Effect of the spacer length on the association and adsorption behavior of dissymmetric gemini surfactants

A series of dissymmetric gemini surfactants with the general formula [C 12H 25(CH 3) 2N(CH 2) s N(CH 3) 2C 14H 29]Br 2 designed as 12– s–14, where s = 2 , 6, and 10, were synthesized and their physicochemical properties investigated. The effect of spacer length on Krafft temperature, adsorption at the air/solution interface, and association in aqueous solution was studied by tensiometry, conductometry, and cryo-transmission electron microscopy. The Krafft temperature was found to increase linearly with spacer length. In the submicellar concentration range the dissymmetric 12– s–14 surfactants display ion pairing and premicellar association. Adsorption at air/solution interfaces and micellization in aqueous solution are similar to the behavior of their symmetric counterparts and depend strongly on spacer length.