Effect of the nature of the counterion on the properties of anionic surfactants. 2. Aggregation number-based micelle ionization degrees for micelles of tetraalkylammonium dodecylsulfates
Effect of the nature of the counterion on the properties of anionic surfactants. 2. Aggregation number-based micelle ionization degrees for micelles of tetraalkylammonium dodecylsulfates
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DOI：
10.1021/jp040289x
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发表时间：
2004-09-30
影响因子：
3.3
通讯作者：
Zana, R
中科院分区：
文献类型：
--
作者：
Bales, BL;Tiguida, K;Zana, R
四甲基，四乙基，四丙基，和四丁基铵十二烷基硫酸盐胶束在水溶液中生长的表面活性剂或添加的电解质浓度增加。前三种表面活性剂的聚集数N的变化描述如下：N = N-0（C-aq/cmc（0））（γ）其中N-0是在不存在添加的电解质cmc（0）的情况下在临界胶束浓度下的聚集数，C-aq是水相中抗衡离子的浓度，γ是常数。N-0值相当小，在25度时为54至64;在10度时为61至74;在40度时为51至56。伽马值对温度不敏感，并且相当小; 0.05到0.1。相比之下，十二烷基硫酸四丁基铵几乎与C-aq成线性增长。通过应用最近引入的假设（J. Phys. Chem. B 2001，105，6798）来研究这些胶束的电离度（α），该假设是在给定温度下的聚集数仅由C-aq决定，而不管这些抗衡离子是由表面活性剂单独提供还是由表面活性剂加上具有共同抗衡离子的添加盐提供。在所有情况下，（x）的值都大于在emc（0）下通过电导率获得的值。为了比较，还研究了十二烷基硫酸铯，我们发现α等于其在cmc（0）处的值。
Tetramethyl-, tetraethyl-, tetrapropyl-, and tetrabutylammonium dodecylsulfate micelles in aqueous solution grow as either the surfactant or added electrolyte concentrations are increased. The variation in the aggregation number, N, of the first three surfactants is described as follows: N = N-0(C-aq/cmc(0))(gamma) where N-0 is the aggregation number at the critical micelle concentration in the absence of added electrolyte, cmc(0), C-aq is the concentration of counterions in the aqueous phase, and gamma is a constant. The values of N-0 are rather small, in the range 54 to 64 at 25degrees; 61 to 74 at 10degrees; and 51 to 56 at 40 degreesC. The values of gamma are insensitive to temperature and are rather small; 0.05 to 0.1. In contrast, tetrabutylammonium dodecylsulfate grows nearly linearly with C-aq. The ionization degrees (alpha) of these micelles are studied by applying the hypothesis recently introduced (J. Phys. Chem. B 2001, 105, 6798) that the aggregation number at a given temperature is determined solely by C-aq whether these counterions are supplied by the surfactant alone or by the surfactant plus added salt with a common counterion. In all cases, the values of (x are larger than those obtained at the emc(0) by conductivity. For comparison, cesium dodecylsulfate is also studied, where we find that alpha is equal to its value at the cmc(0).