Yuichiro Takamatsu

Synthesis and aqueous solution properties of novel anionic heterogemini surfactants containing a phosphate headgroup.

The physicochemical properties of aqueous solutions of novel anionic heterogemini surfactants (POH-n-ODAm) have been studied on the basis of static/dynamic surface tension, fluorescence, dynamic light scattering (DLS) and cryogenic transmission electron microscope (cryo-TEM) data. The surfactants are synthesized from oleic acid: the hydrocarbon chain (n=6, 8 and 10) is covalently bound to the terminal carbonyl group and a phosphate headgroup is introduced to the cis double bond of an oleic acid derivative. The static surface tension and fluorescence measurements demonstrate that the critical aggregation concentration (cac) is decreased significantly with increasing hydrocarbon chain length, resulting from the increased hydrophobicity and the increased degree of dissymmetry of the surfactants. As is generally seen for gemini surfactants, the measured cac is much lower than that of the monomeric phosphate-type surfactant reported previously. At concentrations well above the cac, the heterogemini surfactants spontaneously form vesicular assemblies in bulk solution, which is confirmed with DLS and cryo-TEM measurements.

Characterization of the micelle structure of oleic acid-based gemini surfactants: effect of stereochemistry

In this study, we synthesize a novel oleic acid-based gemini surfactant with carboxylate headgroups, and study the effect of stereochemistry (anti- vs. syn-) on self-aggregation properties in water. We investigate these properties using phase diagrams, static surface tension, and one-dimensional and two-dimensional nuclear magnetic resonance (NMR) measurements. We find that a phase transition from a hexagonal liquid crystal (H1) phase to a lamellar liquid crystal (Lα) phase occurs at a lower surfactant concentration in the syn form, when compared with the anti form. In addition, the syn form gemini surfactant forms micelles with a close packing of the headgroups via hydrogen bonding. This was supported by static surface tensiometry; the area occupied by surfactant molecules at the air/aqueous solution interface is smaller for the syn form than for the anti form. We propose that, for the syn form gemini surfactant, the closer packing of the headgroups as well as the hydrogen bonding network around the micelle interface prevent water penetration into the hydrophobic part of the micelle.