Understanding of surface tension?

The importance of the molar dimensions for surface properties of not too large molecules is stressed. The understanding of surface properties of pure liquids is described in molar units with a simple model of normal liquids. The increasing knowledge makes it necessary to use idealized models. A hypothesis is given for the temperature constancy of the surface energy of small molecules without H-bonds, and a model is developed for the free energy σ_m and its temperature dependency. This seldom example of the direct measurement of the isothermic work or the free energy could help to illustrate the difference between energy and free energy. Received: 24 July 2000 Accepted: 26 October 2000     

基于表面金属有机化学方法的硅胶表面氧化钛的制备及表征

以普通硅胶为载体, 采用表面金属有机化学合成技术, 通过“一锅”反应制备了硅胶表面金属有机钛化合物, 然后经高温煅烧获得了硅胶表面氧化钛. 采用傅里叶变换红外光谱(FTIR)、 X射线光电子能谱(XPS)、 热重分析(TG-DTA)及原子力显微镜(AFM)对硅胶表面金属有机钛化合物和表面氧化钛进行了结构表征. 结果表明, 高温煅烧过程中, 硅胶表面金属有机钛化合物不仅脱除了有机配体, 并且通氧使其表面“再生”羟基, 确保了钛的四配位形式不变; 氧化钛通过Si—O—Ti键锚定在硅胶表面, 呈分散、 孤立状态分布. 高温煅烧后, 硅胶的骨架结构保持完好.     

Surface crystallization and phase transitions of the adsorbed film of F(CF<Subscript>2</Subscript>)<Subscript>12</Subscript>(CH<Subscript>2</Subscript>)<Subscript>16</Subscript>H at the surface of liquid tetradecane

The interaction between a long chain alkane, tetradecane (abbreviated H₁₄), molecule and a semi-fluorinated alkane, 1-perfluorododecyl-hexadecane F(CF₂)₁₂(CH₂)₁₆H (abbreviated F₁₂H₁₆), molecule at the air/ H₁₄ solution interface was studied by measuring the surface tension of the H₁₄ solutions of F₁₂H₁₆ as a function of temperature and bulk concentration under atmospheric pressure. Pure liquid H₁₄ freezes without forming a condensed film at its surface. Nevertheless, a very small amount of F₁₂H₁₆ initiates the surface freezing of H₁₄. In contrast to the F₁₂H₁₆-hexadecane (abbreviated H₁₆) system, the condensed monolayer of H₁₄ has a finite solubility of F₁₂H₁₆ in the F₁₂H₁₆-H₁₄ system. By further increasing the bulk concentration of F₁₂H_16, the F₁₂ chains of the F₁₂H₁₆ molecules form the other closely packed condensed state. Hence, as in the case of the H₁₆ system, the H₁₄ system also exhibits a surface hetero-azeotrope behavior in the lower temperature region. Below the surface hetero-azeotropic point, the condensed H₁₄ monolayer containing a small amount of F₁₂H₁₆ is completely replaced by the condensed monolayer of F₁₂H₁₆. At 2 °C, for example, a surface of H₁₄ solution of F₁₂H₁₆ covered with a gaseous film of F₁₂H₁₆ is replaced by a condensed H₁₄ monolayer containing an almost gaseous state of F₁₂H₁₆, and is then completely replaced by the condensed monolayer of F₁₂H₁₆ with increasing bulk concentration. Above the temperature of the triple point for the F₁₂H₁₆ monolayer, the F₁₂H₁₆-H₁₄ system exhibits a gaseous, expanded, and condensed state.     

Surface thermodynamics of binary mixtures of ethylene glycol + cyclohexanol or cyclopentanol

Surface tension data of binary mixtures of ethylene glycol + cyclohexanol and ethylene glycol + cyclopentanol was measured over the entire concentration range at various temperatures. The experimental values were correlated with temperature and with mole fraction. The values of the surface entropy, surface enthalpy and excess surface tension for these mixtures were also calculated.     

The surface energy of kaolinite

The surface energy of kaolinite was determined from the water adsorption isotherm, the water/kaolinite contact angle, and the surface tension of water, using a formula obtained by combining the Young equation with the general equation of pair interaction. This formula could be represented by a polynomial function whose roots gave one real value of 252.57±2.75 mJ m^–2 for the surface energy of kaolinite. An important feature of the procedure for obtaining this energy is the use of the Young equation to determine the range in which the value of the surface energy lies.     

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.     

二氧化钛纳米材料的非均相光催化本质及表面改性

非均相光催化过程是指多相多尺度体系在光辐射作用下发生的一个复杂的催化过程,被认为最有潜力解决环境污染和能源短缺问题的绿色及可再生的技术之一。在目前已经报道的各种非均相光催化剂中, TiO2纳米材料被证实是应用最广泛、光催化效果最好的催化剂,是当前国际材料、环境和能源等领域的研究前沿和热点,高性能TiO2基光催化材料的设计及改性一直是该领域的难点,其关键问题主要为：如何增强TiO2的表面光催化量子效率、促进光生载流子分离和拓展其可见光响应范围。尽管已经有很多关于TiO2光催化的综述,但大多综述集中在高性能TiO2的制备及各种改性策略研究,而对各种改性策略与光催化分子机理之间的关系阐述较少。为此,本文深入分析了TiO2纳米材料的非均相光催化本质并总结了各种表面改性策略。首先从热力学角度阐明TiO2的热力学能带能够确保其实现各种典型光催化反应(包括光催化降解、CO2还原及光解水),证实其广泛应用的可行性。然后,对TiO2光生载流子的动力学基础进行总结,证实快速的广生载流子复合以及较慢的表面化学反应动力学是限制其光催化活性提高的关键制约性因素。于此同时,对TiO2纳米材料的表面Zeta点位、超亲水性、超强酸光催化剂制备(表面羟基取代)等重要的表面化学性质也进行了详细阐述。从而可以初步得出如下结论：表面改性是设计高性能TiO2光催化材料的重中之重,并将各种改性策略浓缩在6个方面：表面掺杂和敏化,构建表面异质结,负载纳米助催化剂,增加可利用的比表面剂,利用表面氟效应以及暴露高活性晶面等。显然,表面掺杂和敏化可以减小TiO2纳米材料的禁带宽度,从而大幅拓宽其可见光吸收范围及光催化效率。而构建紧密的表面异质结可以创建界面电场,不仅可以促进光生电荷分离效率,而且可以有效提高界面电荷转移效率,最终实现异质结的高光催化效率。负载纳米助催化剂则可以大幅加快表面化学反速率,降低光生载流子的表面复合并增加其利用率,并有可能减少不期望的表面逆反应,从而实现光催化活性提升。增加可利用的比表面剂,可以有效提升光催化剂与吸附质之间的有效接触面积,缩短了载流子的传输距离以及通过多次反射与折射提升光能的利用率,从而全方位地提升TiO2纳米材料的光催化活性。对TiO2纳米材料表面进行氟化,可以增加光生羟基自由基的速率以及浓度,并可以通过调节TiO2表面酸碱性而控制其光催化选择性,从而实现高效高选择性光催化。最后,通过暴露TiO2纳米材料的高活性晶面,也可以促进光生载流子分离、增加吸附性能或羟基自由基生成速率,从而获得高光催化效率。另外,这些表面改性策略的协同效应仍是较有前景的TiO2纳米光催化剂改性技术,值得深入研究。同时,深入的光催化分子机理探索仍然是必须的,其不仅有助于发现影响TiO2纳米材料光催化活性提高的关键性制约因素,而且也可以指导开发新型的TiO2纳米光催化剂改性技术。总而言之,通过总结TiO2纳米材料在光催化、表面化学及表面改性等方面的重要进展,可为设计高效的TiO2基及非TiO2基光催化剂并应用于太阳燃料生产、环境修复、有机合成及相关的领域(如太阳能电池、热催、分离和纯化)等提供新的思路。     

Potential-induced structural deformation at electrode surfaces

The atomic structure on the metal side of the electrochemical interface depends on the applied electric potential and the nature of the adsorbing species in the electrolyte solution. In this short article, we review some recent results probing surface stress and surface relaxation effects in single-crystal metal electrodes that are driven by potential changes. Both the potential and the structure in the electrolyte layers at the interface alter the metal electronic structure so that the surface in the electrochemical environment is strongly modified from the ultra-high vacuum counterpart. A methodology for linking experimental and theoretical approaches for a fundamental understanding of electrochemical reactions is proposed.     

聚酰胺-胺型树枝状高分子水溶液的表面活性

树枝状化合物是一类三维的、高度有序的新型高分子.与传统高分子相比,这类化合物在合成时,可以在分子水平上严格控制,设计分子大小、形状、结构和功能基团,产物一般高度对称,单分散性好.因而具有广泛的潜在用途^[1,2].近年来,已引起广大化学工作者的重视.     

To the problem of first order phase transition at the fluid–fluid interface

The thermodynamic analysis is developed to describe both the surface freezing and the surface melting in various systems. The key physico-chemical parameters determining the shift of the freezing temperature in boundary phases in comparison to the temperature of corresponding bulk phase transition are discussed.     

EFFECTS OF SOLVENT TREATMENT ON SURFACE MORPHOLOGY AND COMPOSITION OF POLY(METHYL METHACRYLATE)-g-POLY(ETHYLENE OXIDE)

Surface morphology and composition of solution-cast films of poly(methyl methacrylate)-g-poly(ethylene oxide)(PMMA-g-PEO) were investigated by using XPS, DSC, SEM and contact angle measurement. The microphase separatedstructure of the copolymers was studied by TEM. Generally, for the same graft copolymer, the surface content of PEO orhydrophilicity can be as follows: Surface treated with petroleum ether or cyclohexane>surface untreated with solvent>surface treated with water or ethyl alcohol. Graft copolymer having longer PEO side chains and higher PEO content shows aseparated PEO phase with even a certain degree of crystallinity on the surface. PEO crystallinity was destroyed by water orethyl alcohol treatment, however, surface treatment with petroleum ether or cyclohexane favors the growth of PEO crystal.TEM shows that graft copolymers with longer PEO side chains (M_n of PEO, 3200) may readily undergo microphase separation and the shape and size of domains depend on the copolymer's composition.     

Surface oxidation of rubber crumb with ozone

Rubber crumb derived from the grinding of used truck tread and tyres is used as a low cost filler in rubber compounds based on diene rubber. In order to expand its application to other fields, the surface modification of the rubber crumb could be an interesting and feasible solution. In fact, the surface modification of rubber crumb may be used as a tool to expand its use in applications to compounds with polar rubber matrices or where hydrophilic surface of the rubber crumb could be desirable, for example in water-based dispersion or as filler for asphalt. In the present work, ozone has been used as the active agent to cause surface oxidation and functionalisation of rubber crumb in a fluidized bed reaction. The rubber crumb reacts swiftly with ozone producing CO₂ in the initial stages of reaction and then leading to the desired surface oxidized product. The rate constant of the reaction between ozone and rubber crumb has been determined by FT-IR spectroscopy, monitoring the consumption of ozone in the gas phase in the presence of the crumb. A rate constant value of 5.03 × 10⁻³ s⁻¹  g⁻¹ of rubber crumb was determined. The degree of the surface oxidation of the rubber crumb can be determined by FT-IR spectroscopy using as reference the intensity of the ketone band at about 1710 cm⁻¹. Additionally the nominal ratio between the amount of ozone (in mg) reacted with rubber crumb (in g) can be used as a parameter for the degree of the surface oxidation. The surface oxidized rubber crumb shows surface acidity and hydrophilicity. Thermogravimetric analysis, differential thermal analysis and pyrolysis-GC clearly demonstrate that the ozonization of the rubber crumb is directed exclusively to the surface of the crumb and does not affect the bulk properties at all.     

表面波在表面活性剂流变学研究中的应用

论述了表面波的原理及其发展，文中进一步讨论了毛细波和纵向波的特点，较为详细地介绍了纵向波的实验方法和装置以及在表面活性剂流学变性质研究中的应用。     

Application of inverse gas chromatography in the characterization of raw material used in manufacturing of abrasive materials

The raw material—aloxite used during the manufacturing of grinding tools was characterized by means of inverse gas chromatography (IGC). The surface properties of the different types of aloxite were determined including: (i) the specific surface area; (ii) the dispersive component of surface free energy as well as the sensitivity of this parameter on the environment humidity; and (iii) acidity and basicity of the examined surfaces. The results of our experiments proved the usefulness of IGC in the characterization of this kind of materials.     

表面波技术研究TBP对C12E8表面流变性质的影响

The influence of antifoaming agent TBP on the surface adsorption and on the surface rheological properties of foaming agent C12E8 is investigated by the damped longitudinal wave method, and the antifoaming mechanism of the antifoaming agent TBP on C12E8 is explored in this paper. The experimental results show that while the concentration of foaming agent C12E8 is smaller than cmc and at ω=6.28 rad•s-1, the decreases of surface dilational modulus, surface dilational elasticity, surface dilational viscosity and the increases of the phase angle when the concentration of TBP increase for the C12E8+TBP aqueous solution (C12E8=0.074 mmol•L-1) have been related to the diffusional exchange between surface and bulk and to the Marangoni effect, which depends on the restored mechanism of surface tension gradient due to the stretched surface. This has been related to the mechanism of antifoaming action.     

表面波技术研究TBP对C12E8表面流变性质的影响

利用表面波技术研究消泡剂ＴＢＰ对起泡剂Ｃ１３Ｅ８表面流变性质的影响,阐述泡沫的排液过程中液膜变形所产生的表面张力梯度修复机理以及液膜强度与表面彭胀模量、表面膨胀弹性和表面膨胀粘度的,探讨了消泡剂ＴＢＰ的消泡机理。实验结果表明,当包剂Ｃ１２Ｅ８浓度泪地ｃｍｃ时,ＴＢＰ能大幅芳地降低Ｃ１２Ｅ８的表面膨胀模量、表面膨胀弹性表面膨胀粘度,其中对表面膨胀性的影响大于对表面膨用粘度的影响,并且增加了Ｃ１２Ｅ１     

熔融碳酸盐燃料电池阳极材料表面改性

选择铌作为合金化元素，通过氟化物熔盐电化学表面合金化的方法对熔融碳酸盐燃料电池阳极材料镍进行表面改性，改性后的阳极材料的耐蚀性能与电催化性能均得到明显的改善。     

The importance of aspect ratio in profile analysis tensiometry

The latest developments in profile analysis tensiometry (PAT) for determining surface tension and interfacial viscoelastic parameters involve the determination of a digital interface profile and its best fit with the Young–Laplace equation. In this short communication, we show that the results for surface tension and other interfacial parameters determined by PAT are extremely sensitive to the (aspect) ratio of length to width of a pixel. Fine calibration (to five decimal digits) for the aspect ratio required to obtain physically consistent results is not always achieved with conventional numerical procedures due to nanometer resolution limit of optical imaging devices but can be manually adjusted using the known surface tension of pure water and/or surfactant solutions at reference temperature.