Carbon-13 nuclear magnetic resonance study of reversed micellar structure of calcium dodecylsalicylates in chloroform.

Abstract

The dynamic structure of calcium dodecylsalicylates, which are employed as principal detergent-dispersant additives in engine oils, in micellar states in chloroform was studied by measurements of 13C-NMR spectra and spin-lattice relaxation times with the following results. The resonances from the aromatic ring and the five carbons of the dodecyl group nearest the aromatic ring, which constitute the inner part of the reversed micelle of salicylates, were broadened as compared to those of dodecylsalicylic acid. This showed that the local mobility of the inner part of the reversed micelles was considerably restricted as in the solid state, whereas the local mobility of the remaining carbons of the dodecyl group were not affected. The relaxation study showed that the segmental mobility of the alkyl chains gradually became greater as the distance separating the carbons from the aromatic ring increased. The effects of the addition of water on the structure of the micelles were also studied. The addition of water decreased slightly the broadening of the resonances from the inner part of the reversed micelles. This is probably due to hydration or formation of aqueous solutions in the micellar core, resulting in an increase in the local mobility.