Synthesis, surface properties and oil solubilisation capacity of cationic gemini surfactants

The critical micelle concentration (CMC) and the surface tension at the CMC have been determined for the gemini surfactants alkanediyl-alpha,omega-bis(dimethylalkylammonium bromide) by means of dynamic surface tension measurements. For the same number of carbon atoms in the hydrophobic chain per hydrophilic head group, geminis have CMC values well below those of conventional single-chain cationic or anionic surfactants. Surface tension values at the CMC do not differ much from those observed for conventional surfactants. The propensity of gemini micelles for oil solubilisation is significantly better than that of conventional surfactants; this is true on a molar basis as well as on a weight basis. Geminis also show enhanced selectivity for aromatic compounds over paraffinic compounds. Some geminis show unusual viscoelastic behaviour at concentrations where this is not observed for conventional surfactants.