The measurement of electrophoretic mobility in surfactant systems using NMR

Abstract

A combined nuclear magnetic resonance (NMR) and electrophoresis method (MREP) is used for the measurement of electrophoretic mobility of charged micelles in surfactant systems. A modified NMR spin-echo pulse sequence with pulsed magnetic field gradients is employed to measure the slow flow rates encountered in electrophoresis of observation of phase shifts in the NMR spinecho. Electrophoretic mobility was determined for anionic sodium dodecyl sulphate and cationic cetyl trimethyl ammonium bromide surfactants at various concentrations. Also, measurements were made with added salt, which alters the ionic environment of the micelles. Finally, an attempt was made to study mixed surfactant systems using an extension of the MREP technique which involved Fourier analysis and observation of the phase shifts due to flow in the frequency spectrum.