TIME-RESOLVED FLUORESCENCE AND SELF-DIFFUSION STUDIES IN SYSTEMS OF A CATIONIC SURFACTANT AND AN ANIONIC POLYELECTROLYTE

The interaction between the anionic polysaccharide hyaluronan (Hy) and the cationic surfactants decyl-(C10TAB) and dodecyl-(C12TAB) trimethylammonium bromide has been investigated by H-1 NMR self-diffusion measurements and by time-resolved fluorescence measurements with pyrene as the probe and dimethylbenzophenone as the quencher. The critical aggregation concentration (cac) was found to be slightly lower than the cmc and about half of the cmc, for C10TAB and C12TAB, respectively. The cac is furthermore seen to depend on the Hy concentration. The steady-state spectra for pyrene in surfactant solutions with and without Hy are almost identical, which indicates a structure of surfactant micelles in the presence of Hy. The fluorescence lifetime, tau-0, for pyrene is increased by the interaction between the surfactants and the polyelectrolyte, due to the ability of the polyelectrolyte to displace the bromide ions from the micellar surface. The increase is considerably larger for the longer surfactant. The tau-0 value furthermore depends on the quotient between Hy and surfactant in the sample. The fluorescence decay curves obtained in the presence of quencher are of the same type as for ordinary micelles, in the presence of Hy, and are well described by the model proposed by Infelta et al. The aggregation numbers for the micelles are relatively unaffected by the presence of Hy.