Phase Diagrams Of Micelle Formation Research Articles

Uptake of iron (III)-ethylenediamine-N, N, N′, N′-tetraacetic acid complex by phosphatidylcholine lipid film. Part II. Effect of film curvature

Mixed micelles formed in a ternary-solute aqueous solution of NaOH, iron (III)-ethylenediamine-N, N, N′, N′-tetraacetic acid complex (Fe-EDTA) and 1,2-diheptanoyl-sn-glycero-3-phosphatidyl choline (DHPC) were studied and compared with the mixed adsorbed film reported in Part I of this series to clarify the effect of the curvature of molecular assemblies on the interactions between their Fe-EDTA and DHPC constituents. The critical micelle concentrations (CMCs), surface tension at the CMC, and solution pH were measured as functions of the mole fractions of NaOH and DHPC. Rigorous thermodynamic equations were derived, in which the overall proton dissociation equilibria of Fe-EDTA and DHPC were taken into consideration, and applied to experimental data to obtain phase diagrams of micelle formation and the micelle-adsorbed film equilibrium. It was found that when the bulk solution was strongly acidic, Fe-EDTA was incorporated in the micelles. However, the adsorbed film was more Fe-EDTA-enriched than the micelle. These findings imply that a flat cell membrane is more permeable to an iron complex than a cell membrane with positive curvature.

Surface adsorption and aggregate formation of aqueous binary mixture of cationic surfactant and sugar surfactant

The surface tension of aqueous solutions of dodecyltrimethylammonium bromide (DTAB) and octyl-β-d-glucopyranoside (OG) mixture was measured as a function of the total molality of surfactants and the relative proportion of OG under atmospheric pressure at 298.15 K by drop volume technique. The results of surface tension measurements were analyzed by originally developed thermodynamic equations then phase diagrams of adsorption and micelle formation were constructed. From the analysis of surface tension data, it was suggested that the addition of relatively small amount of DTAB molecules helps the denser monolayer formation compared with the ideal mixing. Furthermore, it was also suggested that the phase diagram of micelle formation has a negative azeotropic point and that the interaction between different components is stronger in the mixed micelle than in the adsorbed film from the view point of the excess Gibbs energy. From these results, it is concluded that the hydrogen bond formation between OG molecules is the main contribution to determine the physical properties in the adsorbed film whereas the ion–dipole interaction between head groups of different components becomes main cause of attractive interaction in the micelle.

Interaction between Ionic and Nonionic Surfactants in the Adsorbed Film and Micelle. Dodecylammonium Chloride and Tetraethylene Glycol Monooctyl Ether

The surface tension of aqueous solutions of dodecylammonium chloride (DAC) and tetraethylene glycol monooctyl ether (C8E4) was measured as a function of the total molality of surfactants and the composition of C8E4 at constant temperature under atmospheric pressure. The results of the surface tension measurements were analyzed by our thermodynamic procedure, and phase diagrams of adsorption and micelle formation were drawn. The miscibility of the surfactants and their intermolecular interaction in both the adsorbed film and the micelles were examined. Deviation from ideal mixing was observed and an attractive interaction was suggested. Furthermore, the phase diagram of micelle formation was shown to have an azeotropic point, and a stronger energetic stabilization was suggested in the mixed micelle formation than in the adsorbed film at the cmc. This difference suggests that the structures of both the surfactant molecules and the aggregates significantly affect the intermolecular interaction between surfactants.

Volume Properties of Decylammonium Chloride and Micelle-Forming Local Anesthetic Mixtures in the Micelle

The densities of aqueous solutions of a decylammonium chloride (DeAC)−dibucaine hydrochloride (DC·HCl) mixture and a DeAC−tetracaine hydrochloride (TC·HCl) mixture were measured as a function of the total molality and composition of the mixture at 298.15 K under atmospheric pressure. The molar volumes of the mixture in the monomeric and micellar states of both systems were evaluated by applying the thermodynamic equations to the apparent molar volumes obtained from the density data. They varied linearly with composition between the values of pure components. The volume of mixed micelle formation also showed the linear dependence on the composition. These facts indicate that the DeAC and the anesthetic molecules mix ideally in both the monomeric and micellar states from the viewpoint of volume. On the other hand, the micellar composition was calculated from the composition dependence of the critical micelle concentration values. The shape of the phase diagram of micelle formation was slightly distorted cig...

Extremely Strong Interaction of Sodium Decyl Sulfate and Decyltrimethylammonium Bromide in Molecular Aggregates

The thermodynamic behavior of a mixture of sodium decyl sulfate (SDeS) and decyltrimethylammonium bromide (DeTAB) in aqueous solution and in molecular aggregates such as surface adsorbed films and micelles was investigated by measuring the electric conductivity and surface tension of the aqueous solutions. The thermodynamic quantities in solution and those in the molecular aggregates were evaluated from the experimental conductivity and surface tension data. The results for molar conductivity showed that dimerization or ion-pair formation of the SDeS and DeTAB molecules does not occur in aqueous solution and the mixture behaves as uni–univalent strong electrolyte below the critical micelle concentration (CMC). Contrary to the results in the aqueous solution, we found significant nonideal behavior in the phase diagrams of surface adsorption; that is, equimolar mixture of SDeS and DeTAB exists in the adsorbed film at almost all compositions irrespective of the bulk composition in the solution. The same result was also observed in the phase diagram of micelle formation. There was no difference in phase diagrams between surface adsorption and micelle formation at the CMC. The great nonideal mixing of SDeS and DeTAB in the molecular aggregates is undoubtedly attributable to the extreme attractive interaction between oppositely charged polar head groups of surfactants as well as to cohesion between hydrophobic groups. Further, in a low concentration region, it turned out that equimolar composition is preserved in the film during phase transition of the mixed adsorbed film of SDeS and DeTAB from a gaseous state to an expanded state.

Miscibility of dodecylammonium chloride and octylsulfinylethanol in the adsorbed film and micelle

The surface tension of an aqueous solution of a dodecylammonium chloride (DAC) and octylsulfinylethanol (OSE) mixture was measured as a function of the total molality of surfactants and the mole fraction of OSE in the solution. By analyzing the experimental results using thermodynamic relations developed previously, a phase diagram of adsorption representing the equilibrium between the adsorbed film and solution was obtained at a given surface tension. At a low surface tension, the mixture was found to form a negative azeotropic mixed film. It was also observed that the phase diagram of micelle formation has a distinct minimum. Such behavior was attributed to the attractive interaction between DAC and OSE molecules in the oriented states. Further, the molecular interaction was found to be more attractive in the micellar state than in the adsorbed state.