Droplets over lotus leaf
doi:10.1038/nindia.2009.258 Published online 28 July 2009
Why do droplets of water roll over lotus leaves without wetting them? Researchers have found the answer in the invisible micro-bumps with nano-hairs that dot the lotus leaf surface1. The insight might help mimic lotus leaf surface to make water-repellent automobile glasses, self-cleaning clothes and paints or low-drag marine vessels.
Though studies have tried to unveil the secrets of non-wetting of lotus leaf surface, none has shed light on how the leaf's surface microstructures cause non-wetting.
The researchers captured images of fresh lotus leaves using scanning electron microscope and ran computer-based simulation studies on them. They found that the surface of lotus leaf has small bumps. These micro-bumps (or protrusions) are covered with fine nano-hairs (50-130 nm in diameter and 400-1000 nm long). These nano-hairs increase surface roughness and cause superhydrophobicity (water-hating quality) of the lotus leaf surface.
The rolling of a droplet is a function of the flexing and straightening of nano-hairs, which allow the water droplets to bounce on the lotus leaf surface. Micro-bumps provide first level of 'micro-roughness' and increase non-wetting of a hydrophobic surface.
"For the first time, this study shows the role of mechanical properties of nano-hairs in imparting non-wetting of lotus leaf surface," says lead researcher Kantesh Balani.
The authors of this work are from: Materials and Metallurgical Engineering, Indian Institute of Technology Kanpur, India and Mechanical and Materials Engineering, Florida International University, Miami, USA.
- Balani, K. et al. The hydrophobicity of a lotus leaf: a nanomechanical and computational approach. Nanotechnology 20, 305707 (2009) | Article |