Nonflammable and Magnetic Sponge Decorated with Polydimethylsiloxane Brush for Multitasking and Highly Efficient Oil–Water Separation

Developing sponge materials integrating excellent flame retardancy, multitasking separation performance, and efficient emulsion‐breaking ability is significant but challenging for the remediation of oil spills causing fires and environmental damages. Herein, a superhydrophobic oil–water separation sponge material, containing a melamine‐formaldehyde (MF) sponge substrate, magnetic polydopamine (PDA) coating, and branched polydimethylsiloxane (PDMS) brush, through dopamine‐mediated surface initiated atom transfer radical polymerization (SI‐ATRP) is fabricated. The synergistic flame resistance of the MF substrate and PDMS brush significantly improves its adaptability in fire. More importantly, the decorated PDMS brushes can effectively overcome the size mismatch between sponge macropores and tiny emulsified droplets, while remaining the intrinsic macroporous characteristic. When treating W/O emulsions, the PDMS brushes stretch up to act as “interface‐breaking blades” to accelerate the coalescence of emulsified water droplets. Meanwhile, such PDMS brushes can serve as “oil‐trapping tentacles” to efficiently capture oil droplets when treating O/W emulsions. Such material design synergistically contributes to satisfactory separation efficiency (98.7%) and ultrahigh permeation flux (up to 1.35 × 10⁵ L m^?2 h^?1), even for treating high viscosity emulsions. Besides, the reported sponge also inherits robust durability, superior recyclability, and convenient magnetic collection. These features make the sponge promising for multitasking and highly efficient oil–water separation.     

Droplet and Fluid Gating by Biomimetic Janus Membranes

The ability to gate (i.e., allow or block) droplet and fluid transport in a directional manner represents an important form of liquid manipulation and has tremendous application potential in fields involving intelligent liquid management. Inspired by passive transport across cell membranes which regulate permeability by transmembrane hydrophilic/hydrophobic interactions, macroscopic hydrophilic/hydrophobic Janus‐type membranes are prepared by facile vapor diffusion or plasma treatments for liquid gating. The resultant Janus membrane shows directional water droplet gating behavior in air‐water systems. Furthermore, membrane‐based directional gating of continuous water flow is demonstrated for the first time, enabling Janus membranes to act as facile fluid diodes for one‐way flow regulation. Additionally, in oil‐water systems, the Janus membranes show directional gating of droplets with integrated selectivity for either oil or water. The above remarkable gating properties of the Janus membranes could bring about novel applications in fluid rectifying, microchemical reaction manipulation, advanced separation, biomedical materials and smart textiles.     

Tunable Superparamagnetic Ring (tSPRing) for Droplet Manipulation

The manipulation of droplets via a magnetic field forms the basis of a fascinating technology that is currently in development. Often, the movement of droplets with magnets involves adding magnetic particles in or around the droplet; alternatively, magneto responsive surfaces may also be used. This work, presents and characterizes experimentally the formation and properties of a tunable superparamagnetic ring (tSPRing), which precisely adjusts itself around a water droplet, due to liquid–liquid interaction, and enables the physical manipulation of droplets. The ring is made of an oil-based ferrofluid, a stable suspension of ferromagnetic particles in an oily phase. It appears spontaneously due to the oil–water interfacial interaction under the influence of a magnetic field. The ferrofluid–water interaction resembles a cupcake assembly, with the surrounding ring only at the base of the droplet. The ring is analogous to a soft matter ring magnet, showing dipole repulsive forces, which stabilizes the droplets on a surface. It enables robust, controllable, and programmable manipulation of enclosed water droplets. This work opens the door to new applications in open surface upside or upside-down microfluidics and lays the groundwork for new studies on tunable interfaces between two immiscible liquids.     

Interfacial Self‐Assembly of Amphiphilic Dual Temperature Responsive Actuating Janus Particles

Amphiphilic Janus particles feature the combination of two different functional materials in one single colloid, as well as the possibility of self‐assembly at interfaces into complex superstructures. In this article, the self‐assembly of dual temperature responsive amphiphilic Janus particles at liquid–liquid interfaces and their subsequent conversion into an actuating layer‐shaped surface are presented. These microparticles are produced in a capillaries based continuous flow microfluidic device by photoinitiated radical polymerization. The hydrophobic part of the Janus particles contains a liquid crystalline elastomer (LCE), which performs a strong actuation up to 95% during the nematic–isotropic phase transition. The other side consists of a p(NIPAAm) hydrogel, which features volumetric expansions up to 280% below the lower critical solution temperature. A multistep molding process is developed to uniformly align the Janus particles at a toluene/water boundary surface and to embed the particles into a hydrogel matrix. A particle covered hydrogel layer is obtained, which features a collective actuation of the rod‐like LCE parts on the surface and a bundling of the resulting forces during the phase transition.     

Synthesis of Interfacially Active and Magnetically Responsive Nanoparticles for Multiphase Separation Applications

A novel interfacially active and magnetically responsive nanoparticle is designed and prepared by direct grafting of bromoesterified ethyl cellulose (EC‐Br) onto the surface of amino‐functionalized magnetite (Fe₃O₄) nanoparticles. Due to its strong interfacial activity, ethyl cellulose (EC) on the magnetic nanoparticles enables the EC‐grafted Fe₃O₄ (M‐EC) nanoparticles to be interfacially active. The grafting of interfacially active polymer EC on magnetic nanoparticles is confirmed by zeta‐potential measurements, diffuse reflectance infrared Fourier‐transform spectroscopic (DRIFTS) characterization, and thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) images show a negligible increase in particle size, confirming the thin silica coating and grafted EC layer. The magnetization measurements show a marginal reduction in saturation magnetization by silica coating and EC grafting of original magnetic nanoparticles, confirming the presence of coatings. The M‐EC nanoparticles prepared in this study show excellent interfacial activity and highly ordered features at the oil/water interface, as confirmed using the Langmuir–Blodgett technique and atomic force microscopy (AFM). The magnetic properties of M‐EC nanoparticles at the oil/water interface make the interfacial properties tunable by or responsive to an external magnetic field. The occupancy of M‐EC at the oil/water interface allows rapid separation of the water droplets from emulsions by an external magnetic field, demonstrating enhanced coalescence of magnetically tagged stable water droplets and a reduced overall volume fraction of the sludge.     

基于兰姆波在玻璃基板驱动微升油水分离实验

提出了在倾斜玻璃基板上平行安装两片谐振频率为1 MHz的单相叉指换能器(SPT)进行微升级液体油水分离实验探究。结合油水混合液滴在倾斜基板上的受力情况,利用二维Navier Stokes方程和声流理论建立液滴运动力学模型,分析了微升油水分离时间随各影响因素下的变化关系。理论分析和实验结果表明,影响油水分离时间的因素主要有基板倾角、输入峰值电压和油水混合比例,通过调整影响因素,可以高效地把油水混合液滴进行分离。该研究方法可降低传统油水分离的生产成本,为分离两种不相溶的微升混合液滴提供了新思路。     

Temperature-Triggered Dynamic Janus Fabrics for Smart Directional Water Transport

In this study, thermosensitive amino-silica@PDVB/PNIPAM Janus particles (JPs) are synthesized by seed emulsion polymerization-induced phase separation and selective modification methods. Amino-modified silica moieties are covalently bonded to a diverse choice of substrates to achieve robust composite coatings, and a PDVB/PNIPAM abdomen forms a micro-nano-scale hierarchical surface. PNIPAM has a lower critical solution temperature (LCST), which allows the hydrophilic and hydrophobic properties of the coating to reverse with a change in temperature. When the fabrics are coated with the thermosensitive Janus particles, water repellency is observed above 32 °C, while hydrophilicity is revealed below 32 °C. Then, after the composite fabric is worn, the side next to the skin becomes hydrophobic due to the high temperature, and the side facing the environment is hydrophilic. Therefore, sweat can be pumped from the hydrophobic side to the hydrophilic side through the dynamic Janus fabric. The dynamic hydrophobic–hydrophilic Janus structure enables the efficient and fast evaporation of sweat. The perspiration rate of Janus fabrics is five times higher than that of commercial cotton fabrics. While the wettability of the composite coating remains reversible after 20 temperature cycles and 20 tape adhesion cycles, showing good mechanical durability. The reversible thermal sensitivity remains after repeated rubbing and ultrasonic immersion.     

Breaking Polymer Chains with Self-Propelled Light-Controlled Navigable Hematite Microrobots

The increasing use of polymers has led to an uncontrollable accumulation of polymer waste in the environment, evidencing the urgent need for effective and definitive strategies to degrade them. Here, self-propelled light-powered magnetic field-navigable hematite/metal Janus microrobots that can actively move, capture, and degrade polymers are presented. Janus microrobots are fabricated by asymmetrically depositing different metals on hematite microspheres prepared by low-cost and large-scale chemical synthesis. All microrobots exhibit fuel-free motion capability, with light-controlled on/off switching of motion and magnetic field-controlled directionality. Higher speeds are observed for bimetallic coatings with respect to single metals. This is due to their larger mixed potential difference with hematite as indicated by Tafel measurements. As a model for polymers, the total degradation of high molecular weight polyethylene glycol is demonstrated by matrix-assisted laser desorption/ionization mass spectrometry. This result is attributed to the active motion of microrobots, enhanced electrostatic capture of polymer chains, improved charge separation at the hematite/metal interface, and catalyzed photo-Fenton reaction. This work opens the route toward the degradation of polymers and plastics in water using light.     

Bioinspired Dynamic Antifouling of Oil-Water Separation Membrane by Bubble-Mediated Shape Morphing

Oil–water separation membranes easily fail to oil foulants with low surface energy and high viscosity, which severely limits these membranes’ applications in treating oily wastewater. Herein, an oil–water separation membrane by bioinspired bubble-mediated antifouling strategy is fabricated via growing hierarchical cobalt phosphide arrays on stainless steel mesh. The as-prepared membrane is superhydrophilic/superaerophobic and electrocatalytic for hydrogen evolution under water, which helps to rapidly generate and release abundant microbubbles surrounding the oil-fouled region on the membrane. These microbubbles can spontaneously coalesce with the oil foulants to increase their buoyancy and warp their interface tension by morphing the oil shape. And this spontaneous coalescence also increases the kinetic energy of oil foulants resulting from the decreased bubbles’ interface energy and potential energy. The synergy of the warped interface tension, increased buoyancy, and kinetic energy drives the efficiently dynamic antifouling of this membrane. This dynamic antifouling even can remove some solid sediment such as oily sand particles that causes more serious fouling of the membrane. Thus, this membrane maintains high flux (>11920 L m⁻² h⁻¹ bar⁻¹) in the long-term separation of oil–water and oil–sand–water emulsions by dynamically recovering the decayed flux on demand, which exhibits great potential in treating industrial oily wastewater.     

Lossless and Directional Transport of Droplets on Multi-bioinspired Superwetting V-shape Rails

Lossless and directional droplet transport is desirable in biological processes as well as in technical applications such as targeted drug therapies, bioassays, and microfluidics. Conventional methods that use surface energy and Laplace pressure gradients to achieve spontaneous droplet transport often suffer from droplet destruction and loss. Herein, an efficient strategy is reported based on a V-shaped underwater superoleophobic rail and a V-shaped superhydrophobic rail that delivers lossless and directional oil and water droplet transport, respectively. The V-shaped rail not only converts the kinetic energy of the impacting droplets into planar motion but also seriously deforms the droplet to create a 3D Laplace pressure difference that directionally moves the droplet. The superoleophobic and superhydrophobic wettability of a copper rod surface is crucial for achieving lossless water and oil droplet transport, which is attributable to low adhesive forces acting on the droplets. The V-shaped rail can also feasibly be used in droplet sensors, microchemical reactions, droplet-based electricity generators, and water/oil separation applications, thereby significantly expanding the applications of lossless and directional droplet transport.     

基于Ka波段毫米波云雷达多普勒谱的降雪微物理过程的分析

云中过冷水滴的识别对于预警飞机积冰及云-降水物理研究具有重要意义。本文利用美国ARM-AMF2在芬兰的35GHz测云雷达多普勒谱数据,建立了谱峰识别算法,对全局谱进行了谱分离,识别出了过冷水滴然后,经过谱矩计算得到不同类型粒子的反射率因子、多普勒速度、谱宽,最后根据经验关系反演云中液态水含量,并与微波辐射计探测结果进行对比。结果表明：(1)混合云中,雪花主导了毫米波雷达总回波强度,因此根据总雷达反射率因子反演液态水含量会造成低估;(2)冰雪晶粒子在过冷水层(SWL)中多普勒速度随反射率因子的变化梯度比在冰雪层(ISL)中大;(3)多普勒谱反演得到过冷水的液态水路径(LWP)与微波辐射计反演结果一致性较好,说明毫米波雷达能够有效估量云中液态水路径。     

Improved Interfacial Floatability of Superhydrophobic/Superhydrophilic Janus Sheet Inspired by Lotus Leaf

Interfacial materials exhibiting superwettability have emerged as important tools for solving the real‐world issues, such as oil‐spill cleanup, fog harvesting, etc. The Janus superwettability of lotus leaf inspires the design of asymmetric interface materials using the superhydrophobic/superhydrophilic binary cooperative strategy. Here, the presented Janus copper sheet, composed of a superhydrophobic upper surface and a superhydrophilic lower surface, is able to be steadily fixed at the air/water interfaces, showing improved interfacial floatability. Compared with the floatable superhydrophobic substrate, the Janus sheet not only floats on but also attaches to the air–water interface. Similar results on Janus sheet are discovered at other multiphase interfaces such as hexane/water and water/CCl₄ interfaces. In accordance with the improved stability and antirotation property, the microboat constructed by a Janus sheet shows the reliable navigating ability even under turbulent water flow. This contribution should unlock more functions of Janus interface materials, and extend the application scope of the binary cooperative materials system with superwettability.     

Janus Nanoparticles by Interfacial Engineering

Nanosized Janus particles were prepared by ligand exchange reactions of a Langmuir monolayer of hydrophobic alkanethiolate‐passivated gold nanoparticles at relatively high surface pressures with hydrophilic thiol derivatives injected into the water subphase. The ligand intercalation between adjacent particles led to impeded interfacial mobility of the particles. Consequently, ligand place‐exchange reactions were limited only to the side of the particles facing the water phase, leading to the formation of amphiphilic nanoparticles which exhibited hydrophobic characters on one side and hydrophilic on the other, analogous to the dual‐face Roman god, Janus. The unique amphiphilic characters of the Janus particles were confirmed by a variety of experimental measurements, including contact angle measurements, FTIR, UV‐visible, and NMR spectroscopies. Interestingly, the Janus particles might be dispersed in water, forming micelle‐like aggregates, as revealed in dynamic light scattering and AFM measurements.     

Reversible Switching of Liquid Crystalline Order Permits Synthesis of Homogeneous Populations of Dipolar Patchy Microparticles

The spontaneous positioning of colloids on the surfaces of micrometer‐sized liquid crystal (LC) droplets and their subsequent polymerization offers the basis of a general and facile method for the synthesis of patchy microparticles. The existence of multiple local energetic minima, however, can generate kinetic traps for colloids on the surfaces of the LC droplets and result in heterogeneous populations of patchy microparticles. To address this issue, herein it is demonstrated that adsorbate‐driven switching of the internal configurations of LC droplets can be used to sweep colloids to a single location on the LC droplet surfaces, thus resulting in the synthesis of homogeneous populations of patchy microparticles. The surface‐driven switching of the LC can be triggered by addition of surfactant or salts, and permits the synthesis of dipolar microparticles as well as “Janus‐like” microparticles. By using magnetic colloids, the utility of the approach is illustrated by synthesizing magnetically responsive patchy microdroplets of LC with either dipolar or quadrupolar symmetry that exhibit distinct optical responses upon application of an external magnetic field.     

Bioinspired Self‐Propulsion of Water Droplets at the Convergence of Janus‐Textured Heated Substrates

Controlled propulsion of liquid droplets on a solid surface offers viable applications in fog harvesting, heat transfer, microfluidics, and microdevice technologies. A prerequisite for the propulsion of liquid droplets is to break the wetting symmetry of a droplet and contact‐line pinning on the surface by harnessing surface energy gradient. Here, a series of Janus‐textured substrates is constructed to investigate the self‐propulsion of Leidenfrost droplets. It is found that the self‐propulsion of droplets occurs only on two special Janus‐textured substrates. Those are nanostructured silicon substrate bounded by smooth silicon substrate and the nanowire‐decorated microstructured silicon substrate bounded by micropillars with smooth surfaces. The difference in roughness between the two sides of the Janus‐textured substrates creates various numbers and sizes of vapor bubbles. The vapor bubbles cause the droplets to become turbulent, and a pressure gradient is generated. The sufficiently large pressure gradient propels the Leidenfrost droplet to move directionally. The propulsion direction is always toward areas with low roughness.     

Filefish‐Inspired Surface Design for Anisotropic Underwater Oleophobicity

Surfaces with anisotropic wettability, widely found in nature, have inspired the development of one‐dimensional water control on surfaces relying on the well‐arranged surface features. Controlling the wetting behavior of organic liquids, especially the motion of oil fluid on surfaces, is of great importance for a broad range of applications including oil transportation, oil‐repellent coatings, and water/oil separation. However, anisotropic oil‐wetting surfaces remain unexplored. Here, the unique skin of a filefish Navodon septentrionalis shows anisotropic oleophobicity under water. On the rough skin of N. septentrionalis, oil droplets tend to roll off in a head‐to‐tail direction, but pin in the opposite direction. This pronounced wetting anisotropy results from the oriented hook‐like spines arrayed on the fish skin. It inspires further exploration of the artificial anisotropic underwater oleophobic surfaces: By mimicking the oriented hook‐like microstructure on a polydimethylsiloxane layer via soft lithography and subsequent oxygen‐plasma treatment to make the PDMS hydrophilic, artificial fish skin is fabricated which has similar anisotropic underwater oleophobicity. Drawn from the processing of artificial fish skin, a simple principle is proposed to achieve anisotropic underwater oleophobicity by adjusting the hydrophilicity of surface composition and the anisotropic microtextures. This principle can guide the simple mass manufacturing of various inexpensive high surface‐energy materials, and the principle is demonstrated on commercial cloth corduroy. This study will profit broad applications involving low‐energy, low‐expense oil transportation, underwater oil collection, and oil‐repellant coatings on ship hulls and oil pipelines.     

Magnetocontrollable Droplet and Bubble Manipulation on a Stable Amphibious Slippery Gel Surface

Smart manipulation of liquid/bubble transport has garnered widespread attention due to its potential applications in many fields. Designing a responsive surface has emerged as an effective strategy for achieving controllable transport of liquids/bubbles. However, it is still challenging to fabricate stable amphibious responsive surfaces that can be used for the smart manipulation of liquid in air and bubbles underwater. Here, amphibious slippery surfaces are fabricated using magnetically responsive soft poly(dimethylsiloxane) doped with iron powder and silicone oil. The slippery gel surface retains its magnetic responsiveness and demonstrates strong affinity for bubbles underwater but shows small and switching resistance forces with the water droplets in air and bubbles underwater, which is the key factor for achieving the controllable transport of liquids/bubbles. On the slippery gel surface, the sliding behaviors of water droplets and bubbles can be reversibly controlled by alternately applying/removing an external magnetic field. Notably, compared with slippery liquid‐infused porous surfaces, the slippery gel surface demonstrates outstanding stability, whether in air or underwater, even after 100 cycles of alternately applying/removing the magnetic field. This surface shows potential applications in gas/liquid microreactors, gas–liquid mixed fluid transportation, bubble/droplet manipulation, etc.     

Polymer Microparticles with Controllable Surface Textures Generated through Interfacial Instabilities of Emulsion Droplets

A general and versatile route to prepare hierarchical polymer microparticles via interfacial instabilities of emulsion droplets is demonstrated. Uniform emulsion droplets containing hydrophobic polymers and n‐hexadecanol (HD) are generated through microfluidic devices. When organic solvent diffuses through the aqueous phase and evaporates, shrinking emulsion droplets containing HD and polystyrene (PS) will trigger interfacial instabilities to form microparticles with wrinkled surfaces. Interestingly, surface‐textures of the particles can be accurately tailored from smooth to high textures by varying the HD concentration and/or the rate of solvent evaporation. Moreover, composite particles can be generated by suspending different hydrophobic species to the initial polymer solutions. This versatile approach for preparing particles with highly textured surfaces can be extended to other type of hydrophobic polymers which will find potential applications in the fields of drug delivery, tissue engineering, catalysis, coating, and device fabrication.     

Contactless Interfacial Thin-Film Breaking Caused Splash-Like Demulsification of Floating Micron Emulsions via Ionic Wind

Emulsified oil leakage onto the bulk water surface causes severe issues on global ecology and health. Developing efficient, rapid, and universal separation methods of emulsions has been a significant topic in scientific studies. However, a contactless and additive-free strategy to achieve continuous floating emulsion separation and oil collection remains to be discovered. Herein, a universal contactless demulsification, transportation, and collection method to dispose floating emulsions by ionic wind, which contains active charged particles generated by corona discharge is reported. The splash-like demulsification process of floating emulsions is attributed to the rupture of water film enveloped on oil droplet surface, simultaneously and respectively. The evidence of this process recorded by a high-speed camera with 20 000 fps has a referential significance for other works. This study may clean up universal floating emulsions discharged on water in real situations such as oil stations, chemical plants, and restaurants, and furthermore increase the potential of remote control in liquid dynamics by corona discharge.     

Generation of Monodisperse Inorganic–Organic Janus Microspheres in a Microfluidic Device

This study presents a simple synthetic approach for the in situ preparation of monodisperse hybrid Janus microspheres (HJM) having organic and inorganic parts in a PDMS‐based microfluidic device. Based on the mechanism of shear‐force‐driven break‐off, merged droplets of two photocurable oligomer solutions having distinctive properties are generated into an immiscible continuous phase. Functionalized perfluoropolyether (PFPE) as the organic phase and hydrolytic allylhydridopolycarbosilane (AHPCS) as the inorganic phase are used for the generation in aqueous medium of HJM with well‐defined morphology and high monodispersity (average diameter of 162 µm and a 3.5% coefficient of variation). The size and shape of the HJM is controlled by varying the flow rate of the disperse and continuous phases. The HJM have two distinctive regions: a hydrophobic hemisphere (PFPE) having a smooth surface and a relatively hydrophilic region (AHPCS) with a rough, porous surface. In addition, pyrolysis and subsequent oxidation of these HJM convert them into SiC‐based ceramic hemispheres through the removal of the organic portion and etching off the silica shell. The selective incorporation of magnetic nanoparticles into the inorganic part shows the feasibility of the forced assembly of HJM in an applied magnetic field.