脂肪酸十二烷基铵在四氯化碳中的聚集行为

Aggregation Behavior of Dodecylammonium Carboxylates in Carbon Tetrachloride

通过碘光谱法和对水的增溶研究了乙酸十二烷基铵(DAA)、丙酸十二烷基铵(DAP)和丁酸十二烷基铵(DAB)在四氯化碳中的聚集作用;碘光谱测得的(cmc)_I约比水增溶法测得的(cmc)_w低一个数量级.可能因为碘光谱法测得的是开始发生聚集时的cmc,这时聚集体较小,对水无增溶能力;只有当聚集体随浓度升高而长大到一定程度时,才能开始增溶水.实验表明,DAA,DAP和DAB的反胶束对水的饱和增溶能力,分别相当于每一个表面活性分子增溶4.2,9.4和13.5个水分子.根据球型反胶束模型,计算了反胶束聚集数、捕集水团的半径和自由水团的半径.

The Aggregation of dodecylammonium acetate (DAA) , dodecylammonium propionate (DAP) and dodecylammonium Butyrate(DAB) have been investigated by spectrometric iodine method and water solubilization; the (cmc)Is determined by spectrometric iodine method are2.0×10-4, 2. 2 ×10-4 and 4. 3 × 10-4mol·dm-3, respectively; and the (cmc)ws by watersolubilization are 2.0×10-3, 3.5×10-3 and 10.5×10-3mol·dm-3, respectively. The (cmc)Is are lower by one order of magnitude than the corresponding (cmc )ws. The reason is probably that the aggregates with low aggregation number start to form at (cmc)I, which are not capable to solubilize water. Water solubilization starts only when the aggregation number of reverse micelles is high enough, which occur at (cwc)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 spherical reverse micelle model, the aggregation numbers of DAA, DAP and DAB reverse 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.