Search

We investigated here the micellization in water of three surfactants: (N-dodecylamino)lactitol, (N-dodecyl)lactobionamide, and (N-acetyl N-dodecyl)lactosylamine, having n-alkyl chain lengths of 12 carbon atoms and different lactose-based polar heads. The micellization is studied by small-angle neutron and X-ray scattering. The characteristic dimensions of the micelles are derived from the I(q) curve fittings. We demonstrated the existence of spherical or oblate ellipsoidal micellar structures. The differences were attributed to differences in steric hindrance of the polar head enabling or preventing formation of spherical micelles. We pointed out the particular role of steric hindrance at the junction between the hydrophobic chain and the polar head. The formation of oblate ellipsoidal micelles attests to a relatively low steric hindrance at this junction ((N-dodecylamino)lactitol and (N-dodecyl)lactobionamide) whereas the formation of spherical micelle displays an important steric hindrance as observed for (N-acetyl N-dodecyl)lactosylamine which includes a bulky linkage. The surface areas per polar head in the micelles are confronted to the minimum areas per molecules deduced from surface pressure measurements. The results are in good agreement excepted in the case of (N-dodecyl)lactobionamide. The experimental results obtained with micellar solutions of N-dodecyllactobionamide from both neutron scattering and surface pressure measurements exhibit a particular comportment of this surfactant compared with two other surfactants studied in regard to the intermicellar interactions and the minimum area per molecule at the air/aqueous solution interface. We suggest that this particular behavior could be the consequence of a very important solvation of the (N-dodecyl)lactobionamide polar heads due to the presence of an amide group in this molecule. This important solvation could modify the interactions between the micelles and the apparent size ofisolated molecules at the air/aqueous solution interface. Over parallel explanations may be suggested as formation of dimers or trimers below the critical micelle concentration (cmc) and above the cmc the existence of relatively strong intermicellar interactions stemming from the distribution of dipoles over the surface in these micelles due to the presence of the amide group.

We report here a small angle neutron scattering (SANS) study of the micellization of SDS in formamide. We show that a compound with a hydrophobic chain containing 12 carbon atoms forms micelles in formamide. The mechanism of self-association is in agreement with a multiple equilibrium model rather than a pseudophase model, as the aggregates were shown to increase in size over a large concentration domain. This was attributed to smaller solvophobic effects and lower interfacial energy in formamide than in water.

In this study, we investigated the micellization in water of four surfactants from the series of (N-alkylamino)lactitols by small angle neutron and X-ray scattering. These four surfactants differed from one another 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 micelle size was weakly dispersed at small concentrations. The C8 derivative presented a singular behavior which may be attributed to the formation of premicellar aggregates. The characteristic dimensions of the micelles are derived from the I(q) curve fittings. For the calculation of scattered intensity from the micelles, three models of micelles were considered: spherical, oblate ellipsoidal, and prolate ellipsoidal. These models take into account particularities of the studied surfactants, in particular, the size of the sugar head group, which leads us to consider a nonuniform penetration ...

The Krafft temperatures and critical micellar concentrations (cmc) of N-alkylpyridinium halides (CmPyX, m = 12, 16, or 20 and X = Cl, Br, or I) in formamide were determined. The size, structure, and charge of the micelles as a function of chain length and nature of counterion were calculated from the small angle neutron scattered intensity. At a chain length of 12 carbons, only small, relatively unstructured aggregates were formed. At a chain length of 16 carbons, some micelles were also observed at a concentration of twice the cmc and above. At a chain length of 20 carbons, micelles were the sole species. The radii of the cores of the spherical micelles in formamide were always lower than the radii of the corresponding micelles in water. The micelles bear a higher charge in formamide than in water, but similar solvation effects were noted in the two solvents on changing the counterion (I-, Br-, or Cl-).

In this work we investigate lyotropic phases in different sugar-based surfactant/water systems. Studies are carried out with the (N-alkylamino)-1-deoxylactitols (C 8 , C 10 , C 12 ) and β-dodecyl maltoside. Liquid crystal phases are detected and lattice parameters determined by X-ray diffraction. The phases observed are the normal phases found in binary ionic or nonionic surfactant/water systems. Schematic diagrams show the sequences of the lyotropic phases formed by these disaccharide surfactants. The difference in behavior is accounted for by the difference in chain length, hydrophilic ability, and steric hindrance of the polar head.