Sustainable Droplet Manipulation on Ultrafast Lubricant Self-Mediating Photothermal Slippery Surfaces

Designing intelligent slippery surfaces for droplet manipulation is critical for many applications from drug delivery to bio-analysis, while is of great challenging in sustainability for inescapable wastage of lubricant layer. Herein, an ultrafast lubricant self-mediating (self-replenishing/-absorbing) photothermal slippery surface is designed that achieves sustainable transport of droplet under the irradiation of near infrared light (NIL) even if the lubricant layer is wiped clean completely, as well as at other man-made extreme conditions. The ultrafast lubricant self-mediating performance is caused by synergistic effects of interconnection of porous structure and photothermal expansion of the material. When lubricant on surface is lost, photothermal expansion of material can quickly squeeze the lubricant inside the base to flow into and out of the interconnected porous structure to generate a fresh lubricant layer. Attractively, when the NIL is turned off, the rebuilt lubricant layer can be swiftly self-absorbed into the porous to inhibit unnecessary wastage. Moreover, an arbitrary split of droplet in desired configurations can be achieved by controlling the NIL irradiating route. This sustainable droplet manipulation induced by ultrafast lubricant self-mediating can be extensively applied in microfluidics and micro-reactor settings.     

Reconfigurable Surfaces Based on Photocontrolled Dynamic Bonds

Photocontrolled surfaces have attracted increasing interest because of their potential applications in lithography, photopatterning, biointerfaces, and microfluidics. Light provides high spatiotemporal resolution to control functions of such surfaces without getting into direct contact. However, conventional photocontrolled surfaces can only be switched between two states (on and off). The development of photocontrolled reconfigurable surfaces that can be switched among multiple states is highly desirable because these surfaces can adapt to rapid environmental changes or different applications. Herein, recent developments of photocontrolled reconfigurable surfaces are reviewed. Specially, reconfigurable surfaces based on photocontrolled reversible reactions including thiol‐quinone methide, disulfide exchange, thiol‐disulfide interconversion, diselenide exchange, and photosubstitution of Ru complexes are highlighted. As a perspective, other photocontrolled dynamic bonds that can be used to construct reconfigurable surfaces are summarized. Remaining challenges in this field are discussed.     

Droplets Crawling on Peristome‐Mimetic Surfaces

Controlling the mobility of liquids along surfaces is widely exploited in various technologies to achieve self‐lubrication, phase‐change heat transfer, and microfluidics. Despite commendable progress in directional liquid transport on peristome‐mimetic surfaces, liquid merely spreads directionally with a wetted trail remaining. It is a challenge to achieve directional contracting of spreading liquid at the rear side and ultimately unidirectional motion in bulk from one site to another. Here it is shown that liquids resting on the peristome‐mimetic surfaces can crawl directionally and rapidly in an inchworms‐like way under the action of sudden spontaneous bubbles levitation. Vacuuming or chemical reaction induces sudden nucleation, growth, coalescence (Ostwald ripening process), and rupture of bubbles in the asymmetric microcavities of the peristome‐mimetic surface with directional overpressure beneath the liquid, resulting in the guided contracting and spreading of the liquid. Bubbles regulate this new mode of liquid directional motion. The strategy offers opportunities for liquids directional motion for various applications, such as in microfluidic devices, oil–water separation, and water collection systems.     

Strain Engineering of Wave‐like Nanofibers for Dynamically Switchable Adhesive/Repulsive Surfaces

Engineering surfaces that enable the dynamic tuning of their wetting state is critical to many applications including integrated microfluidics systems, flexible electronics, and smart fabrics. Despite extensive progress, most of the switchable surfaces reported are based on ordered structures that suffer from poor scalability and high fabrication costs. Here, a robust and facile bottom‐up approach is demonstrated that allows for the dynamical and reversible switching between lotus leaf (repulsive) and rose petal (adhesive) states by strain engineering of wave‐like nanofiber layers. Interestingly, it is found that the controlled switching between these two distinctive states is sensitive to the shape of the nanofibers. Moreover, it is observed that the structural integrity of the nanofibers is fully preserved during multicycle dynamic switching. The application of these optimal structures is showcased as mechanical hands demonstrating the capture of water microdroplets and their subsequent release in a well‐controlled manner. It is envisioned that this low‐cost and highly scalable surface texture is a powerful platform for the design of portable microfluidics systems, and the fabrication of large‐scale devices for ambient humidity harvesting and water purification.     

基于介质上电润湿的液滴产生器的研究

根据介质上电润湿的基本原理,对用于数字微流控系统的"三明治"结构器件中影响液滴输运和产生的因素进行了理论分析,并研制出了一种新型液滴产生器原型:液体被夹在上下两个电极板之间;下极板采用硅作为衬底、LPCVD掺杂多晶硅微电极阵列上热氧化生长的的SiO2薄膜作为介质层;上极板采用ITO透明导电玻璃板作为地电极;另外,在上下极板的表面都均匀旋转涂覆了一层30 nm厚的Teflon薄膜为表面疏水层.实验结果表明,在空气气氛中,该器件在10 Hz 70 V的脉冲电压下成功地实现了从蓄水池中对去离子水滴的分发.     

A Multiscale Strategy for Constructing Finned Microporous Superhydrophobic Surface for Highly-Efficient Condensation Heat Transfer Enhancement Enabled by Lifespan Regulation of Droplets

Spontaneous droplet jumping on micro-/nano-structured superhydrophobic surfaces has been exploited as an efficient means for enhancing steam condensation heat transfer. However, the good performance of such surfaces quickly decays with raising the degree of subcooling, due to the mismatch between the characteristic length scales and droplet sizes when they grow up. Herein, a novel strategy for multiscale droplet regulation is proposed by combining sub-millimeter fin structure with a hierarchical microporous superhydrophobic surface. A superior condensation heat transfer performance is attained on such hierarchical superhydrophobic finned tube (F-SHB), in comparison to the baseline case of superhydrophobic non-finned (SHB) tube under well-controlled test conditions. Although the droplet jumping is not as vigorous as that on the SHB tube, the finned geometry of the F-SHB tube leads to a condensation heat transfer enhancement even under high degrees of subcooling up to 36 K, because of the accelerated departure of large droplets by imposing Laplace force gradient in the presence of V-shaped sub-millimeter fins. This multiscale enhancement strategy is shown to enable a cascading regulation over the entire lifespan of condensate droplets. The fabrication of F-SHB tubes is facile and easy to be scaled up, showing great potential in practical steam condensation applications.     

Rational Synthesis of Large‐Area Periodic Chemical Gradients for the Manipulation of Liquid Droplets and Gas Bubbles

Synthetic approaches based on the patterned deposition of volatile molecules from the vapor phase are used extensively in the creation of surface‐chemical gradients; however, the ability to generate diffusion‐controlled 1D and 2D gradients from multiple sources remains a challenge. The current work reports a one‐step approach to the synthesis of continuous and periodic chemical gradients with simple and intricate geometries using multiple sources within custom reaction chambers. Specifically, this approach provides precise, simultaneous control over the physicochemical conditions (e.g., concentration, evaporation rate, and direction of diffusion flux of the chemical moieties) and the geometrical parameters (e.g., size, shape, and position) during surface functionalization, thus enabling materials with predictable surface‐chemical gradients applicable to the manipulation and/or organization of liquid droplets and that can generate assemblies of functional solids (e.g., silver nanoparticles) that are transferrable via stamping. These surfaces can be useful to various fields, for example, molecular diagnostics and microfabrication. Furthermore, this work extends the application of these surfaces to the precise placement and manipulation of gas bubbles that can have potential use in, for example, controlling bubble nucleation in processes designed to manage heat transfer.     

Strong,Compressible, and Ultrafast Self-Recovery Organogel with In Situ Electrical Conductivity Improvement

Coordination complexes are widely used to tune the mechanical behaviors of polymer materials, including tensile strength, stretchability, self-healing, and toughness. However, integrating multivalent functions into one material system via solely coordination complexes is challenging, even using combinations of metal ions and polymer ligands. Herein, a single-step process is described using silver-based coordination complexes as cross-linkers to enable high compressibility (>85%). The resultant organogel displays a high compressive strength (>1 MPa) with a low energy loss coefficient (<0.1 at 50% strain). Remarkably, it demonstrates an instant self-recovery at room temperature with a speed >1200 mm s⁻¹, potentially being utilized for designing high-frequency-responsive soft materials (>100 Hz). Importantly, in situ silver nanoparticles are formed, effectively endowing the organogel with high conductivity (550 S cm⁻¹). Given the synthetic simplification to achieve multi-valued properties in a single material system using metal-based coordination complexes, such organogels hold significant potential for wearable electronics, tissue-device interfaces, and soft robot applications.     

Super-Stretchable,Anti-Freezing,Anti-Drying Organogel Ionic Conductor for Multi-Mode Flexible Electronics

Due to their intrinsic flexibility, tunable conductivity, multiple stimulus-response, and self-healing ability, ionic conductive hydrogels have drawn significant attention in flexible/wearable electronics. However, challenges remain because traditional hydrogels inevitably faced the problems of losing flexibility and conductivity because of the inner water loss when exposed to the ambient environment. Besides, the water inside the hydrogel will freeze at the water icing temperatures, making the device hard and fragile. As a promising alternative, organogels have attracted wide attention because they can, to some extent, overcome the above drawbacks. Herein, a kind of organogel ionic conductor (MOIC) by a self-polymerization reaction is involved, which is super stretchable, anti-drying, and anti-freezing. Meanwhile, it can still maintain high mechanical stability after alternately loading/unloading at the strain of 600% for 600 s (1800 cycles). Using this MOIC, high-performance triboelectric nanogenerator (TENG) is constructed (MOIC-TENG) to harvest small mechanical energy even the MOIC electrode underwent an extremely low temperature. In addition, multifunctional flexible/wearable sensors (strain sensor, piezoresistive sensor, and tactile sensor) are realized to monitor human motions in real time, and recognize different materials by triboelectric effect. This study demonstrates a promising candidate material for flexible/wearable electronics such as electronic skin, flexible sensors, and human-machine interfaces.     

Bioinspired Supramolecular Slippery Organogels for Controlling Pathogen Spread by Respiratory Droplets

Surface-deposited pathogens are sources for the spread of infectious diseases. Protecting public facilities with a replaceable or recyclable antifouling coating is a promising approach to control pathogen transmission. However, most antifouling coatings are less effective in preventing pathogen-contained respiratory droplets because these tiny droplets are difficult to repel, and the deposited pathogens can remain viable from hours to days. Inspired by mucus, an antimicrobial supramolecular organogel for the control of microdroplet-mediated pathogen spread is developed. The developed organogel coating harvests a couple of unique features including localized molecular control-release, readily damage healing, and persistent fouling-release properties, which are preferential for antifouling coating. Microdroplets deposited on the organogel surfaces will be spontaneously wrapped with a thin liquid layer, and will therefore be disinfected rapidly due to a mechanism of spatially enhanced release of bactericidal molecules. Furthermore, the persistent fouling-release and damage-healing properties will significantly extend the life-span of the coating, making it promising for diverse applications.     

Self‐Assembling Azaindole Organogel for Organic Light‐Emitting Devices (OLEDs)

This study reports on the use of a self‐assembling organogel, 5‐(4‐nonylphenyl)‐7‐azaindole ( 1 ), as a new emitter in small‐molecule organic light emitting devices (OLEDs). The theoretical calculations along with the photophysical characterization studies suggest the coexistence of the monomer and dimer species at high concentration of compound 1 . The presence of this type of dimer (formed via H‐bonding) is responsible for the increased emission. However, the most notable feature is the 3D network of vastly interconnected fibers formed in the organogel that modifies the photophysical properties. Based on this, several OLED architectures are made in order to understand the mechanism involved in the electroluminescence (EL) behavior of 1 . Although the position of the EL spectra differs from that of the photoluminescence (PL) spectra, the trends observed in the device properties perfectly match with dimer formation. In this framework a better device performance is associated to a higher efficiency of dimer formation, which optimizes in the OLED prepared from the organogel. Therefore, these results show that the rational combination of a moiety showing a strong PL intensity increased upon aggregation with organogel properties is an efficient strategy to create alternative emitters for OLED devices.     

Stable Omniphobic Anisotropic Covalently Grafted Slippery Surfaces for Directional Transportation of Drops and Bubbles

Directional transportation and collection of liquids and bubbles are highly desirable in human life and industrial production. As one of the most promising types of functional surfaces, the reported anisotropic slippery liquid‐infused porous surfaces (SLIPSs) demonstrate unique advantages in liquid directional transportation. However, anisotropic SLIPSs readily suffer from the depletion of lubricant when used to manipulate droplets and bubbles, which leads to unstable surface properties. Therefore, fabricating stable anisotropic slippery surfaces for the directional transportation of drops and bubbles remains a challenge. Here, stable anisotropic covalently grafted slippery surfaces are fabricated by grafting polydimethylsiloxane molecular brushes onto directional microgrooved surfaces. The fabricated surfaces show remarkable anisotropic omniphobic sliding behaviors towards droplets with different surface tensions ranging from 72.8 to 37.7 mN m^?1 in air and towards bubbles underwater. Impressively, the surface maintains outstanding stability for the transportation of droplets (in air) and air bubbles (underwater) even after 240 d. Furthermore, anisotropic self‐cleaning towards various dust particles in air and directional bubble collection underwater are achieved on this surface. This stable anisotropic slippery surface has great potential for applications in the directional transportation of liquids and bubbles, microfluidic devices, directional drag reduction, directional antifouling, and beyond.     

Bioinspired Multiscale Wet Adhesive Surfaces: Structures and Controlled Adhesion

In nature, many organisms are able to accommodate a complex living environment by developing biological wet adhesive surfaces with unique functions such as fixation and predation. Significantly, most of these outstanding functions originate from the specialized micro/nanostructures and/or chemical components of these natural organisms. To design artificial surfaces with remarkable wet adhesive properties, the underlying mechanisms of the fascinating adhesion phenomena are further explored and summarized to provide continuous inspiration. Herein, a systematic overview of biological wet adhesive surfaces and the corresponding artificial counterparts from the perspective of surface micro/nanostructures is provided. First, the research progress of the typical biological wet adhesive surfaces such as the octopus, tree frogs, and mayfly larvae is introduced. Then, the fundamental models of surface adhesion in natural organisms and the commonly used instruments for measuring adhesion force are discussed. Later, the corresponding artificial wet adhesive surfaces inspired by these representative organisms are highlighted. After that, the typical methods for fabricating these surfaces are briefly introduced. Finally, future challenges and opportunities to develop bioinspired multiscaled wet adhesive surfaces with controlled adhesion are presented.     

CO2激光-MAG电弧复合焊接过程中熔滴受力及过渡特征研究

以5.0mm高强钢板为试验材料,进行了CO2激光与金属活性气体(MAG)电弧复合焊接试验。通过高速摄像和熔滴的受力分析研究了激光能量、电弧能量、光丝间距对复合焊接过程中熔滴过渡特征的影响。结果表明,激光的加入稳定了电弧,降低了射滴过渡的临界焊接电流值,由于激光对电弧的引导和压缩作用,改变了熔滴内电流线分布及电磁收缩力的大小及方向,进而影响了熔滴过渡特征。同时激光匙孔中喷射出大量的金属蒸气产生反作用力,改变了熔滴原来的受力状态,使熔滴过渡模式发生改变。随着焊接电流的增加,电弧变得更加稳定,能量更加集中,等离子体流力成为熔滴过渡的主导力。光丝间距的大小影响了熔滴过渡的频率,在光丝间距为4mm时熔滴频率最大。     

Rapid Near‐Infrared Light Responsive Shape Memory Polymer Hybrids and Novel Chiral Actuators Based on Photothermal W18O49 Nanowires

Photoresponsive actuators are built by introducing oligo(ethylene glycol) (OEG)‐modified W₁₈O₄₉ nanowires into cross‐linked polyethylene glycol diacrylate (cPEGDA) polymer matrices. Due to the good compatibility, OEG‐W₁₈O₄₉ NWs disperse well and increase the crystallinity of cPEGDA matrices even in high loading concentrations (4.0 wt%). The cPEGDA/W₁₈O₄₉ nanocomposites show efficient photothermal transition and rapid shape memory behaviors. They can raise the local temperature to 160 °C in only 8.5 s and recover the initial shape within 10 s. Making use of the broad and strong absorption property of W₁₈O₄₉, the cPEGDA/W₁₈O₄₉ NW actuators respond to both ultraviolet and near‐infrared light and make contraction and bending motions. Furthermore, by utilizing oriented chain segments of the crystalline polymer and vector sum of shape recovery forces, the cPEGDA/W₁₈O₄₉ NW hybrid actuators exhibit stable helical deformation (right‐handed and left‐handed).     

Inherently UV Photodegradable Poly(methacrylate) Gels

Organogels (hydrophobic polymer gels) are soft materials based on polymeric networks swollen in organic solvents. They are hydrophobic and possess a high content of solvent and low surface adhesion, rendering them interesting in applications such as encapsulants, drug delivery, actuators, slippery surfaces (self-cleaning, anti-waxing, anti-bacterial), or for oil-water separation. To design functional organogels, strategies to control their shape and surface structure are required. Herein, the inherent UV photodegradability of poly(methacrylate) organogels is reported. No additional photosensitizers are required to efficiently degrade organogels (d ≈ 1 mm) on the minute scale. A low UV absorbance and a high swelling ability of the solvent infusing the organogel are found to be beneficial for fast photodegradation, which is expected to be transferrable to other gel photochemistry. Organogel arrays, films, and structured organogel surfaces are prepared, and their extraction ability and slippery properties are examined. Films of inherently photodegradable organogels on copper circuit boards serve as the first ever positive gel photoresist. Spatially photodegraded organogel films protect or reveal copper surfaces against an etchant (FeCl_{3 aq.}).     

介质上电润湿液滴输运、合并及振荡实验研究

利用MEMS技术制作了平板电润湿芯片,建立了可视化实验研究平台,运用高速CCD对分裂式电极施加交流电压后的液滴传输和合并过程以及相邻电极接地式芯片上液滴的交流振荡过程进行了可视化实验研究。除了对液滴形状的观测外,还重点关注了接触线的运动规律。研究发现,接触角滞后现象将导致接触线在液滴输运、合并以及振荡过程中出现停顿现象,在液滴振荡过程中,只有施加电压足够大时,才能克服这种迟滞现象。当液滴初始位置偏离电极对中心时,在一定条件下交流电作用将造成液滴形态左右摇摆、接触线非对称运动的非对称振荡现象。     

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.     

激励态向列微滴散射理论的修正及其参量拟合

用反常衍射(ADA)理论与实验数据优化拟合方法分析了聚合物分散液晶(PDLC)微滴在633nm激光照射下的散射特性与微滴尺寸、聚合物折射率的关系。在聚合物分散液晶中除了液晶微滴本身的散射以外，还有例如界面散射、杂质散射、材料折射率不均匀等附加散射因子，考虑这些因素以后对反常衍射散射理论进行了修正，提出用参量拟合来测量聚合物分散液晶中聚合物折射率、微滴半径以及液晶体积百分数等参量的方法。测量了微滴的直径在2μm左右聚合物分散液晶的参量。结果表明，对聚合物分散液晶聚合物折射率的误差在5％以内，而对液晶体积分数的测试误差较大，达到10％左右。