Aug 25, 2009
Lotus leaf nanohairs support water droplets
The multi-scale microstructure of a lotus leaf is rendered non-wetting by micro-protrusions and nanohairs present on its surface. The mechanical properties of the surface become important because the water droplet has to be supported on the micro-protrusions without wetting the surface.
Existing materials with low surface energy can produce a non-wetting surface with a contact angle reaching up to 120°, but the lotus leaf portrays contact angles in excess of 165°. This super hydrophobicity (or non-wetting) is related to the ideal spread of micro-protrusions, which are covered with nanohairs and impart two levels of surface roughness.
Researchers based in India and the US are using computational fluid dynamics (SimDrop) to investigate the effect in more detail. Their work correlates the non-wetting phenomena of the lotus leaf with its mechanical properties (Young's modulus and critical flexing stress) and the areal spread of micro-protrusions on the leaf surface.
Quasistatic nanoindentation of nanohairs on the lotus-leaf surface has shown a variation of elastic modulus between 359 and 870 MPa, which in turn dictates the critical flexing strength and consequent non-wetting. A qualitative model is proposed for the way nature has chosen to render the lotus-leaf surface non-wetting.
The researchers presented their results in Nanotechnology.
About the author
Kantesh Balani is an assistant professor in the department of Materials and Metallurgical Engineering at the Indian Institute of Technology Kanpur, India. He earned his doctorate in 2007 at Florida International University, Miami, FL, US. He has more than 30 publications in peer-reviewed journals. His research interests include biomaterials, ab-initio molecular modeling, and nanomechanics and nanotribology of bio/nano composites. Arvind Agarwal is an associate professor in the Mechanical and Materials Engineering (MME) Department at Florida International University, US. He has more than 150 publications in peer-reviewed journals and conference proceedings. His expertise extends from pure science (nanomechanics and nano-tribology) to advanced engineering (near net shape processing of bulk nanostructures materials). He directs the Plasma Forming Laboratory (PFL, since 2004) and the Nanomechanics and Nanotribology Laboratory (NMNTL, since 2006). His current research interests include carbon nanotube reinforced composites for biomedical, automobile, electronic and high-temperature applications.