Design, and Applications Shutao Wang,†,‡ Kesong Liu, Xi Yao, and Lei Jiang*,†,‡,§ †Laboratory of Bio-inspired Smart Interface Science, Technical Institute of Physics and Chemistry, and ‡Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry and Environment, BeiHang University, Beijing 100191, People’s Republic of China Department of Biomedical Sciences, City University of Hong Kong, Hong Kong P6903, People’s Republic of China

Bioinspired Surfaces with Superwettability: New Insight on Theory, Design, and Applications

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.

Special wettable materials for oil/water separation

Development of durable non-wetting surfaces is hindered by the fragility of the microscopic roughness features that are necessary for superhydrophobicity. Mechanical wear on superhydrophobic surfaces usually shows as increased sticking of water, leading to loss of non-wettability. Increased wear resistance has been demonstrated by exploiting hierarchical roughness where nanoscale roughness is protected to some degree by large scale features, and avoiding the use of hydrophilic bulk materials is shown to help prevent the formation of hydrophilic defects as a result of wear. Additionally, self-healing hydrophobic layers and roughness patterns have been suggested and demonstrated. Nevertheless, mechanical contact not only causes damage to roughness patterns but also surface contamination, which shortens the lifetime of superhydrophobic surfaces in spite of the self-cleaning effect. The use of photocatalytic effect and reduced electric resistance have been suggested to prevent the accumulation of surface contaminants. Resistance to organic contaminants is more challenging, however, oleophobic surface patterns which are non-wetting to organic liquids have been demonstrated. While the fragility of superhydrophobic surfaces currently limits their applicability, development of mechanically durable surfaces will enable a wide range of new applications in the future.

Mechanically Durable Superhydrophobic Surfaces

Oil/water separation is a field of high significance as it has direct practical implications for resolving the problem of industrial oily wastewater and other oil/water pollution. Therefore, the development of functional materials for efficient treatment of oil-polluted water is imperative. In this feature article, we have reviewed the recent progress of oil/water separation technologies based on filtration and absorption methods using various materials that possess surface superwetting properties. In each section, we present in detail representative work and describe the concepts, employed materials, fabrication methods, and the effects of their wetting/dewetting behaviors on oil/water separation. Finally, the challenges and future research directions of this promising research field are briefly discussed.

Oil/water separation techniques: a review of recent progresses and future directions

Oil sorbents play a very important part in the remediation processes of oil spills. To enhance the oil-sorption properties and simplify the oil-recovery process, various advanced oil sorbents and oil-collecting devices based on them have been proposed recently. Here, we firstly discuss the design considerations for the fabrication of oil sorbents and describe recently developed oil sorbents based on modification strategy. Then, recent advances regarding oil sorbents mainly based on carbon materials and swellable oleophilic polymers are also presented. Subsequently, some additional properties are emphasized, which are required by oil sorbents to cope with oil spills under extreme conditions or to facilitate the oil-collection processes. Furthermore, some oil-collection devices based on oil sorbents that have been developed recently are shown. Finally, an outlook and challenges for the next generation of oil-spill-remediation technology based on oil-sorbents materials are given.

Advanced Sorbents for Oil-Spill Cleanup: Recent Advances and Future Perspectives

A facile dip-coating process for preparing highly durable superhydrophobic surface with multi-scale structures on paint films

Stable highly hydrophobic and oleophilic meshes for oil–water separation

The stability of superhydrophobic surfaces tested by high speed current scouring

3D Monodisperse Oligofluorenes with Non-Conjugated Triphenylamine-Based Cores: Synthesis and Optoelectronic Properties

A comb copolymer with a fluorinated FPAE main chain and narrowly dispersed PMS graft chains has been prepared. The micellization behavior of this copolymer in a methanol/acetone mixture was studied. DLS studies showed hydrodynamic diameters of the micelles between 50 and 80 nm, while the diameters of dry micelles were ≈40 nm in TEM images. Micelle films with an interesting porous composite structure of nanofibers bearing micelle particles on the surface have been prepared by double coating the micelle solution. Superhydrophobicity with a WCA of 165° and a sliding angle of 3° was observed. As comb copolymers can adjust their molecular weight and block length independently, materials with a high physical strength and controllable morphological structure can be obtained.

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Zhe Cui

Papers

A facile dip-coating process for preparing highly durable superhydrophobic surface with multi-scale structures on paint films

Stable highly hydrophobic and oleophilic meshes for oil–water separation

The stability of superhydrophobic surfaces tested by high speed current scouring

3D Monodisperse Oligofluorenes with Non-Conjugated Triphenylamine-Based Cores: Synthesis and Optoelectronic Properties

Spherical Comb Copolymer Micelles and their Application in the Construction of Superhydrophobic Surfaces