What are Superhydrophobic Surfaces?

Superhydrophobic surfaces are extremely water‑repellent surfaces where water droplets form very high contact angles and roll off with only a small tilt. In practice, a surface is usually called superhydrophobic when the static water contact angle is above about 150° and the contact angle hysteresis is below 10°.

In this article, superhydrophobic surfaces are explored from the basic principles and natural examples to practical applications and the key methods used to characterize their performance.

The lotus effect and natural superhydrophobic surfaces

In nature, the lotus effect is one of the most famous examples of superhydrophobic surfaces, where water droplets roll off the leaf and remove dust and particles at the same time. This is a classic example of a self‑cleaning surface.

Under an electron microscope, the lotus leaf surface looks rough and is covered with a wax‑like material. This combination of:

• Low‑energy, hydrophobic chemistry, and
• Micro‑ and nanostructured roughness 

What makes a surface superhydrophobic: chemistry and roughness

A surface becomes truly superhydrophobic when two things work together: non‑wetting surface chemistry and a micro‑ and/or nanostructured topography. 

Non‑wetting chemistry is often introduced through low‑surface‑energy coatings. Teflon® is a typical example of a fluoropolymer with a high contact angle for a smooth surface, around 120°. But this is still below the ~150° water contact angle required for superhydrophobicity, which shows that chemistry alone is not enough; surface roughness is also needed. 

In an industrial setting, this usually means:

• Modifying or structuring the substrate (etching, patterning, particles, fibers)
• Applying a low‑energy coating on top

This combined design allows to reach very high water contact angles and low hysteresis in a repeatable way.

Traditionally, the non‑wetting part of this design has relied heavily on fluoropolymers such as Teflon®. Today, there is a clear push towards more sustainable and PFAS‑free chemistries, so many developers are working on superhydrophobic coatings that combine suitable surface texture with PFAS‑free formulations instead of conventional fluorinated systems.

In microfluidic and life‑science applications, similar design principles are used in wettability‑patterned surfaces for single‑cell trapping, where controlled wettability and contact angle patterns are used to position and hold individual cells.

Hydrophobic, superhydrophobic and oleophobic surfaces – what’s the difference?

Hydrophobic and superhydrophobic surfaces

A hydrophobic surface is one where water beads up instead of spreading out. The term literally means “fear of water,” and describes surfaces that repel water.

Superhydrophobic surfaces go further. They show water contact angles over about 150° and low contact angle hysteresis, which means water droplets slide off the surface very easily. This is what makes them interesting for self‑cleaning, anti‑icing and drag‑reducing applications.

Oleophobic and superoleophobic surfaces

Oleophobic surfaces repel oils and other low‑surface‑tension liquids, not just water. Superoleophobicity is similarly defined as superhydrophobicity but, instead of water drop, an oil drop must form an angle over 150 ° with the solid substrate.

Achieving this is more difficult since oil has a much lower surface tension and oil molecules are not as strongly bound to each other as in water. This requires very low surface free energy and carefully engineered roughness. 

In many modern coatings, hydrophobic or superhydrophobic behavior is combined with oleophobic properties to control both water and oils (for example fuels, lubricants or fingerprints) on the same surface.

Industrial applications of superhydrophobic surfaces

The strong interest in superhydrophobic surfaces comes from a very broad set of potential applications.  Some of the most relevant industrial use cases include:

• Self‑cleaning and easy‑to‑clean surfaces
  On building facades, road signs, vehicle exteriors or solar panels, superhydrophobic coatings can help reduce cleaning frequency and keep surfaces optically clear for longer. 
• Anti‑fouling and contamination control
  In marine and process environments, reducing how strongly water and particles adhere to surfaces can help limit fouling and buildup of biofilms or other contaminants.
• Anti‑icing and de‑icing
  On outdoor equipment, power lines, instrumentation or wind turbine blades, lower water adhesion can support faster ice shedding and reduce manual or chemical de‑icing.
• Drag reduction and flow control
  In some flow systems, specially designed superhydrophobic textures can maintain an air layer between water and the surface, which may reduce friction and energy losses.
• Thermal management and condensation
  In heat exchangers and condensation processes, superhydrophobic surfaces may support efficient dropwise condensation and rapid removal of condensate. This can improve heat‑transfer efficiency in compact equipment.

How superhydrophobic surfaces are measured in practice

To properly characterize superhydrophobic surfaces, you need to measure both water repellency (contact angle) and droplet mobility, which is described by contact angle hysteresis and related parameters.

Static contact angle

Static contact angle is often the first contact angle parameter to check. A stationary droplet is placed on the surface and its shape is analyzed. For superhydrophobic surfaces, thresholds of static water contact angles above 150° are commonly used.

However, static contact angle alone does not always show which surface has the lowest adhesion to water, so it should not be the only measurement. This is discussed in more detail in our article on contact angle measurements on superhydrophobic surfaces in practice.

Advancing and receding contact angles

Advancing and receding contact angles are routinely measured on superhydrophobic surfaces to calculate contact angle hysteresis.

A common method is the needle method. The drop volume is slowly increased and then decreased, and the advancing and receding angles are determined from the same droplet. The difference between the advancing and receding contact angles is the contact angle hysteresis, which tells you how easily droplets start and continue to move on the surface.

Roll‑off (sliding) angle

The roll‑off (or sliding) angle is the tilt angle at which a droplet starts to move. It is closely connected to contact angle hysteresis and gives a very intuitive picture of how easily water is actually removed from a tilted surface. The measurement of sliding or roll‑off angle is directly related to contact angle hysteresis. 

In summary, characterization of superhydrophobic coatings is typically based on both static and dynamic contact angle measurements, often performed with contact angle goniometers such as those provided by Biolin Scientific. This combination gives a much more reliable picture of performance than static angle alone.

Durability of superhydrophobic surfaces in real‑world use

One of the main questions when working with superhydrophobic surfaces is: “How long will the superhydrophobic effect last in my application?”

Even though hydrophobic chemistry is well understood, it remains challenging to produce coatings that tolerate real‑world wear and tear. In practice, the surface may face:

• Repeated cleaning or wiping

• Abrasion and scratching

• Particulate impact (sand, dust)

• Washing, chemicals or UV exposure

Often, the static contact angle stays fairly high or decreases only slightly, while the biggest change appears in contact angle hysteresis. When hysteresis increases, droplets do not roll off as before, and the surface has functionally lost its superhydrophobic behavior.

To evaluate durability, many different test methods have been used, including sliding and rotating abrasion, tape tests, and water‑jet exposure. The key is to:

• Choose durability tests that mimic real operating conditions

• Track both contact angle values and hysteresis before and after testing

Together, these measurements and durability tests give a realistic picture of how long superhydrophobic performance can be maintained under real‑world conditions.

From research to industrial implementation of superhydrophobic surfaces

Once the self‑cleaning behavior of the lotus leaf was understood, superhydrophobic surfaces attracted significant interest in the research community. Artificial superhydrophobic surfaces have since been developed across many research groups and relatively quickly found use in self‑cleaning, antifogging and anti‑icing materials and coatings on textiles, among other applications.

Today, if you work with coatings or surface treatments, you are likely asking questions such as:

• How can we measure and specify superhydrophobicity in a consistent way?

• How do we secure long‑term durability in real life?

• How can we combine superhydrophobicity with other functions (for example oleophobicity or anti‑corrosion)?

• How do we integrate these coatings into existing manufacturing processes?

As the technology matures, accurate contact angle and dynamic contact angle measurements, together with realistic durability testing, become increasingly important when specifying and comparing coatings.

FAQ: Superhydrophobic surfaces

1. How do you define a superhydrophobic surface?
   A surface is usually called superhydrophobic when the static water contact angle is above 150° and contact angle hysteresis is below 10°, so droplets roll off easily.
2. Why isn’t a high contact angle alone enough?
   A surface can have a high static water contact angle and still show strong droplet pinning. In that case, water does not roll off, and the surface will not behave as a truly superhydrophobic, self‑cleaning surface. This is why advancing/receding angles and roll‑off angle are also measured.
3. How are superhydrophobic surfaces measured in industry?
   Most labs use contact angle instruments to measure static, advancing and receding contact angles, and often roll‑off angle. Characterization of superhydrophobic coatings is thus based on both static and dynamic contact angles.
4. How durable are superhydrophobic coatings?
   Durability depends strongly on the chemistry, structure and environment. Even if the static contact angle stays high, increasing hysteresis and higher roll‑off angles indicate that droplets no longer move as easily, and the surface is losing its functional performance. It is therefore important to combine contact angle measurements with durability tests that mimic real operating conditions.

Conclusion

Superhydrophobic surfaces combine low‑energy surface chemistry with engineered micro‑ and nanostructures to achieve very high water contact angles and low hysteresis. This makes it possible for water droplets to roll off easily, which in turn supports self‑cleaning, anti‑icing, drag‑reducing and other advanced functionalities in industrial applications. With ongoing progress in materials science and surface engineering, new superhydrophobic coatings and applications are expected to be developed in both existing and emerging fields.