The famous quote "Emerging from the mud yet remaining unstained, cleansing in the clear stream yet not seduced," has become the perfect expression of praise for lotus flowers, echoing through the ages.
The lotus leaf, the exclusive cleaner for lotus flowers, plays a crucial role in their cleanliness.
This is because the surface of the lotus leaf exhibits superhydrophobic properties. When rain falls on the lotus leaf, instead of spreading out, it forms tiny droplets that quickly roll off the surface, carrying away any dirt and mud, ensuring the lotus remains immaculate throughout its life.
You might wonder why lotus leaves possess this miraculous ability. Let's use a Scanning Electron Microscope (SEM) to delve into the microcosm of lotus leaves and uncover their secrets.
Structures with exceptional drainage capability:
When magnified 500 times using a scanning electron microscope, the surface of the lush lotus leaf undergoes a remarkable transformation. Instead of its smooth appearance, it reveals a myriad of nearly spherical bumps, known as papillae. With a reference scale, we can estimate that each papilla measures around 10 micrometers (μm) in size.
To put this into perspective, the diameter of human hair ranges from approximately 40 to 50 μm, meaning each papilla is three to four times finer than a strand of hair. Even with keen eyesight, one wouldn't be able to discern these papillae on the surface of a lotus leaf without the aid of a microscope.
Thankfully, our eyes aren't microscopes, allowing us to appreciate the "endless emerald lotus leaves reaching toward the sky" while boating on West Lake, rather than a surface covered in large bumps.
Upon further magnification, reaching a magnification of ten thousand times, we observe that each papilla is adorned with rod-like structures arranged in various orientations. Each rod has a length of approximately 1 μm and a diameter of around 0.1 μm. At this point, one might proudly claim to have scrutinized a lotus leaf thoroughly.
The exceptional superhydrophobicity of lotus leaves is primarily attributed to this microscale structure on their surface.
If we envision each papilla as a mountain peak, the spaces between papillae form valleys. However, these peaks and valleys are only around 10 μm in size.
The valleys are filled with air, creating numerous interconnected air pockets that, along with the peaks, support water droplets, preventing them from spreading and instead forming tiny beads on the lotus leaf's surface. Consequently, any dirt or dust on the lotus leaf's surface will adhere to these water droplets and be carried away as they roll off the leaf. In nature, a simple rain shower is sufficient to cleanse these impurities, or dew condensing into water droplets.
In reality, many other organisms possess similar superpowers, such as butterflies.
Understanding lotus leaves has given us the insight to explore butterflies with ease.
When magnified 200 times using a scanning electron microscope, we observe that their wings are composed of regularly arranged scales, each with a width of around 50 μm.
Further magnification to 1000 times reveals that each scale is adorned with parallel ridge-like structures, termed ridges. At a magnification of 10000 times, we can discern irregularly distributed honeycomb-like pits between the parallel ridges, with the distance between ridges measuring approximately 1.8 μm and the size of the honeycomb-like pits approximately 0.9 μm.
Similar to the principle behind lotus leaves, these pits contain numerous air pockets that, along with the ridges, support water droplets, preventing them from wetting the butterfly's wings. This enables butterflies to gracefully dance in the rain.
Nature has endowed these organisms with extraordinary abilities, and humans can harness biomimicry to create "miraculous tools" that serve us in our daily lives.
