Recent Progress in Preparation of Superhydrophobic Surfaces: A Review
Journal of Surface Engineered Materials and Advanced Technology
In nature, water-repellency (superhydrophobicity) is found, besides in plants, in insects and bird feathers. The booming field of biomimetics allows one to mimic nature to develop nanomaterials, nanodevices, and processes which offer desirable properties. Biomimetics means mimicking biology or nature. Inspired from nature, which reveals excellent superhydrophobicity, researchers have recently developed and implemented biomimetic superhydrophobic surfaces in a variety of smart and simple ways.
... and simple ways. Superhydrophobicity is an effect where surface roughness and chemical composition combine to generate unusual water repellent surface, causing water to bounce and roll off the surface. This review article provides the overview of the recent progress (within the last four years) in the synthesis, characterization, theoretical modelling, and applications of superhydrophobic surfaces, with focus on the different techniques used and how they have developed over the years. At last, the difficulties related to implementation of superhydrophobic surfaces in day to day life are discussed. This review can find interesting for students, scientists and industrial companies working especially on superhydrophobic surfaces. Recent Progress in Preparation of Superhydrophobic Surfaces: A Review 77 so on  . Besides water repellency, other properties such as transparency, colour change, anisotropy, reversebility, flexibility, electrowetting, and breathability have also been incorporated into biomimetic superhydrophobic surfaces     . Although there are many exciting challenges facing this field, there are a number of opportunities in design, synthesis, and engineering of superhydrophobic surfaces and nature serves as a merchant of endless inspirations. Since last decade, many significant review articles have been published describing the different synthesis strategies to fabricate artificial superhydrophobic surfaces       . This review will focus on the most recent developments (the last four years) in the superhydrophobic surface research. The major part of this review is organized in four sections. The first section gives a brief introduction about the superhydrophobic surfaces. In the second section, we review the theoretical basis relevant to the wetting of a solid surface by a liquid. The third section provides a comprehensive overview on the approaches for the preparation of superhydrophobic surfaces, with particular focus on the fabrication methodology, materials, micro-/ nanostructures and potential industrial applications. Finally in the fourth section, we will provide our personal prospects and research directions about the construction of superhydrophobic surfaces. Due to the space limitation, we cannot review all the significant and interesting work in the active superhydrophobic field. (4) Figure 1. The wetting behaviour of a liquid droplet on rough solid surface: (a) Young's mode; (b) Wenzel's mode; (c) Cassie's mode. Recent Progress in Preparation of Superhydrophobic Surfaces: A Review 78 Figure 2. SEM images of ZnO nanostructures grown on the Zn foil with different reaction times in a mixed solution of methanol and water (50 vol% methanol, 1 mass% HF): (a) Sample A, 30 s; (b) Sample B, 1 min; (c) Sample C, 5 min; (d) Sample D, 10 min; (e) Sample E, 15 min; (f) Sample F, 30 min. The length of inserted scale bars is 500 nm. Images reprinted from Ref. , with permission from Elsevier, Copyright 2010. Figure 3. (a) Water contact angle and (b) contact angle hysteresis of anodic copper electrode with the application of 30 V DC voltage in an ethanolic stearic acid solution. The insets show the water drops on the copper surfaces coated for 0.5 h and 3 h. Images reprinted from Ref. , with permission from Elsevier, Copyright 2010. Recent Progress in Preparation of Superhydrophobic Surfaces: A Review 79 Figure 5. SEM images of membranes prepared from (a) 9 wt% PULL, (b) 12 wt% PULL, (c) 9 wt% PULL/PFOTES and (d) 12 wt% PULL/PFOTES using electrospinning method (applied voltage = 15 kV, TCD = 15 cm, and PFOTES concentration = 1 wt%). The water drops on the respective membranes are shown in the insets. Images reprinted from Ref. , with permission from Elsevier, Recent Progress in Preparation of Superhydrophobic Surfaces: A Review 80 Recent Progress in Preparation of Superhydrophobic Surfaces: A Review 81 Figure 14. Photographs of water drops on (a) untreated cotton fabric and (b) superhydrophobic cotton fabric assembled with (PAH/SiO 2 ) 5 multilayers. (c) Untreated (left) and superhydrophobic (right) cotton fabrics being immersed in water. Images reprinted from Ref. , with permission from Elsevier, Copyright 2010.