Fluorescence anisotropy of probes solubilized in micelles of tetradecyltrymethylammonium bromide: Effect of ethylene glycol added

This paper deals with the effect of ethylene glycol on the micelle formatio n of tetradecyltrimethylammonium bromide. The effect of ethylene glycol add ition on the fluorescence anisotropy of several probe molecules residing in different regions of the micelle was investigated to address the solvent p enetration in the micelle structure. Fluorescence depolarization measuremen ts were carried out on micellar systems containing two different hydrophobi c dyes, namely, perylene and diphenylbutadiene, and a hydrophilic one, fluo rescein. The steady-state anisotropy values obtained in these experiments w ere used to estimate the microviscosity of the corresponding micellar regio ns. It is observed that the microviscosity in the hydrophobic regions of mi celles were roughly constant with EG addition, indicating that the micellar interior does not undergo significant structural changes by the presence o f cosolvent in the solution. However, the microviscosity at the micellar su rface, as determined by using fluorescein as a probe, is found to increase with EG addition. This perturbation of the micellar surface is ascribed to the solvent penetration in this region of the micelle, where there is proba bly participation in the solvation layer of the micelle headgroups. (C) 200 0 Academic Press.