纳米级稠化剂颗粒沉积膜在乏脂润滑中的作用机制研究

利用双光束干涉法对点接触区乏脂润滑成膜特性规律以及接触区附近润滑剂的微观迁移特性进行了观测.在试验条件下,接触区会经历充分润滑—乏脂—沉积膜润滑—分离油润滑等润滑状态.借助原子力显微镜,探测到沉积膜是润滑脂的稠化剂被碾压破碎而沉积在滚压轨道表面的一层纳米级颗粒薄膜;而分离油是在剪切过程中润滑脂内逐渐释放基础油.试验初始,接触区周围的润滑脂池因乏脂而迅速消失,但分离油会逐渐形成"第二相油池"以实现回流补给.沉积膜增大了基础油在滚动轨道表面的接触角,阻碍回流补给,但其会随运动逐渐磨损,此后分离油将进入接触区补充润滑膜.初步发现,当分离油不充足时,沉积膜有利于保护润滑轨道.     

Interaction between model poly(ethylene terephthalate) thin films and weakly ionised oxygen plasma

Model films of poly(ethylene terephthalate) were treated by oxygen plasma in order to quantify the etching rate and estimate the contribution of charged and neutral particles to the reaction probability. Model films with a thickness of 50 nm were deposited on a quartz crystal of a microbalance (QCM) by spin‐coating technique. The samples were exposed to oxygen plasma with the positive ion density of 4 × 10¹⁵ m^?3 and neutral oxygen atom density of 6 × 10²¹ m^?3. The etching rate was determined from the QCM signal and was 4.7 nm s^?1. The etching was found rather inhomogeneous as the atomic force microscopic images showed an increase of the surface roughness as a result of plasma treatment. The model films were completely removed from the surface of the quartz crystals in about 12 s. Knowing the etching rate and the flux of oxygen atoms to the surface allowed for calculation of the reaction probability which was found to be rather low at the value of 1.6 × 10^?4. Copyright © 2011 John Wiley & Sons, Ltd.     

Photocatalytic Activity and Photo-Induced Wettability Conversion of TiO2 Thin Film Prepared by Sol-Gel Process on a Soda-Lime Glass

We have developed the transparent photoactive TiO₂ thin film coated on soda lime glass (SLG) by sol-gel process. Titanium dioxide thin films coated on SLG exhibit lower photocatalytic activity due to the thermal diffusion of Na ion from the SLG substrate. Thin SiO₂ film precoating is very effective to prevent the thermal diffusion of Na ion. We have evaluated the photocatalytic decomposition of gaseous acetaldehyde and the photo-induced surface wettability of TiO₂ films with and without SiO₂ precoating layer. As expected, the TiO₂ film on SiO₂/SLG is more photoactive to decompose acetaldehyde than that on SLG. However, as for wettability conversion, there was little difference in the conversion rate between TiO₂ film without SiO₂, and TiO₂ film with SiO₂. Different dependence of Na ion diffusion on two kinds of photo-induced reaction on TiO₂ is discussed based on the difference of the photo-induced reaction mechanism.     

Chemical Dual‐Responsive Wettability of Superhydrophobic PANI‐PAN Coaxial Nanofibers

PANI‐PAN coaxial nanofibers have been prepared by electro‐spinning during polymerization. The surface of the resulting nanofibers is superhydrophobic with a water contact angle up to 164.5°. Conductivity of the PANI‐PAN nanofibers is about 4.3 × 10⁻² S · cm⁻¹. The superhydrophobic nanofibers show a chemical dual‐responsive surface wettability, which can be easily triggered by changing pH value or redox properties of the solution. A reversible conversion between superhydrophobicity and superhydrophilicity can be performed in a short time. The strategy used here may provide an easy method to control the wettability of smart surfaces by using properties of low‐cost functional polymers.

     

Reversible Wettability Switching of Polyaniline‐Coated Fabric,Triggered by Ammonia Gas

A superhydrophobic polyaniline (PANI)‐coated fabric was prepared by in‐situ doping polymerization in the presence of perfluorosebacic acid (PFSEA) as the dopant. It is found that the PANI‐coated fabric undergoes a change in wettability from superhydrophobic (doped state) to superhydrophilic (de‐doped state) when it is exposed to ammonia gas. In particular, a reversible wettability of the PANI‐fabric is observed when it is doped with PFSEA and de‐doped with ammonium gas. It is proposed that the coordination effect of the pore structure of the polyester fabric, low surface energy of the PFSEA dopant, and reversible doping/dedoping characteristics of PANI results in the reversible wettability of the PANI‐coated fabric from superhydrophobicity to superhydrophilicity. Moreover, the tactic used here may provide a new method to monitor the toxic gas.

     

激光刻蚀硅表面的形貌及其对浸润性的影响

利用脉冲激光在Si表面刻蚀具有不同宽度和深度的微槽形貌, 通过测量接触角的大小研究其浸润特性, 并分析了形貌与浸润性的关系. 结果表明, 在Si表面刻蚀微槽深度一定的条件下, 刻蚀微槽宽度越宽, 接触角越小; 在Si表面刻蚀微槽宽度一定的条件下, 刻蚀微槽越深, 接触角越大, 最高可达165°. 而且Si表面上刻蚀后产生的细微尖峰结构对其浸润特性有显著的影响. 因此, 利用激光刻蚀表面方法可以在一定程度上调控固体表面的润湿性能.     

Wettability of cellular polyurethane

Cellular polymers constitute an important field of investigation due to their unique properties as shock absorbers and thermal or acoustic insulators. The knowledge of the wetting properties of these materials is important in applications where adhesion or weathering behavior are an issue. In this study, cellular polyurethane polymers were used to investigate the effect of the cellular structure on the wetting properties. The polymeric substrates were analyzed by scanning electron microscopy and the wetting properties were studied by goniometry. The contact angles of water and diiodomethane were measured as a function of time and the surface tension of the expanded polymers was evaluated by the geometric and harmonic mean methods. It was found that the wettability and the surface energy of the cellular polymers increase as the density decreases. © 1997 John Wiley & Sons, Inc.     

纳米尺度下毛细流动的分子动力学模拟

采用分子动力学模拟研究纳米尺度下壁面润湿性对毛细流动的影响,主要考虑纳米通道两侧壁面润湿性相同与不同两种情况。研究表明：两侧壁面润湿性相同条件下,毛细流动随着壁面润湿性增强而加快, 毛细高度随时间的变化早期偏离Lucas-Washburn理论,但后期与其预测符合。在纳米通道两侧壁面润湿性不同的情况下,液面会发生振荡,两侧壁面毛细高度也不相等,且液面振荡的幅度和两侧壁面毛细高度差都随着两侧壁面润湿性差异的增大而增大。基于能量转化分析,提出两侧壁面湿润性不同情况下纳米通道中毛细流动发生的条件以及毛细流动快慢的判别依据。研究结果加深了对纳米尺度下毛细流动机理的认识,并为相关工程应用提供理论参考。     

Lattice Boltzmann study of the interaction between a single solid particle and a thin liquid film

The isothermal single-component multi-phase lattice Boltzmann method(LBM) combined with the particle motion model is used to simulate the detailed process of liquid film rupture induced by a single spherical particle.The entire process of the liquid film rupture can be divided into two stages.In Stage 1,the particle contacts with the liquid film and moves into it due to the interfacial force and finally penetrates the liquid film.Then in Stage 2,the upper and lower liquid surfaces of the thin film are driven by the capillary force and approach to each other along the surface of the particle,resulting in a complete rupture.It is found that a hydrophobic particle with a contact angle of 106.7° shows the shortest rupture duration when the liquid film thickness is less than the particle radius.When the thickness of the liquid film is greater than the immersed depth of the particle at equilibrium,the time of liquid film rupture caused by a hydrophobic particle will be increased.On the other hand,a moderately hydrophilic particle can form a bridge in the middle of the liquid film to enhance the stability of the thin liquid film.     

A mechanically robust copper mesh with switchable wettability and antibacterial activity for selective oil–water separation

With the continuous improvement in living standards, the discharge of oily sewage in daily life and industry has gradually increased, causing considerable damage to the environment and also great inconvenience to people. Traditional treatment methods cannot meet the increasing demand for sewage treatment, so more efficient treatment methods need to be studied. Research on oil–water separation materials is gradually becoming intelligent, but most of these intelligent materials cannot solve the problem of bacterial growth on the surface, new antibacterial and hydrophobic materials need to be studied. Here, an inexpensive and simple method is presented to prepare an antibacterial copper mesh with pH-responsive wettability between hydrophilic and hydrophobic. First, a copper mesh with a rough surface was prepared by an oxidation method, and then the oxidized copper mesh was immersed in the prepared coating solution of stearate (SA)-TiO₂ to obtain a superhydrophobic copper mesh. Scanning electron microscopy analysis showed that the modified copper mesh changed from the original smooth surface to a rough surface covered with needle-like nano-oxide wires. The SA-TiO₂-coated copper mesh (STCM) has good separation efficiency (about 97%) and separation flux (about 1.1 × 10⁵ L·m⁻²·h⁻¹) for the immiscible oil–water mixture, the separation efficiency remained basically unchanged (about 97%) after 15 separation cycles, and the wettability of this can be changed by soaking in an alkaline solution at a specific pH (from 12 to 14). In addition, the prepared STCM showed good antibacterial properties against Staphylococcus aureus and Escherichia coli. This preparation strategy of STCM provides a low-cost and facile method for wastewater treatment in practical applications.