The key difference between hydrophobic and superhydrophobic is their contact angle for water droplets. The contact angle for water droplets on hydrophobic surfaces is more than 90 degrees, so it repels water. In contrast, the contact angle for water droplets on a superhydrophobic surface is more than 150 degrees, which cause not only to repel water but also to roll water off from the surface.
Both hydrophobic and superhydrophobic surfaces are water-repelling surfaces. The hydrophobic interactions describe the repulsion between water and other substances, while superhydrophobic means more intense than hydrophobic.
CONTENTS
1. Overview and Key Difference
2. What is Hydrophobic
3. What is Superhydrophobic
4. Hydrophobic vs Superhydrophobic in Tabular Form
5. Summary – Hydrophobic vs Superhydrophobic
What is Hydrophobic?
Hydrophobic interactions are repulsion forces between water molecules and other substances. It is the interaction type opposite to hydrophilic interaction (attraction force between water molecules and other substances). In this term, hydro” means “water” and “phobic” means “fear”. Therefore, we can describe substances that do not like water as hydrophobic substances. These substances repel water molecules. Generally, non-polar molecules show this type of interaction because water molecules are polar. In other words, hydrophobic substances tend to attract or interact with or dissolve in non-polar substances such as oil and hexane.
Sometimes, hydrophobic substances are called lipophilic substances because these substances attract lipid or fat components. When a hydrophobic substance is added to water, the substance’s molecules tend to form clumps by combining with each other. This makes hydrophobic solvents important in separating non-polar compounds from water or polar solutions.
What is Superhydrophobic?
Superhydrophobic interaction is the ability to repel water to the degree that droplets do not flatten but roll off instead. It is also known as ultra-hydrophobicity. Superhydrophobic surfaces are extremely hydrophobic surfaces that are extremely difficult to wet. Usually, the contact angle of a water droplet on this kind of surface exceeds 150 degrees. We can also name this interaction the lotus effect because of the behavior of water droplets on a lotus leaf. A water droplet that strikes a superhydrophobic surface can fully rebound, similar to an elastic ball.
The contact angle of the water droplet on a superhydrophobic surface was first described by Thomas Young in 1805. He did this by analyzing the forces that are acting on the fluid droplet that is resting on a smooth solid surface that is surrounded by a gas.
We can find examples for superhydrophobic surfaces in nature, including lotus leaves, fine hairs on some plants, water striders and insects that live on the surface of the water, some birds that are great swimmers, etc.
What is the Difference Between Hydrophobic and Superhydrophobic?
Both hydrophobic and superhydrophobic surfaces are water-repelling surfaces. The key difference between hydrophobic and superhydrophobic is that the contact angle for water droplets on hydrophobic surfaces is more than 90 degrees, whereas the contact angle for water droplets on a superhydrophobic surface is more than 150 degrees. Therefore, hydrophobic surfaces repel water, whereas superhydrophobic surfaces not only repel water but also roll the water off from their surfaces.
The below infographic lists the differences between hydrophobic and superhydrophobic in tabular form for side by side comparison.
Summary – Hydrophobic vs Superhydrophobic
Hydrophobic Interactions are repulsion forces between water molecules and other substances. Superhydrophobic interaction is the ability to repel water to the degree that droplets do not flatten but roll off instead. The key difference between hydrophobic and superhydrophobic is that the contact angle for water droplets on hydrophobic surfaces is more than 90 degrees, whereas the contact angle for water droplets on a superhydrophobic surface is more than 150 degrees. Therefore, hydrophobic surfaces repel water, whereas superhydrophobic surfaces not only repel water but also roll the water off from their surfaces.
Reference:
1. Helmenstine, Anne Marie. “The Definition of Hydrophobic With Examples.” ThoughtCo, Aug. 28, 2020.
Image Courtesy:
1. “Super-hydrophobic paint test” By UCL MAPS/O, Usher – Flickr (CC BY 2.0) via Commons Wikimedia
2. “DropConnectionAngel” By Na2jojon – Own work (Public Domain) via Commons Wikimedia