The Branching of Reversed Polymer-like Micelles of Lecithin by Sugar-Containing Surfactants.

The effects of n-dodecyl-beta-D-glucopyranoside and n-dodecyl-beta-D-lactobionamide on the formation and rheological behavior of lecithin organogels consisting of reverse long cylindrical (polymer-like) micelles were studied by oscillating rheology. The alkylglucoside addition results in a decrease of the zero shear viscosity and plateau modulus of the organogel, whereas the lactobionamide derivative causes an increase of these parameters. Despite their different effects, both the sugar-containing surfactants change the scaling exponents of the zero shear viscosity, plateau modulus, and terminal relaxation time in a similar way. Before their addition, the scaling behavior is in a satisfactory agreement with that expected from a model by Cates who considered polymer-like micelles as linear and flexible. In mixtures of lecithin with n-dodecyl-beta-D-glucopyranoside or n-dodecyl-beta-D-lactobionamide, the power law exponents are close to the theoretical predictions that follow from a model for branched (connected) cylindrical micelles. It was concluded that both the sugar-containing surfactants bring about a change in the growing mechanism of the lecithin micelles in nonpolar media. A molecular model is considered. This takes into account the formation of hydrogen bonds between amphiphile molecules, occurrence of packing constraints, and a change of excess free energy of the micellar endings. Copyright 1999 Academic Press.