Anisotropic Drop Morphologies on Corrugated Surfaces

Abstract

The spreading of liquid drops on surfaces corrugated with micron-scale parallel grooves is studied both experimentally and numerically. Because of the surface patterning, the typical final drop shape is no longer spherical. The elongation direction can be either parallel or perpendicular to the direction of the grooves, depending on the initial drop conditions. We interpret this result as a consequence of both the anisotropy of the contact line movement over the surface and the difference in the motion of the advancing and receding contact lines. Parallel to the grooves, we find little hysteresis due to the surface patterning and that the average contact angle approximately conforms to Wenzel's law as long as the drop radius is much larger than the typical length scale of the grooves.

Anisotropic surface properties of micro/nanostructured a-C:H:F thin films with self-assembly applications

“…The local contact angle along the actual solid-liquid-air contact line is equal to the intrinsic contact angle. 19,20 It also increased substantially after the deposition process. That means that fluorinated carbon films are quite hydrophobic.…”

Directional wetting on patterned surfaces

“…The mechanism for advancing of the droplet is similar to the one described earlier for grooved surfaces [29,41] and is schematically presented in Fig. 3.6.…”

“…Summarizing, in case of the Wenzel state, prior to filling of the next groove the advancing CA condition at the edge of the ridge has to be met. Once the dynamic CA at the edge reaches a value lower than the advancing CA, the droplet remains pinned and spreading in the direction perpendicular to grooves stops [29,41]. In the Cassie-Baxter state, the advancing edge of the droplet 'falls' until it reaches the top of the neighboring ridge at the location corresponding to the area with the largest curvature of the droplet.…”

“…Nevertheless, anisotropic surfaces can provide an important insight into the effect of dynamics on the final shape of the sessile droplet, therewith enabling one to gain a better understanding of the role of surface geometry. One of the first and nowadays still frequently studied anisotropic structured periodic surfaces consists of parallel grooves [28][29][30][31][32].…”

“…The studies are typically carried out either for complete wetting, i.e. systems in the Wenzel state [29,120,121] or for liquid droplets suspended on top of the grooves, i.e. the Cassie-Baxter state [122].…”