乙二醇对烷基三甲基溴化铵胶团化行为的影响

利用电导法研究了烷基三甲基溴化铵表面活性剂(CnTAB,n=12,14,16),即十二烷基三甲基溴化铵(DTAB),十四烷基三甲基溴化铵(TTAB)和十六烷基三甲基溴化铵(CTAB),在混合极性溶剂乙二醇/水(体积分数0～40%)中的胶团化行为。考察了温度对胶团形成的影响,应用相分离模型估算了三个表面活性剂的胶团热力学参数。结果表明临界胶团浓度(cmc)和反离子解离度(α)都随乙二醇组分的增加而增大。在乙二醇/水混合溶剂中胶团形成的标准吉布斯自由能相差很小,混合焓都是负值,而混合熵都为正值,说明焓-熵补偿效应在胶团形成中起主导作用。

Effect of ethylene glycol on the micellization behavior of alkyltrimethylammonium bromides

The micellization behavior of alkyltrimethylammonium bromides,viz,dodecyl-,tetradecyl-and hexadecyltrimethylammonium bromide(DTAB,TTAB and CTAB,respectively)in ethylene glycol(EG)and water mixtures with varying volume fraction of EG(v/v)has been investigated employing electrical conductivity.Temperature dependence of the critical micelle concentration(cmc) was also studied to understand the micellar thermodynamics of these systems.The phase separation model of micellar formation was applied to obtain the thermodynamic parameters of micellization.It is showed that the cmc and the degree of counterion dissociation(α)increase with increasing content of EG in mixed solvent.There are small differences in the standard molar Gibbs free energies of micellization over the temperature range investigated.The enthalpy of micellization is negative in all cases,whereas the entropy is always positive.This behavior indicates that an enthalpy-entropy compensation effect is the governing factor for micellization.