ULTRASONIC RELAXATION STUDY OF FAST EXCHANGE PROCESSES IN MIXED MICELLE SYSTEMS OF ALCOHOL-DECYLTRIMETHYLAMMONIUM BROMIDE-WATER

Recent studies of the fast exchange processes of micellar components b etween mixed micelles of alcohol-surfactant and the aqueous bulk phase are reviewed and discussed in the light of some further work. Ultraso nic absorption measurements (0.6 < f < 210 MHz) of aqueous solutions o f decyltrimethylammonium bromide (DTAB) and short to medium hydrocarbo n chain length alcohols show two relaxation frequencies. The lower fre quency is assigned to the exchange of the monomer surfactant and the h igher frequency to the exchange of alcohol between the micellar and bu lk phases. Conductometric and time resolved fluorescence measurements have enabled complementary information to be obtained regarding the me an aggregation number of the surfactant and, indirectly, of the alcoho l in the aggregates. The ultrasonic data were analyzed according to th e theories of Aniansson and of Hall to obtain estimates of the backwar d rate constants and volume change for the exchange processes of surfa ctant and alcohol between the micellar and bulk phases and of the poly dispersity of the mixed micelles. The Hall model gives larger values o f the kinetic parameters. Generally, the results of the analyses for t he surfactant show that its exit rate from the mixed micelle and the m ean aggregation number and the polydispersity of the micelle decrease as the alcohol chain length increases. Reasons for the observed influe nce of the alcohol on the kinetic and thermodynamic parameters are pre sented.