Deuterium longitudinal nuclear magnetic resonance relaxation of heavy water in surfactant/deuterium oxide systems

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Deuterium longitudinal nuclear magnetic relaxation times of heavy water in binary mixtures of D/sub 2/O and alkylammonium chlorides (CH/sub 3/(CH/sub 2/)/sub n-1/NH/sub 3//sup +/Cl/sup -/ with n = 8, 10, 12, 14) have been measured for the largest available surfactant concentration range. This allows one to study, depending on the surfactant, monomeric systems, spherical or cylindrical micelles, and lyotropic nematic, hexagonal, or lamellar phases. Experiments involving heavy water at several isotopic ratios permit one to rule out any special effect arising from proton and/or deuterium exchange between water and the surfactant polar head. The deuterium longitudinal relaxation rate is shown to be independent of the Larmor frequency in the range 5-13.8 MHz and evolve according to 1/T/sub 1/ = nr/(1 - r)(M/sub w//M/sub s/)((1/T/sup -1/)/sub b/ - (1/T/sub 1/)/sub f/) + (1/T/sub 1/)/sub f/ where n, the number of water molecules per surfactant polar head, and (1/T/sub 1/)/sub b/, the deuterium relaxation rate in the bound state, are independent of the surfactant aggregation state (r is the weight proportion of surfactant, (T/sub 1/)/sub f/ is the deuterium longitudinal relaxation time of free water, and M/sub w/ and M/sub s/ are the water and surfactant molar weights, respectively). These observations suggestmore » that the dynamics of bound water is essentially independent of the surfactant aggregate type and would therefore be dominated by exchange between bound and free states. 16 references, 2 figures.« less