Reverse Micelle Microstructural Transformations Induced by Surfactant Molecular Structure, Concentration, and Temperature

Abstract

We have investigated the microstructural transformations of nonionic surfactant reverse micelles induced by surfactant molecular architecture, surfactant concentration, and temperature in nonaqueous media. The investigations were based on small-angle X-ray scattering (SAXS) and rheometry techniques. Polyglycerol polyoleic acid esters spontaneously self-assembled into reverse micelle in n-decane under ambient conditions, whose shape, size, and internal structure could be controlled by the surfactant molecular architecture, concentration, and temperature. The maximum size of the micelles was found to increase with an increase in the hydrophilic headgroup size of the surfactant. On the other hand, an opposite trend was observed with an increase in the number of oleate chain per surfactant molecules, which was well supported by rheology data; viscosity decreased with the number of oleate chain per surfactant molecule. The SAXS and rheology data have shown a clear evidence of one dimensional micellar growth with increase in the surfactant concentration. The relative viscosity, eta(r), of the reverse micelle exhibited steeper concentration dependence behavior than those predicted for a dispersion of spherical particles based on the Krieger-Dougherty relation which provided a clear evidence of the presence of elongated micelles at higher concentration. An ellipsoidal prolate-to-sphere type transition was observed upon heating.

The structures of hexadecylamine films adsorbed on iron-oxide surfaces in dodecane and hexadecane

“…No self-assembly of the hexadecylamine surfactants was observed in the solutions, which is to be contrasted with the formation of reverse micelles by other friction modifiers such as glycerol derivatives. [34][35][36][37] The atomic interactions of the iron-oxide slabs were given by the Lennard-Jones (LJ) and Coulomb potentials with parameters defined by Berro et al 24 The interactions of the surfactant and lubricant molecules were given by the OPLS-AA force field 38 adapted to amines by Price et al 39 The partial charges on the atoms are given in Table 2. LJ cross interactions were evaluated using the Lorentz-Berthelot mixing rules.…”

Molecular adsorption, self-assembly, and friction in lubricants

“…3(a). Remarkably, GMO and related molecules form reverse micelles in bulk solution [57,58,59,60,30,31,61].…”

Molecular Dynamics Simulations of Glycerol Monooleate Confined between Mica Surfaces

“…50 GMO is known to self-assemble into normal and reverse micelles (RMs) in aqueous and nonaqueous media, respectively. The self-assembly of GMO and related molecules in hydrocarbons to form RMs has been examined experimentally by Shrestha et al [51][52][53][54] The current authors investigated the formation of GMO RMs in n-heptane and toluene using MD simulations and small-angle neutron scattering (SANS), with good agreement being found between the two approaches. 55 From that work, it was determined that the typical radius of gyration of a RM is R g ' 15 Å, and that the number of GMO molecules in a micelle depends on the solvent and the extent to which it penetrates the RM; there are approximately 20 GMO molecules per RM in toluene, and 30 in n-heptane.…”