SMALL-ANGLE X-RAY AND NEUTRON-SCATTERING STUDY OF THE MICELLIZATION OF (N-ALKYLAMINO)-1-DEOXYLACTITOLS IN WATER

In this study, we investigated the micellization in water of four surf actants from the series of (N-alkylamino)lactitols by small angle neut ron and X-ray scattering. These four surfactants differed from one ano ther by the number of carbon atoms in their alkyl chain: 8, 9, 10, or 12. The comparison of the I(q) curves of the intensity scattered from micellar solutions as a function of concentration indicated that the m icelle size was weakly dispersed at small concentrations. The C-8 deri vative presented a singular behavior which may be attributed to the fo rmation of premicellar aggregates. The characteristic dimensions of th e micelles are derived from the I(q) curve fittings. For the calculati on of scattered intensity from the micelles, three models of micelles were considered: spherical, oblate ellipsoidal, and prolate ellipsoida l. These models take into account particularities of the studied surfa ctants, in particular, the size of the sugar head group, which leads u s to-consider a nonuniform penetration of the solvent into the polar o uter layer. On the other hand, the width of the polar head layer is as sumed to be the same along the short and long axes of the ellipsoidal models. This means that the ellipticity of the external surface of the micelle is different from the ellipticity of the core which contains the alkyl chains. The best fit of the scattered intensity curves for t he four surfactants was obtained with an oblate ellipsoidal model. The model produced a constant value of 0.55 for the ellipticity of the co res of the models. We pointed out how this particular packing is adapt ed to the characteristics of the (N-alkylamino)lactitol polar head, an d we compared it to the other models of micelles: spherical and prolat e ellipsoidal. We also studied the evolution of several parameters (ag gregation number, radius of the core,...) as a function of the number of;carbon atoms in the alkyl chain.