Repellency treatments are a category of surface treatments designed to protect various surfaces from both water and oil-based liquids. These coatings create a non-stick barrier on the surface that repels liquids, which in turn prevents stains and other forms of damage. Metal and glass surfaces, as well as those made from sapphire or other materials, are often exposed to both water and oil-based liquids. The coatings are specially formulated based on the substrate, they are not ” one size fits all”. A repellency treatment created for glass will have a different composition compared to a repellency treatment created for metals.
In addition to protecting against water and oil-based liquids, repellency treatments with hydrophobic and oleophobic properties can also resist other types of contaminants, such as dirt, dust, and grime. This can be particularly useful in industrial and commercial settings, where surfaces are exposed to a wide range of substances.
What does “hydrophobic” mean?
Hydrophobic, in simple terms, means “water-fearing.” Hydrophobic molecules are nonpolar, meaning they blend well with other nonpolar or neutral materials. Because water is polar, hydrophobic materials naturally repel it.
Consequently, applying a hydrophobic coating to a surface renders it water-repellent. Consider wax or oil as a real-life example: their nonpolar molecules don’t mix well with the polar molecules of water, resulting in a heterogeneous mixture where they remain separate. Lotus leaves are a famous example of hydrophobicity found in nature. They’re known for their super water-repelling properties and self-cleaning ability, which inspired the concept of the ‘Lotus effect’. These leaves have tiny bumps and a wax-like coating that make them water-resistant. So, when water falls on them, it beads up and rolls off, taking dirt with it.
What does “hydrophilic” mean?
Hydrophilic means “water-loving,” the opposite of hydrophobic. When water touches a hydrophilic material, it spreads out easily and covers the surface completely. Examples of hydrophilic surfaces include glass, concrete, cotton, paper, and wood. These surfaces contain functional groups, such as hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, and phosphate groups, which attract water molecules because they are polar.
What does “oleophobic” mean?
The oleophobic property is very similar to hydrophobicity. In this case, instead of repelling water, the material repelled is oil. This can be very useful for materials like screens, where oil from fingers can cause smudging. Oleophobic coatings are typically made up of different chemical compounds depending on the application and requirements of the coatings.
Silicones and fluoropolymers are popular choices due to their unique properties of being able to create low surface energy and inert surfaces, rendering them protected from oils.
How are hydrophobicity and oleophobicity measured?
To measure hydrophobicity, the water contact angle is used. Similarly, to test oleophobicity, the oil contact angle is used. This test is performed to determine the wettability of a surface. A drop of oil or water is placed on a substrate, then the angle formed between the tangent to the liquid droplet’s surface and the solid surface at the point where they meet is measured.
If the contact angle measures<90° , the surface is hydrophilic. If the contact angle measures ≥90°, the surface is hydrophobic.
How do I make my surface hydrophobic or oleophobic?
To make surfaces hydrophobic or oleophobic, coatings can be applied. These coatings change the chemistry of the surface by introducing molecules that repel water or oil. These molecules form a barrier that prevents water and oil molecules from bonding to the surface, causing droplets to bead up and roll off.
What factors should be considered when choosing a repellency treatment?
There are many ways to apply a hydrophobic or oleophobic coatings to a substrate, including dip, wipe, and spray. Some treatments require a quick cure, however, depending on the application and requirements it might not be necessary. So, what are the most important aspects to consider when selecting a repellency treatment? The following questions will give enough information to get started on finding the perfect treatment for the application:
What is the substrate? The substrate is critical to understanding what technology options are available to consider. For surfaces such as porcelain, there is not an oxide-containing surface, so you need a method to apply a durable treatment and then we are limited to short lifetime options due to this. Most often, customers do not want to reapply on a daily/weekly basis. If a surface is not made of glass/metal/sapphire, there are coatings available that can be used for hydrophobic protection on multiple surfaces.
What are the functional requirements? If customers want a super hydrophobic (water contact angle >150°), it can be applied but it is not an easy application for very large surfaces (reapplication would be tedious and frequent). Also, any superhydrophobic that can be applied (including competitive materials we are aware of as well) is extremely fragile and sensitive, usually only acceptable for one-time use applications or where frequent re-application is acceptable. In most cases, a regular hydrophobic of 120° will meet the need when permanency is needed.
What are the durability requirements? Customers often want a certain level of durability in the magnitude of months, years, or possibly the life of the product. Even for hydrophobic applications on an oxide surface where we can apply a more robust coating, flooring is just a poor application due to the level of aggressive abrasion and wear seen. Outdoor applications should also be considered since most treatments are UV-sensitive and quickly break down in sunlight.
Conclusion
Repellency treatment technology bonds with many different surfaces at the nano-scale to create easy-clean, superhydrophobic (water-repelling) and oleophobic (oil-repelling), anti-smudge coatings. These coatings are currently being used on metals, polymers, glass, and many other materials for numerous applications
Repellency treatments that are both hydrophobic and oleophobic can help prevent damage caused by these substances, ensuring that surfaces remain clean and free of stains. To make a surface hydrophobic or oleophobic, coatings can be easily applied via dip, wipe, or spray methods. Consider the substrate, functional requirements, and durability needs when selecting a treatment. The substrate type impacts available technology options, while functional and durability requirements dictate the level of hydrophobicity needed and the coating’s longevity.
Facing challenges in product selection or encountering difficulties with your application? Let our team of Coatings Experts be your guide. Contact us today, and we’ll navigate the complexities with you to find the perfect solution for your unique needs.
