NMR measurements on microemulsions

Abstract

Fourier transform Nuclear Magnetic Resonance studies, providing information on relative molecular self-diffusion coefficients and nuclear spin relaxation rates in microemulsions, have led to a reassessment of the prevalent ,,droplet" conception of the molecular organization in microemulsions. An O/W-organized system (e. g. a micellarlike) is necessarily characterized by rapid water diffusion and slow surfactant (and hydrocarbon solubilizate) diffusion. W/O systems must likewise exhibit slow water and surfactant diffusion, while the diffusion processes in the continuous hydrocarbon phase remain rapid. The experimentally observed diffusion behaviour in some microemulsion types (e. g. Aerosol OT-water-hydrocarbon) can, essentially throughout the entire extensive composition stability range, be reconciled with a distinct water-in-oil model while the dynamic properties on the molecular level of others (e. g. medium-chain alcohol cosurfactant types), resemble over wide concentration ranges those of partially aggregated liquids. As clearly shown by our multicomponent self-diffusion data, the degree of molecular organization over large composition regions of cosurfactant microemulsion systems is much lower than that in miceUar solutions or normal emulsions, for example. Spin relaxation data indicate, on the other hand, that some supramolecular aggregation prevails during the (organizational) timescale of these experiments (c. 100 ps). In a local frame, this residual organization is probably similar to that found in micelles containing solubilized alcohols or hydrocarbons.

Microemulsion Microstructure Influences the Skin Delivery of an Hydrophilic Drug

“…Fast diffusion is characteristic of free molecules (in solution), while slow diffusion indicates restricted mobility caused by binding to macromolecules or confinement inside droplets (21,22).…”

“…The PFGSE NMR technique yields valuable information with respect to the microstructure of the system (21,22). The measurements were made at the technical platform "Centre Commun de RMN" CCRMN, University of Lyon, Villeurbanne (France) (http://ccrmn.univ-lyon1.fr/).…”

“…Microemulsions are isotropic, whereas lamellar phases are birefringent. The structures of microemulsions (o/w, bicontinuous and w/o) were determined by different methods: electrical conductivity (19,20), Pulsed Field Gradient SpinEcho Nuclear Magnetic Resonance (PFGSE NMR) (21,22) and Small-Angle Neutron Scattering (SANS) (23).…”

Dependence of the activity of a rhizopus lipase on microemulsion composition

“…The temperature of the measurements was 37.0 ~ + 0.5 ~ The FT PGSE measurements were performed by varying the duration of the gradient pulse (~ 1 Gauss/cm) at a constant measuring time interval of 140 ms [10,11].…”

“…Table I shows the self-diffusion coefficients of the water, surfactant, triglyceride, and hydrocarbon molecules in mixtures of varying water content. Determinations were made using a Fourier transform pulsed-gradient spin-echo NMR technique [10,11].…”