Capillary Flow of Cationic Polyelectrolyte Solutions

The flow rates and the dynamic contact angles of aqueous solutions of cationic polyelectrolyte (CPE) in quartz capillaries with radius of 3–4 m are measured. It is shown that the surface tension and viscosity of CPE solutions with concentrations from 10^–1 to 10^–5 g/l are the same as for water. Surface inactivity of CPE leads to the substantial difference between the capillary properties of their solutions and those of surfactant solutions. It is established that, as the solution concentration increases, the advancing contact angles are reduced from 83° to 75°; the receding contact angles lie between 10° and 20°. Large hysteresis of contact angle can probably be related to the formation of metastable wetting film behind the receding meniscus. Surface hydrophobization occurs as a result of the adsorption of CPE molecules on the negatively charged quartz surface. The specific features of the application of CPE solutions in the deposition technology of hydrophobic coatings, the capillary imbibition and displacement of oils from hydrophobic pores are discussed.     

Activity Coefficients of Aqueous Mixed Ionic Surfactant Solutions from Osmometry

Osmotic techniques for measuring thermodynamic activities, such as isopiestic equilibration, are well established for multicomponent solutions, especially mixed salt solutions. Surprisingly, these techniques have not yet been applied to mixed ionic surfactants, despite the numerous practical applications of these systems and the importance of the Gibbs free energy for micelle stability. In this study, mass-action equations are developed for the osmotic coefficients of solutions of ionic surfactant CA + ionic surfactant CB, with common counterion C. Extended Debye–Hückel equations are used for the ionic activity coefficients. The equilibrium constants for mixed micelle formation are evaluated by Gibbs–Duhem integration of critical micelle concentrations. Fitting the derived equations to the osmotic coefficients of aqueous sodium decanoate + sodium dodecylsulfate solutions measured by freezing-point osmometry is used to evaluate the activities of the total surfactant components. Very large departures from ideal solution behavior are indicated, including stoichiometric surfactant activity coefficients and micelle activity coefficients that drop below 0.05 and 10^?8, respectively, relative to unity for ideal solutions. Osmometry offers many interesting and unexplored possibilities for studies of mixed surfactant thermodynamics.     

Dynamics of Capillary Rise

An overview and detailed analysis of the classical theory of capillarity is presented. A number of known equations of capillary rise dynamics are shown to be different limiting cases of one rather general equation. Some internal inconsistencies of the classical equations are pointed out. The role of nonlinear dissipation and flow pattern effects in the front zone of the liquid column and near the capillary entrance is discussed. Numerical simulations and experimental data demonstrating some characteristic types of dynamic behavior predicted by the theory are reported. Special attention is paid to the capillary rise of surfactant solutions. As applied to this special case, the existing theory is substantially elaborated by setting up a closed system of equations describing the surfactant transport and relaxation processes in the adsorption layer. A simplified relation for the capillary rise dynamics in the case of strong depletion of the interfacial region is obtained, which is in qualitative agreement with the experimental behavior. Copyright 2000 Academic Press.     

毛细上升现象的热力学解释*

从热力学的角度讨论毛细上升平衡高度以及毛细上升现象中的能量转换与守恒。在毛细上升的始终态之间设计了可逆途径,计算了可逆毛细上升过程中系统的赫姆霍兹自由能减少值,系统克服重力以及外压做功的值,并根据能量守恒定律推导出了毛细上升平衡高度和球形曲面的拉普拉斯方程。该方法拓展了热力学在表面现象中的应用,并有利于学生理解毛细上升现象的能量来源。     

含氟表面活性剂溶液的动态表面张力研究

本文研究了阳离子氟表面活性剂CF₃CF₂CF₂O(CF(CF₃)CF₂O)₂CF(CF₃)CONH(CH₂)₃N⁺(C₂H₅)₂CH₃I^-(简写FC-4 )的动态表面性质，利用Krüss K12和MBP动态表面张力仪分别测定了该体系的平衡表面张力和动态表面张力。由平衡表面张力测定结果得到了临界胶束浓度和表面吸附量。利用渐进的Ward and Tordai方程对动态数据进行了分析。结果表明：在吸附的最初阶段符合扩散控制模型，而在吸附的后期，证明了吸附势垒的存在，表明在吸附后期属于混合动力学模型。计算得出25 ℃时，该体系势垒约在25到35 kJ/mol. 由于氟表面活性剂分子间作用力小，表面压是导致吸附势垒的主要原因。     

Spreading of Surfactant Solutions over Hydrophobic Substrates

The spreading of surfactant solutions over hydrophobic surfaces is considered from both theoretical and experimental points of view. Water droplets do not wet a virgin solid hydrophobic substrate. It is shown that the transfer of surfactant molecules from the water droplet onto the hydrophobic surface changes the wetting characteristics in front of the drop on the three-phase contact line. The surfactant molecules increase the solid-vapor interfacial tension and hydrophilize the initially hydrophobic solid substrate just in front of the spreading drop. This process causes water drops to spread over time. The time of evolution of the spreading of a water droplet is predicted and compared with experimental observations. The assumption that surfactant transfer from the drop surface onto the solid hydrophobic substrate controls the rate of spreading is confirmed by our experimental observations. Copyright 2000 Academic Press.     

表面活性离子液体溴化N-十二烷基异喹啉与非离子表面活性剂Triton X-100在水溶液中的混合胶束

用等温滴定微量热法测定表面活性离子液体溴化N-十二烷基异喹啉([C₁₂iQuin]Br)与非离子表面活性剂Triton X-100混合物在水溶液中的临界胶束浓度。并以¹H核磁共振(NMR)和二维核Overhauser效应增强谱(2D NOESY)研究[C₁₂iQuin]Br与Triton X-100在混合胶束中的作用机理。研究结果显示：混合胶束中,Triton X-100分子的苯环定位于混合胶束的内核,聚氧乙烯链卷曲在异喹啉环周围。本文还应用规则溶液理论和浊点法对比研究了十二烷基三甲基溴化铵(DTAB)-Triton X-100混合胶束体系的相关性质。     

Quasi-thermodynamics of Viscous Flow of Electrolyte Solutions in Aqueous, Non-aqueous and Mixed Aqueous Solvents

Viscosity B-coefficients for cesium chloride and lithium sulfate in methanol + water mixtures at 25 and 35 °C are reported. A general treatment of the quasi-thermodynamics of viscous flow of electrolyte solutions is described. ΔG ₃ ^Θ (1→1′), the contribution made to the Gibbs energy of activation of the solution by the influence of the solute on the solvent, is a function of solute–solvent interactions only; but, ΔH ₃ ^Θ (1→1′) and ΔS ₃ ^Θ (1→1′) also reflect the solvent–solvent interactions. In aqueous solution all alkali-metal ions except Li⁺ are sterically unsaturated, having solvent co-ordination numbers n<n _max, the maximum allowed sterically. Such complexes exchange molecules with the solvent more readily than saturated ones and have energy–reaction co-ordinate diagrams in forms that explain the negative B or ΔG ₃ ^Θ (1→1′) values found in aqueous solution. Saturated complexes are the norm in non-aqueous solvents, and the ΔG ₃ ^Θ (1→1′) values are determined mainly by the secondary solvation. Behavior in mixed solvents reflects the transition from aqueous to non-aqueous behavior across the range of solvent composition.     

Quantitative Determination of Cationic and Nonionic Surfactants in Aqueous Solutions of Their Mixtures by Capillary Zone Electrophoresis

A method based on capillary zone electrophoresis is developed for a quantitative determination of cationic (dodecylpyridinium bromide) and nonionic (Triton X-100) surfactants absorbing in the UV region. The effect of the pH and ionic strength of the solution on the output time and shape of the resultant peaks is studied, and the optimal conditions of the analysis are determined. For both surfactants, the analytical signal (the area of the peak on the electrophoregram) is found to linearly depend on the concentration. It is established that the presence of a second surface-active component does not affect the signal of the surfactant analyzed; thus, surfactants may be quantitatively determined in both individual and mixed solutions. The method of capillary zone electrophoresis is shown to be applicable for determining the CMCs of surfactants.     

Interfacial Properties of Aqueous Nonionic Fluorocarbon Surfactant Solutions

The equilibrium, dynamic surface tensions, and surface dilatational elasticity of aqueous solutions of nonionic fluorocarbon surfactant are reported. The critical micellar concentration, CMC (0.023 mM) and equilibrium surface tension (24.6 m N . m^?1) at CMC were measured by Wilhelmy plate method for aqueous solution of C₈F₁₇SO₂N(C₃H₇)(C₂H₄O)_nH (n=20), abbreviated as EF122A. The surface tension decay is slower for C₈F₁₇SO₂N(C₃H₇)(C₂H₄O)_nH (n=10) system, abbreviated as EF122B compared to the EF122A system over short time region, which indicates the slow transport of the surfactant molecules to the surface. The relaxation time for surface tension decay is estimated by fitting a series of exponentials to the dynamic surface tension data and it decreases with temperature for EF122A. Slow exchange of monomers between bulk and interface is reflected in the high elasticity value of the air‐liquid interface for EF122B compared with EF122A within measured frequency window (0.125–1.25 Hz).     

The Solubilization of Isophorone in Ionic Surfactant Solutions

Solubilization of isophorone was studied in an anionic and a cationic surfactant solution of SDS and BKC respectively. Solubility of isophorone increases with increase in the surfactant concentrations due to solubilization in micelles. FT NMR spectroscopy was used to understand the location and orientation of isophorone at the micellar interface.     

Properties and Applications of Mixed Packing Capillary Electrochromatography

Mixed packing capillary electrochromatography (MP CEC) with the stationary phase comprising a physical mixture of strong cation exchange (SCX) phase and octadecysilyl (ODS) phase was developed. With the existence of a sulfonic acid group on the surface of SCX, not only could the electroosmotic flow (EOF) remain high at low pH, but also the hydrophilicity of the stationary phase was increased greatly, leading to broad adaptable ranges of both pH and organic modifier concentration in the mobile phase. At the same time, with the coexistence of C₁₈ on the surface of ODS, both the retention and the resolution of samples were improved. Accordingly, MP CEC combined the advantages of both SCX and ODS columns. Effects of operation parameters on EOF and the capacity factors of solutes as well as the retention mechanism of such a column were studied systematically. In addition, MP CEC columns were used in the analysis of strong polar solutes as well as for the high speed separation of acidic, basic, and neutral compounds in a single run.     

混合表面活性剂的表面活性及加溶能力

阴阳离子混合表面活性剂具有很高的表面活性［1］，但该类表面活性剂的浓度超过临界胶团浓度（cmc）以后，就将沉淀而失去表面活性［2］．因此，对该类体系的研究，主要在cmc以下．曾作过许多努力，希望解决阴阳离子混合表面活性剂的沉淀（或分层）问题，但效果均不理想［3，4］．直到最近，在这方面的研究才取得明显的进展，找到了在水溶液中，任何浓度和混合比之下，都不沉淀或分层的一类阴阳离子混合表面活性剂［4］．本文在此基础上，研究了该类表面活性剂的表面活性及其对戊醇和乙烷的加溶，该方面的研究工作，在国内外尚属首次，这对…     

Wormlike Micelle Formation and Rheological Behavior in the Aqueous Solutions of Mixed Sulfate Gemini Surfactant without Spacer Group and Dodecyltrimethylammonium Bromide

The rheological behavior of the aqueous solutions of mixed sulfate gemini surfactant with no spacer group, referred to as d‐C₁₂S, and dodecyltrimethylammonium bromide (C₁₂TABr) at a total concentration of 100 mmol·L⁻¹ but different molar ratios of C₁₂TABr to d‐C₁₂S (α₁) was investigated using steady rate and frequency sweep measurements. The wormlike micelles were formed over a narrow α₁ range of 0.20–0.27. The viscoelastic solutions exhibited Maxwell fluid behavior. At the optimum molar ratio of 0.25, the zero‐shear viscosity was as high as 600 Pa·s and the length of the mixed wormlike micelle was about 0.45–0.85 µm. The present result provides an example to construct long wormlike micelles by anionic gemini surfactant.     

Combination of Flow Injection with Capillary Electrophoresis

Sample introduction is a weak link in capillary electrophoresis (CE) systems, particularly when various pretreatments involving separation and modification of sample matrices are involved. Recently, the application of flow injection (FI) systems as a means of sample introduction and on-line sample pretreatment for CE has shown great potentials in improving the precision,reliability and throughput of CE systems. The advantages are discussed, illustrated by recent developments in the authors' group, including.     

阴离子表面活性剂SDBS胶束溶液的介电弛豫行为

用射频介电谱方法研究了0.1-80 mmol·L-1浓度的十二烷基苯磺酸钠(SDBS)水溶液体系的介质弛豫行为. 测量发现频率接近107 Hz时, 在临界胶束浓度(CMC)附近出现显著的介电弛豫现象. 采用Cole-Cole函数拟合SDBS体系介电数据, 其拟合参数具有明显变化规律: 介电增量(△ε)随SDBS摩尔浓度(cs)的增加而增大, 表现为两种线性关系, 并在cs=36 mmol·L-1附近出现拐点; 特征弛豫时间(τ0)却在cs=45 mmol·L-1出现极小值. 利用胶束电模型分析了介电弛豫机制, 认为束缚Na+对离子数量和胶束体积变化是引起介电增量和特征弛豫时间变化的两个重要原因.     

The Stage of Ultrafast Relaxation in Micellar Surfactant Solutions

The Becker–Döring kinetic equations are employed to describe the stage of ultrafast relaxation in micellar surfactant solutions, which ends in the establishment of a quasi-equilibrium distribution in the premicellar region of aggregate sizes. This is performed by analyzing the spectrum of the eigenvalues of the matrix of kinetic coefficients of the linearized Becker–Döring difference equations, which describes the complete multistage relaxation in a micellar system. The first value of the spectrum ordered as an ascending series is equal to zero (infinite relaxation time), thereby corresponding to the law of conservation of the surfactant quantity. The second value is very small; it differs from the series of subsequent values by several orders of magnitude and determines the time of slow relaxation. The other eigenvalues describe the processes of fast relaxation and comprise the contributions from the relaxation processes in both micellar and premicellar regions of aggregate sizes. In the latter region of the spectrum, the contribution of the ultrafast relaxation can be numerically distinguished. The obtained result is confirmed by the analysis of the spectrum of relaxation times of premicellar aggregates, which are considered as a closed system. It is also shown that the spectrum of ultrafast relaxation times is mainly determined by the first diagonal elements of the matrix of the linearized Becker–Döring equations and can be described analytically.     

Kinetics of Aggregation and Relaxation in Micellar Surfactant Solutions

Theoretical results published in the last 17 years on the kinetics of aggregation and relaxation in micellar surfactant solutions have been reviewed. The results obtained by the analytical and direct numerical solution of the Becker–Döring kinetic equations and the Smoluchowski generalized equations, which describe different possible mechanisms of aggregation and relaxation on all time scales from ultrafast relaxation while reaching the quasi-equilibrium in the region of subcritical molecular aggregates to the last stage of slow relaxation of micelles to the final aggregated state, have been considered in detail. The droplet model and the model linear with respect to aggregation numbers have been used for the work of aggregation to describe the dynamics of the rearrangement of micellar systems consisting of only spherical, only cylindrical, and coexisting spherical and cylindrical aggregates, with the dynamics being both linear and nonlinear with respect to deviations from equilibrium. The results of molecular simulation of the rearrangement kinetics of micellar systems subjected to initial disturbance have been reviewed.     

Micellization of Cationic Surfactant Cetyltrimethylammonium Bromide in Mixed Water-Alcohol Media

The effect of methanol, ethanol, and 1-propanol on cmc and degree of counter ion binding, β, of cetyltrimethylammonium bromide (CTAB) has been studied conductometrically. The micellization of CTAB in these water-alcohol media have been found to be both dependent on nature as well as the concentration of alcohol in water. The cmc values shift toward higher concentration with increase in alcoholic content up to certain concentration beyond which decrease in cmc is registered in case of all the alcohols. However, the maximum in the cmc versus concentration of alcohol shifts to lower concentration with the increase in number of carbons in alcohol. β shows the inverse peaked behaviour in conformity with the cmc variation. The effects viz. solvent modifying tendency of alcohols and their tendency of penetration into the micelles have been used to interpret their effect on micellization of CTAB.     

Hydrophobically Associating Alginate Derivatives: Surface Tension Properties of Their Mixed Aqueous Solutions with Oppositely Charged Surfactants

The comparative study of the interfacial properties of an anionic polysaccharide, sodium alginate (Alg), and its hydrophobically modified derivative (Alg-C(12)), covalently substituted by dodecyl chains (12% mol/mol saccharide unit), was carried out in the absence or in the presence of an oppositely charged surfactant, dodecyltrimethylammonium bromide (DTAB). The drastically different behaviors which were observed are interpreted in terms of the arrangement and mobility of the hydrophobic long alkyl chains, depending on the nature of their fixation, covalent or ionic, on the polysaccharide backbone. Copyright 2000 Academic Press.