Demixing of Fluorinated and Hydrogenated Surfactants into Distinct Aggregates and into Distinct Regions within Aggregates. A Combined NMR, Fluorescence Quenching, and Cryo-TEM Study

The formation of two different kinds of micelles in the cationic surfactant mixture of HFDePC and CTAC as well as the increased mixing with increasing temperature has been investigated. A critical temperature of demixing was appreciated to 42 °C. NMR self-diffusion measurements reveal to us a coexistence of larger fluorocarbon-rich and smaller hydrocarbon-rich micelles, which is also observed using cryo-TEM. We also suggest, from 19 F line width data, that the two surfactant species constituting the demixed micelles are “microphase-separated”. The existence of such aggregates has earlier only been speculated upon. From time-resolved fluorescence quenching measurements, we have estimated the fraction of fluorocarbon surfactant in the hydrocarbon-rich micelles to larger than 0.1.