They are one of the most hydrophobic (or water repelling) surfaces known and American and European researchers have mimicked their surface structure to create a nanomaterial that might be a simpler and more environmentally-friendly way of protecting surfaces from water.
Lead researcher Andrew Barron from Rice University in Houston, Texas, said the hydrophobic characteristics of the lotus leaf are due to papillae within the epidermis and epicuticular waxes on top.
“In our material, there is a microstructure created by the agglomeration of alumina nanoparticles mimicking the papillae and the hyperbranched organic moieties simulating the effect of the epicuticular waxes,” he said.
“Nature knows how to make these materials and stay environmentally friendly. Our job has been to figure out how and why, and to emulate that.”
The material they came up with is a branched hydrocarbon low-surface energy material (LSEM) manufactured by coating synthesised aluminum oxide nanoparticles with modified carboxylic acids that feature highly branched hydrocarbon chains. The chains make the surface rough, trapping a layer of air and minimising contact between the surface and water droplets, which allows them to slide off.
The team observed the angle between the surface of the water and the material to be 155 degrees, more than the 150 degree necessary to qualify as superhydrophobic and essentially equivalent to the best fluorocarbon-based superhydrophobic coatings.
Barron said potential applications include friction-reducing coatings for marine applications where there is international agreement in trying to keep water safe from such potentially dangerous additives as fluorocarbons.
“The textured surfaces of other superhydrophobic coatings are often damaged and thus reduce the hydrophobic nature,” he said.
“Our material has a more random hierarchical structure that can sustain damage and maintain its effects.”
He said the team is working to improve the material’s adhesion to various substrates, as well as looking at large-scale application to surfaces.
Illustration: Shirin Alexander, University of Swansea.