Selective no loss transportation of water droplets based on the superhydrophobic surfaces with controllable high water adhesion

Superhydrophobic ZnO surfaces with controllable high water adhesion have been fabricated by combining both construction of ZnO structures on zinc substrates and the subsequent modification of 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (PDTMS). Different surface morphologies were obtained on the zinc substrates by changing the concentration ratio of (NH₄)₂S₂O₈/NaOH and temperature during the hydrothermal process. After being modified with PDTMS, the as-prepared surfaces show analogous superhydrophobicity but controllable high water adhesion, which ranges from 3 to 5 μL, 8 and 10 μL. Based on the different high water adhesion on the superhydrophobic surfaces, the selective no loss water transportation with different volumes has been achieved. We believed that the results reported here would be potentially used in microfluidic systems to manipulate the liquid droplets.     

A simple approach to fabricate sticky superhydrophobic polystyrene surfaces

We present a facile method for the fabrication of a sticky superhydrophobic polystyrene surface using ethanol as the non-solvent. The obtained surface shows the hierarchical textured morphology as well as the multiple scales of roughness and large numbers of microspheres. Without any chemical modification, the prepared polystyrene surface exhibits sticky superhydrophobicity with a high equilibrium contact angle of 153°. Interestingly, a water droplet on the surface cannot move at any tilt angle even when the substrate is turned upside down. The mechanism of the fabricated surface with high adhesion is discussed in detail. Moreover, the obtained polystyrene surface exhibits the strong adhesion to the liquid droplets of pH value from 1 to 14.     

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。     

Fabrication of superhydrophobic surfaces based on PDMS coated hydrothermal grown ZnO on PET fabrics

Abstract

Wetting behavior of Zinc Oxide (ZnO) based nanomaterials has been the subject of intense investigations and is an active research field for various engineering applications and modifying the surface wettability of ZnO is of great interest. In this study, one-dimensional (1?D) semiconducting ZnO nanorods are grown on a superhydrophobic polyethylene terephthalate (PET) fabric using a hydrothermal method. A facile polydimethylsiloxane (PDMS) coating is applied onto the ZnO grown PET fabrics to improve the hydrophobicity. A wide range of characterization techniques such as field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), UV-vis spectroscopy and contact angle measurement are used to explore the morphology and wetting behavior of the as-prepared samples. The measured water contact angle (WCA) is >150° indicating its superhydrophobicity. This study reports an efficient way to obtain highly hydrophobic semiconducting ZnO grown on PET fabric, which can be of great interest for many future applications.     

Collective behavior of evaporating droplets on superhydrophobic surfaces

We study the evaporation dynamics of multiple water droplets deposited in ordered arrays or randomly distributed (sprayed) on superhydrophobic substrates (SHP) and smooth silicon wafers (SW). The evaluation of mass of the droplets as a function of time shows a power-law behavior with exponent 3/2, and from the prefactor of the power-law an evaporation rate can be determined. We find that the evaporation rate on a SHP surface is slower than a normal surface for both single droplet and collection of droplets. By dividing a large droplet into more smaller ones, the evaporation rate increases and the difference between the evaporation rates on SHP and SW surfaces becomes higher. The evaporation rates depend also on the distance of the droplets which increase with increasing this distance.     

超疏水表面自修复及应用的研究进展

超疏水表面因具有诸多优异特性而展现出良好的应用前景,但在实际应用中容易受到外界机械力损坏或化学侵蚀,赋予超疏水表面自修复性能可以较好地改善表面耐久性,延长其使用寿命。本文针对修复构成超疏水表面的微观结构与低表面能物质展开论述,介绍了在湿度、温度、光等外界因素的引发下超疏水表面对低表面能物质的修复行为与特点,以及以形状记忆聚合物为主制备的超疏水表面对微观结构进行修复的过程。此外,介绍了具有自修复性能的超疏水表面在防腐蚀、油水分离、防覆冰等领域的应用。最后,讨论了通过优化表面结构和化学组成开发自修复超疏水表面的挑战和前景,环保型且无需外界刺激即可迅速对微观结构与低表面能物质进行双重修复的超疏水表面具有重要的研究意义。     

聚乙烯基超疏水材料的制备及研究进展

主要介绍了超疏水性能的基本原理,及以聚乙烯材料为基体制备超疏水材料的方法,包括自下而上、自上而下和两者结合等方法,并指出了聚乙烯基超疏水材料的应用前景和挑战。     

Capillary pumping between droplets on superhydrophobic surfaces

The famous two-balloon experiment involves two identical balloons filled up with air and connected via a hollow tube, and upon onsetting the experiment one of the balloons shrinks and the other expands. Here, we present the liquid version of that experiment. We use superhydrophobic (SHP) substrates to form spherical droplets and connect them with a capillary channel. Different droplet sizes, substrates of different hydrophobicities, and various channel pathways are investigated, and morphometric parameters of the droplets are measured through image processing. In the case of SHP substrates, the pumping is from the smaller droplet to the larger one, similar to the two-balloon experiment. However, if one or both of the droplets are positioned on a normal substrate the curvature radius will indicate the direction of pumping. We interpret the results by considering the Laplace pressures and the surface tension applied by the channel at the connecting points.     

Cell interactions with superhydrophilic and superhydrophobic surfaces

Interactions of cells with biomaterials dictate their biocompatibility and biofunctionality, and are strongly influenced by surface properties. Moreover, it is important to control cell adhesion to surfaces for biological studies and diagnosis. Surface properties influence protein adsorption in terms of conformation and quantity adsorbed that further affects cell adhesion and proliferation. Several works have demonstrated that wettability influences cell attachment and proliferation. However, most studies have reported the influence of the surface energy of smooth substrates within a limited range of wettabilities. By controlling the roughness and the hydrophilicity of the surface, one can obtain biomimetic substrates with a wettability ranging from superhydrophobic to superhydrophilic. This review intends to summarize recent works, where the interaction of cells with surfaces with extreme wettabilities was investigated. Such information may be relevant in different biomedical and biological applications including diagnosis, cell biology, or tissue engineering.     

体相超疏水材料及其在大气污染控制领域的应用研究进展

体相超疏水材料因其优异的疏水性能,可广泛应用于工业防锈、管道运输、光电材料、建筑材料、纺织等领域,成为目前功能材料的研究热点之一。本文首先针对体相超疏水材料的结构特性及制备方法进行了综述。其次,针对体相超疏水材料在对挥发性有机物（VOCs）、NO_x和二氧化硫（SO₂）的净化与检测、对二氧化碳（CO₂）的捕集和还原等大气污染检测与控制领域的应用进展进行了概述。在此基础上,一方面对现有典型气体污染物控制技术的特点及其存在的问题以及体相超疏水材料与现有大气污染控制技术相结合所具备的优势进行了阐述;另一方面,对超疏水材料目前存在的耐久性差、制备过程复杂、制备原料昂贵且污染大等缺点,对体相超疏水材料的改进及应用提出了展望。     

环氧树脂涂层表面亲水性对微藻黏附性能的影响

在固体材料表面黏附成膜是微藻细胞的一种生理特性。近些年基于微藻生物膜的生物过程,如生物膜贴壁培养和防附着技术受到了很多关注。微藻在固体材料表面的黏附受藻细胞与材料表面之间的相互作用的影响,建立黏附强度与材料表面性质参数间的关系对于通过材料选择来强化或控制微藻生物膜具有非常重要的意义。本工作的目的是揭示和明确材料亲疏水性对微藻黏附的影响,提出了一种双酚A环氧(EP)树脂表面亲疏水改性的方法。通过将亲水性的二乙醇胺(DEA)或疏水性的聚甲基聚硅氧烷(PMHS)加入到EP树脂中反应,EP树脂表面水接触角在36.80?~98.34?范围内可通过加入不同量的DEA或PMHS实现任意可调,材料的表面水接触角与DEA或PMHS加入量之间有线性关系。重要的是这种改性方法获得的材料,其形貌、结构、表面粗糙度等表面性质几乎没有变化,从而在研究和关联微藻黏附量与材料表面亲疏水性(表面水接触角)之间的关系时可以排除亲疏水性之外的其他表面性质的影响;其次,考察了小球藻和栅藻在不同亲疏水性材料表面的黏附行为,结果表明小球藻和栅藻在亲水性和疏水性材料表面均能黏附成膜,但在亲水性材料表面黏附更多更快;建立了微藻最大黏附容量与材料表面接触角之间关联关系,表明微藻最大黏附容量随材料表面水接触角的增大而线性降低,栅藻的表面黏附容量比小球藻大。     

Preparation and characterization of superhydrophobic surfaces based on hexamethyldisilazane-modified nanoporous alumina

Superhydrophobic nanoporous anodic aluminum oxide (alumina) surfaces were prepared using treatment with vapor-phase hexamethyldisilazane (HMDS). Nanoporous alumina substrates were first made using a two-step anodization process. Subsequently, a repeated modification procedure was employed for efficient incorporation of the terminal methyl groups of HMDS to the alumina surface. Morphology of the surfaces was characterized by scanning electron microscopy, showing hexagonally ordered circular nanopores with approximately 250 nm in diameter and 300 nm of interpore distances. Fourier transform infrared spectroscopy-attenuated total reflectance analysis showed the presence of chemically bound methyl groups on the HMDS-modified nanoporous alumina surfaces. Wetting properties of these surfaces were characterized by measurements of the water contact angle which was found to reach 153.2 ± 2°. The contact angle values on HMDS-modified nanoporous alumina surfaces were found to be significantly larger than the average water contact angle of 82.9 ± 3° on smooth thin film alumina surfaces that underwent the same HMDS modification steps. The difference between the two cases was explained by the Cassie-Baxter theory of rough surface wetting.     

超亲/疏水性表面池沸腾传热研究

为研究超亲/疏水性表面对沸腾传热的影响,用H₂O₂氧化的方式制备了超亲水表面,用氨水加高分子修饰的方式制备了超疏水表面。在常压下以蒸馏水为工质,采用高速摄影仪对其进行了池沸腾传热实验。结果表明,超疏水表面亲气疏水,在沸腾起始点易于产生气泡,且气泡不易脱离,此时壁面过热度ΔTs仅为2.4K,但随热流密度的增大,气泡易于聚合,所产生的大气泡阻碍了传热的进行,传热开始恶化,临界热流密度（CHF）较低;而H₂O₂氧化的表面由于刀片状微纳结构的存在,增加了表面的粗糙度,不仅增大了相变传热表面积、增加了核化点数量,而且具有超亲水特性,气泡脱离频率较大,大大强化了沸腾传热,最大换热系数约是光表面的1.7倍,且相应地提高了CHF,可达131.0W/cm²,表现出较好的传热特性。     

超疏水/超双疏表面自修复方式的研究进展

超疏水/超双疏材料存在耐久性和稳定性的问题,因此很大程度影响了超疏水/超双疏材料的实际应用。受自然界中荷叶、三叶草等超疏水表面在受到破坏后,表面粗糙结构和表面组成可以恢复直到生物死亡的启发,科研学者通过不断探索研究出修复超疏水/超双疏材料的一些方式。本文从低表面能物质和表面微观结构的自修复角度出发,综述了影响超疏水/超双疏表面的自修复方式。当超疏水/超双疏表面受到物理破坏或者化学破坏时,失去超疏水以及超疏油性能,在温度、相对湿度、机械、UV等诱导条件下,低表面能物质迁移至表面完成自修复过程以及表面微观结构的自修复,从而使超疏水以及超疏油性能得以恢复。价格低廉的环保材料和系统性地研究自修复的机理是将来超疏水/超双疏自修复材料的主要研究方向。     

Capillary bonding of wet surfaces - the effects of contact angle and surface roughness

Capillary bonding of wet solids through a water film is common and important for a variety of problems. An existing experimental technique for the measurement of capillary bonding forces was improved and used to show how fractional wetted area and capillary bonding force vary with water 'tension' for glass, polyethylene, and aluminum on porous ceramic. The effects of contact angle and roughness were explored. The results show that increasing the contact angle clearly reduces the capillary bonding, but the effects of surface roughness were much more complicated. Roughness can increase or decrease capillary bonding, depending on the exact conditions.     

波浪结构超疏水表面对液滴聚并弹跳的影响

液滴自发聚并在自然和工业中广泛存在,如何高效去除聚并液滴是强化滴状冷凝换热、防结冰等的重要环节。采用数值模拟方法研究了不同半径比液滴在超疏水平壁面和超疏水波浪形壁面上的聚并起跳行为。研究发现,在平壁面上聚并的液滴水平速度与竖直速度差1～2个数量级,液滴的水平方向位移小,聚并后难以有效去除;在波浪形壁面上,由于液桥撞击在斜面上,产生较大的水平分力,聚并后其水平速度保持与竖直速度在同一数量级,水平位移显著增大;并且波浪结构对液滴弹跳过程影响显著,随波浪高宽比的增大液滴水平位移增大且弹跳高度减小,有效促进了液滴的水平运动,且当高宽比为0.21时,促进作用接近峰值。研究结果为聚并液滴的有效去除提供了新参考。     

Surface properties of an anhydride-epoxy resin cured against different mould surfaces

An epoxy resin consisting of diglycidylether of bisphenol A (DGEBA) and methyltetrahydrophthalic anhydride (MTHPA) was cured against moulds with different surface characteristics: poly(ethylene terephthalate) (PET), perfluorinated ethylene propylene copolymer (FEP), and air. The epoxy surfaces were analysed using contact angle measurements and X-ray photoelectron spectroscopy (XPS). The results presented are interpreted in terms of differences in surface energy between the surface of the mould and the epoxy resin. With PET as the mould surface, the surface content of ester groups resulting from the anhydride increased as compared to the average bulk content. With the non-polar FEP mould, the amount of ester groups decreased instead. Shear tests on overlap joints obtained by adhesive bonding with polyurethane and epoxy adhesives showed, however, a high adhesive joint strength, both for epoxy surfaces obtained with FEP as mould, and for ground surfaces with a bulk composition. The surfaces generated in PET moulds yielded only poor adhesive joint strength. These differences in joint strength could be related to the concentration of reactive functional groups (-OH, -COOH) in the outermost surface of the cured epoxy resin.     

超疏水表面液滴合并诱导弹跳现象分析

在紫铜基表面上制备了具有微纳结构的十八烷基硫醇自组装超疏水表面,采用高速摄像和显微技术研究了水平表面上液滴合并运动特性。实验结果表明,超疏水表面上液滴合并过程中释放出的表面能可以克服表面黏附作用诱发液滴弹跳现象,液滴越小,弹跳高度越大。考虑液滴表面黏附功、液滴运动引起的黏性耗散能等,根据能量守恒原理进行了理论分析。理论分析结果表明,液滴合并诱导弹跳现象存在最小液滴半径约为39.9 μm;随着液滴半径的增大,液滴弹跳高度增大,液滴半径为83.7 μm时达到弹跳最大高度点,随着液滴半径继续增大,液滴弹跳高度减小,直至最大半径约3.9 mm时,无液滴弹跳现象发生而是在合并位置发生脉动。     

Fabrication of superhydrophobic surfaces with tunable water droplet adhesion force by a two-step method

In this paper, we present a convenient approach to prepare hierarchical structured superhydrophobic coatings with tunable adhesion force, composed of micro-size glass beads, nano-size SiO₂ particles and epoxy resin. Surfaces of two types with different roughness were fabricated, one type is only with single-scale roughness demonstrating lotus effect with low sliding angle, the other type is hierarchically micro-nano-structured roughness exhibiting petal effect with high adhesion force. The surface roughness is pivotal for controlling the wetting behavior and regulating the contact angle including the contact angle hysteresis. Varying the density of micro-size glass beads could adjust the roughness of the surface, which means the adhesion force of the prepared surface could be easily controlled based on the proposed method. Through variation of glass beads’ amount, the surface could be designed to pin the water droplet with different adhesion force when the surface turned upside down. The surface wettability, surface morphology, adhesion force of the prepared samples are investigated and mechanism of the Cassie-to-Wenzel state transition are discussed in detail. Furthermore, the convenient method provides a possibility for controlling surface morphology, composition and corresponding surface adhesion which could be applied to various substrates such as tile, wood, steel and fabric.