Search

Gravitational drainage from thin vertical surfactant solution films and gravitational drainage in a settler column are used to study the behavior of foams based on two-surfactant mixtures. Namely, solutions of the anionic sodium dodecyl sulfate (SDS) and nonionic superspreader SILWET L-77, and their mixtures at different mixing ratios, are studied. It is shown, for the first time, that solutions having a longer lifetime in the vertical film drainage process also possess a higher foamability. An additional and unexpected unique result is that when using a mixed surfactant system, the foamability can be much greater than the foamabilities of the individual components.

With the aid of pH variation, direct transformation of a "1-1" cationic-anionic surfactant pair to a "1-2" cationic-anionic surfactant pair was attained in the system of cetyltrimethylammonium bromide and n-decylphosphoric acid. Owing to the transformation of a "1-1" pair to a "1-2" pair, diverse microstructures and peculiar phase behavior in this cationic-anionic surfactant mixture was obtained at different pH. It is proposed that pH can be manipulated for effectively tailoring the self-assembled organization in this cationic-anionic surfactant system, including spherical micelle, wormlike micelle, vesicle, and lamellar structure. In contrast to the conventional "1-1" surfactant pair, the "1-2" cationic-anionic surfactant pair exhibits unexpectedly weak aggregating ability. It is suggested that the hydrated volume of surfactant headgroup should be taken into consideration to better elucidate the self-assembly behavior of these "1-2" cationic-anionic surfactant mixtures.

The liquid crystalline alignment medium based on a quasi-ternary surfactant system comprising cetylpyridinium bromide (CPBr)/hexanol/sodium bromide [6.5% CPBr/hexanol (1/1.33, w/w), 30 mM NaBr in 1...

We report the synthesis and aqueous solution properties of a novel redox-active surfactant, Fc(CH2)11SO3-Na+, where Fc is ferrocene. Electrochemical oxidation of Fc to the ferrocenium cation (Fc+) reversibly transforms the anionic surfactant (Fc(CH2)11SO3-) into a zwitterionic species (Fc+(CH2)11SO3-). When dissolved at concentrations between 0.15 and 0.4 mM in aqueous solutions containing 10 mM Li2SO4, oxidation is accompanied by the reversible transformation of a solution of monomeric species of Fc(CH2)11SO3- into vesicle-like (Dh = 70 ± 8 nm, Rg/Rh = 1.0 ± 0.3) surfactant assemblies of Fc+(CH2)11SO3-. In contrast, at concentrations above 0.4 mM, oxidation reversibly transforms a solution of globular (Dh = 6 ± 2 nm) micelles into vesicle-like assemblies of Fc+(CH2)11SO3-. These various oxidation-induced changes in aggregation are reflected in the interfacial properties of this surfactant system, which are substantially different from those of ferrocenyl surfactants with cationic headgroups (Fc(CH2)11N+(...

Spherical surfactant aggregates of a new type were recently discovered. Named spherulites or onions, these aggregates are droplets of lamellar phase that can also be seen as vesicles (0.1−20 μm) with a dense multilamellar structure. In this article, we report the formation of an aqueous dispersion of spherulites with a difference in acidity between the bulk phase and the vesicles. This pH difference is achieved by the addition of fatty acids to the surfactant system. A series of fatty acids of varying chain length (from acetic acid to dodecanoic acid) is studied and is shown to induce different values of the pH shift. pH shifts up to 1.5 units are measured. This pH difference is thermodynamical in nature. A theoretical description using simple thermodynamics is proposed; it is used to build up an experimental pH determination without the use of a local probe. It is demonstrated herein that spherulites are a new type of encapsulating system that permits a thermodynamical control of acidity inside the micro...

We present the binary phase diagram of the system dodecaoxyethylene mono-n-dodecyl ether (C12EO12)/water, which is the first pure surfactant system found to exhibit three different type I (oil-in-w...

The adsorption of monodisperaed, isomerically pure anionic surfactant, p-octylbenzenesulfonate, and nonionic surfactant, dodecyloxyheptaethoxyethyl alcohol, and their mixtures on alumina was investigated to determine interactions between such surfactants. In a single surfactant system, only the anionic sulfonate was found to adsorb to any appreciable extent. In the mixed surfactant system, the sulfonate was found to induce significant coadsorption of the nonionic surfactant. This was attributed to hydrophobic interaction between the sulfonate and the alcohol at the mineral/solution interface. Adsorption of the sulfonate was also enhanced due to both hydrophobic interaction and the reduction of electrostatic repulsion between sulfonate head groups which are shielded from each other by the nonionic surfactant molecules.