Cellulose Nanocrystal Coated Paraffin Wax Coating for Fog and Dew Water Harvesting

Abstract

Fresh water scarcity is an urgent global issue. A sustainable and renewable method is harvesting atmospheric water, among which fog and dew water can be passively collected onto a surface. The efficiency of such collecting systems depends critically on the wetting and dynamic behavior of water droplets on the surface. Common approaches to modify surface topography and hydrophobicity often relies on lithographic, plasma, or fluoropolymer-based methods that are costly, complex, and environmentally unsustainable. In contrast, this work proposes a novel, simple, and bottom-up approach for producing surface with functional coatings through cellulose nanocrystal (CNC)–stabilized Pickering emulsions. The first part of the study focuses on understanding the stabilization and formulation behavior of CNC-based oil-in-water emulsions under varying CNC concentration, ionic strength, and oil-to-water ratios. The resulting interfacial coverage and droplet packing efficiency govern the size and assembly of the wax microparticles, allowing fine control of surface roughness and wettability. Coatings derived from these particles exhibit a wide range of wetting states—from hydrophilic to superhydrophobic—depending on CNC surface coverage and aggregation state. In the second part, these coatings are evaluated for fog and dew water collection, emphasizing the differences between liquid water deposition and humid air condensation on surface. The results show that overall water collection performance is governed by two coupled processes: the rate at which moisture is captured on the surface and the efficiency with which the accumulated water is removed. Previous studies have shown that while superhydrophobic surfaces exhibit superior droplet removal efficiency, their performance can degrade under continuous usage due to partial loss of superhydrophobicity and water film formation. On the other hand, surfaces with balanced nucleation density and drainage efficiency are more desirable, especially for condensation. This research establishes a biobased, PFAS-free, and scalable fabrication route for tailoring surface wettability using CNC-stabilized emulsions. Beyond atmospheric water harvesting, the insights gained here into interfacial assembly and condensation dynamics under realistic humid-air conditions contribute broadly to the design of sustainable coatings for humidity control and anti-fogging/anti-icing applications.