A combined C-D stretching Raman and deuterium NMR spectroscopic method was applied to a study of the molecular and phase structure of the C 12 E 5 -water system, where C 12 E 5 denotes a nonionic surfactant CH 3 -(CH 2 ) 11 (OCH 2 CH 2 ) 5 OH. Spectroscopic measurements were performed on aqueous solutions of six selectively alkyl-monodeuterated species, an oxyethylene-partially deuterated species, an alkyl-block-deuterated species, and an oxyethylene-block-deuterated species. The ranges of the compositions and temperatures studied were 40-75 wt % C 12 E 5 and 0-80 °C, where a number of anisotropic and isotropic phases are observed. The Raman results showed that the trans fractions of the C-C bonds of the dodecyl chain decrease continuously with increasing temperature across different phases. The NMR results showed, on the other hand, that, with increasing temperature, the order parameters exhibit distinct discontinuities at the phase transition from the normal hexagonal phase to the lamellar phase. The results from the two spectroscopic methods reflect the difference in their time scale. The behavior of the order parameters was explained by taking account of two factors, the chain order and the conformational order. The observed discontinuities of the order parameters at the phase transition can be ascribed to the change of the chain order, which is caused by wobbling motions of the whole surfactant molecule. The temperature-dependent shift of the position on the alkyl chain, at which the order parameters show their maximum, is explained by the different rates of reduction, with increasing temperature, of van der Waals forces between the alkyl chains and hydrogen-bonding forces between the oligo(oxyethylene) chain and water. The stability of the lamellar phase is maintained by the presence of interlamellar water.

Deuterium NMR spectroscopy was applied to a study of conformational dynamics of alkyl chains in the lamellar phase of a C12E3 (nonionic surfactant)–water system. The order parameter derived has shown that addition of the surfactant in the lamellar phase causes conformational disordering of alkyl chains, leading to a transition to an isotropic solution phase, while addition of water, which eventually leads to phase separation, causes no substantial disordering of alkyl chains.

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The order parameters of lipophilic chains in the liquid crystalline phases of the C12E3/decane/water ternary system have been studied by deuterium NMR spectroscopy. The order parameters derived indicate that the decane molecules added to the C12E3/water system penetrate into the lipophilic alkyl layer of the surfactant and make the structure of the lipophilic layer disordered. The lipophilic layers in the reversed hexagonal phase are more disordered than those in the lamellar phase.

The order parameter and the conformations of the lipophilic chains in the C12E3 / decane / water ternary system have been studied by deuterium NMR and C-D stretching Raman spectroscopy. The order parameter and the trans fraction of the C-C bond of decane molecules decrease steadily or remain nearly constant with increasing decane concentration without noticeable changes at the phase transitions. On addition of decanemolecules to the C12E3 /water system, the effective volume of the lipophilic part of a single surfactant molecule increases as a result of the penetration of the added decane molecules into the lipophilic layer, leading to a high mobility of the alkyl chain. To minimize the resulting increase in the effective cross-sectional area of a surfactant molecule, the molecular chains of the surfactant reorient remarkably in the concentration region near the phase transitions, and the shape of the self-organizing structure changes to the one with a larger packing parameter.