Guo-Xi Zhao

The physicochemical properties of aqueous mixtures of cationic-anionic surfactants: II. Micelle growth pattern of equimolar mixtures

Abstract An investigation of the micelle solution behaviors of the equimolar mixtures of octyltriethylammonium bromide-sodium octyl-, decyl-, and dodecyl-sulfate has been carried out by dynamic and static light scattering. It is shown that micelle size increases with surfactant concentration, the total hydrophobic chain length, and the lowering of temperature. The micelle is a rigid rod when the radius of gyration is below 400 A; above this size; the micelle has the shape of a semiflexible rod. At the limit of micelle growth, either by increase of micelle concentration or by decrease of temperature, a new liquid phase separates from the solution, and the surfactant concentration of this new phase could be rather dilute (could be less than 1.2%). This two-aqueous-phase-coexisting phenomenon may be interpreted as flocculation of micelles. The sphere-to-rod transition model is adapted to the mixed micelles of cationic and anionic surfactant systems, and some thermodynamical parameters in the sphere-to-rod transition are deduced from experimental results and this model.

The physicochemical properties of aqueous mixtures of cationic-anionic surfactants: I. The effect of chain length symmetry

The solution behaviors of equimolar mixtures of cationic-anionic surfactants have been studied by means of the dynamic light scattering technique and surface tension measurements. The surface activity and the micellization properties are different for systems of different hydrophobic chain length symmetry. For systems of lower symmetry (e.g., C6H13NC5H5Br-C12H25SO4Na mixture), the surface tension at cmc (γcmc) is rather high (above 30 mN m−1) and the mixtures form genuinely homogeneous micellar solutions above the cmc. For the systems of high symmetry (e.g., C8H17NC5H5Br-C8H17SO4Na mixture), γcmc is very low (about 24 mN m−1, near the value of pure hydrocarbon) and in the apparently homogeneous and clear mixtures slightly above cmc, the aggregates grow slowly and eventually form small droplets; as the concentration is further increased, all these solutions become turbid. We have proposed a new concept of conformation energy of aggregates to account for all these phenomena. Mixtures of octyltriethylammonium bromide and sodium octylsulfate form clear homogeneous micellar solutions in keeping with predictions based upon this concept.

Dynamic surface tension of the aqueous solutions of cationic-anionic surfactant mixtures

Abstract Using the oscillating jet method, the dynamic surface tension and the surface adsorption kinetics of the aqueous solutions of the following cationic-anionic surfactant mixtures have been studied: octylpyridinium bromide and sodium octylsulfate (I), hexylpyridinium bromide and sodium decylsulfate (II), hexylpyridinium bromide and sodium perfluorooctanoate (III), and these mixtures with sodium bromide as an inorganic electrolyte additive. The results show that the surface adsorption of all these systems is essentially diffusion controlled. From the study of the effect of inorganic electrolytes on the dynamic surface tension, the probable surface structure in the primary and latter stages of the adsorption process has been suggested.

SOLUBILIZATION OF N-OCTANE AND N-OCTANOL BY A MIXED AQUEOUS SOLUTION OF CATIONIC-ANIONIC SURFACTANTS

Abstract The solubilization of n -octane and n -octanol by the single and mixed polyoxyethylenated cationic-anionic surfactants (C 8 H 17 (OC 2 H 4 ) n SO 4 Na-C 8 H 17 (OC 2 H 4 ) m NC 5 H 5 Br(C 8 E n S-C 8 E m Py; n = 1, 3; m = 0, 3) and C 8 H 17 C 6 H 4 (OC 2 H 4 ) 9.8 SO 4 Na-C n H 2 n +1 NC 5 H 5 Br(C 8 ΦE 9.8 S-C n Py( n = 8, 10, 12, 14, 16)) and the viscosity of the solution after solubilization have been measured. The solubilization of octanol by mixed surfactant solution increases with the number of the oxyethylene group increasing in the surfactants of the mixture. The solubilization of n -octane by the mixed surfactant solution is higher than that of n -octanol, and especially the solubilization of n -octane in 1:1 C 8 E 1 S-C 8 Py solution (0.4 M ) is much larger than that of n -octanol. The solubilization of the octanol in the mixed surfactant solution would cause the viscosity of the solution to increase, but the solubilization of the octane in the mixed surfactants causes the viscosity of the solution to decrease. The unusual results showing that the solubilization of n -octane is larger and makes the viscosity of the solution decrease are considered to be due to the change of the micelle form—from rod-like micelle to spherical micelle—during solubilization. Both experimental results and theoretical analysis show that the longer the length of the rod-like micelle, the larger the solubilization of n -octane in the mixed surfactants and the larger the decrease in viscosity of the solution after the change of the micelle form.

Preparation of CdS nanoparticles at the monolayer of N-methyl-p-(p-tetradecyloxystyryl)pyridinium iodine

Abstract CdS nanoparticles were prepared at the monolayer of a cationic functional amphiphile, N -methyl- p -( p -tetradecyloxystyryl)pyridinium iodine, by prior converting of Cd 2+ to CdEDTA 2− . The particles can be transferred onto substrates along with the monolayer. The density and size of the nanoparticles can be controlled.