Effect of pattern topology on the self-cleaning properties of textured surfaces

Abstract

The water contact angle and self-cleaning property of microfabricated surface textures possessing different topologies are compared. In one kind of surface textures, the protruded regions form a connected square network. In the other kind of surface textures, the protruded regions form a regular array of square posts. We find that the water apparent contact angle of the connected textures agrees with the Cassie equation [Discuss. Faraday Soc. 3, 11 (1948)], but that of the disconnected textures is much larger. Nevertheless, the disconnected textures exhibit inferior self-cleaning property, contrary to conventional conception. We discuss the possible reasons for these observations.

Advanced understanding of stickiness on superhydrophobic surfaces

“…We believe that different surface geometries will definitely induce totally different pinning effects, even though these surfaces have the same solid fraction. Our point is well in line with the experimental results of Zhang 17 . All these results and discussion indicate that the surface stickiness should be determined by overall considering the solid fraction and also the surface geometric factor.…”

“…We fabricated several posts arrays with different solid fractions. The TA increases with the solid fraction, which proves that the stickiness/pinning force increases with solid fraction 17 18 19 . Nevertheless, the CAH shows a decreasing tendency while the solid fraction increases.…”

“…However, the result presented herein indicates that the CAH values increase while the solid fraction decreases, which seems unreasonable as it is contrary to the “common sense”. But interestingly, this “common sense” is not challenged for the first time, Zhang et al even found that the CAH is not dependent on the solid fraction, because they observed different CAH values from two different patterns with the same solid fraction 17 . Both these two results imply that CAH could not be simply used to evaluate the surface stickiness.…”

Anisotropic Wetting on Checkerboard-Patterned Surfaces

“…and BD ! directions on the checkerboard surface was also found on the DSS surface, 37 which is caused by pinning to metastable states because of larger contact angle hysteresis for the discontinuous contact line comparing to that for the continuous contact line. 48 surface is similar to that found on the continuous CSS surfaces.…”

Directing the transportation of a water droplet on a patterned superhydrophobic surface

“…1-5 On a hydrophilic surface, the water contact angle ͑CA͒ decreases with the increasing roughness. [19][20][21][22] The rice leaves and butterfly wings are the typical samples with the anisotropic SH property. When this angle exceeds 150°, a water droplet can stay on the surface like a transparent ball.…”