| Steady-state (SSEPR) and time-resolved electron paramagnetic resonance (TREPR) spectroscopy have been used to examine the dynamic motion and spin wavefunction evolution of stable nitroxide radicals or photochemically generated radical pairs in aqueous surfactant aggregates, respectively. Alteration of the surfactant molecular structure has a pronounced effect on the aggregation behavior and physical properties of surfactant aggregates. The surfactant systems discussed here are known to form micelles, vesicles, lamellar phases, surfactant networks, and gels. Both SSEPR and TREPR are sensitive to the nanometer scale confinement of radicals, making these experimental techniques usefully in monitoring phase changes in caused by experimental conditions, such as temperature, concentration, equilibration time, molecular structure, or surfactant mixing. Analysis of the line shape of the EPR spectra of radicals confined in these supramolecular structures is accomplished through spectral simulations and provides information on the physical properties of surfactant aggregates, including size, polarity, and viscosity. |
