动态法测定粉末-液体体系的接触角

润湿通常是指固体表面上的气体被液体所取代的过程。在理论上,可将润湿分成为沾湿(adhesion)、浸湿(immersion)和铺展(spreading)三类。在恒温恒压下,此过程的体系自由能的变化(-△G)为:     

非离子表面活性剂Triton X-100溶液在不同生长期小麦叶片表面的润湿行为

选择不同生长期小麦叶片,利用座滴法研究了非离子表面活性剂Triton X-100在小麦叶片表面接触角,考察浓度对接触角、粘附张力、固-液界面张力及润湿状态的影响。研究表明,在低浓度下,表面活性剂分子在气-液界面吸附量(ΓLV)和固-液界面吸附量(Γ'SL)相似,但吸附量较少形成了不饱和吸附层,接触角保持不变,其润湿状态为Cassie-Baxter状态;当浓度进一步增加,液滴突破叶片表面三维立体结构中存在的钉扎效应,取代空气层而处于Wenzel状态,接触角陡降,同时Γ'SL/ΓLV远大于1;当浓度超过临界胶束浓度(CMC)时,表面活性剂分子在气-液界面和固-液界面形成饱和吸附层,并产生毛细管效应,使溶液在小麦叶片三维立体结构中产生半渗透过程,此时接触角保持不变。     

生物基表面活性剂七叶皂素的界面行为

以天然三萜皂苷七叶皂素为研究对象, 分别采用吊片法、 悬滴法和高速摄像机动态拍摄法探究了七叶皂素分子在气-液、 液-液、 固-液界面的界面行为. 考察了以七叶皂素为乳化剂制备乳液的性质, 以及七叶皂素对液滴在疏水固体表面润湿铺展行为的调控规律, 并从分子层次角度分析了作用机理. 结果表明, 七叶皂素能在气-液界面发生吸附, 将水的表面张力降低至42.1 mN/m, 临界胶束浓度为5×10^?4 mol/L. 七叶皂素还可以在油-水界面吸附, 将亲油端插入油相, 亲水端插入水相, 形成稳定的界面膜, 降低界面张力. 以七叶皂素为乳化剂所制备的乳液, 随着浓度增大可以达到较小的粒径和较大的Zeta电势, 短时间内表现出较好的稳定性. 高浓度的七叶皂素可以很好地抑制液滴在疏水固体表面的弹跳和回缩, 达到很好的铺展效果, 有利于拓展其在诸多领域的应用.     

固体粉末在液体表面上的铺展性能研究

采用不同量的全氟烷基季胺碘化物(JF-111)对膨胀玻化微珠进行表面改性,利用Corel videostudio视频软件和IPP图像软件对改性膨胀玻化微珠在液体表面的铺展性能进行分析,通过测量铺展面积、铺展平均速度和铺展的均匀性研究了固体粉末粒径、固液接触角以及铺展液面性质对固体粉末在液面上铺展性能的影响。并与聚四氟乙烯作了对比研究,探讨粉末类型对粉末铺展性能的影响。研究结果表明:不同的固体粉末在同一液面上铺展,不能用铺展系数的大小对比二者的铺展情况。对于同一种基体粉末,铺展系数越大,即固液接触角越大,越容易铺展,而且铺展越均匀。就膨胀玻化微珠粉末而言,粒径越小,越容易铺展;液面相对于固体的表面能越高,固体粉末越容易在液面上铺展。     

苄基取代甜菜碱对聚四氟乙烯表面润湿性的影响

利用座滴法研究了两性离子表面活性剂苄基取代烷基羧基甜菜碱(BCB)和苄基取代烷基磺基甜菜碱(BSB)在聚四氟乙烯(PTFE)表面上的润湿性质,考察了表面活性剂浓度对接触角的影响趋势,并讨论了粘附张力、固-液界面张力和粘附功的变化规律.研究发现,在低浓度时,表面活性剂通过疏水作用吸附到PTFE表面,疏水链苄基取代支链化使其在固-液界面上的吸附明显低于气-液界面,接触角在很大的范围内保持不变.当体相浓度增加到大于临界胶束浓度(cmc)时, BCB和BSB分子在固-液界面上继续吸附,分子逐渐直立,造成PTFE-液体之间的界面张力(γ_SL)进一步降低,表面亲水性增加,接触角随浓度增加明显降低;另一方面, BSB由于具有较大的极性头,在高浓度时空间阻碍作用明显,导致其对PTFE表面润湿性改变程度小于BCB.     

双头基两亲分子在气液界面的Langmuir铺展膜结构

用表面压-面积等温线,原子力显微镜（AFM）和X射线衍射（XRD）对两种具有不同取代位置的新型双头基两亲分子（bolaamphiphile）A和B在气液界面形成的Langmuir铺展膜的结构进行了研究,化合物1,20-二十碳二β-萘酯（B）在气液界面形成了拉伸型 Langmuir单分子膜,而化合物1,20-二十碳二α-萘酯（A）在气液界面则形成了具有三层分子厚度的二维结晶膜.     

Gibbs吸附公式在固-气和固-液界面吸附中的应用

Gibbs吸附公式本适用于各种界面的吸附研究 ,但由于有固体参与形成的界面界面能测定困难 ,至今Gibbs公式多只用于气 液界面的研究。本文讨论了Gibbs吸附公式在固 气和固 液界面吸附研究中的应用 ,主要是介绍将Gibbs公式与二维气体状态方程结合导出吸附等温式 ,因吸附而引起的固 气和固 液界面能变化规律 ,以及吸附过程中分子状态变化的有关信息     

投影实验之十一——接触面积对化学反应速度的影响

在有固体参加的反应中,由于反应是在固体和液体或固体和气体的界面处发生的,所以如果能够增加固液或固气之间的接触面积,反应速度就会加快,即反应物之间的接触面积越大,化学反应速度越快。     

结构化液体的设计、构筑与应用

结构化液体是近年来基于二元流体体系,利用固体粒子液/液界面自组装和堵塞相变构筑的一类非平衡态软物质材料,兼具固体的结构稳定性和液体的流动性.然而,受限于组装基元和成型方法,制备具有精准结构的智能结构化液体及衍生功能材料仍面临挑战.我们课题组在该领域开展了大量研究工作,在发展界面调控新机制,制备液体/固体新材料,以及实现材料器件新突破等方面取得了系列创新成果.本专论从固体粒子界面自组装机制出发,重点阐述了一种利用纳米粒子和聚合物液/液界面共组装制备纳米粒子表面活性剂,进而构筑结构化液体的普适策略;总结归纳了结构化液体在响应性调控、高效精准构筑以及功能材料制备等方面的研究进展;并对该领域面临的机遇和挑战做出展望.     

十二烷基苯磺酸钠在SiO2表面聚集的分子动力学模拟

采用分子动力学方法研究了阴离子表面活性剂十二烷基苯磺酸钠(SDBS)在无定形SiO2固体表面的吸附. 设置不同的水层厚度, 观察固液界面和气液界面吸附的差异. 模拟发现表面活性剂分子能够在短时间内吸附到SiO2表面, 受碳链和固体表面之间相互作用的影响形成表面活性剂分子层, 并依据吸附量的大小形成不同的聚集结构; 在水层足够厚的情况下, 由于有较多的表面活性剂分子吸附在固体表面,从而形成带有疏水核心的半胶束结构; 计算得到的成对势表明极性头与钠离子或水分子之间的结合或解离与二者之间的能垒有关, 解离能垒远大于结合能垒, 引起更多Na+聚集在极性头周围而只有少数Na+存在于溶液中; 无论气液还是固液界面, 极性头均伸向水相, 与水分子形成不同类型的氢键. 模拟表明, 分子动力学方法可以作为实验的一种补充, 为实验提供必要的微观结构信息.     

Physical significance of contact angles

Summary The physical significance of contact angles has been interpreted on the basis of a model derived from known surface energy relationships. The degrees of non-spreading and spreading have been expressed in terms of the magnitude of contact angles. On the basis of the physical picture, hysteresis of contact angle has been calculated from the experimental values of equilibrium contact angle and surface tension of the liquid. It has been suggested that it is not necessary to assume that hysteresis of contact angles is due to surface roughness of solids. The picture also explains why apparent contact angle on a non-flat solid surface is more than that on a flat solid.With 2 figures and 1 table     

低能量链端对聚苯乙烯薄膜铺展和润湿行为的影响

通过低能量功能端基的表面富集作用,研究了聚苯乙烯（ＰＳ）薄膜在聚甲基丙烯酸甲酯（ＰＭＭＡ）表面上的铺展和润湿动力学．用光学显微镜跟踪了ＰＳ薄膜的润湿行为,并对高分子熔体膜中非连续部分尺寸的增大速率进行了测定．分别用ＸＰＳ和ＡＦＭ对ＰＳ薄膜的表面组成和ＰＳ液滴的平衡接触角进行了测定．发现具有低表面能的氟碳端基在薄膜表面富集使ＰＳ薄膜的表面张力下降,并使ＰＳ液滴在ＰＭＭＡ表面上的平衡接触角减小,从而使高分子熔体膜中非连续部分尺寸的增长速率下降,得到了与液液界面铺展和润湿理论一致的实验结果．     

Droplet morphologies on particles with macroscopic surface roughness

The equilibrium configuration of liquid droplets on the surface of macroscopically rough solid particles was determined by numerical simulations using the volume-of-fluid (VOF) method. The fractional surface coverage of the particle as a function of the droplet size, equilibrium contact angle, and the particle surface roughness amplitude and correlation length has been systematically investigated. Droplet size and contact angle were found to generally have a stronger effect on surface coverage than particle surface roughness. Because of droplet coalescence, a relatively large variation in surface coverage was observed for any given total liquid volume, particularly for larger values of the equilibrium contact angle.     

Robust hydrophobic surfaces displaying different surface roughness scales while maintaining the same wettability

A range of surfaces coated with spherical silica particles, covering the size range from nanometer to micrometer, have been produced using Langmuir-Blodgett (LB) deposition. The particles were characterized both in suspension and in the Langmuir trough to optimize the surface preparation procedure. By limiting the particle aggregation and surface layer failures during the preparation steps, well-defined monolayers with a close-packed structure have been obtained for all particle sizes. Thus, this procedure led to structured surfaces with a characteristic variation in the amplitude and spatial roughness parameters. In order to obtain robust surfaces, a sintering protocol and an AFM-based wear test to determine the stability of the deposited surface layer were employed. Hydrophobization of the LB films followed by water contact angle measurements showed, for all tested particle sizes, the same increase in contact angle compared to the contact angle of a flat hydrophobic surface. This indicates nearly hexagonal packing and gives evidence for nearly complete surface wetting of the surface features.     

Fabrication and Electrowetting Properties of Poly Si Nanostructure Based Superhydrophobic Platform

Poly-silicon based superhydrophobic surface (water contact angle >150°) is being fabricated and its electrowetting properties have been studied. The polysilicon thin film has been deposited over patterned gold electrodes. The polysilicon film is structured to form nanoscale features using Reactive Ion Etching. A thin film of HfO₂ high k-dielectric is deposited over the structured polysilicon surface. The surface was chemically modified with Trichloro (1H, 1H, 2H, 2H-perfluorooctyl) silane (PFOS). Such a surface showed Superhydrophobic behavior with water contact angle of 172° and roll off angle <3°. The electrowetting properties of the fabricated device was studied by applying a DC voltage between the gold electrode and the droplet. The electrowetting commences when the applied voltage was 18 V and the contact angle is reduced to 152°. As the applied voltage was increased there was decrease in contact angles.     

多嵌段聚硅氧烷聚脲共聚物及双离子型聚硅氨酯的表面性质的研究

本文利用光电子能谱(ESCA)和表面接触角研究了多嵌段聚硅氧烷聚脲共聚物(PUSE)和双离子型聚硅氨酯(PUSM)的表面性质,发现PUSE和PUSM中的软段聚硅氧烷均在表面富集;提高本体的相分离程度,更有利于软段的表面富集;但在50层内,硬段仍有一定的比例,表面层仍是多相结构。在PUSE中,接触角和凝血时间随聚硅氧烷软段比例增加而增加,在PUSM中,随离子化程度的提高,亲水性提高,接触角变小,凝血时间缩短。     

Liquid drops on vertical and inclined surfaces; I. An experimental study of drop geometry

Experiments have been conducted to investigate the geometric parameters necessary to describe the shapes of liquid drops on vertical and inclined plane surfaces. Two liquids and eight surfaces have been used to study contact angles, contact lines, profiles, and volumes of drops of different sizes for a range of surface conditions. The results show the contact-angle variation along the circumference of a drop to be best fit by a third-degree polynomial in the azimuthal angle. This contact-angle function is expressed in terms of the maximum and minimum contact angles of the drop, which are determined for various conditions. The maximum contact angle, thetamax, is approximately equal to the advancing contact angle, thetaA, of the liquid on the surface. As the Bond number, Bo, increases from 0 to a maximum, the minimum contact angle, thetamin, decreases almost linearly from the advancing to the receding angle. A general relation is found between thetamin/thetaA and Bo for different liquid-surface combinations. The drop contour can be described by an ellipse, with the aspect ratio increasing with Bo. These experimental results are valuable in modeling drop shape, as presented in Part II of this work.     

Directing droplets using microstructured surfaces

Systematic variation of microscale structures has been employed to create a rough superhydrophobic surface with a contact angle gradient. Droplets are propelled down these gradients, overcoming contact angle hysteresis using energy supplied by mechanical vibration. The rough hydrophobic surfaces have been designed to maintain air traps beneath the droplet by stabilizing its Fakir state. Dimensions and spacing of the microfabricated pillars in silicon control the solid-liquid contact area and are varied to create a gradient in the apparent contact angle. This work introduces the solid-liquid contact area fraction as a new control variable in any scheme of manipulating droplets, presenting theory, fabricated structures, and experimental results that validate the approach.     

Calomel reference electrode in propylene carbonate

Measurements of the contact angle of an air bubble against thin films of silver iodide in an electrolyte solution have been made, using the captive bubble technique, as a function of pAg. The receding contact angle reached its maximum value at a pAg=5.4±0.2. This pAg value coincides closely with the isoelectric point of the silver iodide solution interface. A thermodynamic analysis is given which relates the variation of contact angle to the variation of concentration of potential determining ions and surface charge density.     

Wettability of carbon nanofiber layers on nickel foils

Carbon nanofiber (CNF) layers have been directly synthesized on nickel foils by chemical vapor deposition at 450°C using different H(2) concentrations and reaction times. The addition of 5% H(2) produces thicker, rougher and more porous CNF layers than when 1% H(2) is used. The roughness and porosity increases with reaction time when 5%, 10% or 20% H(2) are used; however, this effect is less pronounced when 1% H(2) is used. CNFs are 50-55 nm in diameter and have a fishbone type structure. We have studied the influence of CNF layer thickness, porosity and surface roughness on the interaction with water by measuring the contact angle. The water wetting properties of the samples are more significantly influenced by the CNF layer thickness than both surface roughness and porosity. When the CNF layer is thicker than ca. 20 μm, the surface is hydrophobic and the contact angle increases with surface roughness and porosity. When the CNF layer is thinner than ca. 20 μm, the surface is hydrophilic and the contact angle decreases with increasing surface roughness and porosity. This behavior is attributed to penetration of water, making contact with the hydrophilic C layer between the CNF layer and the foil.