Modulation in the solute location in block copolymer-surfactant supramolecular assembly: a time-resolved fluorescence study.

Effect of cosurfactant concentration on the location of a dissolved solute in a block copolymer-surfactant supramolecular system has been investigated using time-resolved fluorescence anisotropy and dynamic Stokes' shift measurements. Pluronic F88 and cosurfactant CTAC have been used to form a supramolecular assembly. The anion of coumarin 343 dye has been used as the solute/probe. It is seen that as the CTAC concentration is increased in the F88-CTAC supramolecular assembly, the microviscosity around the probe gradually increases. The result suggests that the probe undergoes a gradual migration from micellar surface to the interior of the micelle as the concentration of the CTAC is increased. This is also supported by the dynamic Stokes' shift results. It is seen that as the CTAC concentration is increased in the system, the observed Stokes' shift gradually increases due to the movement of the probe away from the bulk water. By comparing the present results with those reported in another pluronic-surfactant system, namely, P123-CTAC, it is indicated that the extent of modulation in the position of the probe in such supramolecular systems is largely determined by the composition of the pluronic, especially on the length of its hydrophilic ethyleneoxide block.