Abstract

Deuterium and oxygen-17 longitudinal relaxation times (T1 ) of heavy water in dodecylammonium chloride/D2O system nave been measured at a given temperature which allows to investigate all types of aggregates pertaining to this system (globular micelles, elongated micelles, lyo- tropic nematic and lamellar phases) by varying the amphi- phile concentration. Both relaxation times obey the relation: (1/T1) = (1/T1)f +[ (1/T1)b - (1/T1) f] Cs/Cw, where (T1)f and (T1)b are relaxation times of free bound water respectively. n is the mean number of water molecules per surfactant polar head. Cs and Cw are surfactant and water concenstrations. Both n and (T1)b are shown to be independent of the type of aggregate. From these relations, the ratio of oxygen-17 and deuterium relaxation times in the bound state is obtained. It is, within experimental error, identical to the one of free water. It is suggested that such a result does not necessarily indicate an isotropic motion for bound water but rather a particular orientation of the water molecules with respect to the normal to the aggregate surface.

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