First anionic micelle with unusually long lifetime: self-assembly of fluorocarbon-hydrocarbon hybrid surfactant

The exchange of a fluorocarbon-hydrocarbon hybrid surfactant between monomer and micelle states in deuterium oxide has been investigated through 19F NMR and 1H NMR experiments. The CF3 group in the surfactant gives two kinds of 19F NMR signals corresponding to the monomer and micelle states, indicating slow surfactant exchange on NMR time scale. The lifetime (taumic) of micelle, estimated by line shape analysis of the signals, is 2.0 ms at cmc, 102 to 103 times longer than that of general surfactant micelles. Pulsed-gradient spin-echo (PGSE) experiments show that the hybrid surfactant forms considerably small micelles with a hydrodynamic radius of 0.6 nm. In contrast, at a higher concentration where no slow surfactant exchange is observed, the micelle radius increases to 1.1 nm. The interdigitation between the surfactant molecules in the micelle will contribute to the unusually long lifetime, in other words, slow surfactant exchange on the NMR time scale.