MIXTURES OF NONIONIC AND IONIC SURFACTANTS - DETERMINATION OF MIXED MICELLE COMPOSITION USING CROSS-DIFFERENTIATION RELATIONS

Cross-differentiation relations are used in thermodynamics to describe the behavior of cationic and nonionic surfactants in mixed micelles. This study uses dodecyltrimethylammonium bromide (DTABr) as cationic s urfactant and dodecylpoly(oxyethylene glycol ether)(23), or BRIJ 35, a s nonionic surfactant. One of these cross-differentiation relations al lows us to connect the nonionic surfactant activity with that of the c ationic surfactant by following the variations of DTABr molality with BRIJ 35 molality, at constant DTABr chemical potential. This was possi ble with a reliable DTA(+)-selective electrode. We show that this appr oach gives access to the activity of nonionic species in solution and into the micelle from potentiometric measurements.