Area per surfactant molecule values of gemini surfactants at the liquid-hydrophobic solid interface.

Areas per surfactant molecule at the liquid/hydrophobic solid (A(LS)) and the liquid/air (A(LA)) interface as a function of the spacer length are reported for cationic gemini surfactants having (CH2)n spacer s. A(LA) increases with increasing spacer length up to 6-8 CH2 groups in the spacer and then levels off. A(LS) values indicate a more closely packed arrangement of the surfactant molecules than that at the liquid/air interface. Comparison of A(LA) and A(LS) values indicates that the surfactant molecules at the liquid/hydrophobic solid interface are almost three times as closely packed as those at the liquid/air interface. A comparison of the experimental values of the area per surfactant molecule at both interfaces was made with those calculated from dimensions of the surfactant molecule in vacuo.

Ultralow interfacial tension for enhanced oil recovery at very low surfactant concentrations.

The interfacial tension (IFT) between alkanes and several individual surfactants and their mixtures has been investigated, using three kinds of alkyl hydrocarbons: decane, dodecane, and tetradecane. For individual and mixed surfactant systems, critical micelle concentrations and areas per molecule at the hydrocarbon-aqueous solution interface were calculated; for the mixed surfactant systems, betasigma(LL), the molecular interaction parameter at the hydrocarbon-aqueous solution interface, and beta(M), the molecular interaction parameter in mixed micelle formation, were calculated. It was found that IFT in the 10(-3) mN/m (ultralow) range can be obtained at surfactant concentrations below 0.05 wt % and even at concentrations below 0.01 wt %, when mixtures of certain surfactants are used at the proper ratio. Surfactants with branched-chain alkyl groups show a much better IFT reduction effectiveness than those with straight-chain alkyl groups. Contrary to what has been observed at the air-aqueous solution surface, mixtures of two homologues with two hydrophobic groups show significant molecular interactions, with both betasigma(LL) and beta(M) having negative values in the 4-5 range in some cases, with the betasigma(LL) value more negative than beta(M). The relationship between micellar shape and ultralow IFT was investigated by calculating the critical packing parameter of the surfactants. It was found that ultralow IFT between the surfactant mixtures and the three hydrocarbons investigated could reach ultralow (<10(-2) mN/m) values when the critical packing parameter is very close to 1.

Synergism in the spreading of hydrocarbon-chain surfactants on polyethylene film-anionic and cationic mixtures by a two-step procedure.

A study has been made of the adsorption, interaction, and spreading of mixtures of anionic and cationic surfactants at the aqueous solution/polyethylene (PE) interface. When a drop of an aqueous solution of an anionic or cationic hydrocarbon-chain surfactant is placed on a highly hydrophobic PE film (contact angle of water > 90 degrees ), it spreads to an area very little larger than that of a drop of water of the same volume. If the anionic and cationic hydrocarbon-chain surfactant solutions are mixed prior to being applied to PE film, synergism is small, if any, and the reproducibility of the experimental results is poor. However, when the cationic and anionic aqueous solutions are applied on the PE film in a sequential manner, a remarkable synergism in spreading is observed and the results are very reproducible. The area spread by an aqueous solution of the anionic-cationic mixture may be more than 400 times that of aqueous solutions of the same volume and surfactant concentration of the individual surfactant components. Previous work in this laboratory on surfactant systems showing synergism in spreading on PE film, but only weak interaction at the aqueous solution/air interface, showed that the synergy was due to changes at the aqueous solution/PE interface and not to the changes at the aqueous solution/air or PE/air interface. Investigation of the adsorption behavior at the aqueous solution/solid interface of two of the anionic-cationic mixtures studied here indicates the reason for differences in spreading behavior observed with different anionic-cationic mixtures. The more similar the adsorption tendencies at the solid/aqueous solution interface of the anionic and cationic surfactants, and the closer their adsorption to an equimolar monolayer there, the stronger their interaction there and the greater their enhancement of the spreading. A mechanism is proposed for the synergy in spreading observed, based upon the difference between the surface tension in the precursor film at the spreading interface and that at the top of the spreading drop.

Structural effects on surface and micellar properties of alkanediyl-alpha, omega-bis(sodium N-acyl-beta-alaninate) gemini surfactants.

A study of the equilibrium surface properties (in water and in the presence of 0.01 M NaCl) of a novel series of anionic gemini surfactants, alkanediyl-alpha,omega-bis(sodium N-acyl-beta-alaninates), is described. Parameters studied include cmc (critical micelle concentration), C20 (required to reduce the surface tension of the solvent by 20 mN/m), gamma(cmc) (the surface tension at the cmc), Gamma(max) (the maximum surface excess concentration at the air/aqueous solution interface), Amin (the minimum area per surfactant molecule at the air/water interface), and the cmc/C20 ratio (a measure of the tendency to form micelles relative to adsorb at the air/water interface). The geminis with a spacer consisting of two methylene groups show premicellar self-aggregation, both in water and in 0.01 M NaCl, when the N-acyl group contains more than 12 carbon atoms; geminis with a spacer consisting of four methylene groups show no premicellar aggregation even when the N-acyl group contains 16 carbon atoms. For the acyl chain lengths where premicellar aggregation does not occur, the values of the cmc of the geminis with a two-methylene spacer are lower than those for the corresponding analogous geminis with a four-methylene spacer. The premicellar formation for the geminis with a two-methylene spacer is due to the short-chain linkage. The geminis show little or no break in their specific conductance-surfactant molar concentration plots and an increase in the pH at the cmc. This is attributed to protonation of the carboxylate group and strong Na+ release during micellization.

The Interaction of Alkylglycosides with Other Surfactants.

The interaction of n-decyl-beta-maltoside (C(10)M), n-decyl-beta-glucoside (C(10)G), n-dodecyl-beta-maltoside (C(12)M), 1:1 (molar) C(10)M/C(10)G mixtures, and 2:1 (molar) C(12)M/n-dodecyl-beta-glucoside (C(12)G) mixtures with anionic, cationic, nonionic, and zwitterionic surfactants has been investigated. The non-glycosidic surfactants used were the the anionic surfactant sodium dodecylethoxy sulfate (C(12)ESNa), the cationic surfactants decyl trimethylammonium bromide (C(10)TMAB), dodecyl trimethylammonium chloride (C(12)TMAC), and tetradecylammonium bromide (C(14)TMAB), the nonionic surfactant dodecyl hexaethoxyethanol (C(12)EO(7)), and the zwitterionic surfactant dodecyl-N-benzyl-N-methylglycine (C(12)BMG). The surface properties of the surfactants, critical micelle concentration (CMC), effectiveness of surface tension reduction (gamma(CMC)), efficiency of surface tension reduction (pC(20)), maximum surface excess concentration (Gamma(max)), minimum area per molecule at the air/solution interface (A(min)), and the CMC/C(20) ratio, were determined for both the individual surfactants and their mixtures. The glucosides and maltosides show no significant interaction with each other or with the nonionic surfactant C(12)EO(7). The maltosides interact weakly with the cationic, anionic, and zwitterionic surfactants. The glucosides interact somewhat more strongly with the same surfactants. Interaction is even stronger when glucoside/maltoside mixtures are interacted with the non-glycosidic surfactant. As a result, synergism is most prone to be found in systems containing the non-glycosidic surfactant and glucoside/maltoside mixture. Copyright 2001 Academic Press.