Eo. Alonso et Fh. Quina, DYNAMICS OF COUNTERION EXCHANGE IN AQUEOUS MICELLAR SOLUTION - SALT EFFECTS ON THE COUNTERION EXIT RATE, Langmuir, 11(7), 1995, pp. 2459-2463
Time-resolved fluorescence decay measurements with pyrene as probe hav
e been employed to study the dynamics of exit of the N-ethylpyridinium
ion and Cu2+ from micelles of sodium dodecyl sulfate (SDS) over a wid
e range of concentration of SDS and added common counterion salt (NaCl
or Na2SO4). The rate constants k(q) for intramicellar quenching decre
ase slightly with increasing added salt due to salt-induced micellar g
rowth. The rate constants k(-) for micellar exit are modestly dependen
t on SDS concentration and strongly dependent on the added salt concen
tration. A simple pseudophase model, which assumes that the counterion
exit rate is governed by the micellar surface potential, nicely ratio
nalizes both the detergent and added salt effects on k(-) and provides
an estimate of the effective electrostatic work for counterion escape
from the SDS micelle.