Organometallic amphiphiles are new class of surfactants. Various novel chemical and physical properties of their aggregates, such as selective binding to metal ions, active control of interfacial tension, catalytic behavior and charge transfer, have been widely investigated in recent years. These interesting properties are reviewed in this paper.

Spontaneous vesicle formation was observed in aqueous mixtures of partially hydrolyzed polyacrylamide and single-tailed cationic surfactants. The influences of pH, addition of long-chain alcohols, variation of hydrocarbon chain length, and head group size of the cationic surfactants were investigated systematically. It was found that 30-50% hydrolyzed degree of polyacrylamide and cationic surfactants with 10 or 12 methylene groups are suitable for vesicle formation in the mixed aqueous systems at pH 9.2. Addition of long-chain alcohols was found to be helpful for vesicle formation in some cases. The vesicle stability was also investigated at various temperatures and amounts of ethanol addition.

Anamino acid amphiphile, N-(4-decyloxy-2-hydroxybenzylidene) glycine, wassynthesized. Surface tension measurement, dynamic light scattering, and transmission electron microscopy were used to investigate its surface activity and aggregation in solution. All behavior was sensitive to the pH value of the solution. It was found that these properties occur at pH=12, which is different from the usual situation for carboxylate amphiphiles. The abnormal behavior can be attributed to the formation of a dimeric structure at pH=12.0. Vesicles were found in this kind of system, which are stable even at the concentration of transition metal ions up to 1mM. This phenomenon was attributed to the formation of complexes.

The transition from vesicles to micelles by adding octane into the dodecyl-pyridinium chloride (DPCl)/sodium laurate (SL), and dodecyltrimethylammonium bromide (DTAB)/SL aqueous two-phase systems has been studied. The two-phase systems were transformed into single-phase isotropic solutions with the addition of a certain amount of octane. The results of dynamic light scattering (DLS) demonstrate the decrease of large aggregates (vesicles) and the increase of the small aggregates (spherical micelles) upon octane addition. Such transformation of the surfactant aggregates was also corroborated by the results of time-resolved fluorescence quenching (TRFQ) and viscometry. The change of the phase behavior was discussed on the basis of the interaggregate interactions influenced by the variation of organized assemblies.

The fluorescence properties of an aromatic anion amphiphile, N-(4-decyloxy-2-hydroxy-benzylidene) glycine (C10HG) have been investigated. The fluorescence spectra of C10HG in lipid vesicles showed stronger intensity than that in aqueous solution, which is due to the less polarity of microenvironment in the former case. A blue-shift maximum of C10HG fluorescence spectra caused by the carbonyl and phosphate groups in the membrane lipid was also observed. The fluorescence lifetimes and anisotropy data showed that the C10HG molecule is immobilized in the membrane, and its motion is blocked by phospholipid. Fluorescence quenching suggested that the molecule is embedded but does not penetrate deeply in the bilayer.

Self-organized assemblies in easily precipitated mixed surfactant systems [CmH2m+1N (CH3)3BrC12H25SO4Na m=8, 12, CnH2n+1NH2

The phase behavior as well as the microstructures of the dodecyltrimethylammonium bromide (DTAB)/sodium laurate (SL) aqueous two-phase system has been studied. ByusingFF-TEM, dynamic light scattering (DLS), a viscosity meter, and polarization microscopy, the effects of surfactant concentration and mixing ratio, temperature, salt concentration, and additives (octanol and toluene) on the phase separation have been systematically investigated. The phase separation is found to be strongly dependent on the variation of the surfactant aggregates. The different kinds of aqueous surfactant two-phase system can transit between each other upon the variation of the mixing ratio, the change of the salt concentration, and the addition of toluene and octanol.

The effect of ethanol on the surface properties of bolaamphiphiles and their mixed systems with oppositely charged conventional surfactants is studied and compared with the corresponding conventional surfactant systems. It is found that both the bolaamphiphile and the conventional surfactant have the similar variation tendency of γcmc and Γ∞ in the single surfactant system. However, in the cationic and anionic mixed surfactants system the γcmc decreases with the ethanol addition in the bolaamphiphile systems. This tendency is reverse to that in conventional surfactant system. Surface activity of the asymmetric bolaamphiphiles SHMC decreases greatly when ethanol is added into the system due to the existence of the hydroxyl group in the SHMC molecule. Adding opposite charged surfactant may greatly increase surface activity in the SHMC/C12NEt3Br/ethanol systems.