INTERACTION OF METHYL-ORANGE WITH CATIONIC MICELLES AND ITS EFFECT ONDYE PHOTOCHEMISTRY

The interaction of the azo dye methyl orange with cationic and anionic surfactant micelles was studied by absorption and emission spectrosco py. The dye interacts strongly with the cationic micelles cetyltrimeth ylammonium chloride (CTAC) and cetyltrimethylammonium bromide (CTAB), but does not interact with the anionic micelle sodium dodecylsulphate (SDS). The association constants of the dye to CTAC and CTAB micelles are 5.6 x 10(4) and 5.9 X 10(5) respectively. The fluorescence quenchi ng of pyrene by methyl orange in CTAC micellar solution occurs via non -radiative energy transfer. The variation of the relative fluorescence intensity agrees well with a model in which the dye is almost complet ely associated with the micellar phase. The photolysis of an aqueous s olution of the dye in the presence of acetone gives rise to an irrever sible photoreduction of the azo dye by the ketyl radical formed during photolysis. The presence of CTAB micelles reduces the photodecomposit ion rate of the dye. This effect is ascribed to the micellar cage effe ct which inhibits the second-order disproportionation reaction of the hydrate compound formed.