Time-resolved fluorescence quenching measurements in micellar solutions of ionic surfactants, combined with the simultaneous recovery of decay parameters, demonstrate that the residence time of a quencher in the micelle can be varied by changing the electrostatic interaction between the micellar aggregate and the quencher or the hydrophobicity of the quencher, or by the addition of 1-butanol. When an alkylpyridiniitm chloride is used as a quencher with a cationic group, it always behaves as an immobile quencher in a solution of an anionic surfactant. However, it can, depending upon the length of the alkyl chain, behave as a mobile one in a solution of a cationic surfactant. In the latter case the migration of the quencher is due to the exchange of monomer quenchers among the micelles. The migration of strongly hydrophobic cationic quenchers is observed in sodium dodecyl sulfate solution upon addition of high concentrations of 1-butanol. Global analysis demonstrates that the exit rate constant of quenchers with different lengths of the alkyl chain is in this case identical. Furthermore, the quenching rate constant kq increases initially and then decreases upon the addition of 1-butanol. At a concentration of 1 M added 1-butanol the size of the aggregate becomes larger. Similar results are found in aqueous dodecyltrimethylammonium chloride/1-butanol mixed solutions. These results can be rationalized by the fragmentation-coagulation model of micellar systems. In this model the micelles exchange surfactant-butanol clusters containing the quencher and the excited probe.
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