纳米通道内表面浸润性对气泡的作用

运用分子动力学模拟方法研究了在质量力驱动下不同浸润性壁面纳米通道中气泡的分布及其运动状况, 提出了一种统计纳米通道中气泡运动速度的方法. 结果显示, 在亲水性壁面的纳米通道中, 气泡位于通道中间, 气泡的运动速度接近但小于通道中心流速, 在势能强度较大时, 壁面吸附的分子较多, 气泡也较大, 反之则气泡较小; 对超疏水性壁面, 气泡则位于固壁附近, 两个壁面形成对称的一对气泡, 气泡的运动速度接近但大于边缘速度. 流体总的流动速度随着流体粒子与壁面粒子作用的减弱而增大, 滑移速度则逐渐从负转变为正.  

Bubble formation in a quiescent pool of gold nanoparticle suspension

This paper begins with an extensive review of the formation of gas bubbles, with a particular focus on the dynamics of triple lines, in a pure liquid and progresses into an experimental study of bubble formation on a micrometer-sized nozzle immersed in a quiescent pool of aqueous gold nanofluid. Unlike previous studies of triple line dynamics in a nanofluid under evaporation or boiling conditions, which are mainly caused by the solid surface modification due to particle sedimentation, this work focuses on the roles of nanoparticles suspended in the liquid phase. The experiments are conducted under a wide range of flow rates and nanoparticle concentrations, and many interesting phenomena are revealed. It is observed that nanofluids prevent the spreading of the triple line during bubble formation, i.e. the triple line is pinned somewhere around the middle of the tube wall during the rapid bubble formation stage whereas it spreads to the outer edge of the tube for pure water. A unique ‘stick-slip’ movement of the triple line is also observed for bubbles forming in nanofluids. At a given bubble volume, the radius of the contact line is found to be smaller for higher particle concentrations, but a reverse trend is found for the dynamic bubble contact angle. With the increase of particle concentration, the bubble frequency is raised and the bubble departure volume is decreased. The bubble shape is found to be in a good agreement with the prediction from Young-Laplace equation for given flow rates. The influence of nanoparticles on other detailed characteristics related to bubble growth inside, including the variation of bubble volume expansion rate, the radius of the curvature at the apex, the bubble height and bubble volume, is revealed. It is suggested that the variation of surface tensions and the resultant force balance at the triple line might be responsible for the modified dynamics of the triple line.  

化学吸附自组装偶氮苯小分子单层膜及表面浸润性研究

通过化学吸附自组装的方法, 将小分子量的偶氮苯分子自组装到平滑硅基底表面, 其表面接触角为83.7°. 微结构化硅基底表面的偶氮苯单层膜上表现出超疏水的特性, 接触角达到了151.9°. 经过紫外光照射后, 该表面的接触角没有发生明显的降低.  

Degradation patterns and surface wettability of electrospun fibrous mats

Degradation profiles and surface wettability are critical for optimal application of electrospun fibrous mats as drug carriers, tissue growth scaffolds and wound dressing materials. The effect of surface morphologies and chemical groups on surface wettability, and the resulting matrix degradation profiles were firstly assessed for electrospun poly(d,l-lactide) (PDLLA) and poly(d,l-lactide)-poly(ethylene glycol) (PELA) fibers. The air entrapment between the fiber interfaces clarified the effects of various surface morphologies on the surface wettability. Chemical groups with lower binding energy were enriched on the fiber surface due to the high voltage of the electrospinning process, and a surface erosion pattern was detected in the degradation of electrospun PDLLA fibers, which was quite different from the bulk degradation pattern for other forms of PDLLA. Contributed by the hydrophilic poly(ethylene glycol) segments, the degradation of electrospun PELA fibers with hydrophobic surface followed a pattern different from surface erosion and typical bulk degradation.  

Polymer brushes on hydrogen-terminated silicon substrates via stable Si—C bond

A universal and straightforward method for the preparation of polymer brushes via the formation of Si-C bond on silicon substrates through the UV-induced photopolymerization is demonstrated.  

Liquid crystal alignment induced by controllable surface wettability of BiFeO3 bumps thin layer

The alignment of liquid crystals (LCs) in LC-based optical devices determines the visual quality of devices, and a simple pretreatment is necessary for LC alignment. Here, we present a BiFeO₃ (BFO) thin layer working as an alignment layer, homogeneously aligning LCs after a pre-thermal annealing treatment. Dramatic BFO bumps were observed during the thermal annealing process, and a corresponding enhancement in wettability was detected from measurement of tunable contact angles. LCs in the BFO bump thin layer sandwiched TN cell were found to be perfectly homogeneously aligned due to the enhanced anisotropy and wettability caused by the morphology change of the thin layer.  

Superhydrophobic surfaces with low and high adhesion made from mixed (hydrocarbon and fluorocarbon) 3,4‐propylenedioxythiophene monomers

This work concerns new superhydrophobic surfaces, generated by replacing long fluorocarbon chains, which bioaccumulate, with short chains whilst at the same time retaining oleophobic properties. Here, is described the synthesis of novel 3,4‐propylenedioxythiophene derivatives containing both a short fluorocarbon chain (perfluorobutyl) and a hydrocarbon chain of various lengths (ethyl, butyl and hexyl). Superhydrophobic (θ_water > 150°) surfaces with good oleophobic properties (60° > θ_hexadecane > 80°) have been obtained by electrodeposition using cyclic voltammetry. Surprisingly, the lowest hystereses and sliding angles (Lotus effect) are obtained with the shortest alkyl chains due to the presence of microstructures made of nanofibers on the surfaces, whereas, the longest alkyl chains leads to nanosheets with high adhesion (Petal effect). Such materials are potential candidates for biomedical applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 782–788  

Reversible Wettability of Tungsten Trioxide Films with Novel Dandelion‐like Structures

Tungsten trioxide (WO₃) films with novel dandelion‐like structures were prepared by spin‐coating a sol of WO₃ with CTAB (cetyltrimethyl ammonium bromides) on quartz substrates. The resultant WO₃ films were characterized by X‐ray diffraction (XRD), FT‐IR spectroscopy, scanning electron microscopy (SEM), and X‐ray photoelectron spectroscopy (XPS). The wettabilities of the WO₃ films were evaluated by contact angle (CA) measurements. It was found that the WO₃ film exhibited superhydrophilicity under UV light irradiation, whereas after storage in the dark for a certain time, it turned to be superhydrophobic.  

Surface enrichment and crystallization of polyamide and polytetrafluoroethylene blend

The blend surface of polyamide 6 and polytetrafluoroethylene (PA 6/PTFE) and its change as a function of annealing time are investigated by means of attenuated total reflection (ATR)‐FTIR spectroscopy, contact angle (CA) measurement, as well as atomic force microscopy (AFM) under ambient condition; meanwhile the surface elemental compositions are obtained by X‐ray photoelectron spectroscopy (XPS). The results show that the addition of fluoro content can decrease the surface energy compared with the pure polyamide, while, an evident influence on the surface energy has not been detected with increasing fluoro contents. Upon annealing at 120 °C, there is a profound enrichment of the low‐surface energy component to the sample surface; yet this situation becomes more complex when samples are annealed at 150 °C—not only the segregation effect from the low surface energy PTFE, but also the crystallization of the PA 6 will come into play for the blend with 50% PTFE. These observations are ascribed to the presence of the polar group of the polyamide component, as well as its strong tendency to crystallize when subjected to thermal treatment at sufficiently high temperatures, and this behavior would basically offset the segregation tendency of fluoro component to the sample surface. This assumption is further corroborated by the XPS measurement in the current researches. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 138–152, 2007