Branching and percolation in lecithin wormlike micelles studied by dielectric spectroscopy

Lecithin water-in-oil microemulsions have been shown to form long polymerlike micelles. Dielectric spectra of this system are characterized by two dispersions. The high frequency dispersion, related to the head-group rotation of the lecithin molecule, displays a different dependence on water addition in the same two regimes that show up differently in the dynamics measured with several other techniques. The low frequency dispersion is due to a polymeric Rouse/Zimm type mode, which above a certain concentration starts to decrease and shows the characteristics of percolation. Ln the high water regime the decrease of the relaxation time is accompanied by an increase in conductivity, whereas in the low water regime the conductivity decreases. These data are interpreted in terms of concentration induced percolation and water induced coalescence into a connected network.