Small Angle X-ray and Neutron Scattering Study of the Micellization of (N-Alkylamino)-1-deoxylactitols in Water

Abstract

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 of the solvent into the polar outer layer. On the other hand, the width of the polar head layer is assumed 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 the four surfactants was obtained with an oblate ellipsoidal model. The model produced a constant value of 0.55 for the ellipticity of the cores of the models. We pointed out how this particular packing is adapted to the characteristics of the (N-alkylamino)lactitol polar head, and we compared it to the other models of micelles: spherical and prolate ellipsoidal. We also studied the evolution of several parameters (aggregation number, radius of the core, ...) as a function of the number of carbon atoms in the alkyl chain.

Behavior of Surfactant Mixtures at Solid/Liquid and Oil/Liquid Interfaces in Chemical Flooding Systems

“…The hydrocarbon chain length of n-dodecyl-β-D-maltoside is taken as 1.67 nm in its fully stretched conformation following Tanford's equation [43]. Although the SAXS techniques yield the full length of two glucose units to be 1-1.2 nm [44,45], the real length in the direction of hydrocarbon chain is only 0.62 nm [40]. The difference is due to both the hydrophilic head not aligning with the hydrophobic tail and the outside sugar ring bending towards the inner ring [40].…”

Novos tensoativos derivados da 2-D-glucosamina

“…A intensidade de espalhamento de raios X a baixo ângulo (SAXS) de uma solução monodispersa de partículas esferoidais de pequena anisotropia é descrita por (DUPUY et al, 1996;GUINIER & FOURNET, 1955;ITRI & AMARAL, 1991;KOTLARCHYCK & CHEN, 1983):…”

“…A modelagem dos dados assume que a micela é formada essencialmente por duas camadas de densidades eletrônicas diferentes: um núcleo, composto pelos grupos hidrofóbicos, com densidade ρ par = 0,275 e/Å 3 , e uma camada externa, ao redor do núcleo hidrofóbico, com espessura ε (outro parâmetro ajustável), que inclui os grupos polares e a água de hidratação, com densidade eletrônica ρ pol (outro parâmetro ajustável) (DUPUY et al, 1996;ITRI & AMARAL, 1991).…”

Structural Determination of Membrane Mimics Using Small-angle X-ray and Neutron Scattering

“…A variety of methods have been presented in the past thirty years for extraction and solubilization of membrane proteins (35)(36)(37)(38)(39)(40)(41). Commonalities between approaches include the use of amphiphilic molecules to screen hydrophobic regions of protein from surrounding water.…”

“…Micelle shapes have been debated in the literature (36,37,(39)(40)(41); however, overwhelming evidence indicates that head group properties dictate the ellipticity (aspect ratio; a/b) of the micelle for single chain detergents, where prolate and oblate ellipsoid micelles are observed (15,21,(35)(36)(37). Beyond this simplified treatment of head group interactions, Iyer and Blankschtein (42) and Dupuy et al (35) propose models for nonionic surfactants that predict ellipticity and shape based on the packing and interactions between head groups (and solvent) independent of chain length.…”