Effects of structural and chemical anisotropy of nanostructures on droplet spreading on a two dimensional wicking surface

摘要

When a liquid droplet is deposited onto an array of nanostructures, a situation may arise in which the liquid wicks into the space between the nanostructures surrounding the droplet, forming a thin film that advances ahead of the droplet edge. This causes the droplet to effectively spread on a flat, composite surface that is made up of the top of the nanostructures and the wicking film. In this study, we examined the effects of structural and chemical anisotropy of the nanostructures on the dynamics of droplet spreading on such two-dimensional (2D) wicking surfaces. Our results show that there are two distinct regimes to the process, with the first regime characterized by strong anisotropy in the droplet spreading, following the asymmetric structural or chemical cues provided by the nanostructures. The trend reverses in the second regime, however, as the droplet adopts an increasingly isotropic shape with which it eventually comes to rest. Based on these findings, we formulated a quantitative model that accurately describes the behaviour of droplet spreading on 2D wicking surfaces over a wide range of conditions.