Discover Top Posts Tagged with #wettability

Machine learning proves that graphene is hydrophobic

For more than a decade, a fundamental mystery has surrounded graphene—the one-atom-thick "wonder material" known for its exceptional strength, conductivity, and transparency. Despite its seemingly simple structure, one basic question has remained unresolved: Does graphene attract water, or repel it? The answer has proven surprisingly elusive. In some experiments, water droplets bead up on graphene, suggesting a hydrophobic (water-repellent) surface. In others, water spreads out, implying hydrophilic (water-attracting) behavior. This contradiction has fueled a long-running scientific debate and created uncertainty for applications such as desalination membranes, hydrogen fuel cells, and nanoelectronic devices, where precise control of water at interfaces is essential.

Tea lovers have long been frustrated by the tendency of liquid jets to adhere to solid surfaces -- the so-called teapot effect that makes the last vestiges of every pour drip down the spout. By investigating the effect with vertical rods, researchers found that, at low enough flow rates, a liquid jet is able to adhere completely, forming a liquid helix that coils around the rod. The authors were also able to construct a mathematical model to capture the behavior. They concluded that both the wettability of a surface and the curvature of the solid are critical to determining whether or not a liquid jet will stick. (Image and research credit: E. Jambon-Puillet et al.; via APS Physics; submitted by Kam-Yung Soh)

#fluid dynamics #science #physics #sciblr #tea #teapot effect #wettability #liquid jet

Graphene partially screens van der Waals interactions depending on layer thickness, study reveals

Two-dimensional (2D) materials, which are only a few atoms thick, are known to exhibit unique electrical, mechanical and optical properties, which differ considerably from the properties of bulk materials. Some recent studies have also been probing these materials' "transparency" to intermolecular interactions, such as van der Waals (vdW) forces—weak forces arising from fluctuating electrical charges, which prompt the attraction between molecules or surfaces. Determining the extent to which these forces are screened by atomically thin materials could have important implications for the development of various technologies based on 2D materials. Researchers at Peking University, Nanjing University of Aeronautics and Astronautics and Tsinghua University recently set out to shed light on whether 2D graphene systems fully transmit, partially screen or block vdW interactions.

Overturning a 200-year belief: New surface design enables two distinct wetting states on a single substrate

NIMS discovered a phenomenon in which droplets on a single solid surface exhibit both a "sticky" and "repellent" state simultaneously. Namely, the wetting behavior branches into two states. This is a discovery that overturns interface chemistry scientists' belief held for over 200 years that, on a non-textured surface, the wetting state is uniquely determined by solid/liquid combinations. Furthermore, the research team also clarified a universal surface design principle that causes this phenomenon. This research result was published in Advanced Materials Interfaces on April 2, 2026.

New membrane technology could lead to more effective and efficient water purification systems

A team of NYU Abu Dhabi (NYUAD) researchers has developed a novel approach that utilizes microwave technology to more easily synthesize and fine-tune a new type of membrane which effectively purifies water from a wide range of contaminants. The membrane synthesis technique takes a few minutes, making it one of the fastest methods for creating covalent organic framework (COF) membranes. These membranes act as filters in devices designed to clean polluted water from specific contaminants, allowing its reuse in different applications—an important discovery at a time when efficient wastewater treatment becomes vital in a world threatened by water scarcity. The new type of dual-faced membrane, characterized by its unique superhydrophilic and near-hydrophobic surfaces, enables efficient removal of contaminants like oils and dyes from water. This dual functionality not only enhances the filtration process but also endows the membranes with strong antibacterial properties, crucial for long-term usability and effectiveness.

Understanding liquid droplet behavior has major implications in coating industry, agriculture, and epidemiology, among others. Although well-studied and extensively researched, the mechanism of droplet splashing after impingement still remains unclear. Now, scientists have proposed a new model that quantitatively predicts the splashing conditions in addition to the number of fingers and the size of the ejected secondary droplets for smooth and rough surfaces, deepening our insights into the phenomenon.

The study of liquid droplets and their behavior upon impingement is of major importance in many fields, including agriculture, engineering, and medicine. Droplet behavior prediction has use in spray painting and pesticide sprays, inkjet technology for printing, and aerosol generation during rainfall. A deeper understanding of this phenomenon is, therefore, imperative not only for advancing our knowledge of fluid physics but also technology.

In this regard, a particularly intriguing phenomenon is the splashing of droplets upon hitting solid surfaces. Several studies on liquid film behavior have helped shed light on droplet splashing. However, no consensus has emerged regarding when a droplet can be expected to splash. Moreover, wetting behavior, or the ease with which a liquid adheres to smooth and rough solid surfaces, is equally important to understand.

Against the backdrop, a group of scientists from Japan and China recently conducted a study to address this issue. The research team, led by Associate Professor Yukihiro Yonemoto from Kumamoto University, Japan in collaboration with Professor Tomoaki Kunugi from Zhejiang University, China, has proposed a new model that can predict when a droplet will splash after impinging on a solid surface. Their study was published in Volume 12 of Scientific Reports on 24 March 2022.

Researchers develop novel robust superhydrophobic coating

Lotus-inspired superhydrophobicity attracts the interest of researchers due to its interfacial non-wetting and unique multi-phase contact properties. However, fragile hierarchical structures, fluorine-containing chemicals usage, and strict requirements for substrate scopes remain thorny challenges.

Recently, a research team led by Prof. Hou Baorong and Prof. Duan Jizhou from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) reported a mechanical robust superhydrophobic ZnO@STA@PDMS coating with fluorine-free reagents through wide-applicable and substrate-independent spray-coating method.

The study was published in Materials & Design on Oct. 10.

The hierarchical rough micro-scale bump-porous structure, nano-scale particles and extremely low surface energy of the coating contribute to the eventual water repellent superhydrophobicity.

The |Z|10mHz value of the as-fabricated superhydrophobic coating is three orders of magnitude higher than Q235 carbon steel. The Icorr of the substrate decreases two orders of magnitude after spray-coated with superhydrophobic ZnO@STA@PDMS coating, suggesting a superior corrosion resistant performance.

New study reveals how intermolecular forces inform the design of smart materials

A recent study by researchers from the Chinese Academy of Sciences redefines how liquids maintain their contact with solid surfaces—also known as wettability—from an intermolecular force perspective.

The findings were published in Nano Research on Feb 8.

Wettability is relevant to the design of materials because it determines how layers stick together. Says study author and professor Ye Tian from the Key Laboratory of Bio-inspired Materials and Interfacial Science, it "plays a crucial role in many fields, such as the efficiency of catalytic reaction, separation, electrode materials, and the design of bionic smart materials." For example, smart layers that change their contact depending on moisture could be used in sportswear that adapts to humidity.

Wettability models

High wettability means that a liquid drop spreads, creating a low angle of contact with the surface, whereas low wettability describes a liquid that resists spreading. Classically, wettability, as indicated by contact angle, is characterized using Young's equation, which models an ideal, perfectly smooth surface. If the water droplet spreads out to a contact angle lower than 90 degrees, the surface is categorized as hydrophilic or water-loving. If the water droplet makes a contact angle higher than 90 degrees, the surface is categorized as hydrophobic.

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