In this article we are going to explore the use of superhydrophobic coatings in industry. But first we need to look at what exactly hydrophobic and specifically ‘superhydrophobic’ coatings are. To be hydrophobic means to be something that is insoluble in water or something that repels water. Superhydrophobic refers to something with extreme water-repellency. Water droplets form spherical beads that simply roll away leaving the surface dry.
What are hydrophobic coatings?
Before superhydrophobic we had hydrophobic. The groundwork was laid by hydrophobic for what was to follow with superhydrophobic. Hydrophobic coatings are thin layers applied to surfaces to create a water-repellent barrier, preventing moisture from spreading or adhering. By causing water droplets to bead up and roll off, these coatings protect materials from water damage, corrosion, and contamination. They are widely used in various industries, including automotive, electronics, construction, and textiles, to enhance the durability and cleanliness of surfaces.
Besides water, hydrophobic coatings can also repel other liquids and contaminants like oils, dirt, and dust, making surfaces easier to clean and maintain. This property not only extends the lifespan of the coated objects but also reduces maintenance costs and improves performance in applications where moisture resistance is crucial. However hydrophobic coatings are not perfect. They do allow a certain level of dust, dirt and liquids to pool and collect.
Okay, what are superhydrophobic coatings then?
A material is considered superhydrophobic if it has a water contact angle greater than 150 degrees, making it extremely water-repellent. Superhydrophobic coatings, essentially super waterproof layers, cause water droplets to bounce off the surface like a ball. These coatings are made from materials that exhibit ultrahydrophobicity, creating a rough surface that traps air and minimizes contact with water. This results in water droplets fully rebounding and sliding off easily. The contact angle, which is the angle where the water surface meets the material surface, indicates the level of hydrophobicity. A low angle close to 0 degrees indicates a puddle, while a high angle up to 180 degrees shows minimal contact, resembling a droplet almost entirely spherical.
In nature
In nature, hydrophobic surfaces are common and serve various functional purposes. One of the most famous examples is the lotus leaf, which exhibits remarkable water-repellent properties, a phenomenon known as the “lotus effect.” The surface of a lotus leaf is covered with microscopic structures and a waxy coating, which together create a rough texture that traps air. This structure significantly reduces the contact area between water droplets and the leaf’s surface, causing water to bead up and roll off, carrying away dirt and debris in the process. This natural self-cleaning property not only helps the plant stay clean and free of pathogens but also reduces the risk of mold and algae growth.
The lotus leaf has a superhydrophobic surface resistant to water droplets.
Other examples of hydrophobicity in nature include certain insect wings, like those of butterflies, and the feathers of waterfowl, which help keep them dry and buoyant. These natural hydrophobic surfaces inspire technological advancements in creating water-resistant materials and coatings.
Silica-based Coatings
Silica is used to produce superhydrophobic protective coatings.
Silica-based coatings are engineered to be superhydrophobic by incorporating silica nanoparticles or other silica compounds into a thin layer applied to a surface. The silica particles create a rough, textured surface at the microscopic level, which plays a crucial role in achieving superhydrophobicity. This texture, combined with the inherent hydrophobic properties of silica, minimizes the contact area between the surface and water droplets. As a result, water beads up into nearly spherical droplets and rolls off the coated surface, effectively repelling moisture.
The superhydrophobic nature of silica-based coatings is often achieved by further modifying the silica particles with hydrophobic agents, enhancing their water-repellent properties. These coatings not only prevent water from adhering but also protect surfaces from contaminants like dirt, oils, and chemicals. This makes them highly valuable for a variety of applications, including protecting electronic devices, textiles, glass, and metals. The durability, transparency, and non-toxic nature of silica-based superhydrophobic coatings also make them an attractive option for use in consumer products and industrial applications.
Car windscreens are coated with hydrophobic layers to repel water as shown above.
Lenses
Superhydrophobic coatings on lenses and glasses create a surface that effectively repels water, dust and dirt, significantly reducing the need for frequent cleaning. These coatings work by forming a barrier that prevents moisture from adhering to the lens, causing water droplets to bead up and roll off rather than spreading and smudging.
This same property also prevents dust and dirt from sticking, as particles are easily removed by light wiping or shaking. As a result, superhydrophobic coated lenses stay clearer for longer periods, enhancing visual clarity and comfort while minimizing maintenance. This technology is particularly beneficial for eyewear, camera lenses, and other optical devices, where maintaining a pristine, unobstructed view is crucial.
Glasses have hydrophobic coatings to repel water, dust and moisture.
Maritime industry
Superhydrophobic coatings in the maritime industry offer significant advantages by providing vessels with enhanced protection against water and environmental challenges. These coatings create a surface that repels water, reducing biofouling from organisms like barnacles and algae, which can degrade a ship’s hull and decrease fuel efficiency. By minimizing the accumulation of biofouling, superhydrophobic coatings help reduce drag, leading to improved fuel economy and lower operational costs.
Ships are more fuel efficient when their hulls are coated with superhydrophobic paint.
Additionally, these coatings offer excellent corrosion resistance, safeguarding metal surfaces from saltwater and extending the lifespan of maritime equipment. The durability and low maintenance requirements of superhydrophobic coatings make them a valuable investment for improving the performance and longevity of ships and offshore structures.
The benefits of superhydrophobic coatings in the construction industry
Superhydrophobic acrylic coatings for new or existing buildings repel water, dry quickly, and reduce the growth of mold, mildew, and dirt. These coatings help maintain a building’s appearance and integrity, offer long-lasting protection against the elements, and lower maintenance and recoating costs. They can last up to ten years, compared to two to three years for traditional coatings, and their use of silicone polymer technology enhances fade resistance. Over time, these benefits can save building owners up to 80% in maintenance costs.
Measuring the hydrophobicity of a coating
Manufacturers determine hydrophobicity by measuring the contact angle of a water droplet on a material’s surface; a greater angle indicates higher hydrophobicity. This property enhances a building’s exterior durability by allowing water and dirt to roll off, aiding in quicker drying, and providing resistance against mould, extreme temperatures, UV rays, dirt, and staining, thus preserving the structure’s long-term value.
The info graphic below illustrates the difference between superhydrophilic, hydrophilic, hydrophobic and superhydrophotic. The more acute the angle measured on a droplet, the more hydrophilic the surface is. Conversely the more obtuse the angle, the more hydrophobic the surface is.
Condensation
Hydrophobic and suprehydrophobic coatings prevent condensation and are ideal for windows, roof-lights and steel roof interiors of commercial buildings that operate with high internal humidity such as food production, school halls, sports facilities such as swimming pools.
Indoor pools, sports halls, food production facilities and so on suffer from internal condensation.
Durability
Superhydrophobic surfaces offer notable benefits in managing interface-related challenges, such as reducing friction, preventing liquid adhesion, and enhancing self-cleaning properties. These surfaces are highly effective in applications where controlling moisture and contamination is crucial, such as in electronics, medical devices, and outdoor equipment. By causing water and other liquids to bead up and roll off, superhydrophobic coatings can also protect against corrosion and biofouling, improving the longevity and performance of various materials. The ability of these surfaces to maintain cleanliness with minimal maintenance further underscores their utility in both industrial and consumer products.
However, despite their advantages, the practical application of superhydrophobic surfaces is often constrained by their limited wear resistance and environmental durability. The delicate nanostructures and coatings that impart superhydrophobic properties can easily be damaged or worn away through physical abrasion, chemical exposure, or prolonged environmental stress, such as UV radiation and extreme temperatures. This susceptibility to degradation means that in real-world conditions, the longevity of superhydrophobic coatings can be compromised, reducing their effectiveness over time. As a result, ongoing research is focused on developing more robust and durable superhydrophobic materials that can withstand physical wear and environmental challenges, thereby extending their practical applications and ensuring sustained performance.
Teflon
Teflon has excellent water repulsion abilities.
Teflon, scientifically known as polytetrafluoroethylene (PTFE), is a material renowned for its superhydrophobic properties. This is due to its extremely low surface energy, which results from the strong carbon-fluorine bonds within its molecular structure. These bonds create a surface that is not only chemically inert but also highly non-polar, making it difficult for water and other polar substances to adhere.
When water contacts a Teflon surface, it forms nearly spherical droplets that minimize contact with the surface, a characteristic of superhydrophobicity. This effect is due to the combination of the material’s intrinsic hydrophobicity and the potential microstructuring of the surface, which enhances the water-repellent properties. Consequently, water beads up and rolls off, taking dirt and other contaminants with it. This phenomenon is why Teflon is widely used in non-stick cookware, protective coatings, and various industrial applications where easy cleaning and reduced friction are desirable. The durability and stability of Teflon make it a practical choice for many applications that benefit from superhydrophobicity.
Conclusion
Superhydrophobic coatings protect against moisture, mould, dirt and so on, but they aren’t cheap and they aren’t always the most robust either. There are so many variables to consider with protective coatings, the mind boggles. If you have any questions or would like some advice about a coatings project you have coming up give us a call or drop us a message — we’d be delighted to hear from you. Additionally we hope you have enjoyed this article, its taken our team many weeks of hard work and research to put together and we’d love to hear some feedback.
In the meantime have a fantastic day and “keeeeep – on – coating“! 😊🖌️
