3 + 1 Plants with ‘mercury effect’ (Lotus effect)

As a kid I was already a nerd. I liked science, I liked doing experiments and I have already told you about the time I set my mother’s laundry on fire. I don’t know if you’ve ever broken a mercury thermometer. They almost don’t make them anymore, they’re all digital also because mercury has been banned due to its super toxicity. For me, however, it was an event like Italy winning the European football championships (hehe): I kept the drops of mercury that came out and played with them, fascinated by the behavior of this unusual metal, liquid at room temperature. Sometimes the thermometer breakages were voluntary (don’t tell my mother) and the measuring instrument was sacrificed in the name of science.

Don’t worry, you haven’t got the wrong blog, we will talk about plants.

In the garden of the house, at that time, there was a small pond, with some water lilies and lotus flowers. If you have ever been lucky enough to admire the beautiful Lotus flower up close (Nelumbo nucifera) you probably won’t have missed another very cool feature of this plant: the hydrophobicity of its leaves. Here I spent hours in the garden with this thing.

If you spray water on the lotus leaves you will see it splash away quickly in the form of spheres which have always reminded me of drops of mercury: the lotus leaf will never be wet and your attempt to flood it will be of no avail, the water will always slide over it, accumulating in the center or escaping beyond the edges of the leaf blade.

Even today this phenomenon fills me with curiosity and over the years I have met other plants that present the same characteristic. Furthermore, they are very particular plants and I have sometimes made these discoveries almost by chance. Last week I gave you some strong content and as promised today we are dealing with a slightly lighter and more curious topic (for those experiencing science withdrawal: don’t worry, I’ll put something here too).

THE LOTUS EFFECT

A few weeks ago my dear friend Ellis came to visit me in the nursery and her visit resulted in a beautiful video that I recommend you watch. I wanted to show her the Lotus lake because it is one of my favorite corners of the nursery and I showed her the aforementioned ‘mercury effect’ on the Nelumbo leaves. Incidentally: the correct name given to this phenomenon is precisely ‘Lotus effect‘, from the name of one of the plants that presents this property in a particularly marked way.

We initially hypothesized that this ‘hydrophobic’ property of the leaves had been developed by the plant in order to limit the rotting of the leaves in contact with water, but we did not seem convinced of this (also because the lotus leaf is typically carried high above the surface of the water, unlike those of the water lily which rest on the surface). I did some research in the scientific literature and discovered something exciting.

PLANTS THAT LOVE HYGIENE

The Lotus is a plant venerated in the East, rich in symbolism and considered synonymous with purity. In fact, despite living in environments that are not exactly ‘clean’ such as ponds, rivers and muddy lakes, you will always find it with shiny leaves. The question has not left botanists and scholars in general indifferent who have established how the Lotus (like other plants with the same characteristic) has a natural self-cleaning mechanism: the surface of the leaf does not retain water, which slides over it (often crumbling into a multitude of small spheres) running away. The water is never retained by the Lotus leaves which are consequently always dry

HYDROPHOBIA AND WETABILITY

Hydrophobia is a characteristic of materials that have low wettability. Wettability is defined as the ability of a liquid to maintain contact with a surface: the greater the contact surface between the liquid and the material that makes up the surface, the greater the wettability.

• perhaps adhesion + wettability
• cohesive forces – wettability

When the contact angle exceeds 150° it is called ultrahydrophobia (or superhydrophobia)

fromWiki

In many eastern countries, the lotus is considered a symbol of purity: in fact, lotus flowers, despite having muddy rivers and lakes as their habitat, are never dirty. The botanists who have studied this mechanism have found that in fact these plants have a natural cleaning mechanism: water is not retained on the lotus leaves (in fact these leaves are always dry), but slides away in many droplets which are formed due to the high surface tension present on the leaf, carrying with it the mud and the small insects found in it. This is possible because lotus leaves are coated with nanometer-sized crystals of a hydrophobic wax. On this scale, rough surfaces are more hydrophobic than smooth ones, because the real contact area between the drop of water and the supporting surface is about 3% of the apparent one, so the weight of the drop makes it slide away. The roughness of the leaf is also very useful for the self-cleaning effect, because the drops roll, while on a smooth surface the drops would slide, making the removal of dirt less effective.

except the roots, all parts of the plant are generally covered by a sort of ‘skin’ called the cuticle, the interface of the plant with the outside.

W. Barthlott, C. Neinhuis. Purity of the sacred lotus or escape from contamination of biological surfaces. Botanical Institute and Botanical Garden of the University of Bonn