Triboelectric‘electrostatic tweezers'for manipulating droplets on lubricated slippery surfaces prepared by femtosecond laser processing

The use of‘Electrostatic tweezers'is a promising tool for droplet manipulation,but it faces many limitations in manipulating droplets on superhydrophobic surfaces.Here,we achieve noncontact and multifunctional droplet manipulation on Nepenthes-inspired lubricated slippery surfaces via triboelectric electrostatic tweezers(TETs).The TET manipulation of droplets on a slippery surface has many advantages over electrostatic droplet manipulation on a superhydrophobic surface.The electrostatic field induces the redistribution of the charges inside the neutral droplet,which causes the triboelectric charged rod to drive the droplet to move forward under the electrostatic force.Positively or negatively charged droplets can also be driven by TET based on electrostatic attraction and repulsion.TET enables us to manipulate droplets under diverse conditions,including anti-gravity climb,suspended droplets,corrosive liquids,low-surface-tension liquids(e.g.ethanol with a surface tension of 22.3 mN·m^(-1)),different droplet volumes(from 100 nl to 0.5 ml),passing through narrow slits,sliding over damaged areas,on various solid substrates,and even droplets in an enclosed system.Various droplet-related applications,such as motion guidance,motion switching,droplet-based microreactions,surface cleaning,surface defogging,liquid sorting,and cell labeling,can be easily achieved with TETs.

Carnivorous plants inspired shape-morphing slippery surfaces

Carnivorous plants,for instance,Dionaea muscipula and Nepenthes pitcher plant,inspired the innovation of advanced stimuli-responsive actuators and lubricant-infused slippery surfaces,respectively.However,hybrid bionic devices that combine the active and passive prey trapping capabilities of the two kinds of carnivorous plants remain a challenge.Herein,we report a moisture responsive shape-morphing slippery surface that enables both moisture responsive shapemorphing and oil-lubricated water repellency for simultaneous active-and passive-droplet manipulation.The moisture deformable slippery surface is prepared by creating biomimetic microstructures on graphene oxide(GO)membrane via femtosecond laser direct writing and subsequent lubricating with a thin layer of oil on the laser structured reduced GO(LRGO)surface.The integration of a lubricant-infused slippery surface with an LRGO/GO bilayer actuator endows the actuator with droplet sliding ability and promotes the moisture deformation performance due to oil-enhanced water repellency of the inert layer(LRGO).Based on the shape-morphing slippery surface,we prepared a series of proof-of-concept actuators,including a moisture-response Dionaea muscipula actuator,a smart frog tongue,and a smart flower,demonstrating their versatility for active/passive trapping,droplet manipulation,and sensing.

Fouling-resistant Behavior of Liquid-infused Porous Slippery Surfaces

Marine economy is seriously affected by marine biofouling, which has plagued people for thousands of years. Although various strategies have been developed to protect artificial surfaces against marine biofouling, cost-effective biofouling-resistant coating is still a goal in pursue. Herein, a cost-effective liquid-infused porous slippery surface （LIPSS） was facilely prepared by using poly（styrene-b-（ethylene-co-butylene）-b-styrene） （SEBS） elastomer to form microsphere surfaces, followed by infusing fluorocarbon lubricants into the porous structure. The as-prepared slippery surfaces were characterized by static water contact angle, sliding velocity and sliding angle analysis. We also investigated the adhesion behavior of Escherichia coli （E. coli） and limnetic algae on different surfaces. It is confirmed that the slippery surfaces have better anti-biofouling properties than the porous SEBS reference. This cost-effective approach is feasible and easily produced, and may potentially be used as fouling-resistant surfaces.

Smart Manipulation of Gas Bubbles in Harsh Environments Via a Fluorinert-Infused Shape-Gradient Slippery Surface

Fundamental research and practical applications have examined the manipulation of gas bubbles on open surfaces in lowsurface-tension,high-pressure,and high-acidity,-alkalinity,or-salinity environments.However,to the best of our knowledge,effi cient and general approaches to achieve the smart manipulation of gas bubbles in these harsh environments are limited.Herein,a Fluorinert-infused shape-gradient slippery surface(FSSS)that could eff ectively regulate the behavior of gas bubbles in harsh environments was successfully fabricated.The unique capability of FSSS was mainly attributed to the properties of Fluorinert,which include chemical inertness and incompressibility.The shape-gradient morphology of FSSS could induce asymmetric driving forces to move gas bubbles directionally on open surfaces.Factors infl uencing gas bubble transport on FSSS,such as the apex angle of the slippery surface and the surface tension of the aqueous environment,were carefully investigated,and large apex angles were found to result in large initial transport velocities and short transport distances.Lowering the surface tension of the aqueous environment is unfavorable to bubble transport.Nevertheless,FSSS could transport gas bubbles in aqueous environments with surface tensions as low as 28.5±0.1 mN/m,which is lower than that of many organic solvents(e.g.,formamide,ethylene glycol,and dimethylformamide).In addition,FSSS could also realize the facile manipulation of gas bubbles in various aqueous environments,e.g.,high pressure(~6.8 atm),high acidity(1 mol/L H 2 SO 4),high alkalinity(1 mol/L NaOH),and high salinity(1 mol/L NaCl).The current fi ndings provide a source of knowledge and inspiration for studies on bubble-related interfacial phenomena and contribute to scientifi c and technological developments for controllable bubble manipulation in harsh environments.

Photo-responsive droplet manipulation slippery lubricant-infused porous surface with ultra-high durability

Photo-responsive slippery lubricant-infused porous surface(SLIPS) for droplet manipulation is flexible, noncontact and non-destructive in droplet manipulation, which has promising applications in flexible robotics, microfluidics,biomedicine, and chemical analysis. However, the repeated manipulations for droplets of SLIPSs are quite limited in the works reported so far, the poor durability of droplet manipulation severely limits the practical application of the surfaces. In this paper, an Fe3O4-doped polydimethylsiloxane(PDMS)-based SLIPS is proposed and implemented to achieve ultra-high repeated droplet manipulation numbers under near-infrared ray(NIR) laser irradiation. Firstly, a micron columnar array structure with micro-pits on the top side, as well as, a wall structure out of the array is designed on SLIPS to reserve the lubricant. Secondly, the prototype of the SLIPS is fabricated by a 3-step ultraviolet(UV) lithography, and subsequently immersed in silicone oil for more than 96 h to obtain the ultra-high durability slippery lubricant-infused porous surface(UD-SLIPS). With a power of 25 m W–85 m W NIR laser, the repeated manipulation of microdroplets(≤ 5 μL) in the scale of 1 cm can exceed more than 3000 times which is far beyond that in previous reports. Finally, the droplet manipulation performance of this photo-responsive UD-SLIPS and the influence of infusion time on durability are investigated. The mechanism of the PDMS swelling effect is found to be the key factor in improving the droplet manipulation durability of SLIPS. The findings of this work would be of great significance for the development of highly durable photo-responsive functional surfaces for droplet manipulation.

Anti-attachment Function and Biomimetic Application of Slippery Zone in Nepenthes Pitcher

Carnivorous plants of Nepenthes species have evolved particular organs named pitchers at the tips of their conspicuous leaves, allowing slippery trapping and effective digesting prey to acquire sufficient growing nutrients. Nepenthes pitchers are generally distinguished by several morphological regions exhibiting distinct functions in prey capturing, and combined effect of the several zones results in great trapping efficiency. Depending on specific micro-structures, slippery zone performs an important role in efficiently preying arthropods, and this prey ability inspires an idea for biomimetic development of slippery trapping plate used in controlling agricultural pests. In this paper, combined with our latest results, the authors introduced the recent studies of the slippery zone, including surface structures and anti-attachment functions. They also highlighted the biomimetic application of slippery zone in developing slippery trapping plate for controlling agricultural pest.

Anti⁃icing/De⁃icing Mechanism and Application Progress of Bio⁃inspired Surface for Aircraft

Icing on the surface of aircraft will not only aggravate its quality and affect flight control,but even cause safety accidents,which is one of the important factors restricting all-weather flight.Bio-inspired anti-icing surfaces have gained great attention recently due to their low-hysteresis,non-stick properties,slow nucleation rate and low ice adhesion strength.These bio-inspired anti-icing surfaces,such as superhydrophobic surfaces,slippery liquid-infused porous surfaces and quasi-liquid film surfaces,have realized excellent anti-icing performance at various stages of icing.However,for harsh environment,there are still many problems and challenges.From the perspective of bioinspiration,the mechanism of icing nucleation,liquid bounce and ice adhesion has been reviewed together with the application progress and bottleneck issues about anti-icing in view of the process of icing.Subsequently,the reliability and development prospect of active,passive and active-passive integrated anti-icing technology are discussed,respectively.

Investigation of Anticorrosive Performance of Oil-infused Slippery and Superhydrophobic Brass Surfaces by Laser Texturing

Brass is widely used in machinery,electronic appliances and emerging industries.The corrosion resistance of laser-induced superhydrophobic surface of brass needs to be improved.In recent years,bionic surface with slippery coating has attracted much attention because of its excellent corrosion inhibition performance.Here,we first prepared the superhydrophobic surface of brass by nanosecond laser ablation combined with fluoroalkyl silane modification,and then injected silicone oil into the prepared superhydrophobic matrix to obtain a slippery coating surface.PDP and EIS tests in 3.5 wt.%NaCl solution showed that the corrosion resistance of the slippery surface was better than that of the superhydrophobic surface.This study can play a certain role in promoting the development of metal anticorrosive coating and is of great significance in the preparation of slippery surface by laser induction,and provides a convenient and eff ective means for metal anticorrosion in the industrial field.

Investigation of the Anisotropic Morphology-Induced Effects of the Slippery Zone in Pitchers of Nepenthes alata

Plant of carnivorous genus Nepenthes alata has evolved specific pitchers to prey insects for survival in the barren habitat, especially its slippery zone. The excellent slippery function has received considerable interest because of its potential applica- tion in antifriction surface design. The surface morphologies of intact and de-waxed slippery zones were characterized using scanning electron microscope and scanning white-light interferometer. Hierarchical structures with anisotropic micro- lunate structure and nano- wax crystals were found on the slippery zone. Due to the hierarchical structures, the slippery zone is hy- drophobic. It shows a significant anisotropic wettability with static contact angles 153.3° and 140.1° in the directions perpen- dicular and parallel to the upward direction （toward the peristome）, respectively. The sliding angles are -3° and -10° in the downward and upward directions, respectively. Crawling experiments indicate that the microscopic surface roughness and the brittleness of the wax crystals may reduce insect attachment in different modes according to the insect mass differences. Moreover, artificial slippery surfaces inspired by the slippery zone of Nepenthes alata were fabricated. Traction experiments quantitatively verified that the friction force of replicated lunate structures with Ra-2.54 μm surface roughness was reduced by about 25% as compared to flat surface with Ra-0.56 μm surface roughness for cricket claws.

Slippery Surface of Nepenthes alata Pitcher： The Role of Lunate Cell and Wax Crystal in Restricting Attachment Ability of Ant Camponotus japonicus Mayr

This study attempts to investigate how the slippery surface of Nepenthes alata pitchers restricts the attachment ability of ant Camponotus japonicus Mayr, via climbing behavior observation and friction force measurement. Ants exhibited ineffective climbing behaviors and rather small friction forces when attached to upward-oriented slippery surfaces, but opposite phenomena were shown when on inverted surfaces. Friction forces of intact, claw tip-removed and pad-destroyed ants were measured on intact and de-waxed slippery surfaces, exploring the roles of wax crystals and lunate cells in restricting ant＇s attachment. On downward-directed slippery surfaces, greater forces were exhibited by intact and pad-destroyed ants; on the two slippery sur- faces, pad-destroyed ants presented slightly smaller forces and clawless ants generated considerably smaller forces. Somewhat different force was provided by clawless ants on upward and downward oriented slippery surfaces, and slightly higher force was shown when ants climbed on wax-removed surface. Results indicate that the lunate cells contribute greatly to decrease the friction force, whereas the wax crystals perform a supplementary role. Mechanical analysis suggests that the directionally growing lunate cells possess a sloped structure that effectively prevents the claw＇s mechanical interlock, reducing the ant＇s attachment ability considerably. Our conclusion supports a further interpretation of slippery surface＇s anti-attachment mecha- nism, also provides theoretical reference to develop biomimetic slippery plate to trap agricultural insect.

Slippery Surface with Petal-like Structure for Protecting Al Alloy: Anti-corrosion, Anti-fouling and Anti-icing

The harsh working environment affects the performance and usage life of Al and its alloys,thus limiting their application.In recent years,Slippery Liquid-infused Porous Surface(SLIPS)has attracted much attention due to excellent anti-corrosion,anti-fouling and anti-icing properties.This may be an effective way to improve the properties of Al and its alloys.Here,the SLIPS with petal-like structure was constructed on the Al alloy via simple hydrothermal reaction,Stearic Acid(STA)modification and lubricant injection.A variety of droplets(including oil-in-water emulsions)can slide on the SLIPS at a low angle,even the Sliding Angle(SA)of the water droplet is only 3°.Furthermore,the SLIPS exhibits outstanding mechanical and chemical properties.It can maintain fine oil-locking ability under high shearing force and keep slippery stability after immersion in acid/alkaline solutions.In addition,the SLIPS possesses excellent anti-corrosion,anti-fouling and anti-icing properties,which provides a new way to promote the application of Al and its alloys.Therefore,the SLIPS is expected to be an effective way to improve the properties of Al and its alloys,as well as play a role in anti-fouling and self-cleaning in construction,shipbuilding and automotive manufacturing industries,thereby expanding the practical application of Al and its alloys.

Lubricant self-replenishing slippery surface with prolonged service life for fog harvesting

Slippery lubricant-infused surfaces exhibit excellent fog-harvesting capacities compared with superhydrophobic and superhydrophilic surfaces.However,lubricant depletion is typically unavoidable under dynamic conditions,and reinfused oil is generally needed to recover the fog-harvesting capacity.Herein,an effective strategy for delaying the depletion of lubricant to prolong the service life of fog harvesting is proposed.An ultrathin transparent lubricant self-replenishing slippery surface was fabricated via facile one-step solvent evaporation polymerization.The gel film of the lubricant self-replenishing slippery surface,which was embedded with oil microdroplets,was attached to glass slides via the phase separation and evaporation of tetrahydrofuran.The gel film GFs-150(with oil content 150 wt%of aminopropyl-terminated polydimethyl siloxane(PDMS–NH2))exhibited superior slippery and fog-harvesting performance to other gel films.Furthermore,the slippery surfaces with the trait of oil secretion triggered by mechanical stress exhibited better fog-harvesting capabilities and longer service life than surfaces without the function of lubricant self-replenishment.The lubricant self-replenishing,ultrathin,and transparent slippery surfaces reported herein have considerable potential for applications involving narrow spaces,visualization,long service life,etc.

Oleophobic interaction mediated slippery organogels with ameliorated mechanical performance and satisfactory fouling-resistance

Owing to their inherent semi-solid property and lubricant ability,organogels manifest various unique characteristics and serve as promising candidates for antifouling.However,the poor mechanical properties of organogels often limit their practical applications.Herein,we report a simple and effective method to prepare organogels with reinforced mechanical performance and surface lubricant ability with the synergistic roles played by oleophobic and oleophilic chains.The rigid oleophobic chains have a poor affinity to lubricating solvent,which gives rise to high oleophobic interactions between polymer networks;the soft oleophilic chains possess a high affinity to the low surface energy solvent,which lead to high solvent content to maintain the satisfactory lubricant capacity.The organogel of oleophobic methyl methacrylate(MMA)and oleophilic lauryl methacrylate(LMA)is chosen as a representative example to illustrate this concept.With the optimal composition,the as-prepared organogels offer satisfactory tensile fracture stress,fracture strain,Young’s modulus,toughness,and tearing fracture energy of 480 k Pa,550%,202 k Pa,1.14 MJ m,and 5.14 k J m,respectively,which are far beyond the classical PLMA organogels.Furthermore,the biofouling resistance tests demonstrate 4 to 9-fold reduction of protein and bacteria adhesion on the reinforced organogels surface in comparison to the glass substrate and solvent-free dry organogels.This simple and effective approach to toughen organogels,we hope,can be applied in various fields with different practical functional requirements in the future.

Development of Slippery Liquid-Infused Porous Surface on AZ31 Mg Alloys for Corrosion Protection

The relatively poor corrosion resistance remarkably limits the wide applications of Mg alloys in practice,although they possess many attractive properties,like low density,high specific strength,and good biocompatibility.The formation of a protective coating can effectively suppress the corrosion.In this work,a slippery liquid-infused porous surface(SLIPS),with good surface hydrophobicity,stability,and self-healing property,was formed on AZ31 Mg alloys.The development of SLIPS requires suitable porous micro/nanostructures.Layered double hydroxide(LDH),with effective corrosion resistance for Mg alloys,was a good candidate to accommodate the liquid lubricant.Especially,different temperatures were applied to in situ form MgAl-LDH on AZ31 Mg alloys.The results showed that the temperature of 120℃was the best condition for the SLIPS to provide good corrosion protection for Mg alloys,with the lowest corrosion current density of 3.19×10^(-9)A cm^(−2).In addition,the SLIPS performed well in the long-term immersion test and abrasion test.The AZ31 Mg alloys with superior corrosion resistance and good mechanical and chemical stability can be extensively applied in areas of automotive,electronics,and aerospace.

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.

Spontaneous Self-healing Bio-inspired Lubricant-infused Coating on Pipeline Steel Substrate with Reinforcing Anti-corrosion,Anti-fouling,and Anti-scaling Properties

Superhydrophobic surfaces(SHS)and slippery lubricant-infused porous surfaces(SLIPS)attract great attention due to their multiple properties in both industries and our daily lives.Here,we first fabricated the SHS with micro-scale flower-like structures composed of nano-sheets on pipeline steel substrate.Then,we obtained the SLIPS by spin-coating lubricant into gaps of micro-scale flower-like structures,with the air still trapped among gaps of nano-sheets.The SLIPS shows excellent liquid repellency as the SHS.The SLIPS also shows stability after the scour of flowing water.These results of polarization curves(Tafel)and electrochemical impedance spectroscopies deduced the SLIPS with better and more stable anti-corrosion property than the SHS.Compared with the SHS,the lack of attachment and CaCO_(3) on the SLIPS indicates that the SLIPS demonstrates better anti-fouling and anti-scaling properties than the SHS.Moreover,the SLIPS shows promising wear resistance under the abrasion simulated by sandpaper compared with the SHS.Notably,the air trapped among nano-sheets is conducive to the lubricant flowing to the surface quickly,exhibiting spontaneous self-healing in atmosphere,even if part flower-like structures of the SLIPS subject to damage with the lubricant consumed after scratched.

Research Progress on Corrosion Resistance of Magnesium Alloys with Bio-inspired Water-repellent Properties:A Review

Thanks to its excellent mechanical properties,magnesium alloys have many potential applications in the aerospace and other fields.However,failure to adequately solve corrosion problems of magnesium alloy becomes one of the factors restricting its wide use in many industrial fields.Inspired by nature,researchers designed and fabricated bio-inspired water-repellent(superhydrophobic and slippery liquid-infused porous surface)surfaces with special wetting properties by exploring the surface microstructures of plants and animals such as lotus leaf and nepenthes pitcher,exhibiting excellent corrosion-resistant performance.This article summarizes the research progress on corrosion resistance of magnesium alloys with bio-inspired water-repellent properties in recent years.It mainly introduces the corrosion reasons,types of corrosion of magnesium alloys,and the preparation of magnesium alloys with bio-inspired water-repellent properties to improve corrosion resistance.In particular,it is widely used and effective to construct water-repellent and anti-corrosion coating on the surface of magnesium alloy by surface treatment.It is hoped that the research in this review can broaden the application range of magnesium alloys and provide a powerful reference for the future research on corrosion resistance of magnesium alloys.