Studies on molecular motion in lyotropic mesophases of hexaethylene glycol dodecyl ether-D2O system by 13C nuclear magnetic resonance.

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The 13C spin-lattice relaxation time(T1) and the resonance line width corresponding to T2* were measured for each of the carbons in hexaethylene glycol dodecyl ether–water(D2O) system, which exists as two distinct lyotropic mesophases(neat and middle phase). The line width is very narrow in the isotropic state, such as in organic solvents and in a lower concentration aqueous solution, whereas in a mesophase and in a higher concentration aqueous solution, the line width of the alkyl chain was broadened. Here the line widths for glycol carbons were about an order of magnitude smaller than for an alkyl chain, demonstrating the difference of molecular motion. The chemical shifts of the alkyl chain in the middle phase were different from those in the isotropic state; this difference was clearly shown in the spectrum of the middle/isotropic coexistent phase. 13C-T1 was not sensitive enough to differentiate between the isotropic and the lyotropic phase at room temperature. It was found that T1 did not equal T2* for any of the methylene carbons, the difference being most marked for the terminal methyl carbon in the alkyl chain. The orientational order in the phases had an influence on the T2* values.