Morphological development and environmental degradation of superhydrophobic aspen and black locust leaf surfaces

Authors

  • George Christopher Tranquada,

    1. Department of Materials Science and Engineering, University of Toronto, Toronto, Ontario, Canada
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  • Uwe Erb

    Corresponding author
    1. Department of Materials Science and Engineering, University of Toronto, Toronto, Ontario, Canada
    • Correspondence to: Uwe Erb, Department of Materials Science and Engineering, University of Toronto, 184 College Street, Suite 140, Toronto, Ontario M5S 3E4, Canada.

      E-mail: erb@ecf.utoronto.ca

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ABSTRACT

The complete adaxial surface development and degradation due to weathering of two superhydrophobic leaf species with (black locust, Robinia pseudoacacia and bigtooth aspen, Populus grandidentata) and one without (quaking aspen, Populus tremuloides) a protective downy layer of trichomes was followed over one entire growing season using scanning electron microscopy and wetting property measurements. Scanning electron microscopy micrographs illustrate the initial development period of a dual-scale surface structure consisting of micrometre-sized papillae and nanoscale wax crystals, which was followed by a period of environmental degradation as nanoscale wax features were subjected to environmental stress. It was discovered that robust micropapillae protect nanoscale wax morphologies in-between them for quite some time allowing for a high tolerance to wear and erosion. Weather data was used to demonstrate the correlation between cumulative environmental stresses (temperature, relative humidity, precipitation and wind) and the loss of superhydrophobicity at the end of the growing season. Analysis of all binary combinations of the aforementioned environmental stress factors propose that cumulatively hot and humid weather have the most significant impact on degradation of nanoscale wax crystals and therefore result in the final loss of superhydrophobic behaviour. These findings were also tentatively linked to their importance in ecohydrology suggesting that canopy storage capacity, which has been previously correlated with leaf hydrophobicity, of superhydrophobic leaves may fluctuate considerably throughout an entire growing season. Copyright © 2013 John Wiley & Sons, Ltd.

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