Switchable Elastocapillarity of High-Aspect-Ratio Topographically Structured Surfaces

Elastocapillarity, the interplay between elasticity and capillarity, is of great importance for various fields, including surface control, microfluidics, biotechnology, robotics, medicine, microtechnology, and more. This study investigates the elastocapillarity of surfaces with partially cantilever-like vertical lamellae with switchable mechanical properties, where one side is fixed to a substrate, and the other side can move freely. In this work, we want to understand the interaction between lamellae and water droplets during their sliding. Specifically, we want to understand how the flexibility of the lamellae affects the sliding of water droplets and how the deformation of the lamellae during sliding depends on their flexibility and interaction with the water droplet. We control flexibility by the mechanical properties of the lamellae, which depend on the mechanical properties of the polymer forming them, and how lamellae are attached/adhered to the substrate. Depending on fabrication, lamellae can have three kinds of contacts with the substrate: strong adhesion (fusion of the bottom of the lamellae to the substrate), intermediate adhesion (high-friction lamellae-substrate contact), and weak adhesion (low-friction lamellae-substrate contact─lamellae with an air gap underneath). Moreover, it was found that lamellae neglect the effect of the material of the substrate on water droplet sliding, and freely moving lamellae promote the fastest sliding of droplets due to capillary forces. The water droplets are also able to cause the deformation of lamellae during sliding. We found that rigid lamellae rigidly and strongly/intermediately attached to a substrate are not deformed by droplets; the upper parts of soft lamellae strongly and intermediately attached to a substrate were deformed by the water droplet, while their lower parts remained immobile, and the sliding droplet can deform both rigid and soft lamellae weakly connected to a substrate.