Equilibrium surface tension of aqueous surfactant solutions

Summary The applicability of the drop weight method for determining time dependent surface tension of surfactant solutions was experimentally proved.The presence of CO₂ and traces of lauryl alcohol and long chain homologs lower the surface tension of sodium dodecyl sulfate solutions in a measurable extent. The chemical purification of materials and recrystallizations are insatisfactory to obtain sufficient purity; the cleaning of the surface itself is needed by e.g. foaming. The equilibrium surface tension of pure surfactant solutions that is often required to interpret interfacial phenomena and to calculate theGibbs adsorption excess can be determined with reliable accuracy by linear extrapolation to zero time from measurements made in function of time up from 1 minute on moderately contaminated solutions.As a criterion of surface purity the time dependence of surface tension and the average life-time of thin liquid film are suggested.

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Zusammenfassung Die Tropfengewichtsmethode eignet sich auch zur Bestimmung der zeitabhängigen Oberflächenspannung wäßriger Tensidlösungen. Zur Entfernung von Verunreinigungen, die die Oberflächenspannung von Natriumdodecylsulfatlösungen herabsetzen, wie Spuren von Laurylalkohol und höheren Homologen, reichen weder chemische Methoden noch wiederholtes Umkristallisieren aus, sondern die Oberfläche selbst ist zu reinigen, z. B. durch Ausschäumen. Der Gleichgewichtswert der Oberflächenspannung läß sich mit hinreichender Genauigkeit berechnen, in dem man die an mäßig konzentrierten Lösungen über einer Minute Meßzeit gewonnenen Daten auft = 0 linear extrapoliert. Als praktisches Kriterium für die Reinheit der Oberfläche kann man sowohl die Zeitabhängigkeit der Oberflächenspannung, wie auch die mittlere Lebensdauer von dünnen Lösungsfilmen heranziehen.

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Mixed adsorption and surface tension prediction of nonideal ternary surfactant systems

To deal with the mixed adsorption of nonideal ternary surfactant systems, the regular solution approximation for nonideal binary surfactant systems is extended and a pseudo-binary system treatment is also proposed. With both treatments, the compositions of the mixed monolayer and the solution concentrations required to produce given surface tensions can be predicted based only on the -LogC curves of individual surfactants and the pair interaction parameters. Conversely, the surface tensions of solutions with different bulk compositions can be predicted by the surface tension equations for mixed surfactant systems. Two ternary systems: SDS/Hyamine 1622/AEO₇, composed of homogeneous surfactants, and AES/DPCl/AEO₉, composed of commercial surfactants, in the presence of excess NaCl, are examined for the applicability of the two treatments. The results show that, in general, the pseudo-binary system treatment gives better prediction than the extended regular solution approximation, and the applicability of the latter to typical anionic/cationic/nonionic nonideal ternary surfactant systems seems to depend on the combined interaction parameter, : the more it deviates from zero, the larger the prediction difference. If 0, good agreements between predicted and experimental results can be obtained and both treatments, though differently derived, are interrelated and tend to be equivalent.Poster presentation at the 14th SIS conference, June 2002, Barcelona     

On the determination of equilibrium surface tension values of surfactant solutions

By using values ofdσ/dt as criterion for the establishment of the adsorption equilibrium great errors can result for strong surface active substances (gG_x/a?10^?2 cm). A simple linear extrapolation from curves σ or (σ₀-σ)^?1 on 1/√t (results of dynamic surface tension measurements) can lead to greater errors, too. Conditions are given under which the application of such extrapolation procedures is only possible. To get accurate equilibrium surface tension values of solutions of very strong surfactants (Γ_x/a>10^?1 cm) an extrapolation-interpolation algorithm based on adsorption-desorption measurements is suggested.     

A simplified method for predicting the dynamic surface tension of concentrated surfactant solutions

A simplified method for predicting the dynamic surface tension of concentrated surfactant solutions is proposed. It is implemented using the framework of the Henry's Law analytical solution to the Ward and Tordai equation for diffusion-controlled adsorption, with the necessary parameters being deduced from the measured equilibrium surface tension equation and a value for the surfactant monomer diffusivity. The method is tested by calculating the dynamic surface tension relaxations of aqueous C10E6 and C10E8 solutions over concentration ranges from well below to well above their critical micelle concentrations (cmc). Results are compared with measured relaxations over 0.001-50 s, and semiquantitative agreement is found, with the best results obtained for concentrations near the cmc. The predictive method may prove useful in such applications as the screening of candidate surfactants for inks used in inkjet printing.     

A model for simulating the dynamic surface tension behavior of aqueous surfactant dispersions

A dynamic adsorption model for surface-active materials at air/liquid interfaces with the consideration of aggregate dissolution effect was developed to investigate the dynamic surface tension behavior of aqueous surfactant dispersions. Two catanionic surfactants, cetylpyridinium dodecylsulfate (CP-DS) and dodecyltrimethylammonium dodecylsulfate (DTMA-DS), with low critical aggregation concentrations were chosen as model systems. Dynamic surface tensions of aqueous CP-DS and DTMA-DS systems were measured by a drop volume tensiometer. A model with diffusion-controlled or mixed-kinetic dynamic adsorption mechanisms considering the dissolution effect of dispersed aggregates was developed to simulate the dynamic surface tension data. An analysis by comparing the model predictions with experimental data demonstrated that the dynamic surface tension behavior of aqueous CP-DS and DTMA-DS dispersions could be described with a diffusion-controlled dynamic adsorption model taking the aggregate dissolution effect into account.     

Headgroup and hydrocarbon tail effects on the surface tension of sugar-based surfactant solutions

Measurements of surface tension isotherms were conducted for water solutions of pure and mixed n-decyl-beta-d-glucopyranoside (C(10)-Glu) and n-decyl-beta-d-maltopyranoside (C(10)-Mal) surfactants. By applying the Gibbs surface tension equation, the surface densities of Glu and Mal were derived for different compositions and concentrations. The surface fractions were compared with theoretically calculated values where the headgroups were modeled as hard disks. Satisfactory agreement was found for hard-disk sizes of 22.9 and 11.3 A(2) in the case of a 1:1 mixture. The results of the hard-disk calculations were employed to estimate the configurational free energy of the n-decyl-hydrocarbon chain. The results obtained agree well with previous calculations for the n-dodecyl chain. Comparison with n-dodecyl beta-d-maltopyranoside (C(12)-Mal) indicated a further contribution, with the longer hydrocarbon chain giving rise to a higher surface tension in good agreement with data for hydrocarbon liquids. Furthermore, the interpenetration of the headgroup into the hydrocarbon film was studied by means of comparing surface-tension data for n-decyl- and n-dodecyl-ethylene-oxide-based surfactants and n-decyl- and n-dodecyl-beta-d-thiomaltopyranosides (C(10)-S-Mal and C(12)-S-Mal, respectively) and -maltopyranosides. It was found that lengthening the tetra(etylene oxide) chain by one segment affects the surface tension only marginally, indicating little interpenetration of the additional ethylene-oxide group into the hydrocarbon film. For the thiomaltosides, however, the corresponding effect was found to be remarkably high.     

Simultaneous study of interfacial tension,surface tension,and viscosity of few surfactant solutions with survismeter

Surfaces and interfaces are receptive valuable significant property of chemical molecules due to their potential to develop several phenomena in a self‐controlled mechanism. Science of surfaces is vast and is being used industrially since time immemorial. Their accurate and simultaneous estimation is necessary; therefore, the survismeter was used for measuring them along with viscosity. Individually tensiometers, X‐ray reflective microscope, and viscometers are used for surface tension, interfacial tension, and viscosity, respectively. These devices are sophisticated, expensive, and individually consume much time and resources with poor reproducibility in measurements. Survismeter is an alternative device for similar measurements together with higher accuracies and reproducibility. It works on a principle of capillary flow and pressure gradient (PG) inside liquid‐holding and air‐filled bulbs. Several liquids have been used for study with ± 0.01 mN/m, ± 0.01 mN/m and ± 1 × 10^?5 N s/m² accuracies in respective data. Copyright © 2008 John Wiley & Sons, Ltd.     

Experiments and model for the surface tension of carbonated monoethanolamine aqueous solutions

The surface tension of carbonated monoethanolamine aqueous solutions from 293.15 to 323.15 K was measured by using an automatic surface tension-meter.A model applicable for the surface tension of MEA-CO2-water mixtures was proposed and the calculated results agreed well with the experiments.The influences of temperature,MEA concentration and CO2 loading were demonstrated on the basis of experiments and calculations.     

MEA-CO2-水溶液表面张力实验和模型

用全自动表面张力仪测定了293．15-323．15K温度范围内,具有不同C02载荷的乙醇胺（Monoethanolamine,MEA）水溶液的表面张力,提出了计算MEA-CO2-水体系表面张力的半经验模型,计算结果与实验值吻合良好．通过实验和计算相结合,阐明了温度、MEA浓度和C02载荷对MEA-CO2-水体系表面张力的影响规律．     

Nonequilibrium surface tension for mixed adsorption kinetics

Experimental nonequilibrium surface tension measurements of 1–9 nonanediol solutions obtained by the oscillating-jet method have been interpreted in terms of our theoretical predictions derived for a mixed-controlled adsorption kinetics of the surfactant. The surface tension values have been calculated from the Szyszkowski equation using the Langmuir model of surfactant adsorption. Our theoretical results, obtained by a numerical solution of the adsorption equations, agree well with experimental data giving a value of the kinetics Szyszkowski constant very similar to the thermodynamic equilibrium value determined from experimental measurements of the static surface tension of 1–9 nonanediol solutions of various concentration. The approximate kinetic equation derived by P. Joos, G. Bleys, and G. Petre (J. Chim. Phys.79, 387 (1982)) for purely barrier-controlled adsorption proved to be less accurate.     

Application of the MSA-based models in correlating the surface tension for single and mixed electrolyte solutions

Experimental values for surface tension of single and mixed electrolyte solutions were correlated using the models based on the perturbation theory. The Mean Spherical Approximation (MSA) model, coupled with the Ghotbi–Vera (GV) and the Mansoori et al. (BMCSL) equations of state, were used to correlate the experimental values of the surface tension. The results showed that the models can favourably correlate the experimental values for single electrolyte solutions. However, it was observed that the GV–MSA model can more accurately predict the surface tension for single electrolytes, especially at higher concentrations. Two different expressions for concentration dependency of cation hydrated diameters were used. Therefore, in terms of such dependency different forms of the models, i.e., GV–MSA1, GV–MSA2, BMCSL–MSA1 and BMCSL–MSA2 were introduced. It should be stated that the prediction of the surface tension for the mixed electrolyte solutions were made without introducing any new adjustable parameters. The results showed that GV–MSA2 model can predict more accurately the surface tension of electrolyte mixtures particularly at higher concentrations. Finally, the GV–MSA model was directly used to correlate the experimental results for the surface tension for both single and mixed electrolyte solutions with 2 and 4 adjustable parameters. The results showed that both of the models can accurately predict the experimental data of surface tension. These models can favourably fit and also, predict the surface tension of single electrolyte solutions with less than 1% average absolute relative deviation (AARD). The prediction capability of the proposed models is also acceptable for mixtures of electrolytes.     

On the low surface tension of lung surfactant

Natural lung surfactant contains less than 40% disaturated phospholipids, mainly dipalmitoylphosphatidylcholine (DPPC). The mechanism by which lung surfactant achieves very low near-zero surface tensions, well below its equilibrium value, is not fully understood. To date, the low surface tension of lung surfactant is usually explained by a squeeze-out model which predicts that upon film compression non-DPPC components are gradually excluded from the air-water interface into a surface-associated surfactant reservoir. However, detailed experimental evidence of the squeeze-out within the physiologically relevant high surface pressure range is still lacking. In the present work, we studied four animal-derived clinical surfactant preparations, including Survanta, Curosurf, Infasurf, and BLES. By comparing compression isotherms and lateral structures of these surfactant films obtained by atomic force microscopy within the physiologically relevant high surface pressure range, we have derived an updated squeeze-out model. Our model suggests that the squeeze-out originates from fluid phases of a phase-separated monolayer. The squeeze-out process follows a nucleation-growth model and only occurs within a narrow surface pressure range around the equilibrium spreading pressure of lung surfactant. After the squeeze-out, three-dimensional nuclei stop growing, thereby resulting in a DPPC-enriched interfacial monolayer to reduce the air-water surface tension to very low values.     

双子表面活性剂溶液的表面活性的研究

研究了阳离子型双子表面活性剂,二溴化-N,N'-二(二甲基烷基)乙(已)二铵,以及它们与阴离子表面活性剂十二烷基苯磺酸钠(SDBS)复配体系的表面活性,测定上述体系的平衡态表面张力。结果表明：双子表面活性剂的表面活性大大高于十二烷基三甲溴化铵(DTAB);对于两种双子表面活性剂,其表面活性和表面张力时间效应受其联接基团的影响远大于其烷基链的影响。双子表面活性剂与SDAB复配,其协同效应不如DTAB。动表面张力测定得到它们的各种参：t~i,t~m,γ~m,t*和n等值,结果表面双子表面活性剂的瞬时活性也高于DTAB。     

How surface tension of surfactant solutions influences the characteristics of sprays produced by hydraulic nozzles used for pesticide application

The sprays produced by hydraulic agricultural nozzles are influenced by the surface tension of the spray liquid, but models of spray formation relate only to pure liquids with constant surface tension. The way surfactant solutions affect spray formation is studied by investigating sprays of pure liquids compared with a range of surfactant solutions. Some surfactants caused changes in the appearance of the liquid sheet produced by the nozzles, which did not occur with pure liquids, and smaller spray drop sizes than pure liquids, suggesting that other surface properties may also be important.     

Impact of model perfumes on surfactant and mixed surfactant self-assembly

The impact of some model perfumes on surfactant self-assembly has been investigated, using small-angle neutron scattering. A range of different model perfumes, with differing degrees of hydrophilicity/hydrophobicity, have been explored, and in order of increasing hydrophobicity include phenyl ethanol (PE), rose oxide (RO), limonene (LM), linalool (LL), and dihydrogen mercenol (DHM). The effect of their solubilization on the nonionic surfactant micelles of dodecaethylene monododecyl ether (C12EO12) and on the mixed surfactant aggregates of C12EO12 and the cationic dialkyl chain surfactant dihexadecyl dimethyl ammonium bromide (DHDAB) has been quantified. For PE and LL the effect of their solubilization on the micelle, mixed micelle/lamellar and lamellar regimes of the C12EO12/DHDAB mixtures, has also been determined. For the C12EO12 and mixed DHDAB/C12EO12 micelles PE is solubilized predominantly at the hydrophilic/hydrophobic interface, whereas the more hydrophobic perfumes, from RO to DHM, are solubilized predominantly in the hydrophobic core of the micelles. For the C12EO12 micelles, with increasing perfume concentration, the more hydrophobic perfumes (RO to DHM) promote micellar growth. Relatively modest growth is observed for RO and LM, whereas substantial growth is observed for LL and DHM. In contrast, for the addition of PE the C12EO12 micelles remain as relatively small globular micelles, with no significant growth. For the C12EO12/DHDAB mixed micelles, the pattern of behavior with the addition of perfume is broadly similar, except that the micellar growth with increasing perfume concentration for the more hydrophobic perfumes is less pronounced. In the Lbeta (Lv) region of the DHDAB-rich C12EO12/DHDAB phase diagram, the addition of PE results in a less structured (less rigid) lamellar phase, and ultimately a shift toward a structure more consistent with a sponge or bicontinuous phase. In the mixed L1/Lbeta region of the phase diagram PE induces a slight shift in the coexistence from Lbeta toward L1. The addition of LL to the Lbeta (Lv) region of the DHDAB-rich C12EO12/DHDAB phase diagram also results in a reduction in the lamellar structure (less rigid lamellae), and a shift toward a structure more consistent with a sponge or bicontinuous phase, or a coexisting phase of small vesicles. For the mixed L1/Lbeta region of the phase diagram LL induces a shift toward a greater L beta component.     

Influence of electrolytes on the dynamic surface tension of ionic surfactant solutions: expanding and immobile interfaces

Here, we derive analytical asymptotic expressions for the dynamic surface tension of ionic surfactant solutions in the general case of nonstationary interfacial expansion. Because the diffusion layer is much wider than the electric double layer, the equations contain a small parameter. The resulting perturbation problem is singular and it is solved by means of the method of matched asymptotic expansions. The derived general expression for the dynamic surface tension is simplified for the special case of immobile interface and for the maximum bubble pressure method (MBPM). The case of stationary interfacial expansion is also considered. The effective diffusivity of the ionic surfactant essentially depends on the concentrations of surfactant and nonamphiphilic salt. To test the theory, the derived equations are applied to calculate the surfactant adsorption from MBPM experimental data. The results excellently agree with the adsorption determined independently from equilibrium surface-tension isotherms. The derived theoretical expressions could find application for interpreting data obtained by MBPM and other experimental methods for investigating interfacial dynamics.     

Application of the maximum bubble pressure technique for dynamic surface tension studies of surfactant solutions using the Sugden two-capillary method

Exact knowledge of the dead time as part of the bubble lifetime in the maximum bubble pressure method is an important prerequisite for accurate dynamic surface tension measurements. The duration of the dead time depends essentially on the capillary geometry and affects significantly the measured surface tensions of concentrated surfactant solutions. Increase of the dead time leads to a significant surface tension decrease of a freshly formed bubble surface due to the significantly higher residual adsorption of the surfactant molecules. It is shown that correct dynamic surface tensions are obtained with the experimental procedure of Sugden's method only when in addition to the fixed frequency of bubble formation, also the dead time values for the two capillaries are kept constant.     

Surface properties of mixed anionic/cationic surfactant solutions

Summary Published experimental surface pressures for mixtures of anionic and cationic surfactants are compared to what can be predicted from the surface behaviour of the separate constituents. Simple theory correctly predicts, for soluble surfactants, a large increase of surface pressure upon mixing an anionic and a cationic solution having the same surface pressure, and, for insoluble surfactants, a decrease of surface pressure upon mixing at a given area per long chain ion. These effects are due to the different adsorption characteristics of the four electroneutral combinations involved, and will occur even in the absence of specific surface interactions.

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Zusammenfassung Es wurden bekannte Oberflächendrucke für Mischfilme von Aniontensiden und Kationtensiden mit theoretischen Voraussagen, begründet auf dem Grenzflächenverhalten der einzelnen Komponenten, verglichen. Die einfache Theorie sagt richtig voraus, daß die Mischung zweier wäßriger Lösungen von Aniontensid bzw. Kationtensid mit gleichem Oberflächendruck, eine starke Erhöhung des Oberflächendruckes zur Folge haben muß, während die Mischung zweier unlöslicher Filme bei gegebener Tensidadsorption den Oberflächendruck herabsetzt. Dieses Verhalten wird aufgrund der verschiedenen Adsorptionseigenschaften der vier betreffenden Salze gedeutet, und ist von spezifischen Oberflächenwechselwirkungen unabhängig.

     

Markov chain model of mixed surfactant systems

A new model of mixed surfactant systems have been developed in the work presented. It includes two parameters only connected directly with the Gibbs free energy of the surfactant aggregation. They can be determined using both the aggregation equilibrium constant values or the phase composition data. It has been shown also the relation between these new parameters and the same of the regular solution approximation and the alternative models. The possibility to describe the available experimental information about the micelle composition as a function of the singly dispersed surfactant mixture composition better than by the other models has been shown also.