不同浸润性冷表面上水滴碰撞结冰的数值模拟

对冷水滴撞击不同表面时的动力学行为和相变过程进行了模拟。通过耦合VOF和Level-set方法追踪气液自由界面,结合焓-孔隙度相变模型,模拟水滴撞击冷表面的动力学行为及相变特征。选取亲水（接触角30°）、疏水（接触角114°）和超疏水（接触角163°）3种典型浸润性的表面,计算了多种壁温条件下的水滴撞击结冰过程。结果表明提高表面疏水性,将减小水滴与冷表面的接触时间和接触面积,降低水滴内的相变速率,延缓水滴结冰的时间。在表面温度高于-15℃时,超疏水表面可以避免冷水滴的冻结黏附,保持表面洁净。将模拟得到的最大铺展直径、回缩速率以及冻结情况,与已有实验结果进行对比验证,表明了模拟方法的有效性和准确性。     

太阳能加热液滴在亲疏水表面"黏-滑"蒸发

实验研究了亲水和疏水表面上太阳能加热去离子水及金纳米流体液滴三相接触线动力学。在亲水和疏水表面滴加2μL去离子水和纳米流体液滴,用一定功率太阳能模拟器照射液滴使其蒸发,期间采用高速摄像机实时记录液滴在不同表面上的蒸发过程。由MATLAB程序处理图像得到液滴在不同表面上蒸发过程中接触角和接触圆直径的动态变化过程。发现液滴接触线在不同亲疏水表面上存在不同运动特性。去离子水液滴在亲水表面上常接触面积模式和常接触角模式依次控制蒸发过程。去离子水液滴在疏水表面上都呈现出“黏-滑”蒸发特性,即液滴先以常接触面积模式蒸发,之后接触线快速滑动,接触线固定后再以常接触面积模式蒸发,依次往复。纳米流体液滴在亲水表面上主要以常接触面积蒸发模式为主,在疏水表面上同样呈现“黏-滑”蒸发特性。从液滴表面能角度出发,对液滴接触线“钉扎”和“去钉扎”过程进行详尽分析,得出基底润湿性和纳米颗粒沉积是影响液滴接触线在表面上运动的重要因素。     

Adhesion of blood platelets under flow to wettability gradient polyethylene surfaces made in a shielded gas plasma

Adhesion and activation of platelets are important steps in the thrombosis of blood after contact with a biomaterial surface and are governed, in part, by the wettability of the surface. Since most implanted devices are in contact with blood under flow conditions, it is important to study the effect of wettability of device surfaces on the behavior of platelets also under flow. To this end, wettability gradient polyethylene surfaces were prepared through glow discharge with partial shielding over a length of 5 cm, with advancing water contact angles varying from 95 to 45 degrees and a contact angle hysteresis of 30 degrees. The role of blood flow on the adhesion of platelets was examined by incubating these gradient surfaces in anticoagulated, whole human blood under static conditions or in blood under a flow of 10 or 40 ml/min through a 3 mm diameter circuit or for 5 or 15 min with either the hydrophobic or hydrophilic end upstream. Generally, more platelets adhered on the hydrophilic end of the wettability gradient than on the hydrophobic end, although the increment along the wettability gradient was dependent on both the flow conditions and direction. More platelets adhered under a flow of 10 ml/min than under static conditions, due to higher mass transport. Especially when the hydrophilic end was upstream, there was a more pronounced adhesion. This can be explained in terms of immediate platelet activation by shear stress imposed at the upstream end. During flow of 40 ml/min, platelet adhesion on an upstream hydrophilic end was less than on a downstream hydrophilic end. We conclude that platelets detach from the hydrophilic end at high shear stress due to the spherical form of adhered platelets. Platelets on the hydrophobic end could withstand detachment by strong, flat shaped platelet-material contact.     

Bioinspired steel surfaces with extreme wettability contrast

The exterior structures of natural organisms have continuously evolved by controlling wettability, such as the Namib Desert beetle, whose back has hydrophilic/hydrophobic contrast for water harvesting by mist condensation in dry desert environments, and some plant leaves that have hierarchical micro/nanostructures to collect or repel liquid water. In this work, we have provided a method for wettability contrast on alloy steels by both nano-flake or needle patterns and tuning of the surface energy. Steels were provided with hierarchical micro/nanostructures of Fe oxides by fluorination and by a subsequent catalytic reaction of fluorine ions on the steel surfaces in water. A hydrophobic material was deposited on the structured surfaces, rendering superhydrophobicity. Plasma oxidization induces the formation of superhydrophilic surfaces on selective regions surrounded by superhydrophobic surfaces. We show that wettability contrast surfaces align liquid water within patterned hydrophilic regions during the condensation process. Furthermore, this method could have a greater potential to align other liquids or living cells.     

纳米结构表面液体沸腾传热的分子动力学模拟

为了从纳米尺度了解表面结构和润湿性对池沸腾液体与固体壁面的传热性能,本文采用分子动力学方法研究了超亲水至超疏水不同润湿性的液体氩在光滑表面和含凹、凸半球纳米结构表面的沸腾传热过程,分析了三种表面上液氩在受热过程的形态、温度、热流密度等相关参数的变化情况。结果表明,液氩层沸腾过程大致可分为液氩层吸附于固体表面和液氩层从壁面脱离两个加热阶段,当液氩层吸附于固体表面时,温度升高、热流密度及气态氩原子产生速度均大于液氩层脱离壁面时的情况,在这两个阶段亲水表面上氩原子温度变化有明显的拐点,而疏水表面在两个阶段加热过程相差不大。亲水表面上的微结构能吸附更多液氩原子,促进了气泡产生及加速温度、热流密度的变化,而在疏水及超疏水微结构表面,微纳结构与液氩间的气膜层促进了气泡产生,计算结果为池沸腾传热及微结构选择提供了理论依据。     

Ageing of plasma-treated poly(tetrafluoroethylene) surfaces

Highly hydrophobic poly(tetrafluoroethylene) (PTFE) surfaces were modified with an air glow discharge plasma to improve their wettability. However, the hydrophilic character obtained diminishes with time, due to molecular movement in the polymer. We have determined that the ageing process is strongly affected by the environment and temperature in which the surfaces are stored. A hydrophobic environment and high temperatures promote faster recovery of the original properties of PTFE than low temperatures. Nonetheless, a hydrophilic environment, even at high temperatures, prevents the surface from losing the polar character obtained from the plasma treatment, stopping the ageing process. Moreover, this process is reversible since the character of the treated surface changes when the environment changes (i.e. from water to air). The hydrophilicity of the surfaces was evaluated by contact angle measurements of a droplet of water.     

超疏水/亲水性结构表面流动沸腾传热实验研究

用激光烧蚀方法在抛光后的铜上制备出四种无需涂覆修饰即可获得超疏水/亲水性的规则微阵列结构表面。基于流动可视化与温度数据结果,分析了表面浸润性和过冷度对流动沸腾传热性能的影响,与经典汽化核心密度关联式进行了对比。结果表明：疏水表面可削弱单相对流传热,大幅强化沸腾传热,最大传热系数提高了75.5%,沸腾起始点提前3.5 K,且汽化核心数目较裸铜表面提高了5倍以上,但有较低的临界热通量。超亲水表面可增强单相对流传热、小幅度提升流动沸腾传热。对比亲水表面与疏水表面的气泡生长过程,发现疏水表面尾端气泡容易汇聚,生长周期较长;而亲水表面没有发生明显的气泡汇聚行为,气泡生长周期较短。     

Control over wettability of textured surfaces by electrospray deposition

Microtextured surfaces were prepared by electrospray deposition (ESD) from hydrophilic and hydrophobic acrylic resin solutions. The surface morphologies and topologies were characterized using scanning electron microscopy and laser profile microscopy, respectively. Wetting behaviors on the surfaces were characterized by contact angle and sliding angle measurements. The contact angle of the water droplet on the hydrophilic resin‐coated surfaces decreased with an increase in the surface roughness. On the other hand, the contact angle on the hydrophobic resin‐coated surfaces increased with an increase in the surface roughness. In addition, a patterned surface composed of aligned fibers by ESD showed anisotropy of both wetting and sliding behaviors. These results indicate that ESD is a useful method for designing a textured surfaces and controlling the surface wettability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3811–3817, 2007     

Hydrophobic recovery of femtosecond laser processed silicone rubber insulator surfaces

This article demonstrates the loss and recovery in hydrophobicity of silicone rubber insulator surface processed by a femtosecond laser. The two stages of the wettability conversion were investigated. First, a rough micro/nano structure was formed on the original hydrophobic sample surface processed by the femtosecond laser, and the water contact angle on the surface was reduced from ~ 110° to a minimum of ~ 35°. This hydrophilicity loss was due to the increase in the hydrophilic  OH groups and the reduction of the hydrophobic  CH₃ groups on the surfaces. Second, the roughened samples were stored in a natural ambient environment. Over a certain storage time, the surface hydrophobicity recovered gradually and evolved into a superhydrophobic state. It was found that the migration of low molecular weight cycle and/or linear siloxane oligomers resulted in the recovery of the hydrophobicity property. Coupled with the increase of surface roughness caused by laser irradiation, the further evolution of the hydrophobicity was promoted. Moreover, the higher temperature accelerates the recovery of the surface hydrophobicity. The research on the conversion mechanism of the wettability on the silicone rubber insulator surface processed by femtosecond laser is of great significance for improving its reliability in practical applications.     

液滴撞击亲疏水间隔条纹表面

在高温高压环境下,将线切割成特殊形状的铝片镶嵌在树脂表面,再通过CuCl₂溶液对铝表面腐蚀,利用硬脂酸无水乙醇溶液的恒温水浴,进行表面修饰,适当处理得到亲水区域与疏水区域共存的复合表面。采用高速相机记录了液滴撞击水平与倾斜表面的动力过程,实验结果表明：液滴撞击水平放置的亲疏水复合表面时,其铺展过程与液滴撞击单一润湿性表面相似,但收缩行为差异化明显。液滴在亲疏水间隔表面收缩时,液膜会因亲疏水性并存而产生高度差。液滴撞击倾斜亲疏水复合表面时,液滴撞击的速度越大,其在斜面进行的位移量越大,速度过大的情况下液滴不会被宽度为20mm的斜面捕获;当速度为定值,Oh数越小,液滴跨越的亲疏水段越多,Oh数过小的情况下液滴不会被斜面截留;其他参数不变,比值系数H越小,液滴更易被斜面捕获。     

表面特性对结霜和融霜排液的影响

对亲水表面、裸铝表面和疏水表面上结霜和融霜排液过程进行实验研究,分析了表面特性对冷凝水珠冻结、霜层生长和融霜排液的影响。结果表明：疏水表面上冷凝水珠呈规则球缺状、冻结较晚,而亲水表面和裸铝表面上冷凝水珠形状不规则;相比于亲水表面和裸铝表面上平整霜层,疏水表面上霜层不平整,有凹穴和凸起;疏水表面上霜层平均厚度增长较亲水表面和裸铝表面缓慢;在湿空气温度和冷面温度较低的情况下,表面特性对霜层生长的影响减弱;亲水表面具有较好的排液效果,其循环再结霜量最小。     

Surface modification of a group of polymers using a low temperature cascade arc torch

Surface modification treatments were performed on six different types of polymers using low temperature cascade arc torch (LTCAT) of Ar with or without adding reactive gas of O₂ or H₂O vapor. The effects of the treatments on the wettability enhancement, surface degradation from oligomer formation, and surface stability from the mobility of surface moieties and hydrophobic recovery were investigated. Surface characterization techniques included the static Sessile droplet method and dynamic Wilhelmy balance method. Experimental results indicated that Ar LTCAT treatments of the polymers with shorter treatment times (2 s in most cases) resulted in stable and hydrophilic surfaces without any surface damage from oligomer formation, with the exception of nylon‐6. The excellent results from Ar LTCAT treatments were attributed to the CASING effect (crosslinking via activated species of inert gas). Addition of O₂ into Ar LTCAT resulted in greater wettability of the treated surfaces, but increased surface damage from oligomer formation. Adding H₂O vapor into Ar LTCAT produced extremely hydrophilic surfaces on the polymers, but pronounced surface damage. The surface oligomer formation was attributed to alkoxy degradation reactions and chain scission from overexposure to high energy species. Comparisons of the treatment outcomes for each type of polymer are discussed with respect to the degree of wettability enhancement, the stability of the treated surfaces, and the susceptibility to degradation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

铜基超疏水表面防覆冰/抗霜冻特性分析

超疏水表面具有良好的防覆冰性能,有望改善低温条件下设备和设施的可靠性。本文采用氨气腐蚀法,制备具有微纳结构的铜表面,通过低表面能氟硅烷修饰后,金属铜表面表现出超疏水特性,其水接触角可达152.1°。利用电镜扫描、接触角测量、结冰和结霜实验分别对超疏水铜表面的表面结构、湿润性能和防覆冰性能进行研究。结果表明,超疏水表面的防覆冰/抗霜冻性能不仅与表面的粗糙度有关,还受液滴在固体表面的湿润状态的影响。当液滴在具有微-纳米结构的超疏水表面处于Cassie状态时,液滴与金属表面的接触面积小,液滴结冰速率较慢,金属表面同时具有较好的防覆冰和抗结霜性;而当液滴在金属疏水表面处于Wenzel状态时,霜晶与固体表面的接触面积增加,加快霜层的生长,金属表面的抗结霜性明显降低。     

耐久型超疏水表面的研究进展

超疏水表面因其特殊的润湿性和广泛的应用引起了人们的关注。然而,在使用过程中超疏水表面容易受到机械作用或化学攻击的影响,造成低表面能物质的缺失或微纳粗糙结构的破坏而丧失超疏水性能。因此,如何构建耐久型超疏水涂层是超疏水领域的一个巨大挑战。基于此,本文主要从耐磨和自修复两个角度综述了耐久型超疏水表面的最新研究进展。首先,从引入化学键、引入弹性材料和利用基材表面构筑微纳粗糙结构等方面总结了提升超疏水表面耐磨性的途径。其次,从低表面能物质的自修复、微纳粗糙结构的重构以及本体自修复等方面总结了超疏水表面自修复性的实现途径。并对耐久型超疏水表面的产业化状况进行了讨论。最后,对耐久型超疏水表面今后的发展进行了展望,以期为制备应用广泛的耐久型超疏水表面提供参考。     

Influence of the coating method on the formation of superhydrophobic silicone–urea surfaces modified with fumed silica nanoparticles

Effect of the coating method on the formation of superhydrophobic polydimethylsiloxane–urea copolymer (TPSC) surfaces, modified by the incorporation of hydrophobic fumed silica nanoparticles was investigated. Four different coating methods employed were: (i) layer-by-layer spin-coating of hydrophobic fumed silica dispersed in an organic solvent onto TPSC films, (ii) spin-coating of silica–polymer mixture onto a glass substrate, (iii) spray coating of silica/polymer mixture by an air-brush onto a glass substrate, and (iv) direct coating of silica–polymer mixture by a doctor blade onto a glass substrate. Influence of the coating method, composition of the polymer/silica mixture and the number of silica layers applied on the topography and wetting behavior of the surfaces were determined. Surfaces obtained were characterized by scanning electron microscopy (SEM), white light interferometry (WLI) and advancing and receding water contact angle measurements. It was demonstrated that superhydrophobic surfaces could be obtained by all methods. Surfaces obtained displayed hierarchical micro-nano structures and superhydrophobic behavior with static and advancing water contact angles well above 150° and fairly low contact angle hysteresis values.     

恒热流条件下亲疏水表面液滴蒸发特性

以恒热流方式结合高速摄影技术同步观察记录3 μl的小液滴在不同亲疏水表面的蒸发过程。通过一系列的对比实验观察记录了不同亲疏水表面液滴蒸发时接触角、接触直径、蒸发时间等的动态特性。从实验分析中可以看出亲水表面液滴蒸发速率比疏水表面上液滴蒸发速率快,并且随着热通量的增大,液滴蒸发速率增大。在恒热流条件下亲疏水表面液滴蒸发以CCR模式为主,在蒸发后期呈现混合蒸发模式,全程未出现CCA模式。     

Cellular Behavior of Human Adipose-Derived Stem Cells on Wettable Gradient Polyethylene Surfaces

Appropriate surface wettability and roughness of biomaterials is an important factor in cell attachment and proliferation. In this study, we investigated the correlation between surface wettability and roughness, and biological response in human adipose-derived stem cells (hADSCs). We prepared wettable and rough gradient polyethylene (PE) surfaces by increasing the power of a radio frequency corona discharge apparatus with knife-type electrodes over a moving sample bed. The PE changed gradually from hydrophobic and smooth surfaces to hydrophilic (water contact angle, 90º to ~50º) and rough (80 to ~120 nm) surfaces as the power increased. We found that hADSCs adhered better to highly hydrophilic and rough surfaces and showed broadly stretched morphology compared with that on hydrophobic and smooth surfaces. The proliferation of hADSCs on hydrophilic and rough surfaces was also higher than that on hydrophobic and smooth surfaces. Furthermore, integrin beta 1 gene expression, an indicator of attachment, and heat shock protein 70 gene expression were high on hydrophobic and smooth surfaces. These results indicate that the cellular behavior of hADSCs on gradient surface depends on surface properties, wettability and roughness.     

Preparation of metallic coatings with reversibly switchable wettability based on plasma spraying technology

Plasma spray technology was used for the preparation of metallic coatings with reversibly switchable wettability. By spraying Fe, Cr, and Ni mixture powders with different sizes, a micro/submicro-dual scale morphology was obtained. The resultant metallic coating had a superhydrophilic nature, but could be switched into superhydrophobic by spraying an acetone solution of dodecanoic acid while the sprayed surface remained within a temperature range of 100?C200°C, although dodecanoic acid itself has a hydrophilic nature. The obtained superhydrophobic coating remained stable if the temperature was below 200°C. The surface wettability could further be switched between superhydrophilicity and superhydrophobicity within a time-scale of only seconds by heating above 220°C and re-spraying the acetone solution of dodecanoic acid in the temperature range of 100?C200°C. A chemisorbed molecular layer of dodecanoic acid was responsible for the decrease of the surface energy, and the Fourier transform infrared spectroscopy (FTIR) results suggested that heating the substrate can greatly facilitate the formation of the chemisorbed layer and preferential orientation of the dodecanoic acid molecule.     

Fabrication and superhydrophobicity of fluorinated carbon fabrics with micro/nanoscaled two-tier roughness

Superhydrophobic carbon fabric with micro/nanoscaled two-tier roughness was fabricated by decorating carbon nanotubes (CNTs) onto microsized carbon fibers, using a catalytic chemical vapor deposition and subsequent fluorination surface treatment. The superhydrophobic surfaces are based on the regularly ordered carbon fibers (8-10 μm in diameter) that are decorated by CNTs with an average size of 20-40 nm. The contact angle of water significantly increases from 148.2 ± 2.1° to 169.7 ± 2.2° through the introduction of CNTs. This confirms that the wettability of carbon fabric changes from hydrophobicity to superhydrophobicity due to structural transformation. This finding sheds light on how the two-tier roughness surface induces superhydrophobicity of rough surfaces, and how the presence of CNTs reduces the area fraction of a water droplet in contact with the carbon surface with two-tier roughness.     

十四酸铜超疏水表面的溶剂热法制备及其润湿性

超疏水表面是防止低温条件下风机叶片表面结冰、保证机组安全运行的重要材料之一。本文以十四酸乙醇溶液和铜片为前体,基于溶剂热法将十四酸铜原位生长于铜片表面,通过调控前体浓度和反应时间获得了不同润湿性的疏水表面,实现了疏水表面润湿性的有效调控。此外,采用扫描电子显微镜（SEM）观察了十四酸铜团簇的微结构及分布状态;借助X射线衍射仪（XRD）验证团簇粉末的晶格成分;通过接触角测量仪量化不同条件下样品的表面润湿性。结果表明,随着铜片表面十四酸铜团簇密集程度的增加,液滴与铜片的接触角增大,铜片润湿性降低;十四酸乙醇溶液浓度及反应时间可以显著改变十四酸铜分布状态,进而改变表面润湿性。疏水表面润湿性的变化是由于Ostwald熟化促进晶体生长,使表面的“禾苗”状聚合物逐渐生长成十四酸铜微米花。