Welcome to the world of hydrophobic and super-hydrophobic materials. The technology has revolutionised many sectors from leisurewear to electronics and medtech - but you might not even realise it is there.
What is a hydrophobic coating?
A hydrophobic coating is a thin layer of material that repels water. These coatings cause an imperceptibly thin layer of air to appear on any surface they are applied to, allowing water droplets simply to 'bead up' and roll off. They can be sprayed onto many kinds of surfaces, from metals to plastics and fabrics, ensuring they remain dry and clean even in the wettest conditions.
Like water off a duck’s back?
For thousands of years, humans have admired the water-resistant surfaces they observed in the natural world. From duck feathers to rose petals and insect wings, nature has given some organisms an extraordinary way of repelling rain and remaining dry whatever the weather.
Scientists coined a phrase for this quality - ‘hydrophobic' and sought to find ways to mimic it in the materials they created.
Hydrophobic vs super-hydrophobic surfaces; what’s the difference?
It’s literally a question of degree.
Hydrophobic surfaces have a water contact angle greater than 90 degrees while super-hydrophobic surfaces have a contact angle of more than 150 degrees.
This is the angle at which a droplet of water meets the surface. The higher the contact angle, the more efficient the surface is at ‘beading water’ and enabling it to roll off.
Understanding the Lotus Effect
Lotus leaves held a particular fascination for scientists because they can bead water in almost magical ways.
They weren’t just hydrophobic - they were super-hydrophobic.
The contact angle of water on the surface of a Lotus leaf is greater than 150°. This enables the contact area and the adhesion force between surface and droplet to be significantly reduced and results in a self-cleaning process allowing water to readily roll off the leaf and collect dust deposits on the way.
This is called the Lotus Effect.
The hydrophobic revolution
In the 20th century, chemists began looking to synthesise the extraordinary “Lotus effect’ in the new materials they were creating.
Harnessing these capabilities would increase the ability of equipment to function in wet, suboptimal conditions, as well as extending their overall lifespan.
Now, super-hydrophobic coatings are made from a variety of materials and cover all kinds of surfaces that we encounter every day. Fluoropolymers, such as polytetrafluoroethylene (PTFE or Teflon), are widely recognised examples of hydrophobic materials. However, other options include silanes, silicon-based compounds, nano-structured metals and ceramics.
6 amazing properties of hydrophobic coatings
Hydrophobic and super-hydrophobic materials bring amazing benefits to the surfaces they coat:
Water resistance, preventing damage and degradation caused by moisture.
Self-cleaning properties, water beads up and carries away dirt and contaminants.
Anti-icing and de-icing effects, reducing ice formation and facilitating easier removal.
Improved optical clarity by minimising water droplets and fog on surfaces.
Surface protection from environmental factors, UV radiation, chemicals, and stains.
Energy efficiency through reduced adhesion of water, dirt, and dust, maximising light transmission and energy absorption.
In their most dramatic incarnations, hydrophobic materials can be fully immersed in water or sludge - only to emerge clean, dry and still fit for their original purpose. Just check out this video.
What are the applications of hydrophobic materials?
With such extraordinary properties, these coatings have a range of industrial uses and can be found everywhere in modern life:
Hydrophobic coatings are used on car windscreens, windows, and exterior surfaces to repel water, improve visibility during rain, and make cleaning easier. They can also be applied to car paint to provide protection against water spots, dirt, and environmental contaminants.
Hydrophobic coatings are used on electronic devices, such as smartphones, tablets and wearables, to protect them from water damage. These coatings create a barrier that repels water and prevents it from reaching sensitive, electronic components.
Optics and Eyewear
Hydrophobic coatings are applied to camera lenses, glasses, sunglasses, and other optical devices to prevent water droplets from forming, enhance clarity, and reduce fogging.
Aerospace and Aviation
Hydrophobic coatings are used on aircraft windshields, windows, and exterior surfaces to improve visibility during rain, prevent ice formation, and reduce drag caused by water adherence.
Architecture and Construction
Hydrophobic coatings can be applied to building materials such as glass, concrete, and metal surfaces to enhance water resistance, prevent staining, and facilitate self-cleaning. They can also be used on roofing materials to improve water runoff and prevent the growth of algae or mould.
Hydrophobic coatings are used on boat hulls, sails, and marine equipment to reduce drag, improve fuel efficiency, and prevent the attachment of marine organisms (bio-fouling).
Textiles and Fabrics
Hydrophobic coatings can be applied to textiles and fabrics to provide water resistance, stain resistance, and durability. This is commonly used in outdoor clothing, sportswear, and upholstery. Think about those GORE-TEX boots you love so much!
Medical and Healthcare
Hydrophobic coatings are utilised in medical devices, such as wearables and insertables like catheters. They reduce the adhesion of bodily fluids, prevent bacterial contamination, and improve device performance.
Hydrophobic coatings are applied to solar panels to repel water and reduce the accumulation of dust, dirt, and pollutants. This helps maintain the efficiency of the panels by maximising light absorption.
Packaging and Consumer Goods
Hydrophobic coatings are used in food packaging, beverage containers, and household products to improve water resistance, prevent leakage, and enhance product shelf life.
What are the disadvantages of super-hydrophobic tech?
But these materials can also have a highly negative environmental impact:
- Hydrophobic materials require energy-intensive and resource-intensive production processes.
- Improper disposal of hydrophobic materials can contribute to waste accumulation and environmental contamination. The hydrophobic lining of takeaway coffee cups, for example, is often non-recyclable.
- Some hydrophobic materials may contain chemicals of concern, such as perfluorinated compounds (PFCs), which can be persistent, bio-accumulative, and toxic.
- Release of hydrophobic materials into the environment can contribute to pollution of water bodies, soil, or air.
- Conducting a life cycle assessment (LCA) is important to understand the overall environmental impact of hydrophobic materials.
On the plus side, though, alternatives such as bio-based or biodegradable hydrophobic materials and responsible disposal practices are helping mitigate their environmental impact.
These materials have brought many benefits to the world. In one German town, hydrophobic paint is discouraging anti-social behaviour by deflecting urine onto the feet of those taking late-night comfort breaks against the side of buildings.
On a more serious note - advances in technology are making electronic products more durable and increasing the range of environments where they can function. They are extending the life of products that once would have gone to landfill. Their anti-corrosive and anti-icing properties are bringing functioning tech to even the most inhospitable environments.
And in a world of miniaturisation and IoT, their delicate application, water resistance and anti-bacterial qualities are paving the way for more implantable medical devices that will keep us living for longer.