蝗虫翅表面微观结构及疏水耦合机理

使用体视显微镜、扫描电子显微镜、傅立叶红外光谱仪和视频光学接触角测量仪,研究了4种蝗虫(黄胫小车蝗Oedaleus infernalis、异翅负蝗Atractomorpha heteroptera、花胫绿纹蝗Aiolopus tamulus、中华稻蝗Oxya chinensis)翅表面的微观结构、化学成分及疏水性,建立了蝗虫翅表面的微观结构疏水模型,分析了蝗虫翅表面疏水耦合机理。结果表明,蝗虫翅表面具有规则排列的微米级柱状乳突结构,乳突直径为1.6～2.3μm,高为2.3～3.2μm,间距为6.8～7.6μm。翅表面为长链烃类、脂肪酸酯和脂肪酸醇构成的蜡质层,是天然疏水表面,具有较强疏水性(接触角为139.0°～150.4°)。液滴与翅表面呈复合接触,符合Cassie方程。翅表面的高疏水性是微米级粗糙结构(结构耦元)与蜡质晶体(材料耦元)协同作用的结果。     

蝴蝶翅膀表面非光滑鳞片对润湿性的影响

对8科34属48种蝴蝶翅膀表面的润湿性进行了定性、定量研究。用扫描电子显微镜对蝴蝶翅膀表面进行观察得到:鳞片长为55~150μm,宽为35~105μm,鳞片上突起的高为200~950 nm。用视频光学接触角测量仪对翅膀表面的静态接触角和滚动角进行测量得到:接触角为134.0°~159.2°,表明翅膀表面具有较强的疏水性;顺向滚动角均小于3°,逆向滚动角均大于65°,表明翅膀鳞片结构具有明显的各向异性。蝴蝶翅膀表面的润湿性是由鳞片微米和纳米结构协同作用的结果。     

蜻蜓翅膀微观结构及其润湿性

利用视频光学接触角测量仪对6种蜻蜓翅膀表面的接触角进行了测量,发现蜻蜓翅膀具有疏水性能,接触角在135.14°~149.85°之间,其值与测量部位无关,与蜻蜓种类有关。用扫描电子显微镜对蜻蜓翅膀表面微观结构进行观测,发现蜻蜓翅膀上布满柱状纳米级结构形态,柱直径分布范围为66.90~200.73 nm,柱间距为20.00~650.00 nm,翅膜厚度为1.58~4.08μm。分析了蜻蜓翅膀表面疏水机理,研究表明:蜻蜓翅膀的疏水机理满足Cassie模型,其疏水性能主要由体表纳米级别的柱状结构与体表成分共同作用的结果。蜻蜓翅膀润湿性能的研究为微型飞行器及自清洁材料的制备提供了理论依据。     

多孔微球/纤维复合聚苯乙烯膜表面浸润性研究

采用静电喷涂法,通过调节PS/THF溶液的浓度制备了不同表面结构的PS膜,并通过场发射扫描电镜和静态接触角测定仪对膜表面结构及表面浸润性进行了研究。结果表明,PS/THF溶液的浓度是影响PS膜表面形貌的重要因素,而固体表面的化学组成和微观几何结构对固体表面浸润性起着重要的作用。在PS/THF溶液的质量分数为1%和10%条件下制得的PS膜表面,分别具有平滑和无孔微球与纤维复合的结构,表面接触角分别为96.2°和98.7°,具有疏水特性;而质量分数为5%时所制备的膜表面,具有多孔状的微米颗粒与纳米纤维相复合的粗糙结构,表面接触角高达153°,具有超疏水特性。此外溶剂的挥发性和极性也对表面形貌的变化也起着重要的作用。     

Al2O3纳米流体液滴撞击壁面的动力学行为数值研究

针对纳米流体液滴撞击固体壁面的动力学行为,建立基于相场方法描述液滴动态过程的二维数值模型,引入Kistler动态接触角模型以模拟铺展过程中液滴动态接触角变化以及三相接触线的迁移. 通过模拟分析液滴铺展因子、无量纲高度的变化研究不同纳米颗粒体积分数、惯性力和液滴直径等因素对水基Al₂O₃纳米流体液滴撞击壁面的铺展回缩过程的影响机制. 结果表明：超过一定体积分数的纳米颗粒使流体表现出明显的剪切稀化特性,增加液滴的黏性耗散,抑制液滴的铺展回缩过程;液滴撞击速度的增加会增大其撞击壁面时最大铺展直径和达到稳定状态的耗时,直径的增加使液滴振荡周期加长;体积分数为4%的纳米颗粒可以抑制上述两者带来的影响,使液滴更快到达稳定状态.     

十字交叉型微通道内液滴形成的数值模拟研究

基于Fluent软件的流体体积分数（Fluid Volume Fraction,VOF）模型,针对十字交叉型微通道内液滴的形成过程开展了三维数值模拟研究,分别研究了连续相黏度、分散相黏度、两相界面张力系数、壁面接触角对液滴形成的影响,为实际应用提供参考。研究表明随着连续相流速的增加,液滴生成直径减少,生成频率增大;增加连续相黏度时,液滴生成直径变小,生成频率的变化则相反;当分散相黏度超过连续相黏度时,出现射流现象而不能生成液滴;液滴生成直径随两相界面张力系数的增加而增大,生成频率降低;增大壁面接触角有利于液滴的产生,且两相流速为0.01 m/s和0.02 m/s时,接触角应分别取到150°和120°才能正常生成液滴。     

介电层表面纳米织构化及其电润湿行为影响研究

为了更好地调控液滴的形状,探讨了纳米织构化介电层表面的电润湿行为.采用刻蚀和软压印方法在导电基底上实现了紫外光固化聚合物(NOA61)介电层的纳米织构;搭建了实验平台,观察对比了厚度相同而形貌不同的介电层表面的电润湿响应.结果表明,平整光滑介电层在电压较低时表现为不可逆的电润湿响应,当方波电压大于200V时则表现为可逆的电润湿响应;网格纳米织构介电层的可逆转变临界电压为350V,而纳米锥织构介电层则在高达500V以上直至产生接触角饱和现象也仍保持不可逆的电润湿响应;几种介电层的饱和接触角趋于一致.之所以水滴在纳米织构化的介电层表面发生了不可逆的Wenzel接触模式润湿转变,是由于水滴在电场下与织构微观表面之间具有较高的粘滞作用.     

Cu-Zn合金仿生耦合表面的疏水性能

采用模板法对Cu-Zn合金形态、结构、成分耦合表面仿生制备工艺及其疏水性能进行了研究。模板去除后,表面形成了相间密布的纳米级纯Cu突起及球形洞穴。研究表明:形态、结构、成分的仿生耦合可以使Cu-Zn合金表面由亲水转变为疏水,随着深径比ξ的增加以及水滴下固体面积分数Φs的减少,实际接触角从82.5°增加到了126.1°,实际接触角的变化服从Cassis-Baxter模型。     

不锈钢微米级球冠形表面的润湿性能

分析了不锈钢(1Cr18N i9Ti)微米级球冠形表面点阵的高度和行间距等因素对润湿性能的影响。试验结果表明:材料表面的微米级球冠形点阵增加了水滴与表面的实际接触面积,导致材料表面与水的实际接触角下降,最大下降幅度达28.5%,增加了材料表面的亲水性能。     

冲洗液浸润性对去除砂质土残留油的影响

为获得含表面活性物质冲洗液的浸润性对其去除砂质土中残留油性能的影响关系,用直接量角法和铺展面积法共同对助溶剂、非离子表面活性剂、蒸馏水、柴油与石英玻璃接触角进行了测定,并用乙醇溶液、异丙醇溶液、Tween80和Brij35、蒸馏水等对含油石英砂柱进行冲洗试验.试验表明:随助溶剂浓度增大,其与石英的接触角减小,当乙醇体积分数超过70%、异丙醇体积分数超过40%,其与石英玻璃的接触角小于柴油与之的接触角,而非离子表面活性剂对石英的接触角大于该角度,表明醇类助溶剂比非离子表面活性剂对石英的浸润能力更强;当冲洗液与石英砂的接触角大于柴油与石英砂的接触角时浮油的产率基本不变,而小于该角度后浮油产量迅速增加;单孔隙体积的高浓度助溶剂溶液(体积分数为90%的乙醇)可去除87%残留油,预示助溶剂在修复油污染砂土的力方面有较好的应用潜力.     

Effect of roughness on wettability and floatability: Based on wetting film drainage between bubbles and solid surfaces

Wetting film thinning measurement was introduced to clarify the wettability and floatability of solid surfaces with varying roughness. The wettability was quantified using the contact angle measurement combined with the dynamic force microbalance test between solid surfaces and water droplets, while the floatability was investigated by the bubble-solid surface dynamic attachment observation and the induction time measurement. The results show that the water contact angles reduce (14.53°, 12.74°, and 6.71°) with the increase of glass surface roughness, while the water droplet-glass adhesion forces intensify (11.1, 19.1 and 19.2 μN) owing to the stable wetting film. The distortion of the contact surface and the Wenzel state are the causes. In contrast, the hydrophobized surfaces have the growing apparent contact angles (38.08°, 69.81°, and 81.01°), declining adhesion strength and shortening induction time (863, 352 and 12 ms) along with the increasing surface roughness. The weak wettability and fine floatability on the rough hydrophobized surface is reflected in the fast wetting film drainage dynamics and three-phase contact formation, which may be attributed to the wetting film with short diameter on tiny rough nubs and the entrapped air in the grooves as a bridge between the bulk bubble and the solid surface.     

水中油滴在不同润湿性表面上的铺展行为研究

通过高速显微实验与理论推导相结合的方式,从微观角度研究了水中油滴在光滑铜板基底的铺展行为;通过物理和化学修饰,实现了黄铜表面水下超亲油到超疏油的可控调节,观察了油滴浮升到修饰黄铜表面后铺展长度随时间变化的差异。与空气中液滴撞壁铺展不同,水中油滴的铺展需要同时考虑液滴铺展过程中周围流体对液滴铺展的黏性作用,其在基底表面的铺展过程十分复杂。采用能量守恒方法,得到了油滴在水中基底表面上的特征值之间的定量关系,建立了基于能量守恒方法的油滴在不同润湿性固体基底表面的铺展模型,用以指导新型油水分离设备的制备。     

Adhesion forces for water/oil droplet and bubble on coking coal surfaces with different roughness

Surface roughness plays a significant role in floatability of coal. In the present paper, coking coal surface was polished by three different sandpapers and the surface properties were characterized by contact angle and roughness measurements. The effect of surface roughness on floatability was investigated by adhesion force measurement system for measuring interaction forces between droplets/bubbles and coking coal surfaces with different roughness. The results showed that the contact angle decreased with increasing roughness yet the adhesion force between the water droplet and coal surface increased owing to the increased contact line and the appearance of line pinning. Maximum adhesion forces between water and surfaces were 111.70, 125.48, and 136.42 μN when the roughness was 0.23, 0.98, and 2.79 μm, respectively. In contrast, under a liquid environment, the adhesion forces between air bubble/oil droplet and coal surfaces were decreased with increasing roughness because of the restriction by water. Maximum adhesion forces of increasing roughness were 97.14, 42.76, and 17.86 μN measured at interfaces between air bubble and coal surfaces and 169.48, 145.84, and 121.02 μN between oil droplet and surfaces, respectively. Decreasing roughness could be beneficial to the spreading of oil droplets and the adhesion of bubbles which is conducive to flotation separation.     

The effect of surface anisotropy on contact angles and the characterization of elliptical cap droplets

In this paper, the variation of contact angles of a droplet on grooved surfaces was studied from microscale to macroscale experimentally and theoretically. The experimental results indicated that the contact angle changes nonlinearly with anisotropic factor. To get clear of the changing process of contact angle on grooved surfaces from microscale to macroscale, we carried out theoretical analysis with moment equilibrium method being adopted. In addition, the variation of contact angles in different directions was investigated and a mathematic model to calculate arbitrary contact angles around the elliptic contact line was suggested. For the convenience of potential applications, a symbolic contact angle was proposed to characterize the ellipsoidal cap droplet on grooved surfaces. Our results will offer help to the future design of patterned surfaces in practical applications, and deepen the understanding of wetting behavior on grooved surfaces.     

Thermal-induced transformation of wetting behaviors on laser-textured SiC surfaces

Thermal-induced transformation of wetting behaviors on laser-textured silicon carbide(SiC) surfaces was discussed in this work. To investigate the transformation, a quenching experiment was conducted and an X-ray diffractometer was used to measure the residual stress. The experimental results demonstrate that the significantly enhanced hydrophilicity was induced by the increasing thermal residual stress of SiC materials after the aqueous quenching. It was found that the decrease in the contact angle increased with the increasing quenching temperature. Quenching at 350°C led to the change of contact angle from 89.28° to 70.88° for the smooth surface, while from 72.25° to 33.75° for the laser-textured surface with depth 8 μm. Further, the surface hydrophobicity was enhanced by the release of thermal residual stress after quenching, thereby leading to an increase in the contact angle over time. The transformation of wetting behaviors on laser textured SiC surfaces can be achieved mutually by the aqueous quenching method.     

Study on microscale adhesion between solid surfaces with scanning probe

The adhesion between two parallel solid surfaces is of great interest with the rapid development of micro-nano devices and instruments. The adhesion forces between a flat tip with a diameter ～1.7 μm and some surface have been determined by recording the force-displacement curves with an atomic force microscope (AFM). The flat tip is used to prevent wear and mimic the adhesion between two parallel surfaces. The free energy of the solid surface is calculated by the contact angles between the probe liquids and the surface. The adhesion force between parallel solid surfaces cannot be predicted by the theory of thermodynamic surface free energy. The adhesion measurements were carried out under ambient conditions, in a nitrogen-filled glove box, under distilled water, and under potassium chloride (KCl) solution. The outcome shows that the real contact area without the applied load is only a small proportion of the apparent contact area. The measurement stability and repeatability of adhesion by the AFM depend on the surface characterization, measurement methods and the environment. Under different environments, there are different interactions and factors affecting the adhesion force, and the dominant interactions and factors may be different too. The various interactions and factors are mutually coupled to determine the final adhesion force.