Effective macroscopic interfacial transport equations in strongly heterogeneous environments for general homogeneous free energies

We study phase field equations in perforated domains for arbitrary free energies. These equations have found numerous applications in a wide spectrum of both science and engineering problems with homogeneous environments. Here, we focus on strongly heterogeneous materials with perforations such as porous media. To the best of our knowledge, we provide the first derivation of upscaled equations for general free energy densities. In view of the versatile applications of phase field equations, we expect that our study will lead to new modelling and computational perspectives for interfacial transport and phase transformations in strongly heterogeneous environments.     

超疏水状态的润湿转变与稳定性测试

超疏水材料具有自清洁、防水、低粘附等特性,因此具有重要的应用价值.维持超疏水状态的稳定性,避免水侵入到材料表面微结构内部是实现这些特性的基础.本文在水下超疏水界面全反射的基础上,结合真空技术,提出了一种连续、直观的测试方法来测试超疏水状态的稳定性,并研究了Cassie-Wenzel润湿过渡行为及其临界压力.实验结果表明:对于典型的柱状微凸起结构,Cassie-Wenzel润湿转变过程可分为四个阶段:非润湿阶段、主要润湿阶段、强化润湿阶段和完全润湿阶段.主要润湿过程中的临界压力与理论值一致;强化润湿阶段需在较高的压力作用下进行,从而驱动固/液系统过渡到完全润湿阶段.与柱状结构相比,荷叶的乳突状微结构在润湿过程并不存在非润湿阶段,这是因为二者对外部压力的抵抗方式不同所致:柱状微结构通过增大柱子间悬挂液面的曲率来与外部压力建立平衡,而乳突状微结构则通过润湿过程中三相接触线密度的增加来强化毛细作用力,从而与外部压力建立平衡.     

The potential use of nanosilver-decorated titanium dioxide nanofibers for toxin decomposition with antimicrobial and self-cleaning properties

While chemical and biological attacks pose risk to human health, clean air is of scientific, environmental and physiological concerns. In the present contribution, the potential use of nanosilver-decorated titanium dioxide (TiO₂) nanofibers for toxin decomposition with antimicrobial activity and self-cleaning properties was investigated. Titanium dioxide nanofibers were prepared through sol-gel reaction followed by an electrospinning process. Following the Japan Industrial Standard (JIS) protocol, decompositions of nitrogen oxide (NOx) and volatile organic compound (VOC) by the TiO₂ nanofibers suggested that these materials were capable of air treatment. To further enhance their anti-microbial activity, silver nanoparticles were decorated onto the TiO₂ nanofibers’ surfaces via photoreduction of silver ion in the presence of the nanofibers suspension. Furthermore, tests of photocatalytic activity of the samples were performed by photodegrading methylene blue in water. The nanofibrous membranes prepared from these nanofibers showed superhydrophilicity under UV. Finally, the possibility of using these hybrid nanofibers in environmental and hygienic nanofiltration was proposed, where the self-cleaning characteristics was expected to be valuable in maintenance processes.     

Hydrophobic properties of surfaces coated with fluoroalkylsiloxane and alkylsiloxane monolayers

A comparative analysis of hydrophobicity of fluoroalkylsiloxane and alkylsiloxane monolayers is presented. In order to compare wetting behavior on smooth and rough substrates, a simple model considering various self-assembly degrees of organic molecules and various area fractions of air inclusion is used. Sliding behavior for water on rough silanized needle-like surfaces is also evaluated. On smooth surfaces, regardless of assembly degree of coatings, contact angles of fluoroalkylsiloxane monolayers are always ∼10° larger. The difference, however, decreases when rough substrates with air inclusion are used. It is shown that assembly order of silane molecules and reduced water-solid contact area are the key factors leading to both high contact angles and low sliding angles. Such coatings are expected to be potential snow- and ice-repellent materials.     

Stable highly hydrophobic and oleophilic meshes for oil-water separation

This paper describes a simple method for fabricating both highly hydrophobic and oleophilic meshes by coating thin fluoro-containing films. The static contact angle of such meshes is greater than 150° for water, and close to 0° for kerosene, xylene and toluene. These meshes can separate water from oil effectively without resorting to any extra power or chemical agent. Moreover, they exhibited stable water resisting, anti-chemical erosion and anti-hot aging properties. It promises as a candidate for the separation of oil and water.     

Electrochemical control of surface wettability of poly(3-alkylthiophenes)

The effect of n-alkyl side-chain length on water contact angle with films in neutral and electrochemically doped states are studied. Increasing the side-chain from butyl to hexyl to octyl increases the contact angle of water on conjugated polymer films in both electrochemical states, but decreases the difference in angle between the states in the same film. Devices based on these films have potential application in, for example, guiding water and other liquids through microfluidic channels in lab-on-a-chip and micro-electro-mechanical (MEM) applications.     

双级微结构上二氧化硅粒子对微注压成型PP表面润湿特性的影响

提出一种柔性复制法,采用微注射压缩(μ-ICM)成型具有微拓扑结构的仿生聚丙烯(PP)表面.通过复制模板上的双级微结构,所成型的PP材料表面上呈现具有锥形顶面的双级微结构,即微棱和高纵横比的微锥体.由于微锥体之间的间隙较大,水滴浸润其间隙的上方,这使该表面呈现中等黏附的超疏水特性.在μ-ICM过程中,涂覆在模板上的二氧化硅纳米粒子(SNPs)被转移到熔体中,并牢牢附着于微结构表层,赋予其表面亚微米或微米粗糙度,形成多层次微结构.在附着有亲水SNPs的微结构上,高表面自由能使水滴完全浸润微锥体之间的间隙,表面的水接触角为161.9°、滚动角大于90°,呈现极高黏附的超疏水特性(花瓣效应);在附着有疏水SNPs的微结构上,水滴受疏水SNPs的排斥而减弱与表面之间的黏附作用,表面的水接触角为163.5°、滚动角为3.5°,呈现极低黏附的超疏水特性(荷叶效应).     

Wetting films on a hydrophilic silica surface obtained from aqueous solutions of hydrophobically modified inulin polymeric surfactant

The thickness of wetting films on a hydrophilic silica surface was investigated using a microinterferometric technique. Aqueous solutions of hydrophobically modified inulin (INUTEC^®SP1) at various concentrations, in the presence or absence of NaCl or Na₂SO₄, were studied. The equilibrium film thickness (h _eq) showed a complex dependence on INUTEC^®SP1 concentration. At low electrolyte concentrations, h _eq decreased with an increase in INUTEC^®SP1 concentration, reaching a minimum at 10^?6 mol dm^?3. However, at high electrolyte concentrations, this dependence became less pronounced. At any given INUTEC^®SP1 concentration, the equilibrium film thickness decreased with an increase in electrolyte concentration as a result of the compression of the electrical double layer reaching a minimum value. After that, the film thickness showed a small decrease with further increase in electrolyte concentration. This indicates that the electrostatic component of disjoining pressure can be neglected, and the steric repulsion of the loops and tails of INUTEC^®SP1 determined the film thickness.     

Modeling dewetting of ultra-thin solid films

We review some models for the dynamics of dewetting of ultra-thin solid films. We discuss the similarities and the differences between faceted and non-faceted systems. The faceting of the dewetting rim leads to corrections in the velocity of dewetting fronts both in flat and axisymmetric geometries. The faceting of the edge of the dewetting rim leads to a strong anisotropy of the dewetting instability. Faceting also induces novel dewetting regimes such as layer-by-layer dewetting, and monolayer dewetting.