Waterproof and Water Repellent Textiles and Clothing by John T Williams

Author:John T Williams
Language: eng
Format: epub, pdf
ISBN: 9780081011348
Publisher: Elsevier Ltd.
Published: 2017-11-19T16:00:00+00:00

Fig. 11.4 Schematic diagrams of the expected liquid–vapor interface on two geometries with different equilibrium contact angles. The capillary force can resist the wetting of the grooves if ψ < θ (Cao et al., 2007; Tuteja et al., 2007).

When ψ is larger than the equilibrium contact angle θ, the meniscus (water–air interface) in the groove is concave (seen from the water side). In this case, the net force Fnet generated by the meniscus is downward so that water will enter the grooves and fully wet the surface. For ψ < θ, on the other hand, the meniscus is convex and Fnet acts upward, thereby obstructing the penetration of water into the groove. Cao et al. (2007) demonstrated that re-entrant structures are desirable to construct more stable superhydrophobic surfaces by showing that an originally hydrophilic silicon surface increased the water contact angles to approximately 139–162 degrees when re-entrant structures were fabricated on the surface (Cao et al., 2007). Other studies have also demonstrated that properly designed re-entrant structures, such as dual layer re-entrant structures, can provide superoleophobic surfaces, repelling extremely low surface energy liquids (Tuteja et al., 2007, 2008). In summary, low surface energy and surface roughness (including re-entrant structure) are the key design parameters to attain superhydrophobic surfaces.

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