Deuterium NMR and Raman spectroscopic studies on conformational behavior of lipophilic chains in the C12E3/decane/water system

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 decane molecules 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.