Hydrophobic Smart Material for Water Transport and Collection

Abstract

Stenocara Gracilipes (the Namib Desert beetle) is a desert dwelling beetle which has adapted to make use of fog as an alternative water source in an environment which receives little rain water. Using a combination of hydrophobic and hydrophilic areas on its carapace, the beetle is able to collect condensation on its back which is then channelled towards the mouth. In this paper we attempt to mimic this effect by selectively altering the hydrophobicity of a number of water repellent fabrics. Fabrics were treated using Granger’s Extreme Wash-in to make them hydrophobic and then laser etched to alter the hydrophobicity. We show a clear relationship between the hydrophobicity of the fabric and the laser energy applied to the surface. Laser etching was used to create a herring bone pattern of channels on the surface of the fabrics. Water sprayed onto the surface preferentially followed the channels into a collection vessel, giving a collection efficiency of 81%. To replicate real world conditions dry ice was used to create fog which was then blown, using an electric fan, onto the fabric at a speed of approximately 2.5 km/h. The water vapour condensed on the surface and then followed the channels into a collection vessel. It was found that the patterned fabrics achieved a collection rate of 0.31 l h⁻¹ m⁻².