Superhydrophobic surfaces display water contact angles greater than 150° in conjunction with low contact angle hysteresis. Microscopic pockets of air trapped beneath the water droplets placed on these surfaces lead to a composite solid-liquid-air interface in thermodynamic equilibrium. Previous experimental and theoretical studies suggest that it may not be possible to form similar fully-equilibrated, composite interfaces with drops of liquids, such as alkanes or alcohols, that possess significantly lower surface tension than water (γlv = 72.1 mN/m). In this work we develop surfaces possessing re-entrant texture that can support strongly metastable composite solid-liquid-air interfaces, even with very low surface tension liquids such as pentane (γlv = 15.7 mN/m). Furthermore, we propose four design parameters that predict the measured contact angles for a liquid droplet on a textured surface, as well as the robustness of the composite interface, based on the properties of the solid surface and the contacting liquid. These design parameters allow us to produce two different families of re-entrant surfaces— randomly-deposited electrospun fiber mats and precisely fabricated microhoodoo surfaces—that can each support a robust composite interface with essentially any liquid. These omniphobic surfaces display contact angles greater than 150° and low contact angle hysteresis with both polar and nonpolar liquids possessing a wide range of surface tensions.

Robust omniphobic surfaces

In this review we focus on recent developments in applications of bio-inspired special wettable surfaces. We highlight surface materials that in recent years have shown to be the most promising in their respective fields for use in future applications. The selected topics are divided into three groups, applications of superhydrophobic surfaces, surfaces of patterned wettability and integrated multifunctional surfaces and devices. We will present how the bio-inspired wettability has been integrated into traditional materials or devices to improve their performances and to extend their practical applications by developing new functionalities.

Applications of Bio‐Inspired Special Wettable Surfaces

Superhydrophobic surfaces: From natural to biomimetic to functional

Superhydrophobic and superoleophilic polyester materials are successfully prepared by one-step growth of silicone nanofilaments onto the textile via chemical vapor deposition of trichloromethylsilane. The successful growth of silicone nanofilaments is confirmed with scanning electron microscopy, energy-dispersive X-ray analysis, and investigation of the wetting behavior of water on the textile. Even microfibers deeply imbedded inside a woven material could be coated very well with the nanofilaments. The coated textile is water repellant and could only be wetted by liquids of low surface tension. The applications of the coated textile as a membrane for oil/water separation and as a bag for selective oil absorption from water are studied in detail. Owing to the superwetting properties and flexibility of the coated textile, excellent reusability, oil/water separation efficiency, and selective oil absorption capacity are observed, which make it very promising material, e.g., for practical oil absorption.

Polyester Materials with Superwetting Silicone Nanofilaments for Oil/Water Separation and Selective Oil Absorption

This review article summarizes the key areas of self-cleaning coatings, primarily focusing on various materials that are widely used in recent research and also in commercial applications. The scope of this article orbits around hydrophobic and hydrophilic coatings, their working mechanism, fabrication techniques that enable the development of such coatings, various functions like Anti-icing, Electro-wetting, Surface switchability and the areas where selfcleaning technology can be implemented. Moreover, different characterization techniques and material testing feasibilities are also analyzed and discussed. Though several companies have commercialized a few products based on self-cleaning coating technology, much potential still remains in this field.

A review on self-cleaning coatings

We report a biomimetic procedure to prepare superhydrophobic cotton textiles. By in situ introducing silica particles to cotton fibers to generate a dual-size surface roughness, followed by hydrophobization with polydimethylsiloxane (PDMS), normally hydrophilic cotton has been easily turned superhydrophobic, which exhibits a static water contact angle of 155° for a 10 μL droplet. The roll-off angle of water droplets depends on the droplet volume, ranging from 7° for a droplet of 50 μL to 20° for a 7 μL droplet. When a perfluoroalkyl chain is introduced to the silica particle surface, the superhydrophobic textile also becomes highly oleophobic, as demonstrated by a static contact angle of 140° and a roll-off angle of 24° for a 15 μL sunflower oil droplet.

D. Wu

Papers

Biomimetic Superhydrophobic and Highly Oleophobic Cotton Textiles