Anisotropic drop morphologies on corrugated surfaces

TL;DR

This study investigates how liquid drops spread and form anisotropic shapes on micron-scale corrugated surfaces, revealing the influence of surface patterning on contact line dynamics and final drop morphology.

Contribution

It provides experimental and numerical insights into anisotropic drop morphologies on patterned surfaces, highlighting the roles of contact line motion and hysteresis.

Findings

Drop shape elongation depends on initial conditions and orientation.

Contact line pinning causes large hysteresis perpendicular to grooves.

Wenzel's law approximates contact angles when drops are large.

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. Perpendicular to the grooves, the contact line can be pinned at the edges of the ridges leading to large contact angle hysteresis.