AGGREGATION BEHAVIOR OF DODECYLAMMONIUM C ARBOXYLATES IN CARBON-TETRACHLORIDE

The Aggregation of dodecylammonium acetate(DAA), dodecylammonium propi onate (DAP) and dodecylammonium Butyrate(DAB) have been investigated b y spectrometric iodine method and water solubilization; the (cmc)(I)s determined by spectrometric iodine method are 2.0 x 10(-4), 2.2 x 10(- 4) and 4.3 x 10(-4) mol dm(-3), respectively; and the (cmc)(w)s by wat er solubilization are 2.0 x 10(-3), 3.5 x 10(-3) and 10.5 x 10(-3)mol . dm(-3), respectively. The (cmc)(I)s are lower by one order of magnit ude than the corresponding (cmc)ws The reason is probably that the agg regates with low aggregation number start to form at (cmc)(I), which a re not capable to solubilize water. Water solubilization starts only w hen the aggregation number of reverse micelles is high enough, which o ccur at (cmc)(w), the concentration is much higher than (cmc)(I). The experiment shows that the reverse micelles of DAA,DAP and DAB are able to solubilize up to respective 4.3, 9.4, and 13.5 molecules of water per surfactant molecule respectively, According to simplified spherica l reverse micelle model, the aggregation numbers of DAA, DAP and DAB r everse micelles which solubilize limiting amount of water are 24, 122 and 252; the radii of water pool are 0.90, 2.02 and 2.90nm, and radii of free water pool are 0.33, 1.68 and 2.58nm, respectively.