A contrast variation small-angle scattering study of the microstructure of 2,5-dimethyl-7-hydroxy-2,5-diazaheptadecane–toluene–butanol oil-in-water metallomicroemulsions

Abstract

Metallosurfactants comprising copper(II) (Cu(NO₃)₂) and zinc(II) (Zn(NO₃)₂) nitrate complexes of 2,5-dimethyl-7-hydroxy-2,5-diazaheptadecane were found to form stable oil-in-water microemulsions—metallomicroemulsions—that could solubilise toluene in the presence of butanol. A detailed contrast-variation scattering analysis, employing both neutrons and X-rays, in conjunction with pulsed-gradient spin-echo NMR and simple phase diagram construction, demonstrated that the system formed is that of a conventional microemulsion—a core comprising toluene, separated from the aqueous phase by the surfactant and co-surfactant/co-solvent. This study further demonstrates the versatility of metallosurfactants and the similarity of their physical chemistry behaviour to that of conventional surfactants.