Photophysical study on aggregation of carboxylic perfluoropolyether derivatives in water: Time resolved fluorescence quenching measurements in the temperature range 297–333 K

Aqueous micellar solutions of fluorinated surfactants Cl(C3F6O)2CF2COOX, X = NH4+ or Na+, have been examined in the temperature range 297–333 K by the time resolved fluorescence quenching technique, using cationic pyrene derivative as a luminophore and methylviologen cation as a quencher. Based on the model proposed by Infelta and Tachiya we have determined aggregation numbers, N, and rate constants of intramicellar fluorescence quenching, kqm, and of the quencher exit from micelles, k−. The observed dependencies of N as a function of temperature are compared with those reported from small angle neutron scattering studies [C.M.C. Gambi, R. Giordano, A. Chittofrati, P. Pieri, P. Baglioni, J. Texeira, J. Phys. Chem. A 107 (2003) 11558–11564; C.M.C. Gambi, R. Giordano, A. Chittofrati, P. Pieri, P.Baglioni, J. Texeira, J. Phys. Chem. B 109 (2005) 8592–8598]. The kqm and k− data, and the respective activation energies, are discussed in terms of micellar size, packing of surfactant molecules and charge density at the interface, depending on surfactant concentration and the kind of counterion.