Understanding the Separations of Oil/Water Mixtures from Immiscible to Emulsions on Super-wettable Surfaces

As the frequent oil spill accidents happens and large quantities of oily wastewater from all kinds of industries are being discharged, the environment has been seriously polluted and our living areas have been horribly threatened. To deal with these issues, attentions have been aroused on the treatments of the oily wastewater. Recently, numerous superwettable materials have been fabricated. In this review, we summarize the new development of the materials for the separation of oil/water mixtures, mainly including the immiscible and emulsified mixtures. For the separation of immiscible ones, special materials with fixed wettability are firstly detailed, where three types of materials can be classified based on their wettability, i.e. superhydrophobic and superoleophilic materials, superhydrophilic and underwater superoleophobic materials, and superhydrophilic and su- peroleophobic materials. Then, the smart materials with switchable wettabilities responsive to external stimulus, for instance, light, solvent, pH, temperature, and electrical potential, are presented. Meanwhile, the single, dual, and multiple stimu- lus-responsive materials are also described. As for the separation of emulsified oil/water mixtures, the materials for the sepa- ration of water-in-oil （W/O）, oil-in-water （O/W）, and both water-in-oil （W/O） and oil-in-water （O/W） emulsions are sequen- tially introduced. Finally, some challenges are discussed and the outlook in this filed is proposed.

Characterization of Micro-Morphology and Wettability of Lotus Leaf, Waterlily Leaf and Biomimetic ZnO Surface

The aim of this paper is to characterize the microrelief and wettability of lotus leaf, waterlily leaf and biomimic ZnO surface with potential engineering applications. The characterizations of morphologies reveal that the top surface of lotus leaf is textured with 4 μm - 10 μm size protrusions and 70 nm - 100 nm nanorods, while the top surface of waterlily leaf is textured with wrinkle and decorated with concave coin-shaped geometric structure. The wettabilities of water and oil on lotus leaf and waterlily leaf under different surroundings were systematically researched. It is indeed interesting that the leaves of the two typical plants both living in the aquatic habitats possess opposite wettabilities： superhydrophobicity for top surface of lotus leaf （156°） while quasi-superhydrophilicity for top surface of waterlily leaf （15°）. We have succeeded in fabricating the superhy- drophobic ZnO nanorods semiconductor material （151°） employing a simple method inspired by the detailed structures and chemical composition of lotus leaf.

Underwater Superoleophobic Crucian Fish Scale:Influence of Ontogeny on Surface Morphologies and Wettability

Recent development concerning underwater superoleophobic surface has been motivated by fish scales,which are rendered capable of preventing their surfaces from contamination in oil-polluted water.In this paper,for the first time,the variations in surface topography and chemical composition of crucian fish scales at different growth stages have been investigated.The water and oil contact angles,surface morphology and chemical composition of the fish scales were measured by means of contact angle measurements,scanning electron microscopy and Fourier transform infrared spectroscopy,respectively.It is found that surface morphology and chemical composition both have influences on surface wettability of fish scales;fish scale at infant period seems to possess better hydrophilicity than that of fish scales at mature and senescent period.What is more,it is believed that the wettability heavily depends on the surface structures during their growth procedure,which enlightens us to design and fabricate biomimetic multifunctional underwater superoleophobic surfaces inspired by nature.

Tribological performance of ionic liquid-lubricated carbon brush/collector ring current-carrying friction system

The lubricity and anti-wear ability of ionic liquids(ILs)were studied by a current-carrying friction test on IL-lubricated carbon brushes.The results indicated that the conductivity and wear resistance of different ILs are different,and may vary for different carbon brushes.The E468e carbon brush was found to be more sensitive to IL lubrication than D172 carbon brush.Importantly,an analysis of the wear surfaces of the D172 and E468e carbon brushes revealed that,due to the different materials of the two carbon brushes and the composition of the IL,the lubrication effect on the carbon brushes was different.The viscosity of the IL will affect its wettability on the carbon brush surface.The better the wettability,the easier the movement of ions on the surface,which makes it easier to form a conductive physical adsorption film.Therefore,in practice,a better IL must be selected by considering the wettability of IL and carbon brushes.

Biomimetic Janus Paper with Controllable Swelling for Shape Memory and Energy Conversion

Being inspired by the "seismonastic reaction"of Mimosa pudica,an asymmetric swelling system was constructed to induce the controllable directional deformation of filter paper.In this work,multifunctional biomimetic Janus paper was facilely fabricated via depositing poly(vinylidene fluoride)(PVDF)on one side of Qualitative Filter Paper (QFP),the permeation of polymer solutions within filter paper was well controlled during fabrication.The wetting and swelling behavior of the prepared Janus paper were detected.The Janus paper showed controllable swelling-induced deformations in water.Both the degree and orientation of the deformation were fully investigated.On the one hand,the degree of deformation depends on the gradient wettability and hygroscopicity of the Janus paper,on the other hand,the orientation of deformation is related to the storage and release of stress.Additionally,the steady deformation during swelling endows the Janus paper with novel shape memory property both under idling and loading conditions.The Janus paper was also applied to achieve reversible energy conversion from the swelling potential energy to mechanical potential energy.

Superhydrophobic Plant Leaves with Micro-line Structures： An Optimal Biomimetic Objective in Bionic Engineering

It has been well demonstrated that there are two kinds of surface morphologies, including binary structures （namely micro-and nanostructures） and less common unitary structures （such as micro-line structures）, which play crucial roles in endowing the plant leaves with superhydrophobic properties. In this work, five superhydrophobic plant leaves in nature are introduced, by means of the combination of surface morphology and wettability with the aid of Scanning Electron Microscopy （SEM） and contact angle measurement. The results indicate that either the binary structures or the unitary structures enable the construction of a superhydrophobic surface, and the latter shows likely better mechanics compared with the former according to the corresponding theory. This research aims at introducing two different types of corresponding morphologies of superhydrophobic plant leaves.

Biomimetic Photonic Structures with Tunable Structural Colours： From Natural to Biomimetic to Applications

Natural photonic structure with tunable structural colours is one of the most miraculous structures which always catches our eyes. However, the application of artificial photonic structures is limited. Moreover, because of the ability of tunable colours, photonic structure is the excellent candidate for many fields, such as sensor, bioassay, anti-counterfeiting, optical components, photocatalytic, fibers and fabrics. Considering the superior tunable optical property and other excellent performance such as robust mechanical strength, wettability, there are new domains and novel routes for this material that deserve us to explore. In this review, some natural photonic structures are discussed. Some novel fabrication methods and applications will be mentioned in this article. Furthermore, this review provides an insight and outlook for the photonic material with tunable eolours focusing on fabrication, design and applications.

Bioinspired Edible Lubricant-Infused Surface with Liquid Residue Reduction Properties

Inspired by nature’s water-repellent plants,the superhydrophobic surface(SHS)and the lubricant-infused surface(LIS)possess potentials in various fields of application.In particular,the edible SHS and the edible LIS(ELIS)are suitable for the role of highvalued liquid food residue reduction.In this study,the ELIS was introduced through a facile spray method and direct lubricant infusion.Four types of ELISs were fabricated:carnauba wax with ethyl oleate infusion,carnauba wax with cooking oil infusion,beeswax with ethyl oleate infusion,and beeswax with cooking oil infusion.The carnauba wax-coated ELIS has better slipperiness,while the beeswax-coated ELIS has better transparency.The ethyl oleate-infused ELIS possesses ELIS to SHS transformable ability,and the cooking oil-infused ELIS also possesses better slipperiness and has the affordable advantage.Moreover,the material selection of ELIS is accessible,renewable,green,recyclable,and edible.The results illustrated that ELIS has advantages of long-term effectiveness and impact resistance over edible SHS and indicated that the ELIS can be facilitated for the manufacture of a multifunctional liquid residue reduction surface with food safety assurance.