Surface properties of cationic–nonionic mixed surfactant systems

Effect of Electrolytes on Solution and Interfacial Behaviors of Double Chain Cationic-Nonionic Surfactant Mixtures for Hydrophobic Surface Wetting and Oil/Water Emulsion Stability Applications

The solution behaviors of the binary mixture of double chain cationic surfactant didodecyldimethylammonium bromide (DDAB) with nonionic surfactants of varied head groups, EO-9 and EO-40, in the presence and absence of electrolytes were studied and found nonideal behavior. The different physicochemical properties such as Gibb's surface excess (Γ), minimum area per molecule (A_min), and interaction parameters at bulk (β^M) and interface (β^σ) were calculated. In the presence of nonionic surfactants, lowering of CMC, CVC, and surface tension at these two concentrations of DDAB were observed. The β^M and β^σ values indicate strong interaction between DDAB and EO-40 mixed system. Further, addition of electrolytes to the mixed systems show increased interaction and change of physicochemical properties because of the combination of electrical and salting out effects.

Syntheses, amphitropic liquid crystallinity, and surface activity of new inositol-based amphiphiles

Carbohydrates are interesting starting materials for scientific and industrial syntheses as they allow a versatile chemistry. Moreover, they are of natural origin and environmentally benign. During the past few years, inositol, a rather "exotic" carbohydrate, and its derivatives have gained increasing attention. Here, we describe the syntheses of new regiochemically defined inositol monoethers and monoesters as well as regioisomeric inositol ester mixtures and investigate their amphitropic liquid crystallinity. Furthermore, first results on their surface activity in aqueous solutions are given and compared with classical sugar surfactants.

Binary mixtures of (β-C12G2) with cationic and non-ionic surfactants: micelle and surface compositions

Surfactants used for practical applications are usually surfactant mixtures because they often exhibit a performance that is superior to the individual surfactants. In the present study binary mixtures of the sugar based surfactant n-dodecyl-β-D-maltoside (β-C12G2) with the cationic surfactant dodecyl trimethylammonium bromide (C12TAB) and the non-ionic hexaethylene-glycol dodecyl ether (C12E6), respectively, were investigated at different bulk mole fractions. Surface tension measurements were used to determine the critical micelle concentration and the surfactant composition at the surface. In addition, the regular solution theory was used to calculate interaction parameters as well as the mole fractions of the individual surfactants in the mixed air-water monolayer and in the mixed micelles, respectively. It was found that n-dodecyl-β-D-maltoside interacts weakly with the cationic surfactant (C12TAB) and that it dominates in both the mixed monolayer and the mixed micelles. On the other hand, β-C12G2 and C12E6 mix ideally in solution. For both surfactant mixtures the surfactant composition at the surface determined by surface tension measurements and by the regular solution theory, respectively, were compared and discussed in detail.

Synergistic interactions in the mixed micelles of cationic gemini with zwitterionic surfactants: The pH and spacer effect

Mixed micelle formation of binary cationic gemini (12-s-12, s=4, 6) and zwitterionic (N-dodecyl-N,N-dimethylglycine, EBB) surfactants has been investigated by measuring the surface tension of aqueous solution as a function of total concentration at various pH values from acidic to basic, under conditions of 298.15 K and atmospheric pressure. The results were analyzed by applying regular solution theory (RST), and Motomura's theory, which allows for the calculation of the excess Gibbs energy of micellization purely on the basis of thermodynamic equations. The synergistic interactions of all the investigated cationic gemini + zwitterionic surfactants mixtures were found to be dependent upon the pH of the solution and the length of hydrophobic spacer of gemini surfactant. The evaluated excess Gibbs free energy is negative for all the systems.

A disjoining pressure study of foam films stabilized by mixtures of nonionic and ionic surfactants

Studying the disjoining pressure Pi as a function of the film thickness h (Pi-h curves) of foam films stabilized by ionic and nonionic surfactants, one finds that the surface charge density q0 of films stabilized by ionic surfactants increases with increasing surfactant concentration, while the opposite holds true for nonionic surfactants. Thus, it should be possible to tune the surface charge density with mixtures of nonionic and ionic surfactants. To address this question, we studied foam films stabilized by aqueous solutions of surfactant mixtures. The mixtures consisted of the nonionic beta-dodecylmaltoside (beta-C12G2) and the cationic dodecyl trimethylammonium bromide (C12TAB) with mixing ratios of beta-C12G2/C12TAB = 1:0, 50:1, 1:1, 1:50, 0:1. The addition of small amounts of C12TAB to beta-C12G2 first neutralizes the negative surface charge of the beta-C12G2 films and finally leads to a charge reversal from negatively to positively charged surfaces. On the other hand, by adding small amounts of beta-C12G2 to C12TAB, one observes the formation of stable CBFs which was also observed for the pure C12TAB. However, in contrast to the pure C12TAB, the resulting Pi-h curves for the mixtures cannot be described with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory; the slope of the curves is too steep, and it barely changes with changing electrolyte concentration. A possible explanation for this observation will be given and discussed.

Surface properties of mixtures of surface-active sugar derivatives with ionic surfactants: Theoretical and experimental investigations

Surface properties of systems that are mixtures of ionic surfactants and sugar derivatives-anionic surfactant sodium dodecyl sulfate and n-dodecyl-beta-D-maltoside (SDS/DM) and cationic surfactant dodecyltrimethylammonium bromide and n-dodecyl-beta-D-glucoside (DTABr/DG)-were investigated. The experimental results obtained from measurements of surface tension of mixtures with various ratio of ionic to nonionic components were analyzed by two independent theories. First is Motomura theory, derived from the Gibbs-Duhem equation, allowing for indirect evaluation of the composition of mixed monolayers and the Gibbs energies of adsorption, corresponding to mutual interaction between surfactants in mixed adsorbed film. As second theory we used our newly developed theoretical model of adsorption of ionic-nonionic surfactant mixtures. Using this approach, we were able to describe the experimental surface tension isotherms for mixtures of surface-active sugar derivatives and ionic surfactants. We obtained a good agreement with experimental data using the same set of model parameters for a whole range of studied compositions of a given surfactant mixture. The values of surface excess calculated from both theories agreed with each other with a reasonable accuracy. However, the newly developed model of adsorption of ionic-nonionic surfactant mixtures has the advantage of straightforward determination of surface layer composition. By the solution of equations of adsorption, one can obtain directly the values of surface excess of all components (surfactant ions, counterions, and nonionic surfactants molecules), which are present in the investigated system.