SURFACE AND AQUEOUS-SOLUTION PROPERTIES OF A HIGHLY CHARGED CAGE SURFACTANT

A highly charged cationic cage surfactant which consisted of a macrobicyclic hexaamine cage surrounding a cobalt(III) ion and a branched hydrocarbon tail was investigated. Its behaviour in aqueous solution was characterized through pH and conductivity measurements. The effective headgroup area of the surfactant at a packed interface was calculated from the surface tension curve using the Gibbs adsorption isotherm and the large area obtained indicated that this surfactant should form micelles in solution. However, the c.m.c. values obtained from conductivity and surface tension measurements were about 50% different and this difference was attributed to the unusual nature of the surfactant. The solution aggregation behaviour of this complex surfactant was modelled using the law of mass action and assuming a constant degree of counterion binding to the micelle. Several different definitions of the c.m.c. were studied and it was found that the value corresponding to the maximum free monomer concentration was most appropriate.