MOLECULAR MOBILITY IN LIQUID AND IN FROZEN MICELLAR SOLUTIONS - EPR SPECTROSCOPY OF NITROXIDE FREE-RADICALS

EPR spectra of stable nitroxide radicals in fluid and in frozen micell ar solutions of cationic and anionic surfactants were recorded. Analys is of the obtained spectra gave information on the mobility of molecul es in the electrical double layer, in the core of the micelle and in t he bulk water phase. In fluid solution the viscosity near the surface of the micelle is higher than in the water phase, It increases with in creasing chain length of the surfactant and with increasing atomic num ber of the counterion. The viscosity in the inner cores of the micelle s exceeds that of the water phase by factors up to 30 and that near th e surface by factors between 10 and 20. The mobility within the micell e decreases with increasing atomic number of the counterion, In frozen micellar solutions there is no significant mobility in the core of th e micelle up to the macroscopic melting point. In the double layer, ho wever, mobility is detected at temperatures >240 K. This can be explai ned by local melting point depression because of the high local ion co ncentration in the double layer. (C) 1996 Academic Press, Inc.