Shape Changes of C₁₆TABr Micelles on Benzene Solubilization

The microstructure of C₁₆TABr micelles with solubilized benzene was investigated by field-dependent ²H NMR spin relaxation of C₁₆TABr-α-d₂. The relaxation data, supported by cryogenic transmission electron microscopy that excludes oblate micelle shapes, suggest that the C₁₆TABr micelles, slightly elongated even without benzene, become longer and more polydisperse on benzene addition. Field-dependent 2H spin relaxation measurements on the benzene (C₆D₆) indicate that at low solubilizate content the benzene is predominantly located at the micellar interface, reorients more slowly than in bulk, and has a high lateral diffusion coefficient. Above a particular benzene concentration, the surfactant relaxation data suggest no further elongation but a radial growth, while the benzene relaxation shows that a large part of the benzene is residing in an interior region with near-bulk characteristics; the micelles become slightly elongated microemulsion droplets.