Sumio Ozeki

Micelle molecular weight of dodecyldimethylammonium chloride in aqueous solutions, and the transition of micelle shape in concentrated NaCl solutions

Abstract Light scattering of aqueous NaCl solutions of dodecyldimethylammonium chloride has been measured at different surfactant concentrations for different series of NaCl concentrations, and the micelle size and shape have been determined. At low NaCl concentrations the micelle molecular weight is of the order of 104 and slightly increases with NaCl concentration. The micelle is spherical or globular. At high NaCl concentrations the micelle molecular weight increases with increasing surfactant concentration and reaches a maximum: at the critical micelle concentration (CMC) small spherical micelles would be formed, but beyond the CMC they associate into large micelles. The molecular weight of large micelles increases sharply with increasing NaCl concentration and exceeds 106. The large micelle is rod-like but is flexible. Reduced repulsion among polar head groups induces the transition of micelle shape from sphere to rod. The effect of size of polar head groups on the micelle shape is discussed with reference to the micelle molecular weight of dodecylammonium chloride and dodecyltrimethylammonium chloride.

The sphere—rod transition of micelles and the two-step micellization of dodecyltrimethylammonium bromide in aqueous NaBr solutions

Abstract Light scattering was measured on aqueous NaBr solutions of dodecyltrimethylammonium bromide in the presence of 1.00 to 4.00 M NaBr, and these results are discussed together with the previous data at lower NaBr concentrations. When the NaBr concentration is lower than 1.8 M , spherical micelles alone are formed. At 2.00 and 3.00 M NaBr, the first and second critical micelle concentrations (CMC) exist, but at 4.00 M NaBr they coincide with each other. The primary micelle formed above the first CMC has the molecular weight about 23,500–24,400 in 1.00–4.00 M NaBr and is spherical. The secondary micelle formed above the second CMC has the molecular weight about 29,000–57,500 in 2.00–4.00 M NaBr, and its shape would be rodlike. Combined with the previous data at lower NaBr concentrations, it is found that a linear Corrin-Harkins relation holds for the first CMC up to 3.00 M NaBr, and that a linear double logarithmic relation between molecular weight and ionic strength holds for the spherical micelles. Another linear double logarithmic relation between molecular weight and ionic strength holds for rodlike micelles. The sphere-rod conversion of ionic micelles appears as a sharp transition with respect to the salt concentration, while it occurs as a chemical equilibrium with respect to the surfactant concentration. The sphere-rod transition of dodecyltrimethylammonium micelles induced by the change in counterion species from Cl − to Br − means that such a transition of ionic micelles is caused by the counterion binding, which reduces the electrostatic repulsion among charged head groups.

The viscosity behavior of aqueous NaCl solutions of dodecyldimethylammonium chloride and the flexibility of its Rod-Like micelle

Abstract The relative kinematic viscosity of aqueous solutions of dodecyldimethylammonium chloride in the presence of NaCl of different concentrations has been measured by an Ubbelohde-type capillary viscometer having four bulbs of successive heights. When referred to the solution of critical micelle concentration, the relative viscosity of the solutions is independent of shearing stress, if the NaCl concentration is lower than 2.40 M . However, non-Newtonian viscosity is manifest for solutions of higher NaCl concentrations. Extrapolated to zero shearing stress, the reduced viscosity and the logarithmic reduced viscosity of micellar solutions are obtained at different surfactant concentrations. The intrinsic viscosity for the micelle is derived as the limit of reduced viscosity or logarithmic reduced viscosity to zero micelle concentration at different NaCl concentrations. The double logarithmic plot of intrinsic viscosity for micelle against micellar molecular weight gives two linear sections. The steeper section has a slope of 1.3 and covers the region of molecular weights from 10 5 to 10 6 , which corresponds to NaCl concentrations from 1.5 to 3.0 M . The less steep section has, however, a slope of 0.61 and covers the region of higher molecular weights or of higher NaCl concentrations. This observation indicates that dodecyldimethylammonium chloride forms rod-like micelles in aqueous NaCl solutions of concentrations higher than 1.5 M , but that the micelles are not rigid but considerably flexible.

Surface tension of aqueous solutions of dodecyldimethylammonium chloride, and its adsorption on aqueous surfaces

Abstract The surface tension of aqueous solutions of dodecyldimethylammonium chloride has been measured as a function of surfactant concentration at different NaCl concentrations. By an analysis of the Gibbs adsorption isotherm, the surface excesses of surfactant ions, counter ions (Cl − ), and coions (Na + ) are estimated at different surfactant and NaCl concentrations. The adsorption isotherm of the surfactant ion approximately follows the Langmuir isotherm, having the saturated adsorption around (4 ∼ 6) × 10 −10 mole cm 2 , while the adsorption of Na + is negligibly small at low NaCl concentrations. The structure of the aqueous surface, composed of a charged monolayer and a diffuse double layer, is discussed with reference to the Gouy model of electric double layer.

The interaction of anionic surfactants with an Fe(II) chelate

Abstract The surface tension and light scattering of aqueous solutions of anionic surfactants (NaD), i.e., sodium dodecyl sulfate and sodium dodecanesulfonate, were measured in the presence of 5.0 × 10−5 M [Fe(phen)3](ClO4)2. The surface tension rapidly decreases with increasing concentration at a very dilute region, reaches a minimum, and then slightly increases with a further increase in concentration. Finally it reaches a constant value at the critical micelle concentration, after passing a maximum. The initial decrease in surface tension is mainly induced by the formation and adsorption of the 1:1 association complex, [Fe(phen)3]2+ · D−. The minimum is not the critical micelle concentration but is associated with the premicellar aggregation caused by the formation of the association complexes such as [Fe(phen)3]2+ · 2D− and [Fe(phen)3]2+ · 3D−. The critical micelle concentration can be definitely identified by the light scattering. A similar interpretation is applicable for the behavior of surface tension of aqueous solutions of sodium tetradecanesulfonate or sodium decanesulfonate containing [Fe(phen)3](ClO4)2. In the case of sodium octanesulfonate or sodium decanesulfonate, the micelle formation occurs more readily than the premicellar aggregation.

Size and shape of charged micelles of ionic surfactants in aqueous salt solutions

Light-scattering has been measured on aqueous NaCl solutions of dodecyldimethylammonium chloride and sodium dodecyl sulfate. From molecular weight determination it is confirmed that spherical micelles are formed at low NaCl concentrations, but at high NaCl concentrations the small micelles formed at the critical micelle concentration further associate to form large rod-like micelles with increasing micelle concentration. The reduction of repulsion between charged groups induces the sphere-rod transition of micelle shape. The dependence of molecular weight on ionic strength can be expressed by double logarithmic relations, which are dependent on the micelle shape. While dodecyldimethylammonium chloride dissolves even in 4.00 M NaCl, sodium dodecyl sulfate solutions exhibit some XXX in angular dissymmetry at NaCl concentrations higher than 0.50 M at low temperatures.

Carbon-13 nuclear magnetic resonance study of dodecyldimethylammonium chloride solutions

Abstract Carbon-13 NMR chemical shifts were measured on solutions of dodecyldimethylammonium chloride (DDAC) at various concentrations in the absence of added salt. Downfield chemical shifts, which were interpreted as a steric effect for all carbons, were found on micellization for all carbons except α-carbons (C 1 ). A change from spherical to rodlike micelles has been suggested for DDAC when sodium chloride concentration is higher than 0.6–0.8 M . The effects of this probable shape change on NMR properties were examined. The results are: (a) downfield shifts of all carbons (largest for N-methyl groups), (b) broadening of absorption lines (most significant for C 1 carbons); and (c) little change with respect to the spin-lattice relaxation times.

Adsorption of ions on aqueous surfaces of NaBr solutions of dodecyldimethylammonium chloride

Abstract The surface tension of aqueous NaBr solutions of dodecyldimethylammonium chloride has been measured by the drop weight method at different surfactant and NaBr concentrations. In order to apply the Gibbs adsorption isotherm for this indifferent system, the surface tension of these solutions containing differentially added NaCl has also been measured. From these results the surface excess densities of surfactant ion (D+), Na+, Cl−, and Br− are derived as functions of surfactant concentration at different NaBr concentrations, assuming the ideal solutions below the critical micelle concentration. When the NaBr concentration is lower than 0.05 M, D+ (or Br−) is more preferentially adsorbed on the surface than Na+ (or Cl−), and Br− (or D+) penetrates into the surface, while Cl− (or Na+) is expelled from there. When the NaBr concentration is higher than 0.02 M, the composition of anion on the surface is identical with that in the bulk, and D+ and Na+ are intrinsically adsorbed on the surface, in which the adsorption of Na+ is negative. The specific adsorption of ions in the common anion ternary system is also derived from the present results and compared with the results of previous experiments.

The adsorption of an association complex of anionic surfactants with an Fe(II) chelate on aqueous surfaces

Abstract The surface tension of aqueous solutions of sodium dodecanesulfonate (NaD) has been measured in the presence of different concentrations of Fe(phen) 3 ](ClO 4 ) 2 . An expression of the Gibbs adsorption isotherm is derived for these solutions, by postulating formation of a 1:1 association complex, [Fe(phen) 3 ] 2+ · D − cation, and it is applied for the data of surface tension obtained at dilute surfactant concentrations. Assuming a value of the association constant, the total surface excess densities of surfactant and metal chelate are derived as functions of concentration. From a consideration of the observed molecular area, it is found that the adsorbed layer consists mostly of the association complex. An approximate method for determining the total surface excess density of surfactant is given and applied for previous data on aqueous solutions of interacting systems. Treatments of the Gibbs adsorption isotherm including higher association complexes, [Fe(phen) 3 ] 2+ . p D − ( p > 1), are also given, and the relationship of the isotherm for the ternary system with that for the quaternary system containing NaClO 4 is discussed.