DUAL FLUORESCENCE OF SODIUM P-DIMETHYLAMINOBENZOATE IN AQUEOUS-SOLUTION OF POSITIVE IONIC SURFACTANT - PROBING MICELLE FORMATION AND STRENGTH OF ELECTRIC-FIELD AT MICELLE INTERFACE

Fluorescence spectrum of sodium p-dimethylaminobenzoate (SDMAB) in aqu eous solution was recorded as a function of the concentration of posit ive ionic surfactant, Zeph, CTAC, and CTAB, respectively. Dual fluores cence which is characteristic of the excited state TICT of SDMAB was o bserved in aqueous surfactant solution. Micelle formation can be ident ified by the break that appears in curve of intensity ratio of TICT em ission band to LE band, la/lb, versus surfactant concentration. The TI CT band is shifted to blue in micelle as compared to that in pure wate r, which is an indication that SDMAB is buried in the apolar portion o f the positively charged micelle, and the micellar phase polarity is p robed to be the same for the three micelles. The la/lb ratio in three micelles takes an order as Zeph > CTAC > CTAB. This order is shown to be due to the difference in strength of electric field at micelle inte rface. A blue-shift of TICT band with surfactant concentration before micelle formation was noted, which can be taken as a new evidence for self-ceiling of surfcatnt molecule in aqueous solution.