超疏水-疏水组合表面蒸汽冷凝的实验研究

液滴的快速脱落和移除对蒸汽滴状冷凝传热具有重要的影响,超疏水表面由丁二具有接触角大,接触角滞后小的优点而用于驱动冷凝液滴的自发运动,但是,常压蒸汽在超疏水表面冷凝时,液滴的润湿形态还没有定论。本文设计了超疏水疏水条纹间隔排列的超疏水一疏水组合表面,研究了常压蒸汽在组合表面上的冷凝过程,观测了液滴的运动特性,测量了超疏水一疏水组合表面上常压蒸汽冷凝传热性能。实验结果显示疏水区液滴在表面张力差的作用下从疏水区向超疏水区自发迁移,说明超疏水区液滴处于Wenzel润湿形态,超疏水一疏水组合表面蒸汽冷凝传热性能比完全超疏水和完全疏水表面传热性能的面积加权平均值大。说明液滴的自发迁移运动强化了疏水区的传热性能。     

接触角滞后对组合表面液滴运动的影响

本文通过控制NaOH和(NH_4)_2S_2O_8溶液的刻蚀时间,制备了具有不同接触角滞后超疏水区的0.5 mm-0.5mm超疏水疏水组合表面,可视化研究了常压纯蒸汽下液滴脱落半径,冲刷周期,尺寸分布.电镜表征结果表明,刻蚀时间越长,所制备超疏水表面的微纳结构越细,导致液滴接触角滞后增加。在0.5 mm-0.5 mm超疏水-疏水组合表面冷凝过程中,存在两种排液行为:液滴横向抽吸和液滴跨区脱落。随着超疏水区接触角滞后的增加,对液滴的抽吸作用越强。液滴跨区脱落直径随着超疏水区接触角滞后的增加有减小趋势,表面冲刷周期随超疏水区接触角滞后的增加而减小;与完全疏水表面相比,组合表面疏水区域液滴尺寸较小,主要集中在50μm以内。     

疏水性润湿梯度表面液滴脱离过程的实验研究

基于标准MEMS工艺设计并加工了一种具有微结构的疏水润湿梯度表面,通过光学可视化测试系统,采用高速图像采集装置和标准振动台研究了液滴与润湿梯度表面脱离过程中,形态、接触角、受力等参数的变化规律。结果表明:液滴在与疏水润湿梯度表面脱离过程中,将出现拉伸现象,处于相对疏水侧的边缘脱离速度要快于处于相对亲水侧。脱离过程中液滴高度、宽度和接触角变化可明显分为两个区域,两区域内液滴高度、宽度和左右两侧接触角变化呈现出显著不同。通过液滴与微结构顶部间受力分析发现,润湿梯度造成的液滴受力不均是导致液滴边缘脱离速度出现不对称的原因。     

纳米结构超疏水表面冷凝现象的三维格子玻尔兹曼方法模拟

采用三维多相流格子玻尔兹曼方法 (lattice Boltzmann method, LBM),对纳米结构超疏水表面液滴的冷凝行为进行模拟研究.通过Laplace定律和光滑表面的本征接触角理论对三维LBM模型进行定量验证.模拟分析了超疏水表面纳米阵列的几何尺寸和润湿性的局部不均匀性对冷凝液滴形核位置和最终润湿状态的影响规律.结果表明,较高的纳米阵列使液滴在纳米结构间隙的上部侧面和底部优先形核长大,通过采用上下不均匀的间隙可避免液滴在底部形核长大,而在上部侧面形核的冷凝液滴在生长过程中向上运动,其润湿状态由Wenzel态转变为Cassie态;较低的纳米阵列使液滴在纳米结构底部优先形核长大,液滴的最终润湿状态为Wenzel态;润湿性不均匀的纳米结构表面使液滴在阵列顶端亲水位置处优先形核长大,成为Cassie态.冷凝液滴在不同几何尺寸的纳米结构表面上的最终润湿状态的模拟结果与文献报道的实验结果符合良好.通过模拟还发现,冷凝液滴在生长过程中的运动行为与液滴统计平均作用力的变化有关.本文的LBM模拟再现了三维空间中液滴的形核、长大和润湿状态转变等物理现象.     

疏水-超疏水组合表面倾斜管外混合蒸气冷凝过程

本文在铜管外制备疏水超疏水组合表面,控制铜管和重力方向的倾角为0°、30°、45°、60°,利用高速摄像系统研究混合蒸气冷凝过程中表面润湿性和重力的协同调控机制,观测了液滴的动态特性,测量了组合表面上混合蒸气传热性能.结果表明:倾角增大,组合表面上的冷凝液滴会偏离重力方向沿着疏水环向下冲刷;倾角60°时,疏水区域的液滴会合并到相邻的上下超疏水区域;和亲水光滑铜管相比,组合表面上含不凝气30%的混合水蒸气冷凝传热随倾角度增加先下降、之后保持不变、最后升高,分别提高50%～65%(竖直)、35%～55%(倾角30°和45°)、45%～55%(倾角60°)。     

超疏水和超亲水表面对脉动热管性能的影响

本文实验研究了完全超疏水脉动热管和蒸发段为超亲水,冷凝段和绝热段为超疏水的组合表面脉动热管的性能。超疏水表面自由能较低、滞后角小、液滴在表面容易移动。实验发现,与紫铜脉动热管汽液界面呈凹界面不同,超疏水表面汽液界面呈凸界面。组合表面脉动热管汽液界面的长度显著大于完全超疏水脉动热管。与紫铜脉动热管相比,组合脉动热管液弹脉动的振幅增加,而完全超疏水脉动热管蒸发段出现部分烧干,液弹脉动的振幅显著下降。     

亲水性微观粗糙表面润湿状态转变性能研究

以亲水性微观粗糙表面上不同几何形貌及分布的微柱阵列为对象, 讨论了液滴在亲水性粗糙表面上的润湿过程以及润湿状态的转变阶段. 从能量角度分别考察了微观粗糙结构几何形貌及分布、微柱几何参数、固体表面亲水性、接触角滞后作用等因素对液滴润湿状态转变的影响规律. 研究发现: 在亲水粗糙表面, 正方形微柱呈正六边形阵列分布时, 液滴更容易形成稳定的Cassie状态, 或者液滴仅发生Cassie状态向中间浸润状态的转变; 与此同时, 减小微柱间距、增大方柱宽度或圆柱直径、增大微柱高度、增强固体表面的亲水性将有利于液滴处于稳定的Cassie状态, 或阻止润湿状态向伪-Wenzel或Wenzel状态转变; 然而, 当液滴处于Cassie状态时, 较小的固-液界面面积分数或减弱固体表面亲水性能均有利于增大液滴的表观接触角, 因此在亲水表面设计粗糙结构时应综合考虑润湿状态稳定性和较大表观接触角两方面因素; 此外, 接触角滞后作用对于液滴状态的稳定性以及疏水性能的实现具有相反作用的影响. 研究结果为液滴在亲水表面获得稳定Cassie状态的粗糙结构设计方法提供了理论依据. 关键词： 亲水表面 微观粗糙结构 表面自由能 润湿状态转变     

超疏水翅片表面的抑霜机理和融霜特性

制备了具有微纳复合结构,表面接触角和滚动角分别为159.7°和4.2°的超疏水翅片。通过可视化观测,揭示了超疏水翅片表面的抑霜机理和融霜特性,并与亲水翅片进行了对比。结霜初期,超疏水翅片表面的凝结液滴分布稀疏,呈Cassie状态;亲水翅片表面的凝结液滴分布密集,呈铺展状态,几乎覆盖整个翅片表面。超疏水翅片表面与霜层间实际接触面积小,换热热阻大,使其被霜层覆盖后仍可有效抑制霜层生长。融霜时,超疏水表面的弱黏附性导致霜层整体从翅片表面剥离和脱落,缩短了融霜时间,减少了滞留水量。     

超疏水表面冷凝液滴行为与生长机制

本文制备了具有微-纳二级结构的超疏水表面,并在湿空气自然对流条件下进行了水平表面冷凝实验。实验结果表明,冷凝液滴行为可分为液滴合并、液滴弹跳和液滴扫掠三类。其中液滴弹跳与液滴扫掠行为均是由液滴合并触发的自推进液滴行为。液滴扫掠与液滴弹跳的区别是,目标液滴未能跳离表面,而是沿表面运动,并吞并沿途的液滴,留下狭长的运动轨迹,且轨迹尽头停留一个大液滴。本文亦通过统计方法,获得了超疏水表面上冷凝液滴的粒径分布、平均直径、表面覆盖率等,研究了液滴种群和单个液滴的生长机制。     

竖直表面液滴运动的数值模拟

为研究具有不同润湿特性的表面上液滴运动的规律,本文依据液滴接触角与基底方位角的关系以及运动液滴的动态接触角模型,运用Fluent软件,实现了对竖直表面上静止和运动液滴的数值模拟,得到了液滴的形貌以及内部的速度分布。模拟所得竖直表面上静止液滴和运动液滴的接触角和形貌均与实验结果吻合较好。液滴内部速度分布表明,裸铝表面(亲水)上液滴的运动方式为滑动;114°疏水表面上的液滴内部出现不完整的环流,但仍然以滑动运动为主;而145°疏水表面上液滴以滚动方式向下运动,液滴运动较快。     

Fabrication of superhydrophilic or superhydrophobic self-cleaning metal surfaces using picosecond laser pulses and chemical fluorination

Bioinspired superhydrophilic/phobic self-cleaning surfaces have recently drawn a lot of interest in both fundamental and applied research. A hybrid method to produce the self-cleaning property of micro/nanostructured surface using ultra-fast laser pulses followed by chemical fluorination is proposed. The typical micro/nanocomposite structures that form from microporous arrays and microgroove groups have been processed by picosecond laser on titanium alloy surface. The surface hydrophilic/phobic and self-cleaning properties of micro/nanostructures before and after fluorination with fluoroalkyl-silane were investigated using surface contact angle measurements. The results indicate that surface properties change from hydrophilic to hydrophobic after fluorination, and the micro/nanostructured surface with increased roughness contributes to the improvement of surface hydrophobicity. The micro/nanomodification can make the original hydrophilic titanium alloy surface more hydrophilic or superhydrophilic. It also can make an originally hydrophobic fluorinated titanium alloy surface more hydrophobic or superhydrophobic. The produced micro/nanostructured titanium alloy surfaces show excellent self-cleaning properties regardless of the fluorination treatment, although the fluorinated surfaces have slightly better self-cleaning properties. It is found that surface treatment using ultra-fast laser pulses and subsequent chemical fluorination is an effective way to manipulate surface wettability and obtain self-cleaning properties.     

In situ investigation of ice formation on surfaces with representative wettability

In this work, we have prepared a series of samples with five representative surface wettabilities: i.e. superhydrophilic, hydrophilic, critical, hydrophobic and superhydrophobic. These samples were in situ observed the freezing process of water droplets on clean and artificially contaminated surfaces to investigate the relationship between surface wettability and ice formation. Ice accretion was also tested by spraying supercooled water to samples at different horizontal inclination angles (HIA). Surface topography was proved to be essential to the icing through heterogeneous nucleation. However, the correlation between surface wettability and ice formation was not observed. Finally, we found that the superhydrophobic surface clearly exhibited reduced ice accumulation in the initial stage of ice formation associated with the lower sliding angle (SA) of water droplets.     

Preparation and characterization of large-size halloysite nanotubes particles by a combined technique of interfacial polymerization and condensation polymerization

To granulate halloysite nanotubes (HNTs) into large-size particles, interfacial polymerization and condensation polymerization were combined. The former was used to form surface layer of particles and the latter was used to improve particle strength. Polyethylenimine (PEI) and terephthaloyl chloride were chosen, respectively as hydrophilic monomer and hydrophobic monomer in interfacial polymerization. Condensation polymerization was carried out between PEI and glycerol polyglycidyl ether (GPE). The results show that HNTs particles have sphere shape and its diameters range from 1.7 to 2.5 mm and vary with preparation condition. SEM images show that particles have typical core–shell structure with dense surface layer and porous inner structure and single nanotube is completely encapsulated by polymer material. The characterization of BET shows that because of dense surface layer and encapsulation of nanotubes, the specific surface area of particles determined decreases dramatically.     

DBU液相催化法原位合成四苯氧基酞菁锌/ZnO复合材料的制备及光催化选择性研究

在负载于氧化铟锡(ITO)导电玻璃上、哑铃状纳米ZnO表面配位未饱和锌离子作为“模板”,以苯氧基邻苯二腈作为“分子碎片”,利用DBU液相催化法,在亲水性纳米ZnO表面,原位合成疏水性四苯氧基酞菁锌(ZnTPPc)。通过多种表征手段,分析证实了所合成的ZnTPPc分子结构、ZnTPPc/ZnO界面及光生电荷转移特性。在可见光下,分别以亲水性亚甲基蓝(MB)、疏水性苯酚(PL)及其混合液为待降解反应物,定量分析疏水性ZnTPPc/ZnO复合材料对降解疏水性PL的光催化选择性。结果表明： 原位合成ZnTPPc在ZnO表面呈现单分子层,具有较好的疏水性能,ZnTPPc可优先选择性降解疏水性PL,且在可见光光催化中对PL的相对降解效率是对MB分子的1.21倍。     

A sol-gel based surface treatment for preparation of water repellent antistatic textiles

In this paper a surface treatment is described for preparation of hydrophobic sol-gel coatings that simultaneously offer antistatic properties for an appropriate finishing of textiles and refinement of polymer foils. Sol-gel based formulations are modified with both hydrophilic and hydrophobic components simultaneously. Hydrophobic components are, e.g., alkoxysilanes modified with alkyl chains while the hydrophilic ones are amino-functionalized alkoxysilanes. The basic idea is that due to an enrichment of hydrophobic groups at the solid/air interface the surface of the as prepared coatings will be hydrophobic while the deeper region will be more hydrophilic. Textiles finished with these coatings exhibit sufficient water repellence and simultaneously absorb sufficient amounts of humidity in the deeper areas of the coating guaranteeing antistatic properties. This concept offers interesting approaches for the preparation of multifunctional surface coatings not only focussing on combining water repellence with antistatic properties for textile materials.     

Tuning solid surfaces from hydrophobic to superhydrophilic by submonolayer surface modification

Molecular-scale understanding and manipulation of the wetting behavior of water on solids remains a fundamental challenge. Using diamond as a model system, we show that the naturally hydrophobic behavior of a hydrogen-terminated C(111) surface can be manipulated by replacing the H termination with a monolayer of adsorbate. In particular, a mixed monolayer of 1/3 Na and 2/3 F atoms leads to superhydrophilic behavior, as shown by first-principles calculations. The physical origin of the superhydrophilic behavior is attributed to the ionic nature of the Na adatoms, which mediate the right degree of binding strength between water molecules and the substrate.     

Adsorption of firefly luciferase at interfaces studied by total internal reflection fluorescence spectroscopy

The adsorption of luciferase onto silica surfaces was studied by total internal reflection fluorescence (TIRF) spectroscopy. Two model surfaces were used: hydrophilic and hydrophobic silica. Luciferase adsorbed differently on these two surfaces. Initial kinetics of luciferase adsorption onto the hydrophilic surface showed that luciferase adsorbs over an adsorption energy barrier of 3 kT The quantum yield of luciferase fluorescence decreased at the hydrophilic silica surface, which indicated that the protein conformation was altered during adsorption. Luciferase adsorption onto the hydrophobic silica surface proceeded with a small adsorption energy barrier and the fluorescence efficiency of adsorbed protein remained unchanged after adsorption. The affinity of luciferase for luciferin was measured using quenching of luciferase fluorescence with luciferin. The binding constant of the adsorbed luciferase-luciferin complex at the hydrophilic silica surface was two orders of magnitude smaller than the respective binding constant in the solution. Adsorbed luciferase showed an absence of ATP-dependent visible luminescence, indicating that the adsorbed enzyme was not active at either of the two silica surfaces.     

高温壁面润湿性对气层稳定性及其壁面滑移性能的分子动力学研究

针对流体在纳米通道的小尺度效应,采用分子动力学方法模拟了传热效应以及流体流动行为,研究在壁面温度影响下,不同润湿性壁面上方气层生成状态以及流体流动时气层的稳定特性和相应的减阻性能.结果表明:当壁面为纯疏水壁面时,不能形成气层;疏水基底+亲水组合壁面形成不规则气层;纯亲水壁面和亲水基底+疏水组合壁面能形成规则气层.当流体流动时,疏水基底+亲水组合壁面气层消失,而纯亲水壁面和亲水基底+疏水组合壁面气层较为稳定.纯疏水壁面主流区域速度较大,而纯亲水壁面主流区域最低.对于壁面滑移速度,存在气层的壁面滑移速度与纯疏水表面相对接近,甚至稍优于纯属疏水表面,而疏水基底+亲水组合壁面滑移速度最小.     

液滴在润湿梯度表面运动的分子动力学模拟

本文进行了液滴在不同润湿梯度表面运动的分子动力学模拟,通过改变Lennard-Jones(LJ)势参数来实现表面的不同润湿性。模拟结果表明在润湿梯度差为10°的界面上,疏水表面的液滴运动更快,达到最终界面所需时间最短,并且液滴运动方向距离最远。当润湿梯度差为20°和30°时,液滴在疏水表面工况的运动速度与从疏水跨越到亲水的工况之间的差距越来越小,并且液滴在从疏水跨越到亲水的工况达到了最远的运动距离。同时,润湿梯度差的增加也引起了液滴运动速度的增大。     

The surface modification of cellulose fibres for use as reinforcing elements in composite materials

The interest in using cellulose fibres as reinforcing elements in composite materials based on polymeric matrices is constantly growing, mainly because of the many advantages associated with this renewable material. However, the preparation of cellulose-based composites is perturbed by the highly hydrophilic character of the fibres, which is associated with a low interfacial compatibility with hydrophobic polymeric matrices, as well as with a loss of mechanical properties after moisture uptake. In order to reduce the hydrophilic character of cellulose fibres and to improve the strength of their adhesion to the matrix, it is necessary to undertake a structural modification of their surface. Several approaches have been studied, namely (i) physical treatments such as corona, plasma, laser, vacuum ultraviolet and γ-radiation treatments; (ii) chemical grafting by direct condensation, including surface compatibilisation with hydrophobic moieties and co-polymerisation with the matrix. The copolymerisation approach called upon different strategies: (i) The use of bi-functional molecules capable of reacting with the OH groups of the cellulose surface and leaving the second functions available for further exploitation; (ii) The direct activation of the surface and the subsequent graftingfrom polymerisation; and (iii) The condensation of organometallic compounds, followed by their coupling with suitable reactive molecules or macromolecules. The characterisation of the modified surfaces involved a variety of techniques, including elemental analysis, contact angle measurements, inverse gas chromatography, X-ray photoelectron and FTIR spectroscopy, water uptake, etc. The present survey reviews the different approaches proposed in the literature and critically assesses their respective merits and drawbacks.