Implications of ideas on super-hydrophobicity for water repellent soil

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McHale, G., Shirtcliffe, N.J., Newton, M.I. ORCID: 0000-0003-4231-1002 and Pyatt, F.B., 2007. Implications of ideas on super-hydrophobicity for water repellent soil. Hydrological Processes, 21 (17), pp. 2229-2238. ISSN 0885-6087

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Official URL: http://dx.doi.org/10.1002/hyp.6765

Abstract

Water repellence is an important factor in soil erosion due to its role in inhibiting the re-establishment of vegetation after fire and due to its enhancement of run-off. Water repellence is studied across a range of diverse disciplines, such as chemistry, materials, textiles and soil and reclamation science. In recent years many basic studies of water repellence of materials have focused on the role of the sub-mm surface topography of a material in modifying the intrinsic hydrophobicity imparted by the surface chemistry to create super-hydrophobicity. In this report, we first illustrate the types of hydrophobic effects created by a suitable coupling of small scale surface topography with surface chemistry using three examples of materials: an etched metal, a foam and a micro-fabricated pillar structure. These examples demonstrate the general applicability of the ideas and suggest that they could apply to a granular material, such as a fine sandy soil, particularly when the grains have become coated with a hydrophobic layer. This applicability is confirmed by contact angle measurements of droplets of water on hydrophobic sand. A theoretical model describing the application of these ideas to a loose-packed, but regular, array of uniform spherical grains is then presented and discussed. When the grains are in a dry initial state the effect of the surface is to increase the apparent water repellence as observed through the contact angle. However, when the spaces between the grains are initially filled with water, the effect is to provide greater wetting. To qualitatively confirm the enhancement of contact angle caused by the granular structure, model surfaces using 600 µm and 250 µm hydrophobic glass beads were created. On these surfaces, the contact angle of droplets of water was increased from 108° to 126° and 140°, respectively.

Item Type:

Journal article

Description:

The definitive version is available at www3.interscience.wiley.com
Post-print

Publication Title:

Hydrological Processes

Creators:

McHale, G., Shirtcliffe, N.J., Newton, M.I. and Pyatt, F.B.

Publisher:

John Wiley & Sons Ltd.

Date:

2007