Kazuyuki Tsubone

The interaction of an anionic gemini surfactant with conventional anionic surfactants

The interaction in two mixtures of an anionic gemini surfactant having N ,N -dialkylamide and carboxylate groups in a molecule, (CH2)2[N(COC11H23)CH(CO2H)CH2(CO2H)]2. 2NaOH (GA), and conventional anionic surfactants have been investigated in 0.1 M NaCl at pH 5.0. The two mixtures are GA/sodium dodecylsulfate (SDS) and GA/sodium N -dodecanoylglutamate (AGS) at a molar fraction of GA, alphaGA = 0.25 . Mixtures of both GA/SDS and GA/AGS exhibit synergism in surface tension reduction effectiveness. The GA/SDS mixture also exhibits synergism in surface tension reduction efficiency and mixed micelle formation, whereas the GA/AGS mixture does not. The interaction in mixed adsorption film formation is stronger than that in mixed micelle formation for the two mixtures. The interaction in the formation of the mixed adsorption film and the mixed micelle for the GA/SDS mixture is stronger in both formations than that for the GA/AGS mixture. The stronger interaction for the GA/SDS mixture may be caused by the combination of the smaller minimum area per molecule at the air/water interface (Amin) of the head groups in the GA molecule and the larger Amin in the SDS molecule.

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.

Polymerized assemblies of cationic gemini surfactants in aqueous solution.

A variety of polymerized assemblies of cationic gemini surfactants has been demonstrated as a function of the electrolyte concentration in aqueous solution. The gemini surfactant consists of two cationic monomeric surfactants linked with an ethylene spacer at the level of the quaternary ammonium groups. Polymerizable methacryloxy groups are covalently attached to the terminal of the hydrocarbon chains. In the lower electrolyte concentration region, radical polymerization results in the formation of spherical aggregates [Langmuir 22 (2006) 8293]. However, in the higher electrolyte concentration region, elongated tubular hollow assemblies are observed with transmission electron microscopy, as a result of polymerization of vesicular hollow assemblies spontaneously formed in the aqueous solution. These experimental results suggest that it is possible to prepare different shapes of polymerized assemblies by changing the electrolyte concentration.