Study on premicellar and micellar aggregates of gemini surfactants with hydroxyl substituted spacers in aqueous solution using a probe showing TICT fluorescence properties

摘要

The aggregation properties of two gemini surfactants, 12-3(OH)-12,2Br~- and 12-4(OH)2-12,2Br~- with hydroxyl substituted spacer group have been studied. The changes in photophysical properties of a single probe, trans-2-[4-(dimethylamino)styryl]benzothiazole (DMASBT) showing dipolar nature in its twisted intramolecular charge transfer (TICT) excited state have been exploited rather than using multiple probes to describe various properties of micellar aggregates. Formation of a number of premicellar aggregates has been demonstrated in addition to the description of the micropolarity and the micro-viscosity of environment using steady-state fluorescence spectroscopy and fluorescence anisotropy of DMASBT. Conductometric measurements have been carried out to determine degree of micellar ionization (α) and to verify critical micelle concentration (CMC) values estimated by fluorescence method. Hydroxyl substituted spacer group induces the formation of premicellar aggregates. The micropolarity of environment around probe molecules increases on going from premicellar to micellar aggregates. The growth of micellar aggregates has been demonstrated by a continuous increase in the microviscosity of environment. The micropolarity of micellar environment of 12-4(OH)2-12 is found to be less than that of 12-3(OH)-12. The microviscosity of premicellar and micellar aggregates of 12-4(OH)2-12 are higher than that of 12-3(OH)-12. CMC increases, whereas a decreases with increasing spacer chain length as well as number of hydroxyl substitution of a spacer group.