You have just watched a video broadcasting the self-cleaning and water repellent properties on a leaf surface (lotus effect). What you have seen in the video occurs due to a specific surface phenomenon called superhydrophobicity. It is known that lotus leaf behaves as a super hydrophobic surface. So, Superhydrophobicity is sometimes referred to as the lotus effect. Let us now analyze the characteristics and applications of this phenomenon.

Superhydrophobic surfaces contain micro protrusions that are coated by nano waxy materials. When water droplets are poured, they will sit on the tips of the hydrophobic protrusion. The combined structure will trap a layer of air between the surface and the leaf. So, the liquid droplets will not adhere to the surface but instead will move freely taking dirty particles. As shown in the video, the different liquids used (water and honey) roll easily off the surface of the leaf .The hydrophobic leaf surface has a low surface tension and roughness initiation components. This is why the liquid droplet has a very high contact angle (𝜽greater than150) with respect to the leaf surface. As a result, the contact area between the liquid drop and the surface will be minimized and leads to the droplets forming a spherical shape on the surface. For a surface that has a lotus effect, air can be trapped under the liquid droplet. This will cause the liquid droplet to settle on a surface as if on a bed of nails that have solid and air fractions. Cassie-Baxter equation can be used to describe this. The contact angle is a function of the surface roughness, solid fraction, air fraction and the corresponding contact angle measured at flat surface (Young equation). As the solid fraction approaches 0, the Cassie-Baxter contact angle will approach 1800.

The interest in superhydrophobic surfaces has grown exponentially over recent decades resulting in the development of many practical applications. This phenomenon inspires engineers to produce superhydrophobic surfaces that mimic the natural ones. And because of this, many applications have been already established in food and beverage industry, oil-water separation, microcondensation, mining industries, construction, humidity proof coatings for electronic devices, controlling transportation of fluids, anti-bio fouling and water corrosion prevention. An interesting application which is currently under research is the development of micro fuel cell chips. Some of the chemical and physical methods used by engineers today to fabricate such superhydrophobic surfaces are wax solidification, lithography, vapor deposition, polymer reconformation, Sol-gel processing, electrohydrodynamics and electrospinning. It is our job as engineers to utilize these various methods in order to enhance the applications of superhydrophobic surfaces benefitting the human population in more than one way.