Strategic insights into realizing superhydrophobic surfaces on cellulosic substrates through conventional and sustainable technologies

Abstract

Superhydrophobic surfaces, known for their exceptional water-repellent properties, offer significant potential for various applications. The key characteristic of superhydrophobicity is the micro- and nano-scale roughness that traps a substantial amount of air beneath a liquid droplet. The fragility of their delicate textures greatly hinders the practical applications of these surfaces. Achieving robust superhydrophobicity is crucial for meeting stringent industrial standards and requirements for commercial products. Significant progress is being made in understanding the mechanisms of wetting transitions and in developing design strategies and fabrication techniques for superhydrophobic surfaces. This review introduces the concept of superhydrophobicity, covering surface classification, contact angles, surface wetting, and the fundamentals of wetting theory, including the Young, Wenzel, Cassie-Baxter, and reentrant models. It explores the mechanisms for generating superhydrophobic surfaces through physical, chemical, and hybrid methods. Various techniques for achieving superhydrophobicity such as polymer grafting, dip coating, chemical bath deposition, chemical vapor deposition, wet chemical etching, real-time growth processing, plasma etching, layer-by-layer assembly, spray coating, and both chemical and physical etching—are discussed. Among these, dip coating and layer-by-layer assembly are highlighted for their efficiency and durability, even on a large scale. The review also covers methods for achieving superhydrophobic surfaces using different nanomoieties, fluorocarbons, silicones, and natural waxes. Finally, it addresses the applications of superhydrophobicity, the challenges in achieving it, and potential solutions. In particular, it proposes and extensively discusses a strategic approach to comparing conventional and green strategies for the first time. Therefore, integrating these advanced nanomaterials with flexible design and fabrication techniques provides a clear path for new researchers in the field.