces, are at the heart of colloid and interface science. Certain applications require low or very low surface tensions γAL and surface energies γSL, for example and not limited to: microemulsification, aqueous foams for fire-fighting, hydrophobic, superhydrophobic and oleophobic surfaces to control spreading and wetting of aqueous and oily liquids on solids. In many cases low surface tensions/energies can only be obtained by employing perfluoroalkyl substances (PFAS) as surfactant or polymer additives or surface treatments. Although fluorocarbons and polymers have been employed for over 80 years, with many industrial and commercial benefits, it is now recognized that PFAS are very hazardous to the environment and health. Hence, in the coming years it will be necessary to phase out PFAS entirely, however, at present, there are very few viable alternatives available. This article outlines the chemical principles for designing F-free low surface energy (LSE) additives, and also covers the most recent advances in the quest for non-fluorinated surfactants and polymeric surface coatings.

Drop Friction and Failure on Superhydrophobic and Slippery Surfaces

The mobility of drops on a surface influences how much water and energy is required to clean the surface. By controlling drop mobility, it is possible to promote or reduce fogging, icing, and fouling. Superhydrophobic and slippery liquid-infused surfaces both display high drop mobility despite being 'lubricated' by fluids having very different viscosities. Superhydrophobic surfaces rely on micro- and/or nanoscale textures to trap air pockets beneath drops, minimizing solid-liquid contact. In contrast, on liquid-infused surfaces, these solid textures are filled with an immiscible liquid lubricant. Over the past few years, innovations in experimental and computational methods have provided detailed new insights into the static and dynamic wetting properties of drops on these surfaces. In this review, we describe the criteria needed to obtain stable wetting states with low drop friction and high mobility on both surfaces, and discuss the mechanisms that have been proposed to explain the origins of friction on each surface. Drops can collapse from the low-friction Cassie state to the high-friction Wenzel state on both surfaces, but the transition follows different pathways: on liquid-infused surfaces, the wetting ridge near the drop edge plays a central role in triggering collapse, a phenomenon not observed on superhydrophobic surfaces. This review emphasizes that a liquid-infused surface cannot be simply viewed as a superhydrophobic surface with the air pockets replaced by lubricant. The wetting ridge surrounding drops on liquid-infused surfaces significantly alters most of the drop's properties, including macroscopic shape, friction mechanisms, and the mechanism of collapse to a Wenzel state.

Liquid-like Surface Chemistry Meets Structured Textures: A Synergistic Approach to Advanced Repellent Materials

Liquid-repellent surfaces have advanced significantly over two decades. While super-liquid-repellent surfaces with micro/nano-textures dominate the field, liquid-like smooth surfaces (LLSS) grafted with highly flexible molecule chains offer a compelling alternative, enabling near-ideal dynamic droplet repellency with ultralow contact angle hysteresis (CAH). Prior LLSS studies have focused on optimizing molecular structures, grafting densities, and mechanical stability, enabling applications in anti-fouling, liquid harvesting, and drag reduction. However, innovation challenges and performance bottlenecks hinder practical scalability. This review highlights a transformative approach developed in recent years: integrating liquid-like surface chemistry with structured surfaces to overcome existing limitations. We outline the key requirements for achieving liquid-like surfaces, their structure-related features and unique interface properties including low CAH, reduced adhesion, enhanced slippage, and nucleation inhibition. By synergizing liquid-like chemistry and surface textures, we categorize pioneering works into application-driven areas such as microscopic residue suppression, enhanced droplet mobility, optimized membrane separation, sustainable fabrics and condensation heat transfer. This composite strategy not only deepens fundamental understanding of liquid-like wetting mechanisms but also broadens real-world applicability. We conclude with perspectives on future challenges and opportunities, positioning this promising material system as a frontier in functional interfacial materials.

Material Design for Durable Lubricant-Infused Surfaces That Can Reduce Liquid and Solid Fouling

Liquid and solid fouling is a pervasive problem in numerous natural and industrial settings, significantly impacting energy efficiency, greenhouse emissions, operational costs, equipment lifespan, and human health. Inspired by pitcher plants, recently developed lubricant-infused surfaces (LISs) demonstrate resistance to both liquid and solid accretion under diverse environmental conditions, offering a potential solution to combat various foulants such as ice, bacteria, and mineral deposits. However, the commercial viability for most fouling-resistant LISs has thus far been compromised due to the challenges associated with maintaining a stable lubricant layer during operation. This review aims to address this important concern by providing systematic material design guidelines for fabricating durable LISs. We discuss fundamental design principles, methods for evaluating fouling resistance, and strategies to prevent lubricant loss. By presenting a comprehensive design methodology for this important class of materials, this review aims to aid future advancements in the field of antifouling surfaces, potentially impacting a variety of industries ranging from marine engineering to medical device manufacturing.

Enabling Soft Molds for Manufacturing Polymeric Surface Structures with Overhangs

Surface structures with overhangs are ubiquitous in nature to offer vital functions, yet reproducing them for manufacturing is challenging due to mold interlock during demolding. Soft molds have been proposed to prevent interlock, but they risk stiction-caused collapsing because their intrinsic overhanging features are susceptible to strong intermolecular forces under the microscale. To address this, we model the relationship between overhang geometries and material properties, targeting a balanced relationship between flexibility and structural integrity. We then verify our model using polydimethylsiloxane (PDMS) molds with different moduli and geometries, as well as reported soft molds in the literature. The excellent agreement between our model and all experimental data enables us to proceed with molding using various thermosetting polymers. Employing one of the robust PDMS molds, we replicate doubly re-entrant surface structures exhibiting two levels of hierarchical overhangs, which exhibit high-fidelity reproduction that successfully repels low-energy fluids without a coating. This work establishes key design principles for soft mold fabrication that prevent interlock damage and enable complex overhang formation, paving the way for large-scale manufacturing of intricate biomimetic surfaces with functional overhanging architectures.

Photo- and Thermoresponsive Reversible Wettability and Corrosion Protection of Electrophoretically Deposited TiO2/Pectin Composite Coatings

Stimuli-responsive coatings with reversible wettability hold substantial promise for biomedical, environmental, and industrial applications. Among these, titanium dioxide (TiO2)-based coatings are widely studied for their unique photoresponsivity and high refractive index; however, they often rely on complex and resource-intensive production processes, raising environmental and economic concerns. This study introduces a sustainable alternative with a TiO2-pectin composite coating on stainless steel fabricated via a simple electrophoretic deposition process. Pectin, a renewable hydrophilic polysaccharide, was incorporated specifically to optimize the coating wettability. Here, we show that TiO2-pectin composite coatings exhibit reversible wettability, transitioning from superhydrophobic (154°) to hydrophilic (57.46°) under UV irradiation, with complete recovery through thermal treatment at 80 °C. Fourier-transform infrared and X-ray photoelectron spectroscopy before and after UV exposure confirm the composites' chemical and structural morphology, with pectin concentration playing a key role in modulating this reversible behavior. Mechanistically, pectin's functional groups synergize with TiO2's surface properties to enhance responsive water adsorption and enable switchable wettability. Potentiodynamic polarization tests reveal mixed-type inhibition behavior, with corrosion current densities of 180 and 221.3 nA/cm2 after 1 and 7 days of NaCl solution immersion, respectively, demonstrating sustained corrosion resistance under saline conditions. These eco-friendly TiO2-pectin composite coatings offer a multifunctional solution combining sustainable design with reversible wettability and corrosion resistance.

Advances in small droplets manipulation on bio-inspired slippery surfaces: chances and challenges

The manipulation of droplets with non-destructive, efficient, and high-precision features is of great importance in several fields, including microfluidics and biomedicine. The lubrication layer of bioinspired slippery surfaces demonstrates remarkable stability and self-restoration capabilities when subjected to external perturbations. Consequently, research into the manipulation of droplets on slippery surfaces has continued to make progress. This paper presents a review of the methods of droplet manipulation on bioinspired slippery surfaces. It begins by outlining the basic theory of slippery surfaces and the mechanism of droplet motion on slippery surfaces. Furthermore, droplet manipulation methods on slippery surfaces are classified into active and passive approaches based on the presence of external stimuli (e.g., heat, light, electricity, and magnetism). Finally, an outlook is provided on the current challenges facing droplet manipulation on slippery surfaces, and potential solution ideas are presented.

Tailoring Protein Adsorption at the Solid-Liquid Interface for Long-Term Superhemophobicity

Super-repellent surfaces with micro/nanoscale roughness can sustain blood in the Cassie-Baxter state and minimize the solid-liquid contact area, exhibiting potential for biomedical applications. Conventional superhydrophobic surfaces with hydrophobic solid-liquid interface are susceptible to protein adsorption under blood flow, leading to a transition to the Wenzel state and increasing the risk of thrombosis. Inspired by Salvinia, hydrophilic molecules are incorporated at the solid-liquid contact area based on the interaction between blood and the surface topography as well as chemistry, thereby engineering a chemically heterogeneous superhemophobic surface which effectively prevents protein adsorption and maintains a long-term Cassie-Baxter state. The blood-repellent time of the heterogeneous surface is greater than tenfold those of conventional superhydrophobic surfaces. In vivo rabbit blood circulation confirms sustained hemocompatibility and effective thrombosis resistance, demonstrating prolonged superhemophobicity for over 55 h. The heterogeneous design ensures extended resistance to complex biological fluids and is promising for the development of blood-contacting devices, such as the gas-permeable blood-repellent membranes for extracorporeal membrane oxygenators.

Superhydrophilic Silica Coatings via a Sequential Dipping Process

A superhydrophilic silica coating was prepared using a sequential dipping process involving acid-catalyzed silica, base-catalyzed silica, and 3-(trihydroxysilyl)propanesulfonic acid. Acid-catalyzed and base-catalyzed silica particles with varying diameters were synthesized by hydrolyzing tetraethyl orthosilicate using HCl and NH3·H2O as catalysts, respectively. 3-(Trihydroxysilyl)propanesulfonic acid was obtained by oxidizing mercaptopropyl trimethoxysilane with hydrogen peroxide under acidic conditions. The resulting silica coating exhibited exceptional superhydrophilicity, with a water static contact angle of 5.0°, and demonstrated underwater superoleophobicity, with a hexadecane underwater contact angle exceeding 140°. Surfaces coated with the superhydrophilic silica coatings showed excellent performances in oil-water separation, anti-protein adsorption, and anti-fogging applications.

Cartilage Lubrication from the Perspective of Wettability

Cartilage exhibits an extremely low friction and very low wearability within the liquid environment of the joint. It is also capable of switching wettability between superhydrophilicity and hydrophobicity in both wetting and dry conditions (specific experimental operations or open wounds). Therefore, the understanding of cartilage lubrication from the perspective of wettability provides inspiration for the design of artificial cartilage and sections with motion of soft actuators with extremely low coefficients of friction (COF). In this review, the lubrication of articular cartilage is introduced and discussed from the view of wettability. First, basic principles of articular cartilage lubrication and wettability are described with a focus on compositions and wettability of articular cartilage, and in particular the relationship between the phospholipid layers and wettability on articular cartilage, and the supramolecular synergy of synovial fluid on the lubrication of articular cartilage. Subsequently, the wettability and lubrication of articular cartilage under different stimuli (such as shear, pH, temperature, and electric field) is introduced for insights into cartilage lubrication. Finally, we present a comprehensive summary and delineate the challenges within the domain of cartilage lubrication and wettability for assisting researchers in formulating viable concepts for the design of efficient cartilage substitution or smart soft lubricating devices.

Solution landscape of droplets on rough surfaces: wetting transition and directional transport

Droplets on rough surfaces can exhibit various stationary states that are crucial for designing hydrophobic materials and enabling directional liquid transport. Here, we introduce a phase-field saddle dynamics method to construct the solution landscape of wetting transition and directional transport on pillared substrates. By applying this method, we reveal the full range of Cassie-Baxter and Wenzel states, along with the complete wetting transition paths. We further elucidate the mechanisms of directional droplet transport on both hydrophobic and hydrophilic surfaces, demonstrating how surface design can influence directional movement.

Printing Multi-Layered Functional Devices Using One Stamp with Programmable Surface Energy

Beyond its role in cultural communication, printing technology has emerged as one of the most important approaches to distributing and patterning functional materials for advanced manufacturing. In a printing process, a stamp is employed to transfer functional inks to a target surface, generating a specific pattern that exactly replicates the stamp. Through precise manipulation of different inkdrops, herein, a "one stamp, diverse patterns" printing strategy is developed and achieves deposition of varied patterns utilizing a single stamp. This stamp features patterned surface energy, achieved through regioselective energy injection treatment of an ultralow surface energy solid. It is revealed that inks with different surface tensions can selectively exhibit Cassie or Wenzel state on the stamp to generate diverse ink distributions, which enables the printing of distinct patterns on target surfaces. Leveraging this approach, flexible light-emitting devices and high-density transistor array are successfully printed using single stamps. These findings advance the understanding of finely tuning and patterning surface energy for precise liquid manipulation and offer a leap forward in efficient and versatile printing methodology that will boost the innovative integration of functional materials in a simplified manner.

Anti-smudge superhard transparent coatings via ultra-small nanoparticle pattern surfaces

Anti-smudge coating materials have a broad prospect, but they are susceptible to wear from nails and sand. Therefore, the potential application of such coatings on glass substrates needs coating features such as superhardness and high transparency. However, realizing these key properties combined with anti-smudge function is significantly challenging. In this work, we show a conceptional nanoparticle pattern designing strategy of materials, inspired by stepping on cobblestone roads with the foot feeling of only the hardness of stones. Realize the nanoparticle pattern surface of "cobblestone roads" via facile and scalable interfacial reactions within a molecular compatible system, to successfully achieve the desired coating material properties including anti-smudge, superhardness, and high transparency. The coating was composed of tensely crosslinked sub-10 nm building blocks that bear an anti-smudge molecular layer, exhibiting undistinguished inorganic phase behavior when it was subjected to external forces within the contact point of micro- or above 10 nm nanoscale.

Superwettable Nanomaterials: Fabrication, Application, and Environmental Impact

The increasing global concerns over energy consumption, environmental pollution, and sustainable development have sparked intensive research interest in advanced surface engineering solutions. This perspective critically reviews the development of superwettable surfaces as promising candidates for addressing these challenges. We analyze three key architectures that enable different levels of liquid repellency: micro/nano hierarchical structures for superhydrophobicity, re-entrant features for superoleophobicity, and doubly re-entrant designs for superomniphobicity. Recent developments have demonstrated significant progress in creating more environmentally conscious surfaces, including fluorine-free superhydrophobic textiles that reduce water and energy consumption in maintenance, energy-efficient smart windows with switchable wettability for building temperature regulation, and marine protective coatings that minimize chemical pollution. These advances contribute to environmental sustainability through multiple pathways: reduced resource consumption, improved energy efficiency, and decreased chemical pollution. However, challenges remain in achieving long-term durability, cost-effective fabrication, and comprehensive understanding of environmental impacts. This perspective provides insight into the current state of the field while highlighting the critical balance between performance optimization and environmental considerations in the development of next-generation superwettable materials.

Engineered Surface Wettability of Nanomaterials for Efficient Uranium Extraction from Seawater

The extraction of uranium from seawater offers a sustainable pathway to secure nuclear fuel supplies, crucial for the transition to low-carbon energy systems. However, the low concentration of uranium and interference from competing ions pose significant challenges to extraction efficiency. Surface wettability engineering has become a key factor in enhancing the performance of nanomaterials. In this Perspective, we explore how surface wettability influences the performance of the nanomaterials in three uranium extraction scenarios: chemical adsorption, electro-assisted enhanced adsorption, and photo/electrocatalytic reduction. Strategies for optimizing this property are discussed, alongside recommendations and future directions in material design and characterization methods, aiming to accelerate the practical application of nanomaterials in seawater uranium extraction.

Minimizing the Use of Per- and Polyfluoroalkyl Substances for Textured Wetting-Resistant Surfaces

Per- and polyfluoroalkyl substances (PFAS) have been used as synthetic chemicals to create textured wetting-resistant surfaces, which have a broad range of applications including omniphobic membranes, self-cleaning textiles, and anticorrosion coatings. However, the high persistence, toxicity, and bioaccumulation potential of PFAS have led to rising public concerns and stringent regulations, especially after the U.S. Environmental Protection Agency (USEPA) announced legally enforceable maximum contamination levels for six PFAS species in April 2024. In this paper, we provide our perspective that the use of PFAS can be avoided in the fabrication of textured omniphobic and superomniphobic surfaces, which display high wetting resistance against not only high surface tension liquids but also more importantly low surface tension liquids. We first discuss the role of PFAS in the design of conventional wetting-resistant surfaces. We then discuss the state-of-the-art strategies for creating PFAS-free textured omniphobic and superomniphobic surfaces with high wetting resistance while elucidating the underlying mechanism. Further, we emphasize that PFAS are indeed not always needed for textured surfaces with a sufficiently high wetting resistance in specific environmental applications such as desalination and wastewater treatment. We envision that this paper will motivate the scientific community to rethink and revolutionize the design framework toward more sustainable wetting-resistant surfaces, thereby circumventing the use of PFAS and the consequent health and environmental risks.

Electrically-Induced Droplet Detachment and Transport on Bionic Honeycomb-Fiber Composite Surfaces

The complex regulation of droplet dynamics, based on the application of external electric fields and micro/nano functional surfaces, has garnered widespread attention in fields such as enhanced oil-water separation, self-cleaning systems, and novel imaging technologies. In this study, a PLE surface (composite biomimetic hydrophobic surface with micron-level honeycomb texture and nanoscale villi) was fabricated. Using a high-speed microscopy system, the detachment and movement of droplets on the biomimetic surface under a direct current electric field were experimentally investigated. By introducing a biomimetic surface correction factor, (ξ), a polarization and force model for droplets on the PLE surface was established. The results indicate that the amount of polarized charge (Q) is positively correlated with the radius (R2), while the deformation degree (λ) is proportional to the electric field intensity (Ec). Key parameters for droplet detachment were determined, including the electric field threshold (Ec = 83.4 kV/m) and the correction factor (ξ = 0.1066). The relationship among surface electric field intensity Ec, droplet detachment time (TL), the ratio of droplet height change (Hs) to initial height (Hs0), droplet velocity (Vt), and contact line ratio (L*) was analyzed. It was found that there exists a power-law relationship between Ec and TL. Moreover, the PLE surface exhibits a more sensitive response to the applied electric field compared to the PI (polyimide) surface.

Thermodynamic mechanisms governing icing: Key insights for designing passive anti-icing surfaces

In winter, while the freezing of water can create breathtaking landscapes, it also poses significant operational challenges when ice accumulates on functional surfaces. Ice obstructs solar panels, impairs car windshield visibility, increases energy consumption in appliances due to insulation, and can cause structural failures or collapses due to weight and rigidity. To address these issues, various active de-icing methods are employed in cold regions. However, passive anti-icing solutions are gaining preference for their lower energy consumption, cost-effectiveness, and environmental benefits. While superhydrophobic surfaces delay ice formation, they do not fully resolve the problem. Understanding the interaction between surfaces and moisture-essential for ice formation-can inspire innovative anti-icing design principles. This review examines icing physics, identifies critical environmental factors affecting ice formation, evaluates icephobic surfaces, and discusses practical application challenges. We also outline promising design principles for passive anti-icing surfaces, emphasizing their broad applicability across diverse environments.

Surface Repellency beyond Hydrophobicity: A Review on the Latest Innovations in Superomniphobic Surfaces

Superhydrophobic surfaces have long faced challenges in repelling low-surface-tension liquids like oil and alcohol, limiting their practical applications. Over the past few years, researchers have been actively looking for new alternatives to overcome this issue. Recently, superomniphobic surfaces have attracted significant interest due to their ability to repel both high- and low-surface-tension liquids. Compared with superhydrophobic surfaces, superomniphobic surfaces provide enhanced liquid repellency, making them more suitable for industrial and real-world applications. This Review explores the recent advancements in the fabrication of superomniphobic surfaces. Three basic wetting principles, Young's, Wenzel's, and Cassie-Baxter's equations, are discussed. The vital role of low surface energy and high surface roughness of hierarchical and re-entrant structures in achieving a steady Cassie-Baxter state that has a low contact area between the solid surface and liquid droplet is emphasized. Additionally, a comprehensive description of various fabrication techniques, characterizations, and practical applications of superomniphobic surfaces is provided. Finally, the challenges and future prospects regarding this research area are addressed. This comprehensive review aims to inspire researchers to refine and enhance current development methods of superomniphobic surfaces and stimulate further exploration in the research field.

Facile Fabrication of Binary-Structured Fibrous Membranes with Antifouling and Flame-Retardant Properties for Durable Water/Oil Separation

Membrane fouling from dispersed droplets during water/oil separation undermines performance and limits long-term use. Additionally, there is an urgent need for flame-retardant fibrous membranes capable of purifying high-temperature polluted oils. Inspired by the binary structure of taro leaves, this study introduces a novel fibrous membrane with both antifouling and flame-retardant properties for water/oil treatment. Eco-friendly cellulose acetate (CA) and multifunctional thermoplastic polyurethane (TPU) were used to construct a microfiber-based substrate membrane via electrospinning. A TPU/ammonium polyphosphate (APP) nanofiber layer with a beads-on-string structure was then electrosprayed onto the substrate as a functional layer. This binary-structured composite membrane leverages the adhesive properties of TPU within both the base microfibers and the functional nanofibers, enhancing stability and structural integrity. The functional layer's re-entrant structure effectively prevents dispersed droplets from adhering under the continuous phase, enabling efficient separation performance in both oil-in-water and water-in-oil emulsions. The membrane demonstrated strong antifouling properties and excellent recyclability, maintaining stable flux and a consistently high separation efficiency (>99.6%) across multiple cycles. Additionally, its flame-retardant properties allowed the membrane to self-extinguish when removed from direct flame. This study presents a novel strategy for fabricating multifunctional separation membranes, with detailed analysis of the underlying mechanisms.

Scalable Multistep Roll-to-Roll Printing of Multifunctional and Robust Reentrant Microcavity Surfaces via a Wetting-Induced Process

Owing to their unique structural robustness, interconnected reentrant structures offer multifunctionality for various applications. a scalable multistep roll-to-roll printing method is proposed for fabricating reentrant microcavity surfaces, coined as wetting-induced interconnected reentrant geometry (WING) process. The key to the proposed WING process is a highly reproducible reentrant structure formation controlled by the capillary action during contact between prefabricated microcavity structure and spray-coated ultraviolet-curable resins. It demonstrates the superior liquid repellency of the WING structures, which maintain large contact angles even with low-surface-tension liquids, and their robust capability to retain solid particles and liquids under external forces. In addition, the scalable and continuous fabrication approach addresses the limitations of existing methods, providing a cost-effective and high-throughput solution for creating multifunctional reentrant surfaces for anti-icing, biofouling prevention, and particle capture.

Robust, Fluorine-Free Superhydrophobic Films on Glass via Epoxysilane Pretreatment

Durable and fluorine-free superhydrophobic films were fabricated by a simple two-step process involving the pretreatment of glass substrates with an epoxysilane, which acted as an adhesive. The next step involved the aerosol-assisted chemical vapor deposition of a simple mixture of polydimethylsiloxane (PDMS) and SiO2 nanoparticles (NPs). Various parameters were studied, such as deposition time as well as PDMS and SiO2 loadings. The optimum film generated was with a 1:1 loading of PDMS and SiO2, deposited at 360 °C for 40 min. The resultant film demonstrated excellent water repellency with a water contact angle of 165 ± 3° and a sliding angle of 2°. The epoxysilane underlayer provided the adhesion between the film and substrate. The films maintained superhydrophobicity and durability after being exposed to solvents such as diethyl ether, toluene, and ethanol for up to 5 h, 400 tape peel cycles, UV exposure, and heat exposure at 400 °C. The robustness results indicated enhanced durability relative to the superhydrophobic film without the epoxysilane underlayer.

Dynamic omniphobic surfaces enable the stable dropwise condensation of completely wetting refrigerants

Condensation is a vital process integral to numerous industrial applications. Enhancing condensation efficiency through dropwise condensation on hydrophobic surfaces is well-documented. However, no surfaces have been able to repel liquids with extremely low surface tension, such as fluorinated solvents, during condensation, as they nucleate and completely wet even the most hydrophobic interfaces. Here, we introduce a surface functionalization methodology that enables dropwise condensation of fluorinated refrigerants. This approach, compatible with various substrates, combines low contact angle hysteresis Parylene-C with low surface energy silane (P-HFDS) using a highly scalable atmospheric vapor phase deposition technique. Our experimental results demonstrate that the omniphobic P-HFDS coating facilitates dropwise condensation of both natural refrigerants (water, ethanol, hexane, pentane) and synthetic low-global-warming-potential refrigerants (HCFO R1233zd(E) and HFO R1336mzz(Z)) with surface tension as low as 14.6 mN m-1 at 25°C. The P-HFDS coating improves condensation heat transfer coefficients by 274%, 347%, 636%, and 688% for ethanol, hexane, pentane, and R1233zd(E), respectively, compared to filmwise condensation on uncoated metal surfaces. Additionally, the coating demonstrates long-term durability, sustaining steady dropwise condensation for 170 days without apparent degradation. This work pioneers stable dropwise condensation of multiple refrigerants on a structure-less surface, offering a durable, substrate-independent, and scalable solution for low surface energy coatings.

Optimizing oil-water separation using fractal surfaces

Oil has become a prevalent global pollutant, stimulating the research to improve the techniques to separate oil from water. Materials with special wetting properties-primarily those that repel water while attracting oil-have been proposed as suitable candidates for this task. However, one limitation in developing efficient substrates is the limited available volume for oil absorption. In this study, we investigate the efficacy of disordered fractal materials in addressing this challenge, leveraging their unique wetting properties. Using a combination of a continuous model and Monte Carlo simulations, we characterize the hydrophobicity and oleophilicity of substrates created through ballistic deposition (BD). Our results demonstrate that these materials exhibit high contact angles for water, confirming their hydrophobic nature while allowing significant oil penetration, indicative of oleophilic behavior. The available free volume within the substrates varies from 60% to 90% of the total volume of the substrate depending on some parameters of the BD. By combining their water and oil wetting properties with a high availability of volume, the fractal substrates analyzed in this work achieve an efficiency in separating oil from water of nearly 98%, which is significantly higher compared to micro-pillared surfaces made from the same material but lacking a fractal design.

Surface and Interfacial Engineering for Multifunctional Nanocarbon Materials

Multifunctional materials are accelerating the development of soft electronics with integrated capabilities including wearable physical sensing, efficient thermal management, and high-performance electromagnetic interference shielding. With outstanding mechanical, thermal, and electrical properties, nanocarbon materials offer ample opportunities for designing multifunctional devices with broad applications. Surface and interfacial engineering have emerged as an effective approach to modulate interconnected structures, which may have tunable and synergistic effects for the precise control over mechanical, transport, and electromagnetic properties. This review presents a comprehensive summary of recent advances empowering the development of multifunctional nanocarbon materials via surface and interfacial engineering in the context of surface and interfacial engineering techniques, structural evolution, multifunctional properties, and their wide applications. Special emphasis is placed on identifying the critical correlations between interfacial structures across nanoscales, microscales, and macroscales and multifunctional properties. The challenges currently faced by the multifunctional nanocarbon materials are examined, and potential opportunities for applications are also revealed. We anticipate that this comprehensive review will promote the further development of soft electronics and trigger ideas for the interfacial design of nanocarbon materials in multidisciplinary applications.

In situ growth of octa-phenyl polyhedral oligomeric silsesquioxane nanocages over fluorinated graphene nanosheets: super-wetting coatings for oil and organic sorption

Superhydrophobic surfaces offer significant advantages through their hierarchical micro/nanostructures, which create optimal surface roughness and low surface energy, making the development of robust surfaces essential for enhancing their physical and chemical stability. Here, we introduce in situ growth of octa-phenyl polyhedral oligomeric silsesquioxane (O-Ph-POSS) nanocages over multi-layered fluorinated graphene (FG) nanosheets through hydrolysis/condensation of phenyl triethoxysilane in an alkaline medium to produce a robust POSS-FG superhydrophobic hybrid. The efficient in situ growth of O-Ph-POSS nanocages over FG nanosheets was confirmed by FT-IR spectroscopy, PXRD, SEM, TEM, TG analysis, 29Si NMR spectroscopy, N2 adsorption-desorption isotherms and XP spectroscopy. The as-synthesized O-Ph-POSS over FG becomes superhydrophobic with a water contact angle (WCA) of 152 ± 2° and a surface free energy (SFE) of 5.6 mJ m-2. As a result of the superhydrophobic property and robust nature of the POSS nanocage, O-Ph-POSS over FG nanosheets revealed the absorption capability for oils/organic solvents ranging from 200 to 500 wt% and were applied to coat onto the polyurethane (PU) sponge to effectively separate various oils and organic solvents from water mixtures, achieving separation efficiencies between 90% and 99%. Importantly, O-Ph-POSS-FG@Sponge still retained a separation efficiency of over 95% even after 25 separation cycles for hexane spill in water. The sponge efficiently separates toluene and chloroform using a vacuum pump, achieving flux rates of up to 20 880 and 12 184 L m-2 h-1, respectively. Weather resistance tests of O-Ph-POSS-FG@Sponge, prepared at intervals of 1 week and 1 year, showed that aged samples retained similar WCA values to freshly prepared sponges, confirming their long-term durability and performance. Mechanical stability assessments indicated that O-Ph-POSS-FG@Sponge maintained superhydrophobic properties, with WCA values of 151 ± 2° for tape peeling and emery paper treatments and 150 ± 2° for knife cutting, highlighting its excellent stability under physical deformation. Additionally, leveraging the exceptional resistance of O-Ph-POSS, the superhydrophobic O-Ph-POSS-FG@Sponge exhibited excellent stability and durability, even under supercooled and hot conditions during oil/water separation. Optical microscopy analysis of O/W and W/O emulsions, both stabilized by a surfactant, revealed complete droplet separation, further confirming the O-Ph-POSS-FG@Sponge's effectiveness for emulsion separation applications. The present work provides a straightforward method for the large-scale production of robust, superhydrophobic materials suitable for cleaning up oil spills on water surfaces.

Superhydrophobicity With Self-Adaptive Water Pressure Resistance and Adhesion of Pistia Stratiotes Leaf

Superhydrophobic surfaces are promising for optimizing amphibious aircraft by minimizing water drag and adhesion. Achieving this involves ensuring these surfaces can resist high liquid pressure caused by deep water and fluid flow. Maximizing the solid-liquid contact area is a common strategy to improve liquid pressure resistance. However, this approach inevitably increases solid-liquid adhesion, making it challenging to guarantee a trade-off between the two wetting characteristics. Here, it is found that the Pistia stratiotes leaf exhibits superhydrophobicity with high water pressure resistance and low adhesion, attributed to its self-adaptive deformable microstructure with unique re-entrant features. Under pressure, these microstructures deform to increase the solid-liquid contact area, thereby enhancing water pressure resistance. The re-entrant features elevate the deformation threshold, enabling higher modulus microstructures to achieve adaptive response. This facilitates the recovery of deformed microstructures, restoring the air layer and maintaining low adhesion. Following these concepts, Pistia stratiotes leaf-inspired surfaces are fabricated, achieving an 183% improvement in water impact resistance and an ≈80% reduction in adhesion after overpressure compared to conventional superhydrophobic surfaces. The design principles inspired by Pistia stratiotes promise significant advancements in amphibious aircraft and other trans-media vehicles.

Enhancing Resistance to Wetting Transition through the Concave Structures

Water-repellent superhydrophobic surfaces are ubiquitous in nature. The fundamental understanding of bio/bio-inspired structures facilitates practical applications surmounting metastable superhydrophobicity. Typically, the hierarchical structure and/or reentrant morphology have been employed hitherto to suppress the Cassie-Baxter to Wenzel transition (CWT). Herein, a new design concept is reported, an effect of concave structure, which is vital for the stable superhydrophobic surface. The thermodynamic and kinetic stabilities of the concave pillars are evaluated by continuous exposure to various hydrostatic pressures and sudden impacts of water droplets with various Weber numbers (We), comparing them to the standard superhydrophobic normal pillars. Specifically, the concave pillar exhibits reinforced impact resistance preventing CWT below a critical We of ≈27.6, which is ≈1.6 times higher than that of the normal pillar (≈17.0). Subsequently, the stability of underwater air film (plastron) is investigated at various hydrostatic pressures. The results show that convex air caps formed at the concave cavities generate downward Laplace pressure opposing the exerted hydrostatic pressure between the pillars, thus impeding the hydrostatic pressure-dependent underwater air diffusion. Hence, the effects of trapped air caps contributing to the stable Cassie-Baxter state can offer a pioneering strategy for the exploration and utilization of superhydrophobic surfaces.

Self-cleaning electrode for stable synthesis of alkaline-earth metal peroxides

Alkaline-earth metal peroxides (MO2, M = Ca, Sr, Ba) represent a category of versatile and clean solid oxidizers, while the synthesis process usually consumes excessive hydrogen peroxide (H2O2). Here we discover that H2O2 synthesized via two-electron electrochemical oxygen reduction (2e- ORR) on the electrode surface can be efficiently and durably consumed to produce high-purity MO2 in an alkaline environment. The crucial factor lies in the in-time detachment of in situ-generated MO2 from the self-cleaning electrode, where the solid products spontaneously detach from the electrode to solve the block issue. The self-cleaning electrode is achieved by constructing micro-/nanostructure of a highly active catalyst with appropriate surface modification. In experiments, an unprecedented accumulated selectivity (~99%) and durability (>1,000 h, 50 mA cm-2) are achieved for electrochemical synthesis of MO2. Moreover, the comparability of CaO2 and H2O2 for tetracycline degradation with hydrodynamic cavitation is validated in terms of their close efficacies (degradation efficiency of 87.9% and 93.6% for H2O2 and CaO2, respectively).

Superabsorbent Capped Truncated Silica Microcone Arrays: Fabrication and Extended Laplace Pressure and Gibbs Free Energy Study

The ability of a surface to completely absorb a liquid droplet is an important property that can be controlled by geometrical structure and chemical composition of the surface. Here, using Laplace pressure and Gibbs free energy (GFE) considerations, a capped truncated microcone array geometry is proposed to obtain a near zero degree for contact angle (θ) of a water droplet. Our results showed that two essential conditions must be met to achieve a superabsorbent surface. First, negative Laplace pressure and, second, absence of a relative minimum in the plot of GFE versus contact angle. To investigate the effect of surface tension on the wettability, capped truncated microcone array films were prepared on Si (100) substrate using a lithography method. To validate the proposed geometry as a super water-absorbent surface, we compared theoretical calculations with the experimental results. Our theoretical and experimental studies show that the capped truncated SiO2 microcone array film is a superabsorbent surface with nearly zero contact angle. The amount of 130° ± 3 was measured for the water contact angle of the capped truncated Si microcone array in the hydrophobic state, which is very close to the calculated water contact angle using the minimum of GFE (126.1°). Results proved that the predicted water contact angles are in very good agreement with the experimental measurements.

The Role of Re-Entrant Microstructures in Modulating Droplet Evaporation Modes

The evaporation dynamics of sessile droplets on re-entrant microstructures are critical for applications in microfluidics, thermal management, and self-cleaning surfaces. Re-entrant structures, such as mushroom-like shapes with overhanging features, trap air beneath droplets to enhance non-wettability. The present study examines the evaporation of a water droplet on silicon carbide (SiC) and silicon dioxide (SiO2) re-entrant structures, focusing on the effects of material composition and solid area fraction on volume reduction, contact angle, and evaporation modes. Using surface free energy (SFE) as an indicator of wettability, we find that the low SFE of SiC promotes quick depinning and contact line retraction, resulting in shorter CCL phases across different structures. For instance, the CCL phase accounts for 55-59% of the evaporation time on SiC surfaces, while on SiO2 it extends to 51-68%, reflecting a 7-23% increase in duration due to stronger pinning effects. Additionally, narrower pillar gaps, which increase the solid area fraction, further stabilize droplets by extending both CCL and constant contact angle (CCA) phases, while wider gaps enable faster depinning and evaporation. These findings illustrate how hydrophobicity (via SFE) and structural geometry (via solid area fraction) influence microscale interactions, offering insights for designing surfaces with optimized liquid management properties.

Dominant Role of Surface Peak-Valley Features in Droplet Infiltration Dynamics

In this study, droplet infiltration dynamics on microtextured surfaces is explored to demonstrate the dominant role of surface peak-valley features in the capillary-driven wetting process. Even though two rough surfaces have nearly the same roughness, the microtopography and distribution of surface peaks and valleys may be completely different, leading to variations in liquid infiltration characteristics. Experimental results show that under the same surface roughness (Sa = 12.0 μm), the positively skewed surface dominated by micropillars (Ssk > 0) is more conducive to liquid infiltration compared with the negatively skewed surface dominated by micropits (Ssk < 0). The physical mechanism is fully analyzed in terms of the equilibrium of the air-liquid interface by constructing a hydrodynamic model. This study also demonstrates that the dominant influence of surface peak-valley features on droplet infiltrating dynamics is independent of the materials. Moreover, the cooling efficiency of the prepared surfaces is compared, and the results indicate that the micropillar surfaces with positive skewness exhibit superior heat dissipation performance under similar conditions because of their excellent infiltration features and large spreading area, proving that positively skewed surfaces have high utilization potential in high-density heat dissipation technology.

Surface-Templated Polymer Microparticle Synthesis Based on Droplet Microarrays

Polymer microparticle synthesis based on the surface-templated method is a simple and environmentally friendly method to produce various microparticles. Unique particles with different compositions can be fabricated by simply annealing a polymer on a liquid-repellent surface. However, there are hurdles to producing particles of homogeneous sizes with large quantities and varying the shape of particles. Here, a new approach to synthesizing multiple polymer microparticles using micropatterns with wettability contrast is presented. Polymer microparticles are formed in two steps. First, a layer of poly(sodium-4-styrenesulfonate) is deposited on the hydrophilic regions by dipping and withdrawing this micropattern from a polymer solution, and an array of microdroplets is formed. A dewetting-inducing layer on the pattern is introduced, and then target polymer patches are sequentially generated on it. By annealing over Tg, the contact line of the target polymer patch is freely receded, creating a particle form. The size and shape of the microparticle can be controlled by varying the micropatterns. In addition, it is demonstrated that microparticles made of polymer blends or polymer/nanoparticle composite are easily produced. This versatile method offers the potential of surface-templated synthesis to tailor polymer microparticles with different sizes, shapes, and functionalities in various research and applications.

Probing the contact time of droplet impacts: From the Hertz collision to oscillation regimes

Droplet rebound on nonwetting surfaces is a common phenomenon. However, the underlying physics regulating the contact time remains unclear. In this work, we investigate droplet impacts on superamphiphobic surfaces through experiments and theoretical analyses. By analyzing the spreading and retraction of droplet impinging processes over a wide range of Weber numbers (We), it is revealed that droplet impacts experience three regimes as We is varied, which are denoted as the Hertz collision (We<1), transition (110) regimes. In the Hertz collision regime, the droplet impinging process is temporally symmetric, i.e., the spreading time, t_{S}, and the retraction time, t_{R}, are almost the same. Furthermore, t_{S} and t_{R} decrease with increasing We and follow a power-law dependence, which is different from previous theories. In the transition regime, t_{S} remains dominated by the Hertz collision, while t_{R} is governed by droplet oscillation. In the oscillation regime, t_{S}, t_{R}, and the total contact time, t_{C}, become independent of We. These three regimes are valid for both monophase and compound droplets. The findings in this work advance the understanding and offer a clear picture of droplet impact dynamics.

Bifunctional TiO2-Coated SSM for Efficient Emulsion Separation and Photocatalytic Degradation of Soluble Organic Pollutants

The oily wastewater containing complex organic pollutants poses a great threat to the environment and human beings. At present, the membrane used to treat oily wastewater has some problems, such as complicated preparation and serious membrane pollution. Superhydrophilic/underwater superoleophobic membranes overcome the problems of the surface of the membrane being easily polluted or even blocked by oil, so they have been widely studied by many researchers. In this work, we used an electrochemical deposition method to uniformly load titanium dioxide (TiO2) nanoparticles onto pretreated stainless-steel mesh for efficient oil-in-water (O/W) emulsion separation (TiO2@SSM). The membrane of TiO2@SSM exhibited superior superhydrophilicity and underwater superoleophobicity, ensuring high O/W separation efficiency, reaching 99.8%, and fast water flux of up to 208.0 L·m-2·h-1 for various O/W emulsions. Meanwhile, the membrane possessed a desirable photocatalytic degradation property under visible light irradiation and a degradation efficiency of 98.1% for RhB pollutant. Specially, the as-prepared membrane had long-lasting robustness, sustainability, and recyclability through the cyclic experiments of emulsion separation and photocatalytic degradation. Our results provide a simple and universally applicable route to construct a multifunctional membrane for simultaneously achieving water purification in complex oily wastewater.

Tunable Topological Wetting State of Water Droplets on Planar Surfaces: Closed-Loop Chemical Heterogeneity by Design

Understanding droplet wetting on surfaces has broad implications for surface science and engineering. Here, we report a joint theoretical/experimental study of the topological wetting states of water droplets on chemically heterogeneous closed-loop and planar surfaces. Interestingly, we provide both simulation and experimental evidence of biloop or even multiloop transition wetting states of water droplets. Specifically, in our molecular dynamics simulations, we designed surfaces patterned with alternating closed-loop superhydrophilic and hydrophobic nanobands. On these surfaces, we find that the contact shape and contact angle of water nanodroplets can be tailored by changing the shape of the nanobands. Overall, the contact angle of the droplets is dependent on the initial location of the water droplet, the interaction between the water molecules and hydrophobic particles, and the width of the superhydrophilic and hydrophobic nanobands. The wetting-state transition dynamics is also dependent on the nanoband shape. In the biloop or multiloop transition wetting states, the three-phase contact line is not limited to only one loop nanoband but can be located at two or more distinct loops. Guided by the simulation results, the corresponding experiments confirmed the presence of topological wetting states and multiloop wetting states on planar chemically heterogeneous surfaces with closed-loop microbands. Importantly, we provide an explanation of the mechanism of the topological wetting state formation and transition. Our study facilitates a deeper understanding of the droplet-surface interactions and offers an alternative way to tune the droplet shape and contact angle on planar surfaces by engineering chemically heterogeneous surface textures.

Functional Silsesquioxanes-Tailoring Hydrophobicity and Anti-Ice Properties of Polylactide in 3D Printing Applications

To explore the tailoring of hydrophobicity in 3D-printed polylactide (PLA) composites for advanced applications using additive manufacturing (AM), this study focuses on the use of Fused Deposition Modeling (FDM) 3D printing. PLA, a material derived from renewable sources, is favored for its eco-friendliness and user accessibility. Nonetheless, PLA's inherent hydrophilic properties result in moisture absorption, negatively affecting its performance. This research aims to modify PLA with organosilicon compounds to enhance its hydrophobic and anti-icing properties. Incorporating fluorinated siloxane derivatives led to significant increases in water contact angles by up to 39%, signifying successful hydrophobic modification. Mechanical testing demonstrated that the addition of organosilicon additives did not compromise the tensile strength of PLA and, in some instances, improved impact resistance, especially with the use of OSS-4OFP:2HEX:2TMOS, which resulted in an increase in the tensile strength value of 25% and increased impact strength by 20% compared to neat PLA. Differential scanning calorimetry (DSC) analysis indicated that the modified PLA exhibited reduced cold crystallization temperatures without altering the glass transition or melting temperatures. These results suggest that organosilicon-modified PLA has the potential to expand the material's application in producing moisture and ice-resistant 3D-printed prototypes for various industrial uses, thereby facilitating the creation of more durable and versatile 3D-printed components.

Bioinspired Slippery Surfaces for Liquid Manipulation from Tiny Droplet to Bulk Fluid

Slippery surfaces, which originate in nature with special wettability, have attracted considerable attention in both fundamental research and practical applications in a variety of fields due to their unique characteristics of superlow liquid friction and adhesion. Although research on bioinspired slippery surfaces is still in its infancy, it is a rapidly growing and enormously promising field. Herein, a systematic review of recent progress in bioinspired slippery surfaces, beginning with a brief introduction of several typical creatures with slippery property in nature, is presented. Subsequently,this review gives a detailed discussion on the basic concepts of the wetting, friction, and drag from micro- and macro-aspects and focuses on the underlying slippery mechanism. Next, the state-of-the-art developments in three categories of slippery surfaces of air-trapped, liquid-infused, and liquid-like slippery surfaces, including materials, design principles, and preparation methods, are summarized and the emerging applications are highlighted. Finally, the current challenges and future prospects of various slippery surfaces are addressed.

Pinning Forces on the Omniphobic Dry, Liquid-Infused, and Liquid-Attached Surfaces

Omniphobic coatings effectively repelling water, oils, and other liquids are of great interest and have a broad number of applications including self-cleaning, anti-icing surfaces, biofouling protection, selective filtration, etc. To create such coatings, one should minimize the pinning force that resists droplet motion and causes contact angle hysteresis. The minimization of the free surface energy by means of the chemical modification of the solid surface is not enough to obtain a nonsticky slippery omniphobic surface. One should minimize the contact between the solid and the droplet. Besides coating the surface with flat polymer films, among the major approaches to create omniphobic coatings, one can reveal "lotus effect" textured coatings, slippery liquid-infused porous surfaces (SLIPS), and slippery omniphobic covalently attached liquid (SOCAL) coatings. It is possible to turn one surface type into other by texturizing, impregnating with liquids, or grafting flexible liquid-like polymer chains. There are a number of models describing the pinning force on surfaces, but the transitions between states with different wetting regimes remain poorly understood. At the same time, such studies can significantly broaden existing ideas about the physics of wetting, help to design coatings, and also contribute to the development of generalized models of the pinning force. Here we review the existing pinning force (contact angle hysteresis) models on various omniphobic substrates. Also, we discuss the current studies of the pinning force in the transitions between different wetting regimes.

Comparative Molecular Dynamics Simulation of Wetting on Liquid-like Surfaces

We utilize molecular dynamics simulations to comparably investigate the wetting and motion behavior of droplets on liquid-like surfaces (LLS) with varying grafting conditions. Polydimethylsiloxane (PDMS) and perfluoropolyether (PFPE) have been considered to be flexible molecules versus rigid molecules of trichloro(octadecyl) silane (OTS) and trichloro(1H,1H,2H,2H-perfluorooctyl) silane (PFOS), respectively. Our findings reveal that droplets on surfaces tethered with either PDMS or PFPE brushes can generate indentations and wetting ridges, providing microscopic evidence of their liquid-like nature. The grafting density of mobile chains exerts a dominant influence on the wetting properties compared to the molecular weight. A parameter map is created to pinpoint the precise range of grafting densities essential for the optimal construction of LLS at predetermined molecular weights. Furthermore, the investigation of droplet motion dynamics on LLS demonstrates that droplets consistently exhibit a rolling state, regardless of the intensity of the applied lateral force. The movement pattern of the droplet shifts only under conditions where the grafting density is significantly reduced and the substrate exhibits hydrophilic tendencies. These findings and the developed model are anticipated to offer valuable guidelines for optimal designs of LLS.

Nature-inspired adhesive systems

Many organisms in nature thrive in intricate habitats through their unique bio-adhesive surfaces, facilitating tasks such as capturing prey and reproduction. It's important to note that the remarkable adhesion properties found in these natural biological surfaces primarily arise from their distinct micro- and nanostructures and/or chemical compositions. To create artificial surfaces with superior adhesion capabilities, researchers delve deeper into the underlying mechanisms of these captivating adhesion phenomena to draw inspiration. This article provides a systematic overview of various biological surfaces with different adhesion mechanisms, focusing on surface micro- and nanostructures and/or chemistry, offering design principles for their artificial counterparts. Here, the basic interactions and adhesion models of natural biological surfaces are introduced first. This will be followed by an exploration of research advancements in natural and artificial adhesive surfaces including both dry adhesive surfaces and wet/underwater adhesive surfaces, along with relevant adhesion characterization techniques. Special attention is paid to stimulus-responsive smart artificial adhesive surfaces with tunable adhesive properties. The goal is to spotlight recent advancements, identify common themes, and explore fundamental distinctions to pinpoint the present challenges and prospects in this field.

Transition of Liquid Drops on Microstructured Hygrophobic Surfaces from the Impaled Wenzel State to the "Fakir" Cassie-Baxter State

Low adhesion of liquids on solid surfaces can be achieved with protrusions that minimize the contact area between the liquid and the solid. The wetting state where an air cushion forms under the drop is known as the Cassie-Baxter state. Surfaces where liquids form macroscopic contact angles above 150° are called superhydrophobic and superhygrophobic, if we refer to water or any liquid, respectively. The Cassie state is desirable for applications, but it is usually unstable compared to the Wenzel state, where the drop is in direct contact with the rough surface. The Cassie-to-Wenzel transition can be triggered by an increase in pressure and vibrations, but the inverse Wenzel-to-Cassie is much more difficult to observe. Here, we examine under what conditions the Wenzel-to-Cassie transition is triggered when the microscopic contact angle changes abruptly. For this, we applied a lubricant of low surface tension around drops that were in the Wenzel state on microstructured surfaces. The increase of the microscopic contact angle lifted the drop from the rough surface, when the pillar height and spacing are large and small, respectively. Numerical calculations for the drop-lubricant interface showed that the surface geometry requirements for the Wenzel-to-Cassie transition are stricter than the ones for the stability of the Cassie state. A surface geometry where the Cassie state is more stable than the Wenzel for a given Laplace pressure of the drop may not always allow the Wenzel-to-Cassie transition to take place. Therefore, the stability of the Cassie state is a necessary but insufficient condition for the inverse transition.

Enhanced Anti/De-Icing Performance on Rough Surfaces Based on The Synergistic Effect of Fluorinated Resin and Embedded Graphene

Icing negatively impacts various industrial sectors and daily life, often leading to severe safety problems and substantial economic losses. In this work, a fluorinated resin coating with embedded graphene nanoflakes is prepared using a spin-coating curing process. The results shows that the ice adhesion strength is reduced by ≈97.0% compared to the mirrored aluminum plate, and the icing time is delayed by a factor of 46.3 under simulated solar radiation power of 96 mW cm-2 (1 sun) at an ambient temperature of -15 °C. The superior anti/de-icing properties of the coating are mainly attributed to the synergistic effect of the fluorinated resin with a low surface energy, the rough structure of the sandblasted aluminum plate, which reduces the contact area, and the embedded graphene nanoflakes with a superior photothermal effect. Furthermore, the hydrogen bonding competition effect between the exposed-edge oxygen-containing functional groups of the embedded graphene nanoflakes and water molecules further improves the anti-icing properties. This work proposes a facile preparation method to prepare coatings with excellent anti/de-icing properties, offering significant potential for large-scale engineering applications.

Unconventional Dually-Mobile Superrepellent Surfaces

The ability of water droplets to move freely on superrepellent surfaces is a crucial feature that enables effective liquid repellency. Common superrepellent surfaces allow free motion of droplets in the Cassie state, with the liquid resting on the surface textures. However, liquid impalement into the textures generally leads to a wetting transition to the Wenzel state and droplet immobilization on the surface, thereby destroying the liquid repellency. This study reports the creation of a novel type of superrepellent surface through rational structural control combined with liquid-like surface chemistry, which allows for the free movement of water droplets and effective repellency in both the Cassie and Wenzel states. Theoretical guidelines for designing such surfaces are provided, and experimental results are consistent with theoretical analysis. Furthermore, this work demonstrates the enhanced ice resistance of the dually-mobile superrepellent surfaces, along with their distinctive self-cleaning capability to eliminate internal contaminants. This study expands the understanding of superrepellency and offers new possibilities for the development of repellent surfaces with exceptional anti-wetting properties.

Impact of Droplets on Surfaces Designed with Wettability-Gradient Properties: Directional Migration, Oblique Rebound, and Reduced Contact Time

Efficiently regulating the rebound behavior of droplets post-impact is crucial for various fields, mainly including the development of self-cleaning applications, the design of surface functional materials, and the advancement of industrial techniques. By performing molecular dynamics simulations, we investigated the impact and jumping behavior of droplets on heterogeneous substrates with different wetting regions. We found that, during the impacting evolution process, the retracted droplets would move toward regions with stronger wettability due to the unbalanced force caused by the wettability difference, revealing the directional migration ability. The values of the wettability difference strongly affect the degree of oblique rebound and contact time when droplets can jump off the substrate. We then designed the surfaces with a wettability gradient and found that the oblique rebound angle could be well controlled and the contact time further reduced. Our findings may provide valuable insight into the relationship between the wettability gradient and the behavior of liquid droplets on surfaces, with broad implications for various fields such as surface engineering, materials science, microfluidics, etc.

Multifunctional Superamphiphobic Coating Based on Fluorinated TiO2 toward Effective Anti-Corrosion

The application of superamphiphobic coatings improves the surface's ability to repel fluids, thereby greatly enhancing its various functions, including anti-fouling, anti-corrosion, anti-icing, anti-bacterial, and self-cleaning properties. This maximizes the material's potential for industrial applications. This work utilized the agglomeration phenomenon exhibited by nano-spherical titanium dioxide (TiO2) particles to fabricate 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTES) modified TiO2 (TiO2@fluoroPOS) fillers with low surface energy. This was achieved through the in-situ formation of protective armor on the surface of the agglomerates using the sol-gel method and fluorination modification. Polyvinylidene fluoride-tetrafluoropropylene (PVDF-HFP) and TiO2@fluoroPOS fillers were combined using a spraying technique to prepare P/TiO2@fluoroPOS coatings with superamphiphobicity. Relying on the abundance of papillae, micropores, and other tiny spaces on the surface, the coating can capture a stable air film and reject a variety of liquids. When the coatings were immersed in solutions of 2 mol/L HCl, NaCl, and NaOH for a duration of 12 h, they retained their exceptional superamphiphobic properties. Owing to the combined influence of the armor structure and the organic binder, the coating exhibited good liquid repellency during water jetting and sandpaper abrasion tests. Furthermore, the coating has shown exceptional efficacy in terms of its ability to be anti-icing, anti-waxing, and self-cleaning.

Topological wetting states of microdroplets on closed-loop structured surfaces: Breakdown of the Gibbs equation at the microscale

Microdroplets are a class of soft matter that has been extensively employed for chemical, biochemical, and industrial applications. However, fabricating microdroplets with largely controllable contact-area shape and apparent contact angle, a key prerequisite for their applications, is still a challenge. Here, by engineering a type of surface with homocentric closed-loop microwalls/microchannels, we can achieve facile size, shape, and contact-angle tunability of microdroplets on the textured surfaces by design. More importantly, this class of surface topologies (with universal genus value = 1) allows us to reveal that the conventional Gibbs equation (widely used for assessing the edge effect on the apparent contact angle of macrodroplets) seems no longer applicable for water microdroplets or nanodroplets (evidenced by independent molecular dynamics simulations). Notably, for the flat surface with the intrinsic contact angle ~0°, we find that the critical contact angle on the microtextured counterparts (at edge angle 90°) can be as large as >130°, rather than 90° according to the Gibbs equation. Experiments show that the breakdown of the Gibbs equation occurs for microdroplets of different types of liquids including alcohol and hydrocarbon oils. Overall, the microtextured surface design and topological wetting states not only offer opportunities for diverse applications of microdroplets such as controllable chemical reactions and low-cost circuit fabrications but also provide testbeds for advancing the fundamental surface science of wetting beyond the Gibbs equation.

Engineered Sustainable Omniphobic Coatings to Control Liquid Spreading on Food-Contact Materials

The adhesion of sticky liquid foods to a contacting surface can cause many technical challenges. The food manufacturing sector is confronted with many critical issues that can be overcome with long-lasting and highly nonwettable coatings. Nanoengineered biomimetic surfaces with distinct wettability and tunable interfaces have elicited increasing interest for their potential use in addressing a broad variety of scientific and technological applications, such as antifogging, anti-icing, antifouling, antiadhesion, and anticorrosion. Although a large number of nature-inspired surfaces have emerged, food-safe nonwetted surfaces are still in their infancy, and numerous structural design aspects remain unexplored. This Review summarizes the latest scientific research regarding the key principles, fabrication methods, and applications of three important categories of nonwettable surfaces: superhydrophobic, liquid-infused slippery, and re-entrant structured surfaces. The Review is particularly focused on new insights into the antiwetting mechanisms of these nanopatterned structures and discovering efficient platform methodologies to guide their rational design when in contact with food materials. A detailed description of the current opportunities, challenges, and future scale-up possibilities of these nanoengineered surfaces in the food industry is also provided.

Achieving Extreme Pressure Resistance to Liquids on a Super-Omniphobic Surface with Armored Reentrants

Static repellency and pressure resistance to liquids are essential for high-performance super-omniphobic surfaces. However, these two merits appear mutually exclusive in conventional designs because of their conflicting structural demands: Static liquid repellency necessitates minimal solid-liquid contact, which in turn inevitably undercuts the surface's ability to resist liquid invasion exerted by the elevated pressure. Here, inspired by the Springtail, these two merits can be simultaneously realized by structuring surfaces at two size scales, with a micrometric reentrant structure providing static liquid repellency and a nanometric reentrant structure providing pressure resistance, which dexterously avoids the dilemma of their structural conflicts. The nanometric reentrants are densely packed on the micrometric ones, serving as "armor" that prevents liquids invasion by generating multilevel energy barriers, thus naming the surface as the armored reentrants (AR) surface. The AR surface could repel liquids with very low surface tensions, such as silicone oil (21 mN m-1), and simultaneously resist great pressure from the liquids, exemplified by enduring the impact of low-surface-tension liquids under a high weber number (>400), the highest-pressure resistance ever reported. With its scalable fabrication and enhanced performance, our design could extend the application scope of liquid-repellent surfaces toward ultimate industrial settings.