Through-drop imaging of moving contact lines and contact areas on opaque water-repellent surfaces. Issue 13 (7th March 2023)

• Record Type: Journal Article
• Authors: Vieira, Arthur; Cui, Wenjuan; Jokinen, Ville; Ras, Robin H. A.; Zhou, Quan
• Is Part Of: Soft matter. Volume 19:Issue 13(2023)
• Page Start: 2350
• Page End: 2359
• Publication Date: 2023-03-07
• Subjects: Soft condensed matter -- Periodicals; 530.413
• DOI: 10.1039/d2sm01622b
• Languages: English
• ISSNs: 1744-683X

Abstract

Abstract : The progressing wetting interface on opaque hydrophobic surfaces is observed and quantified using a transparent droplet probe and contact angles near 180° are measured with an uncertainty as low as 0.2°. Abstract : A myriad of natural surfaces such as plant leaves and insect wings can repel water and remain unwetted inspiring scientists and engineers to develop water-repellent surfaces for various applications. Those natural and artificial water-repellent surfaces are typically opaque, containing micro- and nano-roughness, and their wetting properties are determined by the details at the actual liquid–solid interface. However, a generally applicable way to directly observe moving contact lines on opaque water-repellent surfaces is missing. Here, we show that the advancing and receding contact lines and corresponding contact area on micro- and nano-rough water-repellent surfaces can be readily and reproducibly quantified using a transparent droplet probe. Combined with a conventional optical microscope, we quantify the progression of the apparent contact area and apparent contact line irregularity in different types of superhydrophobic silicon nanograss surfaces. Contact angles near 180° can be determined with an uncertainty as low as 0.2°, that a conventional contact angle goniometer cannot distinguish. We also identify the pinning/depinning sequences of a pillared model surface with excellent repeatability and quantify the progression of the apparent contact interface and contact angle of natural plant leaves with irregular surface topography.