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    Patterned Polymer Coatings Increase the Efficiency of Dew Harvesting

    Year: 2017

    Journal: ACS Appl. Mater. Interfaces, Volume 9, APR 19, page 13676–13684

    Authors: Al-Khayat, Omar; Hong, Jun Ki; Beck, David M.; Minett, Andrew I.; Neto, Chiara

    Organizations: Australian Research Council

    Keywords: thin films; water harvesting condenser; biomimetic; polymers; dew

    Micropatterned polymer surfaces, possessing both topographical and chemical characteristics, were prepared on three-dimensional copper tubes and used to capture atmospheric water. The micropatterns mimic the structure on the back of a desert beetle that condenses water from the air in a very dry environment. The patterned coatings were prepared by the dewetting of thin films of poly-4-vinylpyridine (P4VP) on top of polystyrene films (PS) films, upon solvent annealing, and consist of raised hydrophilic bumps on a hydrophobic background. The size and density distribution of the hydrophilic bumps could be tuned widely by adjusting the initial thickness of the P4VP films: the diameter of the produced bumps and their height could be varied by almost 2 orders of magnitude (1-80 mu m and 40-9000 nm, respectively), and their distribution density could be varied by 5 orders of magnitude. Under low subcooling conditions (3 degrees C), the highest rate of water condensation was measured on the largest (80 mu m diameter) hydrophilic bumps and was found to be 57% higher than that on flat hydrophobic films. These subcooling conditions are achieved spontaneously in dew formation, by passive radiative cooling of a surface exposed to the night sky. In effect, the pattern would result in a larger number of dewy nights than a flat hydrophobic surface and therefore increases water capture efficiency. Our approach is suited to fabrication on a large scale, to enable the use of the patterned coatings for water collection with no external input of energy.
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