【作者】 张泓筠；

【导师】 李文；

【作者基本信息】 湘潭大学 ， 材料科学与工程， 2013， 博士

【摘要】 浸润性是材料表面的一个重要性质；有关物理化学过程如吸附、润滑、黏合、分散和摩擦等均与表面的浸润性密切相关。近来，受“荷叶效应”的启发而发展起来的超疏水性在自清洁、微流体系统和生物相容性等方面的潜在应用激发了学术界和工业界的广泛兴趣。然而到目前为止，无论是实验研究还是理论研究均达不到使超疏水表面上升到实用化的高度，实验上还没有开发出简易方法制备出经久耐用的超疏水表面；理论上也还未完全揭示超疏水表面的微观润湿机理。就固体表面的润湿及液滴运动而言，Young方程、Cassie方程、Wenzel方程仅仅是对液滴状态的一种静态描述，未能涉及到液滴的运动或接触角滞后的定量描述，也没有深入地建立起表面润湿性能同微观结构之间的定量联系。相关研究者尽管做出过很大努力企图通过热力学方法建模解决固体表面上液滴运动的定量描述问题，但所用方法在数学上大多繁琐难懂且主要倾向于唯像的描述。基于以上研究现状，我们以超疏水表面作为研究对象寻求解决问题的方法，将静态表观接触角(对应于液滴–超疏水表面系统的最小自由能)同运动角(前进、后退接触角及滚动角)联系起来，将超疏水表面的疏水性能同表面的微观结构联系起来。同时，研究发现超疏水表面对于宏观尺度水滴带来的覆冰具有抑制作用；它能延缓结冰时间、减少覆冰量、降低冰块与固体表面的粘附。因而，我们试图将超疏水表面研究成果应用到高压电缆的防冰，并进一步分析超疏水表面的防冰机制和可能实现防冰的方法。纵观整个研究过程，我们主要做了如下系列工作：第一，首先从宏观角度建立起超疏水表面上液滴的静态表观接触角(如Cassie接触角和Wenzel接触角)和动态接触角之间的定量关系。针对接触角滞后定性定量实验，宏观上分析了超疏水表面上液滴运动滞后过程中初始态、预前进态、前进态、预后退态与后退态的表观接触角的变化(静态表观接触角、前进角、后退角)、三相接触线半径的变化、液滴表面自由能的变化等。提出了用于解释超疏水表面上液滴运动的两个新概念，如自由能变化(Changes in free energy)和可用于三维液滴的自由能能垒(Free energy change)。第二，针对超疏水表面的疏水性能主要取决于表面的微观结构形貌这一结论，我们分别在Cassie方程、Wenzel方程的基础上讨论了超疏水表面和液滴系统在复合和非复合润湿状态的下润湿性能，通过三维模型的固体份数和粗糙度因子建立起了疏水性能和表面微结构之间的定量关系，并根据微结构参数的变化讨论了超疏水表面性能的变化。(1)针对某些人工和自然超疏水表面的一级微结构，提出了一级柱形微结构模型；将一级柱形微结构表面的疏水性能同方柱的宽度、间距和高度联系起来；分别针对复合和非复合润湿状态，建立起超疏水表面上液滴的表观接触角(Cassie接触角、Wenzel接触角)、接触角滞后、自由能变化、自由能能垒、粘附功和铺展系数与柱形微结构之间的数学关系。通过比较粘附功和能垒的变化，从数学角度解释了液滴运动时所需克服的能垒与固–液界面的润湿状态没有关系，而是由三相接触线附近的接触状态和表面的材料化学性质来决定。并从数学的角度解释了超疏水表面对于凝结的水分子团簇丧失疏水性。(2)同样，受荷叶表面二级微结构和仿荷叶表面微结构的启发，我们亦提出了仿荷叶的二级微结构柱形模型，通过以上同样的方式建立起仿荷叶表面的超疏水性能和表面微结构之间的关系。从结构参数的数量变化解释了二级结构为何能够有效降低接触角滞后；并从能垒和粘附功的角度讨论了超疏水表面上的液滴润湿状态的复合非复合转换。(3)基于以上工作，利用分形几何建模讨论了具有不同等级(或多尺度)微结构的超疏水表面的疏水性质，提出液滴润湿状态的转换与分形维度没有关系(外界条件相同)，而是由表面的微观粗糙度来决定，并求出用于转换的临界粗糙度大约为1.8，这与以往的研究者从接触角滞后的变化求得的临界粗糙度基本一致。进一步对比发现：单从疏水性能来看，构造具有二级微结构的超疏水表面已能满足疏水性要求，高于二级的微结构表面，如三级分形微结构，是不必要的。考虑到力学性能的持久性和表面加工的方便，一级微结构的表面也许是理想选择。第三，在超疏水表面研究基础上，讨论了超疏水表面防冰性能的热力学机制。鉴于冰粒粘附力的不便测定和已有的测定方法不统一，本文主要从粘附功的角度分析了超疏水表面的防冰属性。研究发现：超疏水表面的防冰性能同疏水性能一样主要由表面的材料和微结构决定；当表面–水滴系统处于复合态时，超疏水表面的确具有防冰功能；反之，当表面–水滴系统处于非复合态时，表面覆冰性能跟材料有关，材料亲水时表面会更倾向于覆冰，材料疏水时，表面倾向于防冰。第四，考虑到覆冰防冰的复杂性和超疏水技术的不足，我们以目前用于重冰区的紧缩型钢芯铝合金绞线为基础，结合电热技术设计了实用新型的防冰高压电缆。该电缆设计了两套防线用于防冰，两套防线可相互协作，亦可独立工作，工艺上没有大幅度改变传统生产方法，不会带来新的不便。第一套防线，采用内嵌铁铬铝线加热融冰，第二套防线采用在电缆上涂敷超疏水复合涂层防冰。当铁铬铝线加热电缆时，冰与电缆表面直接接触的冰首先融化，覆冰转化为疏水，覆冰融化到一定程度，在疏水表面的作用下，借助冰块本身的重力自动滑落电缆，达到除冰的目的。更多还原

【Abstract】 The wetting of the surfaces, as an important property, is associated with therelevant physical and chemical process, i.e., absorption, lubrication, adhesion,dispersion and friction. Recently, the superhydrophobic surfaces (SHS) have attractedthe widespread attentions from both academic and industrial fields due to its potentialapplications in self–cleaning, micro–fluid system and biologic compatibility.However, up to now, two aspects of both theoretical and experimental study are faraway the level of making the SHS be of practicality. There are experimentally nopractical methods exploited to prepare the durable SHS or the special SHS that areapplied to the specific environment; and also there are theoretically no perfectconceptions used for explantion of micro–wetting mechanisms of the SHS. From boththe wetting and movement of the droplets, both Young and Cassie equations as wellas Wenzel equation are only a static description for the droplets, not involving thequantitative description for the movement and the hysteresis of the droplets, and alsonot establishing the relationships between the surface wetting properties and themicrostructures. Although the researchers have made a great effort to settle down thedescription for the movement in thermodynamics, the used methods aremathematically obscure and fall into the phenomenon description. Based on thepresent situation, we attempt to search for the methods to solve the problems on thebasis of the wetting of the SHS for the purpose of establishing the relationshipsbetween the static apparent contact angle (CA) with dynamic angle (includingadvancing, receding CAs together with sliding angles) as well as between thehydrophobic properties and the surface microstructures.Meanwhile, the SHS again shows a new application in the icing of thetransmitting lines. The study indicates that the SHS can effectively inhibit the icingfrom the droplets with macro–scale, delay the time to ice, and reduce the quantity ofthe icing and the adhesion between the icing and them. Therefore, we attempt to applythe SHS to the anti–icing of the high–voltage cables and further analyze the anti–icingmechanism of the SHS and the possible methods used for the anti–icing.Reviewing the study, we have finished the following work:Firstly, the relationships have been established between the static apparent CAand the dynamic CAs, including advancing or receding CAs, by considering the SHSas our object of our study. Based on the quantitative and qualitative experiments, we analyzed the variations of both the apparent CA and the changes in the radius of thethree–phase–contact line along with free energy among the initial, pre–advancing,advancing, pre–receding, receding states, and put forward two new conceptions ofboth changes in free energy (CFE) and free energy barrier (FEB) to explain themovement of the droplets on the SHS.Secondly, based on the conclusion that the hydrophobic properties of the SHSdepends mainly on the surface microstructures, we discussed the wetting of thesystem of both the droplets and the surfaces in the composite/non–composite wettingstates on the ground of the Cassie/Wenzel equations respectively, and established therelationships between the hydrophobic properties and the surface microstructures byboth the solid fraction and the roughness factor of a three–dimensional model, anddiscussed the variations of the properties of the SHS with the microstructures.(1) On the basis of the one–step microstructures of some artificial and naturalSHS, we proposed one–step model for simulation of the SHS, and established therelationships between the hydrophobic properties, i.e., the apparent CAs, CAH, CFE,FEB, adhesion work (Wa), the spreading coefficient (SS/L), and the width, heighttogether with spacing of a pillar according to composite/non–composite wetting state;and explained that the energy barrier, being overcome by a droplet while it moves, isindependent of the state of the solid–liquid interfaces within the three–phase contactline, and depends mainly on the materials and microstructures near the three–phasecontact line; meanwhile mathematically explained that the SHS, e.g., a lotus leafsurface, lost their hydrophobic ability to the condensed vapor.(2) Similarly, enlightened by a two–step micro–structure, we developed thetwo–step model to simulate the lotus leaf surfaces, and established the relationshipsbetween the hydrophobic properties of the lotus–simulating surfaces andmirostructures; and mathematically explained why the two–step microstructures caneffectively reduce the CAH; and discussed the transition between the composite andnoncomposite wetting states from both the energy barrier and adhesion work point ofview.(3) Then on the basis of the above work, we discussed the hydrophobicproperties of the SHS with different dimension by modeling in fractal geometry; andproposed that the transition between composite and non–composite wetting isindependence of the fractal dimension and only determined by the microscopicroughness; and found that the critical roughness factor for the transition is1.8or so, which is in agreement with the one from the changes in CAH. By comparing, wefurther found that designing the SHS with two–step microstructure is enough tosatisfy the requirement of the hydrophobicity; higher dimensional surfaces, forexample, three–dimensional surfaces are unnecessary; meanwhile, the SHS withone–step microstructures may be an ideal selection, if our considering both thedurability and the surface formation.Thirdly, based on the study of the SHS, the thermodynamic mechanism for theanti–icing was also discussed. In view of the inconvenience of the measurement of theadhesion force and the existing measurement not being uniform, the anti–icingproperty of the SHS was analyzed only from the adhesion work point of view in thisstudy. The study indicates that the anti–icing property of the SHS depends mainly onboth the surface materials and microstructures as demonstrated for the hydrophobicproperty；when the system of both the surfaces and the droplets is in the compositewetting state, the SHS surely have the ability to anti–icing due to the main role of themicrostructures; conversely, the anti–icing property was related to the materials in thenon–composite wetting state, both the hydrophilic and hydrophobic materials showingthe icing and anti–icing respectively.Fourthly, considering both the complexity of the anti–icing process and theimperfect techniques for the superhydrophobicity, we have designed a new–type ofhigh–voltage cable with anti–icing property based on the compressed steel–corealuminum alloy twisted lines used in the heavy icing area, integrating theelectricity–heating techniques. The cable was designed to anti–ice with two lines:those which the iron–chrome–aluminum lines inserted into the cable are to heat withthe action of the current; the others which the superhydrophobic coatings are towaterproof and anti–ice. With the iron–chrome–aluminum lines connected to thepower, the ice directly contact with cable surface is melted firstly; and thecorresponding water is repelled by the hydrophobic coatings. When the ice is meltedto some extent, the ice will slide off the cables with its gravitation. The two lines canwork cooperatively or independently as well.更多还原