Dynamic Interfacial Tension Behavior of Water/Oil Systems Containing In situ-Formed Surfactants

Time-dependent interfacial tension (IFT) has been investigated for an interfacially reactive immiscible system composed of model-acidified oil and alkaline water. The acidified oil was composed of either lauric acid or linoleic acid dissolved in n-dodecane. Drop volume tensiometry was employed to measure the interfacial tension between the two phases. In the case of lauric acid, the IFT value was found to decrease sharply with increasing alkali concentration, even at low drop formation times. In the case of linoleic acid, the IFT decrease with the drop formation time was more gradual, especially at low alkali concentration. The rate of formation of the interfacial area was also found to be dependent on alkali concentration.     

表面能与晶体生长/溶解动力学研究的新动向

界面现象使物质在结晶过程中出现了临界现象.但最近的研究指出在物质溶解过程中,在表面能量的控制下也存在着临界现象以及尺寸效应.实验发现,当晶体自身小到一 定的程度时(通常在纳米尺度上并和临界蚀坑的大小相近),在溶解过程中其速度会自发降 低,反应被抑制乃至停止.尽管在热力学上表面能的因素可以赋予小颗粒晶体较大的溶解度 ,但表面能却也能通过对临界条件的控制而使这些微粒在动力学上不被溶解.这个发现不仅 解决了纳米颗粒在水溶液中稳定性的问题,而且还从动力学的角度解释了生物矿物选择纳米 尺度作为其基本构成单元的原因.由于表面能和晶体生长/溶解的动力学有着密切的关系, 我们可以通过对表面能的调节来修改它们的动力学速度和晶体的形貌.反过来,也可以用动力学的方法来测定表面能及表面吸附/脱附常数等.相对于常规的界面研究手段,通过生 长和溶解动力学途径所得的数据有着很好的可靠性及重复性.我们认为,晶体生长和溶解的 动力学和表面能的研究相结合,不仅为界面研究提供了新的思路和方法,而且也会推动晶体生长和材料科学的发展.     

辣素微胶囊的原位聚合法制备与热降解动力学

在乳液体系中,以尿醛为壁材,以原位聚合法制备了辣素同系物———N-香草基壬酰胺微胶囊。红外光谱证实了尿醛的形成,X-射线衍射显示了同样作为半晶高分子囊壁,尿醛包裹囊心前后出现的结构晶型差异。根据吸附等温曲线假设微胶囊为紧密堆积形式,对于尿醛单体颗粒和尿醛微胶囊的TGA,采用Achar-B rind ley-Sharp-W endworth方法,对两者进行热重数据的处理,以作图法求得了动力学参数,确定了热降解动力学模式函数,回归系数良好。TGA求解的活化能数据证明由于晶型差异,导致单体与微胶囊热稳定性不同,从而与XRD结论一致。     

A DIAGNOSTIC STUDY OF FORMATION AND MAINTENANCE OF BLOCKING SITUATION ON THE NORTHERN HEMISPHERE USING E-P FLUX

In this paper, the variations of the mean flow, the E-P flux and its divergence of planetary waves in the process of the formation, maintenance and collapse of the blocking situation in the second half of February, 1979 are analysed with the transformed Eulerian mean-motion equations.Analysed results show that because the basic flow changes from the easterly into the westerly in the lower troposphere at high latitudes, the planetary wave for wavenumber 2 strongly propagates upwards, and because of the interaction between the upward propagating planetary wave and the basic flow, the westerty is weakened and approaches to the resonant flow of wavenumber 2 in the middle and upper troposphere (then, in the lower and middle Stratosphere). This may cause the anomalous amplification of planetary wave for wavenumber 2, and moreover make the mean flow change from the westerly into the easterly in the lower and middle stratosphere, following the upper troposphere. Therefore, the blocking situation can be formed a     

Investigation of glow discharge plasma for surface modification of polypropylene

Material surface properties of polymers, plastics, ceramics and textiles can be modified by atmospheric or low‐pressure glow discharge plasma. The aim of the present work is to study the surface modification of biaxially oriented polypropylene (BOPP) film in order to improve its hydrophilic and wetting properties. In this article we used low‐pressure, low‐temperature oxygen plasma for the surface treatment of BOPP. Scanning electron microscopy indicates that plasma treatment causes mainly physical changes by creating microcraters and roughness on the surface and increasing surface friction. Attenuated total reflectance infrared spectra show oxygen‐containing groups such as ? OH at 3513 cm^?1 and C?O at 1695 cm^?1. Microscopic investigations of water droplets on BOPP (treated, untreated) show that the interfacial adhesion of treated surfaces is increased. Copyright © 2003 John Wiley & Sons, Ltd.     

An empirical equation-of-state for solid-fluid interfacial free energies

The contact angle,, formed by a liquid on a solid surface in air depends on the solid-air ( _S ), liquid-air ( _L ) and solid-liquid ( _SL ) interfacial free energies, as described by Young's equation. Critical examination of reported contact angles for numerous liquids and solids leads to an empirical correlation between _sL and both _Y and _S . Combination of this correlation with Young's equation gives an empirical relation allowing calculation of _S from _L and Calculations made with these empirical relations agree well with estimations of _S obtained by the method of critical spreading, and are consistent with Young's equation.Founded and supported by F. Hoffmann-La Roche and Co., Limited Company, Basel, Switzerland.     

Carbenium ion pairs on silica: UV-spectroscopic and electrokinetic measurements of triarylmethylium/halide-aerosil in 1,2-dichloroethane

The interaction of carbenium ion pairs with silica is studied by means of UV-spectroscopy, electrokinetic and adsorption measurements using triphenylmethyl derivatives, (RC₆H₄)₃CX, (X=F, Cl, Br, SCN, OH; R=Cl, I, H, CH₃, C(CH₃)₃, OCH₃, N(CH₃)₂) in interaction with silica particles suspended in 1,2-dichloroethane. The adsorption of triarylmethyl-halides onto silica is accompanied by the heterolytic dissociation of the tertiary carbonhalogen bond. The degree of ionization depends on the basicity of the counter anion and acidity of the cation, respectively. The influences of both concentration and structure of triarylmethyl halides on the zeta-potential are discussed with regard to steric and electronic factor. The zeta-potential values of the adsorbates decrease significantly, as compared with the free silica surface, from a certain triarylmethyl halide concentration where ionization takes place, to a constant level which is characteristic of the carbenium ion pair. These constant zeta-potential values of the adsorbates depend on the basicity of the counter ion and the _p Hammett constants of the ring substitutents, with exclusion of sterically hindered substituents and salt derivatives, e.g., crystal violet and malachite green.     

Some theoretical aspects on morphology development in seeded composite latexes. I. Batch conditions below monomer saturation

In seeded emulsion polymerization, during the second stage, new interfaces appear and the surface area changes. A thermodynamic equilibrium approach is presented which predicts particle morphology of a whole range of non-spherical particles upon polymer conversion. Simulation takes into account swelling ratio, molar volumes and interfacial tension. As the particle geometry is complex, a new mathematical procedure is detailed.The computed data are useful to discuss either the stability or the instability of the particles morphology. These results must be compared with actual experimental structures.Abreviations and symbols G Gibbs' free energy - reduced Gibbs' free energy - _i interfacial tension - ₁₂ interfacial tension between polymer 1 and polymer 2 - _1w interfacial tension between polymer 1 and water - _2w interfacial tension between polymer 2 and water - r ₁ polymer 1 swollen by monomer 2 sphere radius - r ₂ polymer 2 swollen by monomer 2 sphere radius - r _i interfacial radius - h ₁ sphere 1 distance to minimal section - h ₂ sphere 2 distance to minimal section - h _i interfacial sphere distance to minimal section - sign ofh _i, positive when the interface sphere is on the side of the sphere 2, negative when the interface sphere is on the side of the sphere 1 - A ₁₂ surface between polymer 1 and polymer 2 - A _1w surface between polymer 1 and water - A _1w ⁰ surface between polymer 1 and water before polymerization - A _2w surface between polymer 2 and water - v ₁ volume of the polymer 1 swollen by monomer 2 - v _i volume of the polymer 1 swollen by monomer 2 before polymerization - v ₂ volume of the polymer 2 swollen by monomer 2 - V _p1 polymer 1 molar volume - V _p2 polymer 2 molar volume - V _m2 monomer 2 molar volume - n _p2 polymer 2 number of mole - n _p1 polymer 1 number of moles - n _m21 monomer 2 number of mole in the swollen polymer 1 - n _m22 monomer 2 number of mole in the swollen polymer 2 - n _m2 monomer 2 total number of mole - n _m2 monomer 2 number of mole before polymerization - TGn ₁ polymer 1 swelling rate - TGn ₂ polymer 2 swelling rate - TGn _i maximum number of mole of monomer 2 in polymeri by mole of polymeri - x polymer 2 conversion rate - K, p, q mathematical variables - D, r, a mathematical variables     

Microphase separation of PEG-modified urethane acrylate and the swelling behavior of its gels

The viscosity of PEG-modified urethane acrylate (PMUA) showed peculiar behavior in the course of soap-free emulsification. Moreover, the viscosity change with added amounts of water was influenced by the reaction molar ratio of polyethylene glycol (PEG). The rate of increase in viscosity slowed and the ratio of increase in viscosity increased as the reaction molar ratio of PEG increased. This peculiar viscosity behavior was due to the microphase separation between hydrophilic and hydrophobic segments of PMUA, and the orientation of polyoxyethylene groups at O/W interface which influenced droplet size of the soap-free PMUA emulsion. The location of polyoxyethylene groups of this resin at O/W interface was confirmed using the adsorption isotherm measurement of PMUA molecules containing polyoxyethylene groups at water/benzene interface. The microphase separation behavior of PMUA between hydrophilic and hydrophobic segments could apply to the preparation of the PMUA gels containing peculiar structure. PMUA gels were prepared using dioxane (UAG) and the swelling behavior of these gels were compared to that of gels prepared using water (UAHG) in the same medium. In the same medium, the swelling behavior of UAHG gels differed from that of UAG gels because of the difference in the microstructure of gel due to the microphase separation between hydrophilic and hydrophobic segments. This phase separation in the course of gelation in water could be confirmed using contact angle measurement.     

Monolayer films of PS-b-PEO diblock copolymers at the air/water- and an oil/water-interface

 Amphiphilic diblock copolymers consisting of a hydrophobic polystyrene block (PS) and a hydrophilic poly(ethylene oxide) block (PEO) with block sizes of 1000 or 3000 g/mol for both blocks were studied at the air/water and toluene/water interface. Measurements of the film pressure π of spread monolayers at the water surface reveal two limiting regimes of the π−a _m isotherms, in which the mean molecular area a _m is determined either by the size of the hydrophilic or the hydrophobic blocks of the PS-PEO molecules. The interfacial activity of the block copolymers at the toluene/water interface was studied by measuring the interfacial tension σ over a wide range of concentrations. Pronounced differences in the temperature dependence of the interfacial tension were observed, depending mostly on the block length of the hydrophilic PEO block. From the temperature dependence of σ it is inferred that for the block copolymers with the PEO block size of 3000 g/mol the phase inversion temperature (PIT) is well above 60 °C while for those with a PEO block size of 1000 g/mol the PIT is below or near 25 °C in the toluene/water system. Received: 5 February 1998 Accepted: 16 February 1998