Advances in organic adsorption on hydrophilic hierarchical structures for bionic superhydrophobicity: from fundamentals to applications

Abstract

Generally, fabricating bionic superhydrophobic surfaces on hydrophilic smooth materials involves preparing microstructures/nanostructures and chemical modification. Recent breakthroughs regarding organic adsorption on hierarchically structured surfaces for creating superhydrophobicity have been very promising and interesting in the wetting field. In this review, we firstly introduce classic Wenzel and Cassie theories. In fact, superhydrophobicity in the Cassie state was theoretically obtained in the hydrophilic smooth surface. We also provide wetting theories of hierarchical structures and summarize the development of Wenzel and Cassie theories based on various microstructures. Thereafter, we illustrate the mechanism of wettability transition due to organic adsorption on the hierarchically structured surface and summarize the conditions of organic adsorption on hierarchically structured hydrophilic surfaces for superhydrophobicity. Moreover, we highlight the effects of organic adsorption on hierarchically structured hydrophilic surfaces, which includes defects, storage time in air, heating/vacuum treatment, and storage environment. The self-repairing property due to organic readsorption and the reversible superhydrophobicity–superhydrophilicity transition are also introduced. Next, we summarize various hierarchical structures for superhydrophobicity due to organic adsorbates and their fabrication methods. Moreover, we compare the applications and stability of hierarchically structured superhydrophobic surfaces functionalized with organic adsorption and the usual modified superhydrophobic surface. Finally, we propose the challenges and opportunities of this field in future.