-
[show abstract]
[hide abstract]
ABSTRACT: 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.
Journal of Colloid and Interface Science 10/2005; 289(2):560-5. · 3.07 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 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.
Langmuir 05/2005; 21(9):3749-56. · 4.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 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.
Langmuir 04/2005; 21(6):2342-8. · 4.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Spreading of mixed aqueous hydrocarbon-chain surfactant solutions on the solid polyethylene (PE) surface has been studied. Synergistic effect on the spreading of the mixed surfactant solution on the PE film has been observed, and the obtained spreading is comparable to superspreading normally obtainable from trisiloxane-based surfactants. Some other interfacial phenomena related to surfactant spreading, such as surfactant−surfactant molecular interactions in the mixtures adsorbed at various interfaces, dynamic contact angle change of the mixed surfactant solutions during the process of spreading on the hydrophobic PE substrate, and surfactant adsorption at the solid/liquid and air/liquid interfaces have been investigated. It is suggested that stronger surfactant−surfactant attractive interactions and greater adsorption at the PE powder/aqueous solution interface than at the air/aqueous solution interface account for the observed spreading enhancement in the mixed hydrocarbon-chain surfactant systems, which is also accompanied by lower dynamic contact angles, implying greater dynamic spreading coefficients.
08/2003;
-
[show abstract]
[hide abstract]
ABSTRACT: 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.
Journal of Colloid and Interface Science 07/2003; 262(2):516-24. · 3.07 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Interfacial adsorptions of aqueous solutions of trisiloxane surfactant (SILWET L77), N-alkyl pyrrolidinones [N-butyl-(C4P), N-cyclohexyl-(CHP), N-hexyl-(C6P), N-2-ethyhexyl-(C2,6P), N-octyl-(C8P), and N-decyl-(C10P)], and their mixtures have been measured. The adsorptions at the air/aqueous solution interface were obtained from the plots of surface tension versus log(C) by use of the Gibbs equation. The adsorptions onto the powdered polyethylene surface were determined by the use of UV spectroscopy for pyrrolidinones and two-phase titration for SILWET L77, respectively. The adsorptions at the solid/air interface were evaluated by the use of an equation derived from the Gibbs and Young equations. It was found that the addition of the N-alkyl pyrrolidinones to the solution produces little or no enhancement of the total surfactant adsorption at the air/aqueous solution interface. At the solid/aqueous solution interface, the enhancement effectiveness of the pyrrolidinones decreases in the order C2,6P > C8P > C6P > CHP > C4P, and their enhancement efficiency decreases in the order C2,6P > C8P > CHP > C6P > C4P. However, C10P, the most effective surface-active agent among the pyrrolidinones, produces no enhancement in the adsorption of L77 at both the air/aqueous solution and the solid/aqueous solution interfaces. The adsorptions of the individual surfactants and their mixtures at the solid/air interface are shown to be smaller by 1 order of magnitude than those at the air/aqueous solution and solid/aqueous solution interfaces. Consequently, the most significant fact of the addition of N-alkyl pyrrolidinones to an aqueous solution of L77 is the enhancement of the adsorption of L77 at the solid/aqueous solution interface.
10/2001;
-
[show abstract]
[hide abstract]
ABSTRACT: 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-α,ω-bis(sodium N-acyl-β-alaninates), is described. Parameters studied include cmc (critical micelle concentration), C20 (required to reduce the surface tension of the solvent by 20 mN/m), γcmc (the surface tension at the cmc), Γmax (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.
Journal of Colloid and Interface Science.
