Synthesis and solution properties of gemini surfactants containing oleyl chains

Gemini surfactants 18:1-s-18:1, where s = 2, 3, and 6 methylene groups and 18:1 refers to oleyl carbon chains, have been synthesized, characterized and a number of micelle solution properties measured by using electrical conductance, fluorescence probe emission, light scattering (DLS), surface tension and isothermal titration calorimetry (ITC) methods at 25 degrees C. The cmc values of 18:1-2-18:1, 18:1-3-18:1, and 18:1-6-18:1 were found to be 26.9, 23.4, and 18.0 microM, respectively, using the electrical conductance method. Surface tension results suggest that in 0.01 N NaCl solutions, the s = 2 and 3 members of the series form multilayer rather than monolayer structures, while the s = 6 homologue adopts a close-packed arrangement. This is consistent with DLS and EM measurements which show vesicle formation for the s = 2 and 3 compounds, and micelle formation for the s = 6 compound. The enthalpies of micellization (deltaH degrees (M)) are more exothermic for the 18:1-s-18:1 series of surfactants, than for the 12-s-12 series. The differences are rationalized in terms of steric and configurational contributions to deltaH degrees (M) arising from difficulties associated with packing of the bulky cis-9-octadecene tails.