Super‐hydrophobic surfaces, with a water contact angle (CA) greater than 150°, have attracted much interest for both fundamental research and practical applications. Recent studies on lotus and rice leaves reveal that a super‐hydrophobic surface with both a large CA and small sliding angle (α) needs the cooperation of micro‐ and nanostructures, and the arrangement of the microstructures on this surface can influence the way a water droplet tends to move. These results from the natural world provide a guide for constructing artificial super‐hydrophobic surfaces and designing surfaces with controllable wettability. Accordingly, super‐hydrophobic surfaces of polymer nanofibers and differently patterned aligned carbon nanotube (ACNT) films have been fabricated.

Water striders (Gerris remigis) have remarkable non-wetting legs that enable them to stand effortlessly and move quickly on water, a feature believed to be due to a surface-tension effect caused by secreted wax. We show here, however, that it is the special hierarchical structure of the legs, which are covered by large numbers of oriented tiny hairs (microsetae) with fine nanogrooves, that is more important in inducing this water resistance.

A novel superhydrophilic and underwater superoleophobic polyacrylamide (PAM) hydrogel‐coated mesh is successfully fabricated in an oil/water/solid three‐phase system. Compared to traditional oleophilic materials, the as‐prepared hydrogel‐coated meshes can selectively separate water from oil/water mixtures with the advantages of high efficiency, resistance to oil fouling, and easy recyclability.

Figure 6. Typical biological materials with superwettability and corresponding multiscale structures. (a) Lotus leaves demonstrate low adhesive, superhydrophobic, and self-cleaning properties, due to randomly distributed micropapillae covered by branch-like nanostructures. (b) Rice leaf surfaces possess anisotropic superhydrophobicity arising from the arrangement of lotus-like micropapillae in one-dimensional order. (a and b) Reproduced with permission from ref 7. Copyright 2002 Wiley. (c) Butterfly wings exhibit directional adhesion, superhydrophobicity, structural color, self-cleaning, chemical sensing capability, and fluorescence emission functions due to the multiscale structures. Reproduced with permission from ref 45. Copyright 2007 American Chemical Society. (d) Water strider legs have robust and durable superhydrophobicity arising from directional arrangements of needlelike microsetae with helical nanogrooves. Reproduced with permission from ref 46. Copyright 2004 Nature Publishing Group. (e) Mosquito compound eyes demonstrate superhydrophobic, antifogging, and antireflection functions due to HCP microommatidia covered by HNCP nanonipples. Reproduced with permission from ref 47. Copyright 2007 Wiley. (f) Poplar leaves possess superhydrophobic and antireflection properties originating from dense hairs with the hollow fibrous structure. Reproduced with permission from ref 48. Copyright 2011 The Royal Society of Chemistry. (g) Gecko feet present superhydrophobic, reversible adhesive, and self-cleaning functions due to the aligned microsetae splitting into hundreds of nanospatulae. Reproduced with permission from ref 49. Copyright 2012 The Royal Society of Chemistry. (h) Red rose petals exhibit superhydrophobicity with high adhesion and structural color arising from periodic arrays of micropapillae covered by nanofolds. Reproduced with permission from ref 31. Copyright 2008 American Chemical Society. (i) Salvinia leaves demonstrate the superhydrophobic and air-retention properties due to the Salvinia Effect. Reproduced with permission from ref 50. Copyright 2010 Wiley. (j) Fish scales present drag reduction, superoleophilicity in air, and superoleophobicity in water due to oriented micropapillae covered by nanostructures. Reproduced with permission from ref 33. Copyright 2009 Wiley. (k) Clam shell shows low adhesive superoleophobicity underwater arising from the surface multiscale structures and special chemical composition. Reproduced with permission from ref 51. Copyright 2012 Wiley. (l) Peanut leaves exhibit high adhesive superhydrophobicity and fog capture properties originating from the special surface multiscale structures and chemical composition. Reproduced with permission from ref 52.

We showed directional adhesion on the superhydrophobic wings of the butterfly Morpho aega. A droplet easily rolls off the surface of the wings along the radial outward (RO) direction of the central axis of the body, but is pinned tightly against the RO direction. Interestingly, these two distinct states can be tuned by controlling the posture of the wings (downward or upward) and the direction of airflow across the surface (along or against the RO direction), respectively. Research indicated that these special abilities resulted from the directiondependent arrangement of flexible nano-tips on ridging nano-stripes and micro-scales overlapped on the wings at the one-dimensional level, where two distinct contact modes of a droplet with orientation-tuneable microstructures occur and thus produce different adhesive forces. We believe that this finding will help the design of smart, fluid-controllable interfaces that may be applied in novel microfluidic devices and directional, easy-cleaning coatings.

Oil/water separation is an important field, not only for scientific research but also for practical applications aiming to resolve industrial oily wastewater and oil-spill pollution, as well as environmental protection.Recently, research into the role of special wettability for oil/water separation has attracted much attention. In this review we summarize the design, fabrication, applications and recent developments of special wettable materials for oil/water separation. Based on the different types of separation, we organize this review into three parts: "oil-removing" type materials with superhydrophobicity and superoleophilicity (that selectively filter or absorb oil from oil/water mixtures), "water-removing" type materials with superhydrophilicity and superoleophobicity (that selectively separate water from oil/water mixtures), and smart controllable separation materials. In each section, we present in detail the representative work, introduce the design idea, outline their fabrication methods, and discuss the role of special wettability on the separation. Finally, the challenges and outlook for the future of this subject are discussed.

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.

Two-dimensional (2D) transition metal oxide systems present exotic electronic properties and high specific surface areas, and also demonstrate promising applications ranging from electronics to energy storage. Yet, in contrast to other types of nanostructures, the question as to whether we could assemble 2D nanomaterials with an atomic thickness from molecules in a general way, which may give them some interesting properties such as those of graphene, still remains unresolved. Herein, we report a generalized and fundamental approach to molecular self-assembly synthesis of ultrathin 2D nanosheets of transition metal oxides by rationally employing lamellar reverse micelles. It is worth emphasizing that the synthesized crystallized ultrathin transition metal oxide nanosheets possess confined thickness, high specific surface area and chemically reactive facets, so that they could have promising applications in nanostructured electronics, photonics, sensors, and energy conversion and storage devices.