Recent advances in slippery liquid-infused surfaces with unique properties inspired by nature

The slippery liquid-infused porous surface(s)(SLIPS)that imitates the Nepenthes pitcher plant has proven to be highly versatile and can be combined with various surface characteristics such as dynamic response,antifouling,selective adhesion,and optical/mechanical tunability.In addition,the introduction of a lubricating fluid layer also gives it extremely low contact angle hysteresis and self-repairing properties,which further expands its application range.Currently,SLIPS has been proven to be suitable for many frontier fields such as aerospace,communications,biomedicine,and microfluidic manipulation.In this review,we explain the theoretical background of SLIPS and the preparation methods currently available,including the choice of substrate materials and lubricants,and we discuss the design parameters of the liquid injection surface and how to deal with the consumption of lubricants in practical applications.In addition,the paper focuses on current and potential applications,such as preventing pathogen contamination of and blood adhesion of medical equipment,manipulation of tiny droplets,and directional transportation of liquids.Finally,some weaknesses that appear when SLIPS is used in these applications are pointed out,which provides a new perspective for the development of SLIPS in the future.

Fabrication of bioinspired edible liquid marble with phase transition and tunable water barrier property

Based on aphid wax-honeydew marble and the hydrophobic wax structure of lotus and its derived applications with superareophilic and superhydrophobic properties,edible carnauba wax and beeswax particles were mixed and utilized to mimic lotus wax and wrap liquid,thus forming liquid marbles(LMs).Through the utilization of continuous production system(CPS),wax as an interfacial surfactant,water and solid,air-phase or mixed-phase marble content was produced.The edible liquid marble(ELM)could encapsulate water and food droplets.Edible solid marble(ESM)and edible solid hollow marbles(ESHMs)could be fabricated by applying pectin or syrup.Moreover,through the heating of wax powders with different melting temperatures,stable tablets and hollow capsules could be produced.The wax powder as interfacial surfactant could firmly bind with pectin through hydrogen bonds on ESM.The edible LMs can therefore be applied for residue reduction,corrosion reduction,biohazard prevention and cleaning in the food industry.The other phase LMs could act as novel tools in the pharmaceutical and food industries with the above-mentioned water transport,preservation,sustained releasing and selective releasing abilities.

Low friction of superslippery and superlubricity:A review

The issues regarding energy dissipation and component damage caused by the interface friction between a friction pair attract enormous attention to friction reduction.The key-enabling technique to realize friction reduction is the use of lubricants.The lubricants smooth the contact interfaces,achieving an ultralow friction contact,which is called superslippery or superlubricity.At present,superslippery and superlubricity are two isolated research topics.There is a lack of unified definition on superslippery and superlubricity from the viewpoint of tribology.Herein,this review aims at exploring the differences and relations between superslippery and superlubricity from their origin and application scenarios.Meanwhile,the challenges for developing superslippery surface and superlubricity surface are discussed.In addition,perspectives on the interactive development of these two surfaces are presented.We hope that our discussion can provide guidance for designing superslippery or superlubricity surfaces by using varies drag-reduction technologies.

Advance in Structural Classification and Stability Study of Superamphiphobic Surfaces

Superamphiphobic surfaces have great potential applications in flame resistance,anti-icing,self-cleaning,anti-adhesion,micro-flow control and so on.However,the surface durability is poor owing to the limitation of design principles.In recent years,a lot of efforts have been carried out on the morphology,structure,and stability of superamphiphobic surfaces,resulting in significant improvement in their surface superwetting properties.In this review,we present a brief classification of the morphological types of superamphiphobic surfaces and summary of the recent progress of researches on the stability of superamphiphobic surfaces.Several testing methods of mechanical and chemical stability are listed in the article,together with the characteristic results,to provide a better and more detailed understanding of the current research status on superamphiphobic surface stability,which will be of considerable importance as a reference guide for our future researches.Of course,there are still some issues that need to be addressed for the application of superamphiphobic surfaces at large scale,and this is where our future researches will be directed.Finally,we discuss the challenges as well as the prospects in the study of superamphiphobic surfaces.

Nature-inspired Polysaccharide-based Aerogel for Oil–water Separation

Oily wastewater pollution is an urgent problem to be solved.Complicated preparation process,toxic hydrophobic modifiers and poor mechanical properties limit the application of polysaccharide-based aerogel in oil–water separation.Inspired by the Strider’s Leg structure in nature,an eco-friendly and reusable polysaccharide-based composite aerogel was prepared by hydrophobic modification with zein for efficient oil–water separation.The introduction of hydrophobic zein into aerogel by simple immersion method without the use of toxic modifiers can build micro/nanostructures similar to the villi on a water strider’s leg to increase the surface roughness and the hydrophobicity.And three degradable,non-toxic and economical polysaccharides including chitosan,carboxylated cellulose nanofibers and starch were used to construct aerogel skeleton,endowing aerogel with porous structures and good mechanical properties.The resulting composite aerogel(ZOMA)showed low density(0.11 g/cm^(3)),good oil absorption capacity(9 g/g),high flux oil–water separation(5595 L m^(−2)h^(−1))and excellent oil–water separation performance(99.8%).And ZOMA still had good tensile strength and elasticity after 50 compression cycles.After 10 cycles of absorption and desorption,ZOMA aerogel remained still more than 90%of its initial absorption capacity.This study provides new insight for the design of environmentally friendly and efficient adsorbents for oil–water separation.

A robust membrane with dual superlyophobicity for solving water-caused lubricant deterioration and water contamination

Lubricants are often contaminated by water in different ways. Water-polluted lubricants extremely accelerate wear corrosion, leading to the deterioration of lubricity performance. Recently, multiphase media superwettability has been developed to endow one surface with compatible functions, such as on-demand separation of oily wastewater. However, realizing the robustness of the dual superlyophobic surface to solve water-caused lubricant deterioration and water contamination as needed remains challenges. Herein, a robust dual superlyophobic membrane is presented to realize on-demand separation for various lubricant–water emulsions. Compared to pure lubricants, the purified lubricants have equivalent tribology performance, which are much better than that of water-polluted lubricants. The as-prepared membrane maintains dual superlyophobicity, high-efficient for water or lubricant purification, and excellent tribology performance of the purified lubricant, even after immersion in hot liquids for 24 h, multicycle separation, and sandpaper abrasion for 50 cycles. Water-polluted lubricant extremely accelerates wear corrosion to promote catalytic dehydrogenation of lubricants, generating too much harmful carbon-based debris. This work shows great guiding significance for recovering the tribology performance of water-polluted lubricants and purifying water by the dual superlyophobic membrane.

One Step and In Situ Synthesis of Edible Lubricant-infused Surface Using All-in-one Solution

Edible Lubricant-Infused Surface(ELIS)was fabricated through antisolvent method by adding ethyl oleate(lubricant/antisolvent),ethanol(solvent)and shellac(solute/base layer of ELIS)into an all-in-one solution to in-situ prepare ELIS through single step of solvent evaporation.The ELIS comprising sub-micro-to micro-scaled shellac particles shows water and food liquid slippery,transparency,stability against abrasion and lubricant retaining ability against sheer force.Using all edible material to fabricated ELIS is a more efficient route for application when compared with other Lubricant-Infused Surface(LIS).Traditional fabrication for LIS included steps such as:base layer fabrication,lubricant infusion,excess lubricant removal,UV light treatment and chemical etching.The method proposed in this article could further simplify the preparation to an all-in-one solution and simplify the synthesis process to only 60-degree heating.Furthermore,Shellac ELIS coating could withstand abrasion and hold performance when compared with other ELIS coatings.

Electron transfer dominated triboelectrification at the hydrophobic/slippery substrate-water interfaces

Triboelectric nanogenerator(TENG)based on triboelectrification has attracted wide attention due to its effective utilization of green energy sources such as marine energy.However,researches about liquid-liquid triboelectrification are still scanty as solid-liquid triboelectrification has been widely studied.Herein,this work focuses on the hydrophobic/slippery substrate-water interfacial triboelectrification based on the solid friction materials of polytetrafluoroethylene(PTFE)nanoparticles.The hydrophobic/slippery substrate-water interfacial triboelectrification are studied by assembling PTFE coated Al sheets and perfluoropolyether(PFPE)infused PTFE coated Al sheets(formed the slippery lubricant-infused surfaces(SLIPSs))as the friction electrode,and water as liquid friction materials,respectively.The results show that the hydrophobic TENG output performances improved as the PTFE nanoparticles cumulating,and the SLIPSs TENG output performances increased with the thinner PFPE thickness.Both the triboelectrification behavior of hydrophobic/SLIPSs TENG assembled in this work are dominated by the electron transfer.Thanks to the introduction of SLIPSs,the SLIPSs TENG exhibits superior stability and durability than the hydrophobic TENG.The investigation of hydrophobic/slippery substrate-water interfacial triboelectrification contributes to optimize the TENG performances,and expands the application in harsh environments including low temperature and high humidity on the ocean.

Simple and Ultrahigh Efficient Superhydrophilic Polydopamine-coated TiO_(2) Cotton for Oil-water Separation

Oil–water mixing has brought many problems to a society, and it is of great significance to develop a simple, convenient, efficient, and durable separation material to solve the problem of oil–water mixing. In this paper, modified cottons were successfully prepared using polydopamine as the in situ mineralization site of TiO_(2) nanoparticles combined with synergistic crosslinking with KH550. A large number of hydrophilic groups endowed the cotton with superhydrophilic ability, which greatly shortened its water spreading time. The prepared modified cotton could be successfully separated from oil and water, and still had a separation efficiency of 99.999% after 50 cycles. In addition, after 24 h immersion in 1 M HCl, NaOH, and NaCl solutions and 50 abrasion experiments, the modified cotton showed excellent oil–water separation ability, and the separation efficiency was above 99.990%. Successfully provided a simple preparation method to prepare high-efficiency and clean cottons for oil–water separation.

Bionic multifunctional fibrous materials for efficient oil/water separation

Special wettability fibrous materials have received a lot of attention because of their good connectivity,mechanical flexibility,large specific surface area,and ease of shape manipulation.Their outstanding performance paves the way toward efficient oil/water separation in a variety of environments and for separation requirements.This paper discusses the distinct advantages,challenges,and future research directions of various substrates for fibrous materials,such as nonwoven natural biomass fibers,fabrics,electrospinning fibers,metallic fibers,and inorganic nonmetallic fibers.The special wettability fibrous filter materials and fibrous adsorbents are summarized based on the different separation methods.The principles of preparation of various special wettabilities are introduced,and the unique advantages of fibrous adsorbents are emphasized.The preparation strategy of fibrous filter materials is discussed,as well as some representative work and research progress.The benefits,drawbacks,and research directions in terms of various materials are examined.This article emphasizes the pollution resistance of fibrous filter materials and the elasticity of fibrous adsorbents.Finally,the prospects in terms of the problems,challenges,and future development of special wettability fibrous materials used in oil/water separation are discussed.

仿生超润湿材料的研究进展

近年来,除了荷叶结构,更多具有特殊润湿性的超润湿表面受到了广泛的关注.由于其独特的润湿性能,在工农生产和人们日常生活中具有非常广泛的应用前景.通过将多重维度的结构和化学成分相结合,可设计及构筑超润湿表面.本综述详细地总结了自然界的超润湿现象,并且将超润湿体系分为零维、二维及三维材料.针对近几年超润湿材料在设计、制备和应用方面存在的问题,从仿生理念出发,介绍了多种具有特殊润湿性的超润湿材料,并对其功能进行了系统的总结.最后对超润湿材料研究的未来发展进行了展望.

Interfacial Effects of Superhydrophobic Plant Surfaces： A Review

Nature is a huge gallery of art involving nearly perfect structures and properties over the millions of years of development. Many plants and animals show water-repellent properties with fine micro-structures, such as lotus leaf, water skipper and wings of butterfly. Inspired by these special surfaces, the artificial superhydrophobic surfaces have attracted wide attention in both basic research and industrial applications. The wetting properties of superhydrophobic surfaces in nature are affected by the chemical compositions and the surface topographies. So it is possible to realize the biomimetic superhydrophobic surfaces by tuning their surface roughness and surface free energy correspondingly. This review briefly introduces the physical-chemical basis of superhydrophobic plant surfaces in nature to explain how the superhydrophobicity of plant surfaces can be applied to different biomimetic functional materials with relevance to technological applications. Then, three classical effects of natural surfaces are classified： lotus effect, salvinia effect, and petal effect, and the promising strategies to fabricate biomimetic su- perhydrophobic materials are highlighted. Finally, the prospects and challenges of this area in the future are proposed.

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.

Biomimetic Superhydrophobic Surfaces with Transition Metals and Their Oxides： A Review

Transition metals and their oxide materials have been widely employed to fabricate superhydrophobic surfaces, not only because of their surface topography with controllable microstructures leading to water-repellence, diverse adhesion even tun- able wettability, but also due to a variety of special properties like optical performance, magnetism, anti-bacterial, transparency and so on. At the meantime, biomimetic superhydrophobic surfaces have attracted great interest from fabricating hierarchical micro-/nano-structures inspired by nature to imitate creature＇s properties and many potential applications, including self-cleaning, antifogging, antireflection, low drag and great stability and durability. In this review, natural surfaces and biomimetic materials with special wettability are introduced by classification according to the similar microstructure of mor- phology, like array structure, sheet overlapped structure, high density hairs and seta shaped structure. Not only do we exhibit their special performances, but also try to find out the true reasons behind the phenomenon. Then, the recent progress of a series of superhydrophobic transition mental and their oxide materials, including TiO2, ZnO, Fe304, CuO, Ag, Au and so on, is pre- sented with a focus on fabricating methods, microstructures, wettability, and other properties. As followed, these superhydro- phobic surfaces can be applied in many fields, such as oil/water separation, self-cleaning, photo-controlled reversible wet- tability, surface-enhanced Raman scattering, antibacterial, anticorrosion, and synthesis of various applications. However, few of them have been applied in practical life. Hence, we discuss the remaining challenges at present and the development tendency in future at the end of this article. This review aims to present recent development of transition metals and their oxides applied in biomimetic superhydrophobic surfaces about fabrication, microstructure, water repellence, various properties, and potential applications.

Fabrications and Applications of Slippery Liquid-infused Porous Surfaces Inspired from Nature: A Review

The slippery liquid-infused porous surfaces inspired by the microstructure of carnivorous nepenthes have aroused widespread attention,which show stable liquid repellency,glorious self-repairing powers and effective anti-fouling properties.The surfaces are manufactured via the infusion of lubricant oil into porous structures,a process which allows other fluids to slide off the interfaces readily.However,the practical applications of slippery liquid-infused surfaces are limited to the complicated preparation processes and poor oil lock ability.We aim to,in this review,present the fundamental theories of the slippery liquid-infused porous surface.Some typical natural examples are clarified while representative fabricating methods such as liquid flame spray,layer-by-layer assembly,lithography and so on are listed.The slippery surface can facilitate the manufacture of transparent and multi-functional slippery materials by means of straightforward procedures.The slippery liquid-infused porous surfaces were applied in hot water repellency,anti-fouling,ice-phobic,water condensation,control of underwater bubble transport and drag reduction.This article discusses all these issues along with emerging applications as well as future challenges.

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.

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.

A Facile Modifier-free Approach to Fabricate Antistatic Superhydrophobic Composite Coatings with Remarkable Thermal Stability and Corrosion Resistance

Research on antistatic superhydrophobic surfaces has attracted widespread attention in some fields.However,in the application of superhydrophobic materials,fabricating stable and practical superhydrophobic surfaces through facile and low-cost approaches still faces considerable challenges.Herein,a polyphenylene sulfide(PPS)-based antistatic superhydrophobic composite coating with a high water contact angle(166°)and a low sliding angle(2°)was fabricated on a Q345 steel surface through a simple spray-coating method without any modifier.Furthermore,the as-prepared superhydrophobic coating also displayed excellent superhydrophobicity for water droplets at different pH values,as well as self-cleaning,anti-fouling and anti-icing properties.Importantly,the superhydrophobic coating still exhibited superhydrophobicity after calcination at 350°C for 1 h,indicating its outstanding thermal stability.Excellent antistatic and anticorrosion properties were obtained on the prepared coating surface,which allows the coating to be applied under harsh conditions.Benefiting from the above characteristics,compared with the commercial coating,the as-obtained antistatic superhydrophobic coating may be applied more widely in related fields.

Bio-inspired Fog Harvesting Materials:Basic Research and Bionic Potential Applications

With the explosive growth of the world's population and the rapid increase in industrial water consumption,the world's water supply has fallen into crisis.The shortage of fresh water resources has become a global problem,especially in arid regions.In nature,many organisms can collect water from foggy water under harsh conditions,which provides us with inspiration for the development of new functional fog harvesting materials.A large number of bionic special wettable synthetic surfaces are synthesized for water mist collection.In this review,we introduce some water collection phenomena in nature,outline the basic theories of biological water harvesting,and summarize six mechanisms of biological water collection:increased surface wettability,increased water transmission area,long-distance water delivery,water accumulation and storage,condensation promotion,and gravity-driven.Then,the water collection mechanisms of three typical organisms and their synthesis are discussed.And their function,water collection efficiency,new developments in their biomimetic materials are narrated,which are cactus,spider and desert beetles.The study of multiple bionics was inspired by the discovery of Nepenthes,moist and smooth peristome.The excellent characteristics of a variety of biological water collection structures,combined with each other,are far superior to other single synthetic surfaces.Furthermore,the main problems in the preparation and application of biomimetic fog harvesting materials and the future development trend of materials fog harvesting are prospected.