液体的表面张力与内压力

建立了液体表面张力与内压力间的定量关系,并据此得到了液体表面层的厚度或分子间的有效作用距离。     

十二烷基硫酸钠/聚氧乙烯体系饱和蒸汽压和表面张力

表面活性剂／聚合物体系具有多种工业用途，尤其在提高石油采收率方面具有广泛的应用前景。另外，此类体系中存在复杂而特殊的相互作用．因此，聚合物／表面活性剂体系物理化学性质的研究具有十分重要的理论和实际意义．文献中对此方面的研究已有不少报导[1－6]．1967年，Jones     

Surface Tension Measurements in Microgravity and their Relevance to Marangoni Convection

The physical properties of liquids, such as surface tension, Marangoni convection and surface segregation are important in many technical fields and are of fundamental interest. However, inaccuracy of experiments has prevented us from fully understanding these phenomena. Recent advances in experimental techniques, such as the containerless technique and the utilization of microgravity, are described.     

Aqueous Solutions of Sodium Deoxycholate and Hydroxypropylmethylcellulose: Dynamic Surface Tension Measurements

Interfacial tension changes and interaction between sodium deoxycholate (DOC) and a nonionic polymer hydroxypropylmethylcellulose (HPMC) were studied by the Wilhelmy plate method. The concentration of HPMC was fixed at 8x10(-5), 2x10(-4), and 1x10(-3)% (w/v) while DOC ranged form 0 to 8x10(-2) M, i.e., concentrations below and above the critical micellar concentration (cmc) for DOC. Emphasis was placed on the highly diluted solutions of the polymer in order to lessen possible contributions of the effects of the bulk phase on the observed surface behavior. The dynamics of the surface tension was investigated in the presence and absence of DOC. The kinetics of the interfacial tension changes were explained in terms of adsorption of the polymer molecules and conformational changes of already adsorbed molecules at the interface. The molecules above a critical DOC aggregation concentration (cac) formed clusters, which was evidenced by these surface tension measurements. A synergism in surface activity was observed below that cac. The cmc of DOC remained unchanged by the presence of HPMC. Copyright 2000 Academic Press.     

Dependence of Surface Tension of Near-boiling Non-associated Liquids on Their Molar Volume and Some Critical Constants

Abstract

The equation proposed for near-boiling non-associated liquids describes a new functional dependence of their surface tension on such physico-chemical characteristics as: critical volume, critical temperature and molar volume at the temperatures which are near their normal boiling points. It is shown that, in the case of some low-boiling liquids, possessing small molecules, this equation can be used for the adequate calculation of surface tension at different temperatures in the liquid phase.     

Inconsistency in the Stability Constants of Inorganic Polyphosphate Anions Determined by Potentiometry and Spectroscopy

Compared with cyclo -triphosphate anions, cyclo -tri- w -imidotriphosphate anions (Figure 1), cP 3 (NH) 3 3 m , form stable complexes with transition metal ions. Two experimental procedures, potentiometry and spectroscopy, have been applied to determine the stability constants of the complexes with Co 2+ , Ni 2+ , and Cu 2+ ions at 25;C and at I = 0.10 (NaClO 4 ). One-to-one (ML) complex formation has been assumed for the analyses. In the presence of sufficiently high concentration of metal ions, the log g 1 values determined by both methods are consistent with each other, whereas the log g 1 value determined by spectroscopy decreases with the decrease in metal ion concentration. This peculiar phenomenon cannot be explained by the presence of additional complexes, that is, ML 2 or M 2 L. One possible reasoning is agglomeration formation of ligand molecules mediated by countercations in aqueous solution.     

Application of the Bjerrum Association Model to Electrolyte Solutions. III. Temperature and Pressure Dependencies of Association Constants

The Bjerrum association model, developed in 1926, is now incorporated in many conductance theories of electrolyte systems to extract ₀ and K _A from experimental data. The Bjerrum concept is simply a convenient way of taking into account short-range electrostatic interactions between ions. The equations of the Bjerrum model can be applied to the prediction of the temperature and pressure dependencies of K _A from the value of K _A at a reference T and P and from the dielectric properties of the solvent. This feature will be essential when the relaxation effect is taken into account when applying the model to heat capacities and compressibilities. These equations were tested against literature K _A values (obtained from treatment of conductance data by equations that incorporate the Bjerrum concept) in aqueous electrolyte solutions at high temperatures and pressures and in some electrolyte systems in acetonitrile, 2-butanone, propylene carbonate, -butyrolactone, and propanol. In the absence of specific interactions in solution, the agreement between experimental and predicted K _A are generally quite good. Notable exceptions are acids and bases in water, lithium perchlorate in most solvents, and the majority of electrolytes in propylene carbonate, suggesting that specific interactions in these systems may cause the model to fail.     

Viscosity, Surface Tension, and Refractive Index Measurements of Mixtures of Isomeric Butanediols with Water

Solution properties of aqueous mixtures of isomeric butanediols have been investigated employing viscosity, surface tension, and index of refraction measurements as functions of temperature. The deviation of viscosity, surface tension, and molar refraction from ideal solution behavior is evaluated from the experimental data. The deviation from ideality is discussed in terms of molecular interactions between the components. Surface activity of the diols is evident from the surface tension measurements. It is found that the degree of hydrophobicity of the diols varies in the order 1,2 > 2,3 > 1,3 > 1,4. The strength of interaction of diols with the water varies in the order 2,3 > 1,4 1,3 > 1,2.     

Studies on the Effects of Additional Components on Micellization of CTAB via Surface Tension Measurements

The effects of Tris-HCl buffer solution on the cmc of cetyltrimethylammonium bromide (CTAB) were studied by surface tension measurement. The result shows that the effect of the buffer solution depends on the interaction between CTAB and NaCl and the structure accelerants of water, Tris. A series of parameters, including the critical micelle concentration (cmc), the surface tension at cmc (γ_cmc), the adsorption efficiency (pC₂₀), and the effectiveness of surface tension reduction (∏_cmc) were obtained from the surface tension measurements in the presence of glycine with different concentration in the Tris-HCl buffer solution at 27°C. In addition, maximum surface excess concentration (Γ _max) and minimum surface area per molecule (A_min) at the air-water interface were estimated according to the Gibbs adsorption isotherm. The thermodynamic parameters (Δ C _p,m , Δ H _m,tr , Δ C _p,m,tr ) of micellization for CTAB in the absence and presence of glycine at different temperature were also been obtained.     

Determination of Cyclodextrin-Guest Association Constants by Competition with Indicator Dyes

Abstract

The competition of some biologically interesting guests with methyl orange and phenolphthalein indicators for α- and β-cyclodextrin, respectively, has been monitored using visible spectrophotometry. A mathematical model has been developed to calculate the cyclodextrin-guest association constants using a linear plotting method.     

计时电量法求NiCl2(bpy)3在DMF中的扩散系数和速率常数

讨论了NiCl₂(bpy)₃(bpy：2,2-联吡啶)在DMF中的电化学行为. 控制电位使电极过程处于扩散控制下, 采用计时电量法求得了29 ℃时NiCl₂(bpy)₃在DMF中的扩散系数为5.99×10^－6 cm²•s^-1, 不同温度下的扩散系数随温度升高而增大. 选择合适的电极电位, 使电极过程处于扩散和电化学混合控制下, 采用计时电量法求得了不同电极电位下的反应速率常数k_f, 以及不同温度下的标准速率常数k⁰, 求得了表观活化能为14.4 kJ•mol^-1.     

Surface Stoichiometry of CdSe Nanocrystals Determined by Rutherford Backscattering Spectroscopy

Rutherford backscattering spectroscopy has been applied to study the surface stoichiometry of CdSe nanocrystals prepared by the high temperature pyrolysis of organometallics in trioctylphosphine oxide (TOPO). The diameter of the nanocrystals was varied from 22 to 56 Å. For all nanocrystal sizes we find the nanocrystals are Cd rich with an average Cd:Se ratio of 1.2±0.1. The Cd:Se stoichiometry is independent of the Cd:Se starting ratio used for the nanocrystal synthesis, indicating the excess Cd is not associated with the initial abundance of Cd but is an intrinsic property of nanocrystals prepared by this method. The surface coverage of the passivating TOPO ligands has also been determined and is larger than reported in previous X-ray photoelectron spectroscopy (XPS) studies of Bowen Katari et al.[1] The origin and structural implications of nonstoichiometric nanocrystals are discussed.     

Crown Ethers Analogues and their Complexes with NaSCN: Stoichiometry and Stability Constants Determined by 13C NMR Spectroscopy

¹³C NMR spectroscopy was used to study thecomplexation reaction between sodium ion and12-crown-4, 15-crown-5, methylurazolyl-12-crown-4 andmethylurazolyl-15-crown-5 in CD₃OD solutions. Thetype of complexes, the stability constants and therelative chemical shifts have been established byfitting experimental titration curves with theoreticalfunctions of the observed chemical shifts. Thesingle-crystal X-ray diffraction measurements for anew crystalline complex confirmed the stoichiometry ofthe complex.     

Three-Dimensional Aspect of the Surface Tension: An Approach Based on the Total Pressure Tensor

The conditions of mechanical equilibrium were considered, and the generalized notion of the surface tension at an arbitrarily curved surface layer was analyzed on the basis of the total nondiagonal pressure tensor including the external fields and anisotropic even in the bulk phases. It was shown that the transverse surface tension can be eliminated using the selection of a dividing surface; however, in the general case, this surface does not exhibit the properties of the tension surface. On the whole, three-dimensional and nondiagonal character of the tensors of excess surface stresses determined by the integration over the volume and the cross section of the surface layer is retained at any selection of the dividing surface.     

应用相敏HMQC和HSQC谱准确测定异核碳-氢偶合常数

准确测定各种同核和异核偶合常数是核磁共振（NMR）方法研究的一个非常跃的领域。首先,各种三键偶合常数通过Karplus关系式^[1]反映了相应二面角的大小,因此,多键偶合常数的准确测定直接影响分子结构确定的精确性。其次,由于稀液晶溶剂体系NMR方法的发展^[2],准确测定各种异核键偶合常数也显得非常重要,特别是应用场相关偶合常数研究分子在磁场中的取向时,对异核－键偶合常数测定的准确性要求更加严格^[3]。异核－键偶合常数的最准确的测定方法是异核偶合调制的HSQC（Heteronuclear Single-Quantum Coherence)实验^[3],它通过测定一系列异核耦合调制的二维HSQC谱,对交叉峰的强度进行分析来精确确定相应的异核－键偶合常数。这一方法的缺点是比较费时。作者在异核多键偶合常数的准确测定方面也做了一些有意义的工作^[4-6 α]。在前文^[5]工作的基础上,本文提出了二维相敏HMQC（Heteronuclear Multiple-Quantum Coherence)和HSQC（Heteronuclear Single-Quantum Coherence)实验,用于准确测定异核－键偶合常数。     

Diffusion Measurements vs. Chemical Shift Titration for Determination of Association Constants on the Example of Camphor–Cyclodextrin Complexes

Measurements on camphor–cyclodextrin complexes reveal that precise association constants are more easily determined by chemical shift titration. Diffusion measurements using HR-DOSY allow easy following of the complex composition at different concentration ratios and estimation of the binding energy. Linear dependence of the diffusion coefficients on the molecular mass of free and associated cyclodextrins has been observed in D₂O. The solution structures of α- and β-cyclodextrin complexes of camphor in D₂O were deduced from intermolecular cross-relaxation data. Different preferential orientation in the 2:1 α-CD and 1:1 β-CD species have been derived in contrast to the loose 1:1 complex with γ-CD. Proton NMR chemical shift values proved to be much more sensitive to diastereomeric complex formation than diffusion coefficients.     

关于表面张力和表面自由能的讨论

简要地回顾了表面物理化学中表面张力和表面吉布斯自由能(以下简称为表面自由能)两个基本概念的发展历史,讨论了表面张力和表面自由能形成的机制,以及键能与表面张力的关系,最后指出了尽管表面相可以在理论上抽象为几何面,但它是真实存在的独立相,而且由于表面自由能的原因它始终处于亚稳定状态.     

Diffusion Measurements vs. Chemical Shift Titration for Determination of Association Constants on the Example of Camphor–Cyclodextrin Complexes

Measurements on camphor–cyclodextrin complexes reveal that precise association constants are more easily determined by chemical shift titration. Diffusion measurements using HR-DOSY allow easy following of the complex composition at different concentration ratios and estimation of the binding energy. Linear dependence of the diffusion coefficients on the molecular mass of free and associated cyclodextrins has been observed in D₂O. The solution structures of α- and β-cyclodextrin complexes of camphor in D₂O were deduced from intermolecular cross-relaxation data. Different preferential orientation in the 2:1 α-CD and 1:1 β-CD species have been derived in contrast to the loose 1:1 complex with γ-CD. Proton NMR chemical shift values proved to be much more sensitive to diastereomeric complex formation than diffusion coefficients.     

界面张力弛豫法研究芳香侧链酰基牛磺酸钠的界面相互作用

采用界面张力弛豫方法研究了表面活性剂N-(α-苯氧基)十四酸牛磺酸钠(12+B-T),N-(α-乙基苯氧基)十四酸牛磺酸钠(12 +2B-T)和N-(α-己基苯氧基)十四酸牛磺酸钠(12+6B-T)在空气-水表面和癸烷-水界面上的扩张流变性质,考察了芳环支链链长变化对分子界面行为的影响,获得了表面活性剂结构对极限扩张弹...