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 mu M, 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 (Delta H 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 Delta H degrees(M) arising from difficulties associated with packing of the bulky cis-9-octadecene tails.