The kapok petal: superhydrophobic surface induced by microscale trichomes.

For the first time it is reported that the kapok petal shows a superhydrophobic characteristic with a static water contact angle higher than 150°. Intriguingly, there exist single-scale micro-trichomes and no more nanocrystals on a kapok petal in contrast to most natural superhydrophobic surfaces with hierarchical morphologies, such as the lotus leaf and rose petal. Experimental results show that the kapok petal has an excellent self-cleaning ability either in air or oil. Further scanning electron microscopy characterization demonstrates that the superhydrophobic state is induced by densely distributed microscale trichomes with an average diameter of 10.2 m and a high aspect ratio of 17.5. A mechanical model is built to illustrate that the trichomes reentrant curvature should be a key factor to inducing the superhydrophobic state of the kapok petal. To support the proposed mechanism, gold-wire trichomes with a reentrant curvature are fabricated and the results show that a superhydrophobic state can be induced by the microstructures with a reentrant curvature surface. Taking the scalability and cost-efficiency of microstructure fabrication into account, we believe the biomimetic structures inspired by the superhydrophobic kapok petal can find numerous applications that require a superhydrophobic state.