Fabrication of Superhydrophobic Water-Pinning Surfaces through Integration of Silica Colloids into Cellulose Nanocrystals

Abstract

The water-pinning effect is a phenomenon in which water droplets adhere to a surface and do not roll off, even when the surface is tilted or turned upside down. This effect holds great potential for applications in various areas, such as dew collection in arid regions, anti-drip function for a greenhouse, and liquid transport and control. However, creating surfaces that exhibit this effect poses challenges, necessitating materials with both hydrophobicity and high adhesive force along with a scalable, cost-effective method to produce the essential geometries that have not yet been established. To address these challenges, we propose a straightforward coating approach involving silica nanoparticles (SiO2) and cellulose nanocrystals (CNCs) to fabricate artificial water-pinning surfaces. We assessed the water-pinning ability of the coated surface through measurements of the contact angle, contact radius, and hysteresis. Remarkably, the coated surface exhibited a contact angle of approximately 153.87° and a contact radius of around 0.89 mm when a 10 μL water droplet was applied, demonstrating its resistance to rolling off, even at a tilting angle of 90°. The droplet only began to fall when its volume reached approximately 33 μL, requiring a substantial water pinning force of 323.4 μN. We also investigated the physicochemical characteristics of the SiO2@CNC coating surface, including morphology, chemical composition, and chemical structure, to unravel the underlying mechanism behind its water-pinning ability. Our proposed fabrication method offers a promising avenue for the development of functional biopolymer-based surfaces capable of precisely manipulating water droplets. © 2023 American Chemical Society.