Physicochemical characterization of bromide mono- and dimeric surfactants with phenyl and cyclohexyl rings in the head group.

In this work the two monomeric surfactants N-benzyl-N,N-dimethyl-N-(1-dodecyl)ammonium bromide (PH12,Br(-)) and N-cyclohexylmethyl-N,N-dimethyl-N-(1-dodecyl)ammonium bromide (CH12,Br(-)) and their two dimeric counterparts N,N'-(1,3-phenylenebis(methylene))bis(N,N-dimethyl-N-(1-dodecyl)ammonium dibromide (12PH12,2Br(-)) and N,N'-(cyclohexane-1,3-diylbis(methylene))bis(N,N-dimethyl-N-(1-dodecyl)ammonium dibromide (12CH12,2Br(-)) were prepared and characterized. The critical micelle concentration, the micellar ionization degree and the average aggregation number were obtained by using different techniques. The results are discussed with the help of (1)H NMR two-dimensional, 2D, rotating frame nuclear Overhauser effect spectroscopy measurements, ROESY, which seem to indicate that the phenyl and cyclohexyl rings present in the head groups of the surfactants are bent towards the micellar interior in order to avoid contact with water. The surface activity of the surfactants was studied by means of surface tension measurements. The occurrence of morphological transitions upon increasing surfactant concentration and the variations in the polarity and in the microviscosity of the interfacial region accompanying this sphere-to-rod transition were investigated. It was shown that the formation of spherocylindrical micelles also causes changes in the (1)H NMR spectra of the surfactant solutions.