Soot normally means dirt, but it could be the key to creating transparent materials that can repel both oil and water – perfect for self-cleaning lenses, windows or touchscreens.
A candle flame will coat a glass slide with black soot. The soot looks uniform, but a scanning electron microscope reveals a fractal-like network of carbon particles that makes it superhydrophobic, or incredibly water-repellent.
The coating doesn't last long, however: water drops rolling off the surface drag loose particles with them, destroying the superhydrophobic properties.
Now, researchers at the Max Planck Institute for Polymer Research in Mainz, Germany, and the Technical University Darmstadt, also in Germany, have realised that coating the soot particles in a thin layer of silica replicates their water-repelling structure. They then heat the surface to 600 °C for 2 hours to destroy the soot particles, leaving behind the see-through silica.
The resulting coating is both water and oil-repellent, even when damaged or exposed to high temperatures, and could be applied to a variety of heat-resistant surfaces such as aluminium, copper or stainless steel.
Researchers at Harvard University have also recently created a similar self-cleaning surface, inspired by carnivorous plants rather than candle soot.
Journal reference: Science, DOI: 10.1126/science.1207115
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