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The phase behavior of dimeric (gemini-type) anionic surfactant (sodium 1,2-bis(N-dodecanoyl β-alanate)-N-ethane, GS) in water is similar to that of the corresponding monomeric surfactant (sodium N-dodecanoyl-N-methyl β-alanate, MS). Aqueous micellar phase (Wm), hexagonal (H1), bicontinuous cubic (V1), and lamellar (LR) phases are successively formed with increasing the surfactant concentration. SAXS data for cross-sectional area per surfactant molecule in H1 and LR phases reveal that GS molecules are more tightly packed in the aggregates than MS molecules, and this is due to the bridging of two hydrocarbon chains by the short spacer chain (-C2H4-). In the ternary water/surfactant/dodecane or m-xylene systems, the phase behavior of both surfactants is also practically similar. Upon addition of oil, the H1 phase is changed to the discontinuous micellar cubic (I1) phase in both surfactant systems. The phase transition mechanism is discussed according to the geometrical packing model. In the 3 wt % NaCl aqueous/MS or GS/cosurfactant-(hexanol or butanol)/dodecane systems, a single-phase microemulsion is formed at an equal brine/dodecane ratio over a wide range of surfactant concentration in the MS systems whereas the LR phase is mainly formed and the microemulsion is produced only in a very narrow region in the GS/hexanol system. By replacement of hexanol with butanol, wide microemulsion regions appear, even in the GS system. Hence, GS molecules in the surfactant layer are considered to be packed more tightly than MS, even in the presence of oil.

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A polymerizable cationic gemini surfactant, [CH(2)=C(CH(3))COO(CH(2))(11)N(+)CH(3))(2)CH(2)](2).2Br(-), 1 has been synthesized and its basic interfacial properties were investigated (in water and in the presence of 0.05 M NaBr). For comparison, the properties of monomeric surfactant corresponding to 1, CH(2)=C(CH(3))COO(CH(2))(11)N(+)(CH(3))(3).Br(-), 2, were also investigated. Parameters studied include cmc (critical micelle concentration), C(20) (required to reduce the surface tension of the solvent by 20 mN/m), gamma(cmc) (the surface tension at the cmc), Gamma(cmc) (the maximum surface excess concentration at the air/water interface), A(min) (the minimum area per surfactant molecule at the air/water interface), and cmc/C(20) ratio (a measure of the tendency to form micelles relative to adsorb at the air/water interface). For the polymerizable gemini surfactant, 1, the methacryloxy groups at the terminal of each hydrophobic group in a molecule have no contact with the air/water interface in the monolayer, whereas for the corresponding monomeric surfactant, 2, the methacryloxy group contacts at the interface forming a looped configuration like a bolaamphiphile. Polymerized micelles of the gemini surfactant are fairly small monodisperse and spherical particles with a mean diameter of 3 nm.

A systematic study of the equilibrium surface properties (in water and in the presence of 10 −2 M NaCl) of a novel series of anionic gemini surfactants, (CH 2 ) 2 [N(COC n H 2n+1 )-CH(COOH)CH 2 COOH]·2NaOH (GA), where (n + 1) = 8, 10, 12, 14, and 16, was investigated. The responses of humans to closed patch tests with (CH 2 ) 2 [N(COC 11 H 23 )CH(COOH)-CH 2 COOH] 2 ·2NaOH (GA-12) were also investigated. Premicellar self-aggregation (both in water and 10 −2 M NaCl) occurred when the N-acyl group contained more than 14 carbon atoms, since the critical micelle concentration (CMC) values decreased and the pC 20 values increased as (n + 1) increased for (n + 1) ≤14; the CMC values increased and the pC 20 values decreased as (n + 1) increased for (n + 1) > 14, both in water and in 10 −2 M NaCl. The absence of a break in the specific conductance-surfactant molar concentration plots for the GA homologs indicates protonation of the carboxylate group and strong Na + release during micellization. This is a structural characteristic of the anionic geminis having N-dialkylamide and carboxylate groups in a molecule. The skin irritation potential of GA-12 is lower than that of the corresponding "monomer," C 11 H 23 CON(CH 3 )CH(COOH)CH 2 (COOH)·NaOH, and the analog, C 11 H 23 CON(CH 3 )CH 2 COONa·H 2 O.