仿生超疏水表面的抗冷凝失效研究进展

在存在一定过冷度或蒸汽过饱和度的条件下,水蒸汽可在固体表面凝结成核.随着过冷度增大,液滴成核半径将随之减小,冷凝液滴的生长融合将无法避免地发生在超疏水表面不可或缺的微/纳米结构内.若液滴不能及时排出,则会滞留在表面结构内并挤出空气,形成局部浸润,导致材料表面的超疏水性能下降或失效,甚至引起泛洪.本文首先总结了表面因冷凝...     

超疏水表面微纳二级结构对冷凝液滴最终状态的影响

从超疏水表面(SHS)上初始冷凝液核长大、合并、形成初始液斑开始,分析计算了冷凝液斑变形成为Wenzel或Cassie液滴过程中界面能量的变化,并以界面能曲线降低、是否取最小值为判据,确定冷凝液滴的最终稳定状态.计算结果表明:在只有微米尺度的粗糙结构表面上,冷凝液滴的界面能曲线一般都是先降低再升高,呈现Wenzel状态;而当表面具有微纳米二级粗糙结构,且纳米结构的表面空气面积分率较高时,冷凝液滴的能量曲线持续降低,直至界面能最小的Cassie状态,因此可以自发地形成Cassie液滴.还计算了文献中具有不同结构参数的SHS上冷凝液滴的状态和接触角,并与实验结果进行了比较,结果表明,计算的冷凝液滴状态与实验观察结果完全吻合.因此,微纳二级结构是保持冷凝液滴在SHS上呈现Cassie状态的重要因素.     

分子自组装法制备具有可控浸润性的铜表面简

通过简单浸泡的方法在铜基底上制备出了具有微纳米复合结构的氧化铜,再利用混合硫醇溶液[含HS(CH2)9CH3和 HS(CH2)11OH]对浸泡后的表面进行修饰,通过控制溶液中HS(CH2)11OH的浓度,制备出一系列具有不同浸润性的铜表面,实现表面从超疏水到超亲水的有效调控. 研究发现,表面浸润的可控性源于表面复合结构与不同化学组成的协同作用,微纳米复合结构的存在为表面浸润性的调节提供了必要的条件.     

超疏水性表面在冷凝条件下的润湿特性

采用测量接触角和观测偏光显微镜对超疏水表面在冷凝条件下的疏水特性进行了研究, 发现冷凝蒸汽进入超疏水表面的微凸起内冷凝, 表面的疏水特性被破坏, 表面的润湿特性变得不均匀, 部分区域甚至呈现亲水状态. 根据实验结果提出了冷凝条件下粗糙表面表观接触角的计算模型, 并使用冷凝条件下表面接触角的测量结果进行了验证.     

超声刻蚀法构建分级结构的超疏水表面

在湿法刻蚀和超声空化的基础上, 采用超声刻蚀法制备了具有微纳米分级结构的超疏水表面. 以等体积比的硝酸/乙醇(体积分数为4%)和双氧水(质量分数为30%)的混合溶液作为刻蚀剂, 在室温下对60Si2Mn钢、 60^#钢、 T10钢、 Cr06钢、 65Mn钢和硅钢表面超声刻蚀2~10 min, 构建出多种形貌的微纳米分级结构. 上述表面经氟硅烷修饰后具有超疏水性, 水的表观接触角高达157.0°, 155.8°, 157.4°, 154.9°, 157.6°和156.8°, 滚动角分别为6.5°, 19.2°, 6.1°, 7.8°, 6.7°和7.2°. 与常规刻蚀方法相比, 超声刻蚀的化学刻蚀作用因与空化作用耦合而得到强化和改变, 从而在钢表面构建出分级结构. 由于材料表面微结构形貌和固/液界面接触状态不同, 制得的超疏水表面表现出的润湿行为也不同. 超声刻蚀法简单易行, 成本低廉, 适用于其它金属表面构建微纳米分级结构和超疏水表面.     

分子自组装法制备具有可控浸润性的铜表面

通过简单浸泡的方法在铜基底上制备出了具有微纳米复合结构的氧化铜, 再利用混合硫醇溶液[含HS(CH₂)₉CH₃和 HS(CH₂)₁₁OH]对浸泡后的表面进行修饰, 通过控制溶液中HS(CH₂)₁₁OH的浓度, 制备出一系列具有不同浸润性的铜表面, 实现表面从超疏水到超亲水的有效调控. 研究发现, 表面浸润的可控性源于表面复合结构与不同化学组成的协同作用, 微纳米复合结构的存在为表面浸润性的调节提供了必要的条件.     

光响应固体表面的浸润性调控

物质表面能和表面微观结构是影响物质浸润性的两大主要因素,表面能决定了平滑表面的液体接触角,而表面微观结构影响表面的浸润性。在受到外界刺激时,物质表面可发生表面能和表面微观结构的变化,从而实现表面浸润性的变化。本文综述了近年来物质表面的浸润性在光刺激下发生转变的研究进展,其中包括无机氧化物表面超疏水和超亲水之间的转换,光响应聚合物表面液滴的运动及接触角的变化,以及光响应聚合物表面黏附性的变化。     

超疏水表面上冷凝液滴发生弹跳的机制与条件分析

使用液滴合并前后的体积和表面自由能守恒作为两个限制条件,确定了合并液滴的初始形状,即为偏离平衡态的亚稳态液滴,具有缩小其底半径而向平衡态液滴转变的推动力.进而分析了液滴变形过程中的推动力和三相线(TPCL)上的滞后阻力,建立了液滴变形的动态方程并进行了差分求解.如果液滴能够变形至底半径为0mm的状态,则根据该状态下液滴重心上移的速度确定液滴的弹跳高度.不同表面上冷凝液滴合并后的变形行为的计算结果表明,光滑表面上的液滴合并后,液滴只能发生有限的变形,一般都在达到平衡态之前就停止了变形,因此冷凝液滴不会发生弹跳;粗糙表面上的Wenzel态液滴的三相线上的滞后阻力更大,因而液滴更难以变形和弹跳;具有微纳二级结构表面上只润湿微米结构,但不润湿纳米结构的部分Wenzel态液滴能够变形至Cassie态,但没有明显的弹跳;只有在纳米或微纳二级结构表面上的较小Cassie态液滴合并后,液滴易于变形至底半径为0mm的状态并发生弹跳.因此,Cassie态合并液滴处于亚稳态,并且其三相线上的移动阻力很小,是导致冷凝液滴弹跳的关键因素.     

结冰过程对溶解性有机质典型组分还原Cr(Ⅵ)的影响

研究了结冰过程对溶解性有机质(DOM)的4种典型组分草酸、 酒石酸、 苹果酸和柠檬酸还原Cr(Ⅵ)的影响. 结果表明, 在低浓度下Cr(Ⅵ)在水溶液中不能被4种有机酸所还原; 而在冰中, 不同的有机酸对Cr(Ⅵ)的去除均有促进作用, 且去除效果随着有机酸浓度的增大逐渐增强. 4种有机酸的作用效果强弱顺序为草酸>酒石酸>苹果酸>柠檬酸. 通过使用不同浓度的无机盐和无机酸可以改变冰表面上类似液体层的厚度来抑制Cr(Ⅵ)的还原, 作用效果与无机盐种类无关. 溶液的初始pH值和有机酸结构是影响Cr(Ⅵ)还原的重要因素. 实验条件下冷冻浓缩效应的富集倍数至少可达10³, 对冰中草酸去除Cr(Ⅵ)有明显的促进作用.     

具有水下超疏油性能的MXene高效油水分离膜

基于二维材料MXene(Ti₃C₂T_x)的化学组成和纳米片状结构, 在不锈钢网上制备了具有MXene微纳结构表面的新型亲水和水下超疏油分离膜. 对于不同类型的油-水混合物, 该膜材料可实现重力驱动的高效油水分离, 收集的水中残油量小于4 mg/L, 具有高分离效率(>99.99%), 水通量高达57.52 L·m^-2·s^-1. 此外, 经高温处理和多种有机溶剂浸泡后MXene膜仍具有高效的油水分离性能, 并表现出优异的稳定性和循环性.     

Quantification of surface-bound proteins by fluorometric assay: Comparison with quartz crystal microbalance and amido black assay

Protein adsorption is of major and widespread interest, being useful in the fundamental understanding of biological processes at interfaces through to the development of new materials. A number of techniques are commonly used to study protein adhesion, but few are directly quantitative. Here we describe the use of Nano Orange, a fluorometric assay, to quantitatively assess the adsorption of bovine fibrinogen and albumin onto model hydrophilic (OH terminated) and hydrophobic (CH3 terminated) surfaces. Results obtained using this method allowed the calibration of previously unquantifiable data obtained on the same surfaces using quartz crystal microbalance measurements and an amido black protein assay. Both proteins were found to adsorb with higher affinity but with lower saturation levels onto hydrophobic surfaces. All three analytical techniques showed similar trends in binding strength and relative amounts adsorbed over a range of protein concentrations, although the fluorometric analysis was the only method to give absolute quantities of surface-bound protein. The versatility of the fluorometric assay was also probed by analyzing protein adsorption onto porous superhydrophobic and superhydrophilic surfaces. Results obtained using the assay in conjunction with these surfaces were surface chemistry dependent. Imbibition of water into the superhydrophilic coatings provided greater surface area for protein adsorption, although the protein surface density was less than that found on a comparable flat hydrophilic surface. Superhydrophobic surfaces prevented protein solution penetration. This paper demonstrates the potential of a fluorometric assay to be used as an external calibration for other techniques following protein adsorption processes or as a supplemental method to study protein adsorption. Differences in protein adsorption onto hydrophilic vs superhydrophilic and hydrophobic vs superhydrophobic surfaces are highlighted.     

Wrinkled Graphene Monoliths as Superabsorbing Building Blocks for Superhydrophobic and Superhydrophilic Surfaces

Superhydrophobic and superhydrophilic surfaces are of great interest because of a large range of applications, for example, as antifogging and self‐cleaning coatings, as antibiofouling paints for boats, in metal refining, and for water–oil separation. An aqueous ink based on three‐dimensional graphene monoliths (Gr) can be used for constructing both superhydrophobic and superhydrophilic surfaces on arbitrary substrates with different surficial structures from the meso‐ to the macroscale. The surface wettability of a Gr‐coated surface mainly depends on which additional layers (air for a superhydrophobic surface and water for a superhydrophilic surface) are adsorbed on the surface of the graphene sheets. Switching a Gr‐coated surface between being superhydrophobic and superhydrophilic can thus be easily achieved by drying and prewetting with ethanol. The Gr‐based superhydrophobic membranes or films should have great potential as efficient separators for fast and gravity‐driven oil–water separation.     

Control of superhydrophilicity/superhydrophobicity using silicon nanowires via electroless etching method and fluorine carbon coatings

Surface roughness is promotive of increasing their hydrophilicity or hydrophobicity to the extreme according to the intrinsic wettability determined by the surface free energy characteristics of a base substrate. Top-down etched silicon nanowires are used to create superhydrophilic surfaces based on the hemiwicking phenomenon. Using fluorine carbon coatings, surfaces are converted from superhydrophilic to superhydrophobic to maintain the Cassie-Baxter state stability by reducing the surface free energy to a quarter compared with intrinsic silicon. We present the robust criteria by controlling the height of the nanoscale structures as a design parameter and design guidelines for superhydrophilic and superhydrophobic conditions. The morphology of the silicon nanowires is used to demonstrate their critical height exceeds several hundred nanometers for superhydrophilicity, and surpasses a micrometer for superhydrophobicity. Especially, SiNWs fabricated with a height of more than a micrometer provide an effective means of maintaining superhydrophilic (<10°) long-term stability.     

A facile and patternable method for the surface modification of carbon nanotube forests using perfluoroarylazides

A facile patterning method for the functionalization of vertically aligned carbon nanotubes is described. Modification of the surface of nanotube forests with hydrophilic, hydrophobic, or polymerizable small molecules was achieved via UV-triggered attachment of perfluoroarylazides. Multiple functionalizations of the tube surface can be achieved. Macro- and micropatterning of forest substrates were demonstrated. Superhydrophobic surfaces containing superhydrophilic regions were prepared.     

Fabrication and characterization of superhydrophobic silica nanotrees

Superhydrophobic silica nanotrees were obtained by sol–gel method with hybrid silica sol and jelly-like resorcinol formaldehyde resin. Rough surfaces were obtained by removing the organic polymer at high temperature. After the films with rough surface were modified by trimethylchlorosilane (TMCS), the wettability of the film changed from superhydrophilic to superhydrophobic. The surface roughness of the silica nanotrees film is about 20 nm, and it is transparent and superhydrophobic with a water contact angle higher than 150°.     

一步法合成聚苯胺/十二烷基苯磺酸钠超疏水复合材料

在阴离子表面活性剂十二烷基苯磺酸钠(SDBS)体系中,采用一步法制得聚苯胺/SDBS超疏水复合材料.利用场发射扫描电子显微镜(FESEM)观察产物形貌并测定其元素组成.通过傅里叶变换红外光谱仪、紫外-可见光谱仪、X射线衍射等对其结构进行表征,用视频接触角测量仪测定材料的亲疏水性.考察SDBS浓度和溶液酸度对产物形貌及疏水性能的影响,探讨疏水机理.结果表明:在pH=1-9,SDBS浓度大于0.016 mol?L-1条件下,所制备复合材料的水接触角大于150°,SDBS掺杂使得苯胺单体的转化率高达98%.两亲分子SDBS亲水磺酸基与聚苯胺主链上的亚胺基不仅存在静电引力,而且能形成磺酰胺键,聚苯胺主链间又以氢键相互连接,SDBS分子的疏水烃基有序排列朝向聚苯胺主链外侧,从而组装形成具有微纳结构的聚苯胺/SDBS超疏水复合材料.本文结果有利于更好地理解聚苯胺/SDBS超疏水性复合材料的形成机理,对超疏水材料的设计提供新思路.     

Dynamic effects of bouncing water droplets on superhydrophobic surfaces

Superhydrophobic surfaces have considerable technological potential for various applications due to their extreme water repellent properties. Superhydrophobic surfaces may be generated by the use of hydrophobic coating, roughness, and air pockets between solid and liquid. Dynamic effects, such as the bouncing of a droplet, can destroy the composite solid-air-liquid interface. The relationship between the impact velocity of a droplet and the geometric parameters affects the transition from the solid-air-liquid interface to the solid-liquid interface. Therefore, it is necessary to study the dynamic effect of droplets under various impact velocities. We studied the dynamic impact behavior of water droplets on micropatterned silicon surfaces with pillars of two different diameters and heights and with varying pitch values. A criterion for the transition from the Cassie and Baxter regime to the Wenzel regime based on the relationship between the impact velocity and the parameter of patterned surfaces is proposed. The trends are explained based on the experimental data and the proposed transition criterion. For comparison, the dynamic impact behavior of water droplets on nanopatterned surfaces was investigated. The wetting behavior under various impact velocities on multiwalled nanotube arrays also was investigated. The physics of wetting phenomena for bouncing water droplet studies here is of fundamental importance in the geometrical design of superhydrophobic surfaces.     

绿色环保特殊浸润性纺织品的前沿进展

介绍了仿生超疏表面的工作机制以及疏水整理液的发展, 系统综述了近10年来特殊浸润性在开拓多功能绿色纺织领域的研究进展, 讨论了双面超疏、 超疏/超亲、 图案化及可响应浸润性纺织品的制备技术及应用, 介绍近几年在纺织品疏水化功能改性方面取得的前瞻性工作, 包括自清洁防污、 油水分离、 机械耐久、 图案化、 自修复、 单向运输等, 特别是在智能响应、 电子可穿戴、 能源等新兴领域方面的应用. 最后, 对超疏水纺织功能材料目前所面临的挑战及未来发展的方向进行了展望.     

Superhydrofobic effect of hybrid organo-inorganic materials

Superhydrophobic films were obtained on the basis of sol–gel-derived titania or alumina/dodecylamine hybrid materials. It has been shown that wettability of surfaces of the inorganic oxides changes from superhydrophilic to superhydrophobic. For superhydrophobic materials, the surface roughness of the hybrid films on the basis of titania and alumina is 39 and 55 μm, respectively, and water contact angle is about 150°.     

A Simple,Low-cost Method to Fabricate Drag-reducing Coatings on a Macroscopic Model Ship

A low-cost method was used to fabricate superhydrophobic coatings on a macroscopic model ship and the drag-reducing effect was investigated at both low and high speed. Hierarchical structures of the superhydrophobic copper coatings were characterized by means of scanning electron microscopy(SEM) and X-ray diffraction(XRD). Drag coefficient tests on surfaces with different wettability(superhydrophilic, hydrophilic, hydrophobic and superhydrophobic surfaces) showed that the as-prepared superhydrophobic surface exhibited a high remarkable drag reduction of 81% at a low speed of 1 mm/s. In the drag-reducing tests with model ship, the superhydrophobic coatings also exhibited around 16% drag reduction at a velocity of 0.3 m/s.