Study of Aqueous Tetradecyltrimethylammonium Bromide-Brij 35 Solutions by Ion Activity Measurements

Abstract

Measurements of surfactant ion (tetradecyltrimethylammonium) and counterion (bromide) activities in binary tetradecyltrimethylaznmonium bromide (TTAB)-Brij 35 surfactant mixtures have been performed by using ion-specific electrodes. From the data obtained in the TTAB solutions in the absence of Brij 35, a TTAB critical micelle concentration (cmc) of 3.6 (±0.2) mM was evaluated. The degree of counterion binding on TTAB micelles was calculated from the concentration dependence of bromide activity above the cmc, Bth, and by applying the charged phase separation model to the surfactant and counterion activity data obtained, βcps. Values found were βth= 0.75 and βcps= 0.8. From the data obtained in the surfactant mixtures, the micellar composition and the counterion binding degree (βth) of the mixed micelles have been evaluated. It was found that (1) in dilute solutions (total surfactant concentration lower than 5 mM) mixed micelles having a very low fraction of associated counterions are f