Equilibrium structure and dynamics of (2R, 3R)-(+)-bis(decyloxy)succinic acid at the air-water interface

Insights into the Assembly of the Pseudogemini Surfactant at the Oil/Water Interface: A Molecular Simulation Study

The interfacial assembly process and configuration of the pseudogemini surfactant fabricated by sodium dodecyl benzene sulfonate (SDBS) and 4,4'-oxydianilinium chloride (ODC) were studied using quantum mechanical calculations and molecular dynamics (MD) simulations. The MD simulation results revealed that SDBS and ODC showed the vertical and horizontal arrangements at the oil/water interface, respectively, and the interfacial assembled configuration presented an unexpected "H" shape rather than the traditional "U" shape. The radial distribution functions between the head groups and water molecules were employed to explore the effects of the surrounding water molecules on the SDBS/ODC interaction. Furthermore, the results of the nonbonded interaction calculations and the reduced density gradient method directly confirmed that the cation-π interaction should be responsible for the SDBS/ODC assembly mechanism and the final configuration at the oil/water interface.

Novel Synthesis of Anionic Gemini Surfactants from 1, 4-Diol as a Key Block Material

In this study, a series of all-hydrocarbon anionic gemini surfactants containing COOH (adipic acid-type and suberic acid-type), SO3Na, OSO3Na, and OP=O(OH)2 functional groups was developed from 1,4-diol and 1,4-diketone as a key block material. The effect of the surfactant head groups on the surface properties was investigated by surface tension and surface pressure-area (π-A) measurements. We found that the critical micelle concentrations (CMC) of the studied geminis were smaller by one order of magnitude than those of the corresponding 1+l-type surfactants. From π-A measurements, the limiting areas of COOH-type geminis were less than twofold of the area of the corresponding 1+1-type, which indicates that the gemini structure enabled tighter packing than is possible in surfactants of the 1+l-type. In contrast, the limiting area of the OP=O(OH)2-type gemini was larger than those of the COOH-type geminis. Furthermore, the suberic acid-type gemini showed a smaller limiting area than that of adipic acid-type gemini. Therefore, we can conclude that the flexibility of the gemini at the connecting position has a significant effect on formation of the monolayer at the air/water interface.

Syntheses of Tartaric Acid-Based Hybrid Gemini Surfactants Containing Fluorocarbon and Hydrocarbon Chains

Tartaric acid-based symmetric and hybrid gemini surfactants having dodecyloxy (C12H25O-) and tridecafluoro nonyloxy groups (C6F13(CH2)3O-) as hydrophobic groups were synthesized, and their surface properties were studied by surface tension (γ)-concentration and surface pressure-area (π-A) measurements. All geminis showed superior surfactant properties to 1+1 type surfactant. Especially, hybrid gemini showed high efficiency of lowering the surface tension comparable to that of bis(C6F13(CH2)3O) gemini. Further, hybrid gemini showed an unusual existence of two breakpoints at γ = ∼25 and 18 mN m−1. In the π-A measurements, regardless of symmetric or hybrid structures, geminis having fluoroalkyl group formed only liquid condensed monolayers while the bis(dodecyloxy) gemini formed solid monolayer. Molecular occupied areas of hybrid gemini were subequal to the mean of those of symmetric geminis.

Chiral cones and vesicles from Gemini-type fatty acid-heteroditopic amine mixtures

A twin-chiral and twin-tailed Gemini-type fatty acid with a rigid spacer, 2,3-bis(decyloxy) succinic acid, formed chiral self-assembled structures in aqueous solution with heteroditopic amines, such as 6-aminohexanoic acid and 4-aminobutyric acid. The morphology of such structures was governed by the stoichiometry between the fatty acid and the amine. Mixtures with 1 : 2 molar ratio formed exclusively spherical vesicles, while the 1 : 1 mixtures resulted in entropically driven chiral cones in addition to spherical vesicles. Surface tension measurements, light scattering, and TEM studies proved the existence of vesicles in aqueous solution. Cones were formed through disclinations introduced in the hexatic chiral membrane with specific angles, in accordance with θ = arcsin (1 - (n/6)), [0 < θ < π/2, 1 < n < 5]. Mixtures prepared with 4-aminobutyric acid formed only spherical vesicles and no conical self-assemblies, emphasizing the geometry of the Gemini-heteroditopic amine pair, which directs the morphology of the final self-assembled structures.