Ionic Micellar Systems Research Articles

The mass action law theory of micellar solutions

Theories of micellization based on the application of the mass action law to aggregation processes in surfactant solutions are reviewed. The rigorous thermodynamic justification of the approach, explanation of the critical micelle concentration, inter-relations between the main micellization parameters, and an analysis of the surface tension isotherm of a micellar solution are given. Properties of ionic micellar systems, including counterion binding and the behavior of free monomeric ions, are discussed in detail with illustrative estimations for sodium dodecylsulfate and other surfactants.

Micellar solutions in shear: Viscosity and normal stress

We apply a recent non-equilibrium statistical mechanical theory for nonionic micellar solutions to study their viscoelastic properties. It is shown that shear-induced growth in average micellar size does not lead to the shear-thickening observed experimentally in ionic micellar systems, suggesting that intermicelle electrostatic interactions may be responsible for the viscosity build-up. Instead, we find shear thinning and gradual increase of normal stress throughout the studied range of shear rates.

Electroanalytical kinetic and diffusion studies in surfactant media

Voltammetry yields kinetic data for electron transfer in surfactant media. An electrocatalytic cycle is set up so that reactants exchange electrons in a rate-determining step following production of one reactant (the activated catalyst) at an electrode. Microdisk electrodes of radii < 10 μm are used to measure a ratio of catalytic limiting current (catalyst and substrate present) to that for catalyst alone. This “catalytic efficiency” can be used to find the apparent rate constant for reaction of activated catalyst with substrate. Microelectrodes can be used in highly resistive microemulsions. Electron transfer from the Co (I) form of vitamin B 12 to alkyl vicinal dihalides in AOT water-in-oil microemulsions is discussed. Apparent diffusion coefficients ( D′) from cyclic voltammetry decrease with increasing concentration of electroactive probe ( C X) in many ionic micellar systems. Analysis of D′ versus C X data with approximate models provided micelle diffusion coefficients for systems with one or two types of micelles. Similar studies by steady state voltammetry at microdisk electrodes of radii < 13 μm gave D′ values with no C x dependence in aqueous micellar systems. The latter experiments appear to yield average diffusion coefficients.

Photochromism of a surface-active spirobenzopyran moiety in dioxane–water mixtures and self-assembled surfactant aggregates

The photochemical and physicochemical properties of 1′-hexadecyl-3′,3′-dimethyl-6-nitrospiro [2H-1-benzopyran-2,2′-indoline](SP-16) in micellar self-assembled surfactant aggregates have been investigated. For comparison the properties of 1′,3′,3′-trimethyl-6-nitrospiro [2H-1-benzopyran-2,2′-indoline](SP-1) in 1,4-dioxane–water mixtures and, to a lesser extent, some neat organic solvents have also been examined. In all the media studied, both SP-16 and SP-1 undergo heterolytic cleavage when irradiated with UV light. This process may be reversed thermally or by irradiation with visible light. The spirobenzopyran open form, which is generated by the UV irradiation, is solvatochromic. A complex interplay of open-form stereoisomer contributions complicates the analysis of the solvatochromism, especially for micellar systems. In all the media, the thermal decoloration of the open forms of SP-16 and SP-1 follows single first-order kinetics. In the micellar systems, the first-order rate constants are interpreted in terms of interfacial solvent and charge stabilization effects and steric restrictions. pH induced UV–VIS spectral changes of the open forms of SP-16 and SP-1, in the low to medium region of the pH scale, are ascribed to the phenoxide moiety functioning as an acid–base group. The apparent pKa of SP-16 in non-ionic micellar systems reflects solely a solvent effect whilst the apparent pKa of SP-16 in ionic micellar systems reflects solvent and electrostatic effects as well as either a complexation of anionic species to the indolenium nitrogen or a ‘Debye–Huckel’ screening effect. Light-induced UV–VIS spectral modifications of the protonated open forms of SP-16 and SP-1 are explained in terms of a cis–trans photoisomerization process. pH (adjusted with NaOH) induced UV–VIS spectral changes are indicative of a partially reversible hydroxide degradation of the open forms of SP-16 and SP-1. A photochemical and physicochemical scheme is presented which summarizes the behaviour of 1′-alkyl-3′,3′-dimethyl-6-nitrospiro [2H-1-benzopyran-2,2′-indoline] derivatives in environments that have an aqueous component.

A study of competitive counterion binding to micelles using the acid-catalyzed reaction of hydrogen peroxide with iodide ions

The reaction involving the acid-catalyzed reduction of hydrogen peroxide by iodide ions has been used to study the competitive counterion binding of hydrogen ions to sodium dodecyl sulfate (SDS) micelles and iodide ions to both dodecyltrimethylammonium bromide (DTAB) and dodecyltrimethylammonium chloride (DTAC) micelles. It has been demonstrated that a pseudophase ion-exchange model can be employed to quantitatively describe, within certain limits, the competitive counterion binding in these ionic micellar systems. Ion-exchange constants have been determined for the hydrogen/sodium ion-exchange at the surface of SDS micelles, the iodide/bromide ion-exchange at the surface of DTAB micelles, and the iodide/chloride ion-exchange at the surface of DTAC micelles. These ion-exchange constants are 1.3 ± 0.4, 3.1 ± 0.3, and 8.2 ± 0.8, respectively.

Thermodynamic analysis of polydispersity in ionic micellar systems and its effect on small-angle neutron scattering data treatment

The authors analyze small-angle neutron scattering (SANS) data of sodium dodecyl sulfate (SDS) and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) ionic micellar solutions taking into account the effect of size polydispersity on the particle form factor. The intermicellar structure factor is computed by a generalized one-component macroion theory (GOCM) assuming a constant fractional charge. The model fittings to SANS data for different concentrations allow us to extract the free energy parameters of micelle formation and growth, the size distribution function of micelles, and the minimum micelle size which is consistent with the fully stretched hydrocarbon tail lengths of the surfactant molecules. The critical micellar concentration (cmc) is predicted from the free energy parameters correctly. Combining the free energy of micelle formation with the double-layer free energy around the averaged micellar surface calculated by the nonlinear Poisson-Boltzmann equation, they obtain the hydrophobic free energy of micellization which is in quantitative agreement with the literature value. These analyses confirm the applicability of the ladder model of micellar growth in salt free ionic micellar solutions at moderate concentrations. The degree of polydispersity in size is about 11% for 2% SDS solution at 40/degrees/C and 17% for 1% AOT at 22.6/degrees/C.

Fluorescence properties of some substituted acyclic azines

Fluorescence spectra of some acyclic azines (2,3-diazabutadienes), namely ō-hydroxybenzaldizine (1), p̄-N, N-dimethyl-amino abenzaldazine (2) and 2-hydroxy-1-naphthaldazine (3) were determined in different solvents at ambient temperature and at 77 K. The results showed that radiative and nonradiative rates are essentially controlled by the structure of the molecules. The fluorescence of compounds (1)-(3) is enhanced sufficiently by affecting the nπ∗ nature of the S 1 state in different media. The fluorescence quantum yield Φ F increases significantly as the viscosity of the homogeneous medium increases and as the temperature is lowered to 77 K. However, Φ F reaches a limiting small value, indicating the existence of an important nonradiative decay channel involving formation of different rotamers and E-Z isomers. The results of quantum chemical calculations based on the Hückel MO method, show that optical excitation decreases bond alternation in the S 1 state, leading to increasing nonradiative decay. Furthermore, the results demonstrate that the photophysical properties of these compounds in an ionic micellar system (CTAB) differ from analogous properties in homogeneous solitions. Optical excitation of azines containing a hydroxyl group ((1) and (3)) gives rise to a large increase in their acidic properties suggesting that intramolecular proton transfer in these molecules can be switched on by optical excitation. We have focussed our interest on ō-hydroxybenzaldazine (1) since preliminary studies show that it may be a useful indicator for fluorimetric determination of the microproperties of the surrounding environment.

Structural properties of solutions of spherical micelles: Effect of finite size of small ions

The effects of a finite size of the small ions (counterions and ions of 1–1 electrolytes added to the supporting solution) on the structural properties of solutions of spherical micelles are studied. This study is based on the primitive model of the solution and the mean spherical approximation. The structure obtained using the primitive model is contrasted with that of the one component macrofluid model for these systems. At high ionic strengths, interesting effects are observed in the short-range correlations between the macroparticles, directly related with the finite size of the small ions. Similar effects are also observed on the structure of the electrical double layer around each macroparticle. The consequences of these results for the interpretation of recent neutron scattering experiments from ionic micellar systems are briefly discussed. It is found that for small amounts of added salt a given experimental structure factor can be reproduced with a smaller effective charge on a micelle in the present model than in the previously used one-component macrofluid model. For large amounts of added salt, however, the finite size of the small ions may give rise to the opposite trend.

The dynamic behaviour of I − in aqueous dodecyltrimethylammonium chloride solutions : A model for counter-ion movement in ionic micellar systems

The quenching of pyrene fluorescence by I − in aqueous dodecyltrimethylammonium chloride (DDTAC) solutions was found to follow non-exponential behaviour. Analysis of the fluorescence decays according to the model proposed by Dederer et al. allows for a detailed quantitative description of the dynamic behaviour of I − in micellar DDTAC solutions.

ChemInform Abstract: ON THE DYNAMICS OF PYRENE FLUORESCENCE QUENCHING IN AQUEOUS IONIC MICELLAR SYSTEMS, FACTORS AFFECTING THE PERMEABILITY OF MICELLES

Chemischer InformationsdienstVolume 4, Issue 51 Physical Organic Chemistry ChemInform Abstract: ON THE DYNAMICS OF PYRENE FLUORESCENCE QUENCHING IN AQUEOUS IONIC MICELLAR SYSTEMS, FACTORS AFFECTING THE PERMEABILITY OF MICELLES M. GRAETZEL, M. GRAETZELSearch for more papers by this authorJ. K. THOMAS, J. K. THOMASSearch for more papers by this author M. GRAETZEL, M. GRAETZELSearch for more papers by this authorJ. K. THOMAS, J. K. THOMASSearch for more papers by this author First published: December 18, 1973 https://doi.org/10.1002/chin.197351061AboutPDF 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 onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume4, Issue51December 18, 1973 RelatedInformation

Dynamics of pyrene fluorescence quenching in aqueous ionic micellar systems. Factors affecting the permeability of micelles

Dynamics of pyrene fluorescence quenching in aqueous ionic micellar systems. Factors affecting the permeability of micelles