Solubility properties of Eosin Y and Rose Bengal triplet state in sodium dodecyl sulfate micellar solutions

Solubility properties of the Eosin Y and Rose Bengal triplet states in aqueous solutions of sodium dodecyl sulfate have been explored by means of flash photolysis and electron paramagnetic resonance techniques. Eosin Y triplet state does not associate with the surfactant aggregates while the Rose Bengal triplet state appears to be in dynamic equilibrium between the micellar and aqueous pseudophases. The corresponding equilibrium constant depends on the detergent concentration between the critical micelle concentration and about 60 mol dm-3. The exit rate constant of the Rose Bengal triplet state out of a micelle is found to decrease in this concentration range. This is attributed to an increase of the hydrophobic character of the sodium dodecyl sulfate micelle resulting from its partial dehydratation. Between 60 and 200 mmol dm-3, the equilibrium and exit rate constants seem to be constant.