Micellar Solutions Of Ionic Surfactants Research Articles

Quantitative Prediction of the Structure and Viscosity of Aqueous Micellar Solutions of Ionic Surfactants: A Combined Approach Based on Coarse-Grained MARTINI Simulations Followed by Reverse-Mapped All-Atom Molecular Dynamics Simulations.

We address the problem of the quantitative prediction of micelle formation in dilute aqueous solutions of ionic surfactants using sodium dodecyl sulfate (SDS) as a model system through a computational approach that involves three steps: (a) execution of coarse-grained simulations based on the MARTINI force field (with slightly modified parameters to afford the formation of large micelles); (b) reverse mapping of the final self-assembled coarse-grained configuration into an all-atom configuration; and (c) final relaxation of this all-atom configuration through short-time (on the order of a few tens of nanoseconds), detailed isothermal-isobaric molecular dynamics simulations using the CHARMM36 force field. For a given concentration of the solution in SDS molecules, the modified MARTINI-based coarse-grained simulations lead to the formation of large micelles characterized by mean aggregation numbers above the experimentally observed ones. However, by reintroducing the detailed chemical structure through a strategy that solves a well-defined geometric problem and re-equilibrating, these large micellar aggregates quickly dissolve to smaller ones and equilibrate to sizes that perfectly match the average micelle size measured experimentally at the given surfactant concentration. From the all-atom molecular dynamics simulations, we also deduce the surfactant diffusivity DSDS and the zero-shear rate viscosity, η0, of the solution, which are observed to compare very favorably with the few experimental values that we were able to find in the literature.

Micellar solutions of ionic surfactants and their mixtures with nonionic surfactants: Theoretical modeling vs. Experiment

Here, we review two recent theoretical models in the field of ionic surfactant micelles and discuss the comparison of their predictions with experimental data. The first approach is based on the analysis of the stepwise thinning (stratification) of liquid films formed from micellar solutions. From the experimental step-wise dependence of the film thickness on time, it is possible to determine the micelle aggregation number and charge. The second approach is based on a complete system of equations (a generalized phase separation model), which describes the chemical and mechanical equilibrium of ionic micelles, including the effects of electrostatic and non-electrostatic interactions, and counterion binding. The parameters of this model can be determined by fitting a given set of experimental data, for example, the dependence of the critical micellization concentration on the salt concentration. The model is generalized to mixed solutions of ionic and nonionic surfactants. It quantitatively describes the dependencies of the critical micellization concentration on the composition of the surfactant mixture and on the electrolyte concentration, and predicts the concentrations of the monomers that are in equilibrium with the micelles, as well as the solution’s electrolytic conductivity; the micelle composition, aggregation number, ionization degree and surface electric potential. These predictions are in very good agreement with experimental data, including data from stratifying films. The model can find applications for the analysis and quantitative interpretation of the properties of various micellar solutions of ionic surfactants and mixed solutions of ionic and nonionic surfactants.

Micellar Solutions of Ionic Surfactants and Their Mixtures with Nonionic Surfactants: Theoretical Modeling vs. Experiment

Micellar Solutions of Ionic Surfactants and Their Mixtures with Nonionic Surfactants: Theoretical Modeling vs. Experiment

Binding of solvent molecules by micelles of ionic surfactants

The distribution of molecules between the free (intermicellar) and the micelle-bound states is found from the results of selective measurements of their self-diffusion coefficients in micellar solutions of ionic surfactants, i.e., sodium dodecylsulfate and cetyltrimethylammonium bromide.

Conductivity of micellar solutions of ionic surfactants and surface conductivity of micelles

Within the effective medium model, a method is proposed for determining the surface conductivity of micelles. The known experimental data on the conductivity of aqueous sodium dodecyl sulfate micellar solutions are analyzed employing the developed approach. Specific surface conductivity λs of micelles is shown to be 10−8Ω−1. The high values of λs are indicative of a noticeable contribution of the dense part of the electrical double layer, which is comparable with the contribution of its diffuse part, to the micellar solution conductivity. This estimate is strongly dependent on the initial information obtained in different studies. The marked influence of the micelle surface conductivity on the effective conductivity of micellar solutions allows one to put the question of the correctness of the method commonly used to determine the degree of counterion binding from the slopes of the dependences of the solution conductivity on the overall surfactant concentrations in the premicellar and micellar regions.

The electrical double layer of micelles in ionic surfactant solutions in the presence of a background electrolyte: 2. Moderately concentrated micellar solutions of sodium dodecyl sulfate

To continue previous studies [1], a model is developed for calculating electrostatic potentials 1ψ0 and 1ψd corresponding to the surface of micelle core and the Stern layer, respectively, and the degree 1β of binding of counterions in moderately concentrated micellar solutions of ionic surfactants. By the example of sodium dodecyl sulfate micellar solutions, dependences of 1ψ0 and 1ψd on overall concentration n varying over the range from 0.1 to 0.9 M are determined at different NaCl concentrations in the system. The absolute values of 1ψ0 and 1ψd potentials are found to grow with a rise in the degree of micellization and a reduction in the average intermicellar distances. This growth is greatly pronounced at a low content of the background electrolyte, whereas, in concentrated NaCl solutions (of approximately 0.1 M), potentials 1ψ0 and 1ψd remain practically constant. Dependence 1 − 1β(n) is monotonically decreasing function.

Prediction of Solubility of Nonpolar Gases in Micellar Solutions of Ionic Surfactants

The solubilities of methane, carbon dioxide, ethane, and propane have been determined experimentally at 1 atm partial pressure and 25°C in aqueous solutions of sodium dodecyl sulfate and cetyltrimethylammonium bromide. For this purpose a specially developed apparatus is used, which is relatively simple compared to those reported in the literature hitherto. Above the CMC, the solubility of each gas increases linearly with surfactant concentration indicating micellar solubilization. The degree of solubilization is greatest for propane and decreases in the order propane > ethane > carbon dioxide > methane. Both the length of the alkyl chain and the properties of the head-group region (i.e., the micelle–water interfacial tension) are observed to determine the intramicellar solubility. A method for estimating the solubilities is also proposed based on the rationale that the micellar phase may be represented by a droplet of a “model solvent” into which the solubilizate molecule dissolves as it would in a bulk solvent. The mixture of the solute species and the model solvent is assumed to behave as a regular solution. Accordingly, a characteristic solubility parameter is estimated for the model solvent from the interaction potential between two adjacent surfactant molecules in a micelle. The solubility computed using the regular solution approximation is further corrected for the Laplace pressure that acts across the curved micelle–water interface and generally reduces the intramicellar solubility. It is concluded that for small nonpolar solutes, micellar solubilities may be reasonably well predicted by assuming that the model solvent has a solubilizing capacity (i.e., solubility parameter) close to that of a bulk equivalent alkane.

Aqueous Solutions of Zwitterionic Surfactants with Varying Carbon Number of the Intercharge Group. 2. Ion Binding by the Micelles

Electrical conductivity, spectrofluorometry, and self-diffusion measurements have been used to provide evidence for, and study of, the binding ofions (Na + , Cl - ) to the micelles of series of zwitterionic surfactants of the alkanediyl-α-(dodecyldimethylammonio)-ω-carboxylate type with the intercharge alkanediyl group being CH 2 , C 3 H 6 , C 5 H 10 , and C 10 H 20 (referred to as C12N1C02, C12N3C02, C12N5C02, and C12N10C02, respectively). These surfactants permitted us to assess the effect of the carbon number of the intercharge group on the binding of Na + and Cl - to the zwitterionic micelles. The propanediyl-1-(dodecyldimethylammonio)-3-sulfonate (C12N3S03) has also been investigated to check the effect of the headgroup. In most experiments, the molar concentration ratio [surfactant]/[salt] was kept constant and equal to 1. The degrees of ion binding have been obtained for both Na + and Cl - as a function of the surfactant concentration, from self-diffusion measurements. The degree of binding is always larger for the anion and follows the sequence C12N1CO2 < C12N3SO3 < C12N3CO2 < C12N5CO2 C12N1OCO2, both for Na + and Cl - . The results show that, contrary to what is observed for micellar solutions of ionic surfactants, the binding of ions by zwitterionic micelles starts only well above the cmc and increases rapidly with concentration. A mass action model has been developed and provides a quantitative account of the results.

Adsorption kinetics from concentrated micellar solutions of ionic surfactants at the water—air interface

The dynamic surface tension of concentrated ionic surfactant solutions was studied both theoretically and experimentally. Formulae (in agreement with the experimental data) were derived and these establish connections between surface-active monomer concentrations and total surfactant concentration. The problem of the kinetics of adsorption from concentrated micellar ionic surfactant solutions on a freshly-formed surface was formulated and numerically solved. The possibility of an abnormal (increasing) dependence of dynamic surface tension on total surfactant concentration is demonstrated. Also, approximate analytical expressions for dynamic surface tension in the region of long and short surface lifetimes have been derived. Experimental studies on the dynamic surface tension of sodium tetradecylsulphate and hexadecylsulphate in the concentration range up to 200 times the CMC were performed. The maximum bubble pressure method has been improved and a fully automated and computerized instrument for measurements of surface tension and surface lifetimes developed. It has been established that at surfactant concentrations 5–10 times (or more) greater than the CMC, dynamic surface tension does not depend on the total surfactant concentration. Within the scope of existing theoretical knowledge this result agrees with the adsorption mechanism, which is controlled by slow dissociation of micelles and the surface barrier at long surface lifetimes, and also by monomer diffusion and fast micelle dissociation in the region of short lifetimes. Rate constant values for the fast and slow dissociation of micelles, obtained from dynamic surface tension measurements, show good agreement with results of relaxation studies.

Thermodynamics of ionic surfactant micelle—comments

The assumptions made in deriving a recently published micellar Gibbs-Duhem equation applicable to micellar solutions of ionic surfactants which may contain several counterion species are stated explicitly and reviewed critically. Possible improvements are suggested. The merits of an alternative and essentially exact description of the cmc behavior are emphasized.

Electrokinetic chromatography with micellar solution and open-tubular capillary

Fundamental characteristics of a new type of chromatography with micellar solutions of ionic surfactants were examined. Electrokinetic phenomena in open-tubular capillaries move two phases, aqueous and micellar, with different velocities and micellar solubilization operates as the distribution process of solutes. Sodium dodecyl sulfate (SDS) solutions and a 0.05 mm i.d. x 650 mm fused silica tube were employed and high dc voltages up to 25 kV were applied. Linear relationships were observed between current and migration velocities of water, micelle, and any solute, but not between applied voltages and the velocities. This discrepancy can be reasonably interpreted in terms of the temperature rise of the solution in the tube resulting from Joule heating. Optimum resolutions can be obtained when the capacity factor is about 2, because retention times are limited between those of an insolubilized solute or water and a totally solubilized solute or micelle. Observed dependence of capacity factors on current can also be explained by the temperature rise. Thermodynamic parameters in micellar solubilization were presented. 22 references, 10 figures, 4 tables.

ChemInform Abstract: ULTRASONIC RELAXATION STUDIES OF THE EXCHANGE OF BUTOXYETHANOL WITH MIXED MICELLES IN AQUEOUS MICELLAR SOLUTIONS OF IONIC SURFACTANTS

Chemischer InformationsdienstVolume 14, Issue 10 Article ChemInform Abstract: ULTRASONIC RELAXATION STUDIES OF THE EXCHANGE OF BUTOXYETHANOL WITH MIXED MICELLES IN AQUEOUS MICELLAR SOLUTIONS OF IONIC SURFACTANTS N. P. RAO, N. P. RAOSearch for more papers by this authorR. E. VERRALL, R. E. VERRALLSearch for more papers by this author N. P. RAO, N. P. RAOSearch for more papers by this authorR. E. VERRALL, R. E. VERRALLSearch for more papers by this author First published: March 8, 1983 https://doi.org/10.1002/chin.198310073AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume14, Issue10March 8, 1983 RelatedInformation

Ultrasonic relaxation studies of the exchange of butoxyethanol with mixed micelles in aqueous micellar solutions of ionic surfactants

Ultrasonic absorption measurements have been used to study the dynamics of micellar systems and to obtain semiquantitative information on the kinetic and thermodynamic parameters for the cosurfactant exchange process from mixed micelles of surfactant and cosurfactant. Ultrasonic relaxation parameters for the micellar systems containing water, surfactant (cetyltrimethylammonium bromide, myristyltrimethylammonium bromide, cetylpyridinium bromide, and Dowfax 2A1), and cosurfactant (butoxyethanol) are reported. The kinetic parameters for the exchange of butoxyethanol between the mixed micelles containing cetyltrimethylammonium bromide and myristyltrimethylammonium bromide are estimated and the results are discussed in light of the proposed mechanism.

Electric birefringence measurements on micellar solutions of ionic surfactants

Measurements of electric birefringence were made on surfactant solutions which are known to form anisotropic aggregates. Both amplitude and relaxation time constants of the dynamic Kerr effect were studied as functions of total surfactant concentration, electric field strength, temperature, and counterion concentration. Results indicate the existence of rod-like micelles whose lengths and number density increase with critical concentration. Results of the study of the anisotropy of the electric polarizability of the counterion atmosphere were compared with theory. 31 references.

Adsorption maxima from solutions of ionic surfactants. A thermodynamic analysis

By regarding adsorbed and dissolved surfactant as independent species whose chemical potentials are equal at equilibrium, general expressions are derived which specify the conditions for the Gibbs surface excess of surfactant, Γ, and the contribution from an adsorbed monolayer, Γm, to exhibit maxima with increasing surfactant concentration. These conditions do not appear to be thermodynamically or otherwise forbidden and lead to the conclusion that situations may arise in which the total number density of solute in an interfacial region decreases with increasing bulk concentration. An example based on a simplified model is used to show that the appropriate conditions might be fulfilled in practice by some micellar solutions of ionic surfactants. Similar reasoning could also apply to surfactant binding on polymers.

Fast exchange of alcohol molecules between micelles and surrounding solution in aqueous micellar solutions of ionic surfactants

In the presence of alcohol, aqueous micellar solutions of ionic surfactants with long alkyl chains show a relaxational excess ultrasonic absorption characterized by a single relaxation frequency f R . The dependence of f R and of the ultrasonic relaxation amplitude R on various parameters can be readily explained by assigning the observed relaxation process to the fast exchange of alcohol molecules between micelles and surrounding solution. A quantitative treatment of this relaxation process should yield thermodynamic and kinetic information on the exchange of alcohol molecules between micelles and surrounding solution.

Theory of the kinetics of micellar equilibria and quantitative interpretation of chemical relaxation studies of micellar solutions of ionic surfactants

ADVERTISEMENT RETURN TO ISSUEArticleNEXTTheory of the kinetics of micellar equilibria and quantitative interpretation of chemical relaxation studies of micellar solutions of ionic surfactantsE. A. G. Aniansson, S. N. Wall, M. Almgren, H. Hoffmann, I. Kielmann, W. Ulbricht, R. Zana, J. Lang, and C. TondreCite this: J. Phys. Chem. 1976, 80, 9, 905–922Publication Date (Print):April 1, 1976Publication History Published online1 May 2002Published inissue 1 April 1976https://doi.org/10.1021/j100550a001RIGHTS & PERMISSIONSArticle Views2047Altmetric-Citations708LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts