Thermodynamics of micellization of aqueous solutions of binary mixtures of two anionic surfactants

Properties of some nonionic fluorocarbon surfactants and their mixtures with hydrocarbon ones

The adsorption of Zonyl FSN-100 (FSN100, having an average 14 oxyethylene units and 6 -CF₂ groups) and Zonyl FSO-100 (FSO100, having an average 10 oxyethylene units and 5 -CF₂ groups) as well as of their mixtures with p-(1,1,3,3-tetramethylbutyl) phenoxypoly(ethylene glycols) having 10, 16 and 8 oxyethylene groups in molecule (TX100, TX165, TX114) and cetyltrimethylammonium bromide (CTAB) at the solution-air and polytetrafluoroethylene (PTFE)-solution and polymethyl methacrylate (PMMA)-solution interfaces as well as the composition of the surface mixed layer was discussed based on the literature data. The adsorption properties of nonionic fluorocarbon surfactants were compared to those of the classical ones on the basis of the Gibbs standard free energy of adsorption determined by different ways and the intermolecular interactions of the surfactant molecules through the water phase. The synergetic effect in the reduction of the water surface tension by the mixture of fluorocarbon and classical nonionic surfactant was shown and explained by the comparison of the composition of the mixed surface layer to those in the bulk phase. The composition of the mixed fluorocarbon and classical surfactant layer at the solution-air interface was compared to that formed at the PTFE-solution and PMMA-solution interfaces. The changes of the surface tension of the aqueous solution of the fluorocarbon surfactants and their mixtures with classical hydrocarbon ones and their adsorption were analyzed taking into account the PTFE and PMMA surface wettability. This analysis was also based on the components and parameters of the head and tail of the surfactants surface tension as well as those of PTFE and PMMA. Apart from adsorption and wetting properties the aggregation of the fluorocarbon surfactants and their mixtures was discussed. A specific attention was paid to the possibility of two CMC values in the case of nonionic fluorocarbon surfactants as well as the synergism in CMC of mixtures of nonionic fluorocarbon and hydrocarbon surfactants.

Surfactant-Amino Acid and Surfactant-Surfactant Interactions in Aqueous Medium: a Review

An overview of surfactant-amino acid interactions mainly in aqueous medium has been discussed. Main emphasis has been on the solution thermodynamics and solute-solvent interactions. Almost all available data on the topic has been presented in a lucid and simple way. Conventional surfactants have been discussed as amphiphiles forming micelles and amino acids as additives and their effect on the various physicochemical properties of these conventional surfactants. Surfactant-surfactant interactions in aqueous medium, various mixed surfactant models, are also highlighted to assess their interactions in aqueous medium. Finally, their applied part has been taken into consideration to interpret their possible uses.

Phase Behaviour of the Microemulsion Systems Formed by the Composite Surfactants Alkyl Polyglucoside and Sodium Dodecyl Sulfate

The phase behavior of microemulsions containing composite surfactants of non-ionic alkyl polyglucoside and anionic sodium dodecyl sulfate was studied by the ∊-β fishlike phase diagram method. In microemulsion systems APG(SDS)/alcohol/alkane/water, there exists an obvious synergistic effect in terms of the composition of the interfacial layer and the solubilization ability. In the interfacial layer the number of surfactant and alcohol molecules notably decrease, resulting in a significant improvement in the solubilization ability of the system. The effects of alcohols, alkanes and salinity on the ∊-β fishlike phase diagrams of APG/SDS/alcohol/alkane/brine microemulsion systems were also discussed.

The Adsorption Layer in the System: Carboxymethylcellulose/Surfactants/NaCl/MnO(2)

The influence of surfactants (anionic sodium dodecyl sulfate, and nonionic tert-octylphenol ethoxylate with 9.5EO) and their mixtures on the adsorption of carboxymethylcellulose (CMC) in the presence of 0.001 M NaCl on the manganese dioxide surface (MnO₂) was studied. The increase in CMC adsorption was observed in all measured systems in the presence of surfactants. The reason for this is the formation of complexes between polymer macromolecules and surfactants. Moreover, the dependence between the amount of surfactants adsorption and the CMC initial concentration was also studied. It proves that surfactant adsorption does not depend on the initial concentration of CMC. Another observation is that the increase in pH caused the decrease in CMC adsorption. The explanation of this phenomenon is connected with the influence of pH on the dissociation degree of the polyelectrolyte, kind and concentration of the surface active groups of the adsorbent. To characterize the compact and diffuse adsorption layer the surface charge density and the zeta potential of MnO₂ in the presence of CMC and surfactants were measured. The surface charge density of MnO₂ decreases in the presence of CMC or CMC/surfactant complexes. This is due to the presence of negatively charged groups in the compact part of the electric double layer. The zeta potential of MnO₂ is also lower in the presence of CMC and the CMC/surfactants complexes. The main reason for that is the shift of the slipping plane towards the bulk solution.

Phenomenological approaches in the thermodynamics of mixed micelles with electric charges

The stability of mixed micelles in general has been extensively studied by the molecular thermodynamic approaches as well as by the phenomenological or thermodynamic approaches. In this article, phenomenological approaches in the thermodynamics of charged mixed micelles, mostly on ionic/nonionic mixed micelles, are reviewed. The electrostatic interaction constitutes a main contribution to the excess free energy per monomer (in kT unit) g(ex) in the case of ionic/nonionic mixed micelles and the corresponding contribution is generally negative, known as the electric synergism. The origin of the electric synergism is shown to reside in positive curvatures of g(ex,el) (the electric part of g(ex)) when plotted against the mole fraction of the ionic species x. Two types of the micellar Gibbs-Duhem (MGD) relations with (type 1) or without (type 2) the contribution from counterions are discussed to clarify various confusions found in the literature. Effects of varying ionic strengths with the micelle composition in the case of charged mixed micelles without any supporting electrolyte are discussed and a relevant way to correct for the effects is proposed. For ionic/nonionic mixed micelles, the regular solution model (RSM) and some two-parameter models to overcome the limitations inherent to the RSM are discussed. For mixed micelles subject to type 2 MGD relation, hydrogen ion titrations could provide g(el) experimentally just as in the case of linear polyelectrolytes and for those micelles subject to RSM, the titration curve becomes a straight line. Useful information is presented originating from the thermodynamic analysis on the difference of the intrinsic proton dissociation constants between the micelle and the monomer. An analytical expression of the dependence of the degree of counterion binding on x is discussed in comparison with the molecular thermodynamic results. The Corrin-Harkins relation is compared with the degree of counterion binding for ionic/nonionic mixed micelles. Mixed micelles in the concentration range higher than the critical micelle concentration (cmc) are discussed for three cases, the general method of Funasaki-Hada, the ideal mixing case, and the RSM.