乙二醇对烷基三甲基溴化铵胶团化行为的影响

第24卷第2期化学研究与应用 Vol.24, No.22012年2月 Chemical Research and Application Feb.,2012文章编号:1004-1656(2012)020322-05乙二醇对烷基三甲基溴化铵胶团化行为的影响凌锦龙,徐敏虹,洪迪,张艳(湖州师范学院生命科学学院,浙江湖州313000)摘要:利用电导法研究了烷基三甲基溴化铵表面活性剂(CTAB,n=12,14,16),即十二烷基三甲基溴化铵(TAB),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(a)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都为正值说明补偿效应在胶团形成中起主导作用。关键词:烷基三甲基溴化铵;乙二醇/水混合溶剂临界胶团浓度;胶团热力学中图分类号:0647.2文献标识码:A Effect of ethylene glycol on the micellization behavior of alkyltrimethylammonium bromides LING Jin-long', XU Min-hong, HONG Di, ZHANG Yan Abstract: The micellization behavior of alky um bromide( DTAB, TAB and CTAB, respectively) in ethylene glycol(EG) and water mixtures with varying volume fraction of EG (/)has been investigated employing electrical conductivity. Temperature dependence of the critical micelle concentration() was also studied to understand the micellar thermodynamics of these systems. The pha odel of micellar formation was applied to obtain the ther of micellization. It is showed that the cmc and the degree of counterion dissociation (a) increase with increasing content of EG in mixed solvent. all differences in the standard molar Gibba free energies of micellization over the temper ated. The enthalpy of micellization is negative in all cases, whereas the entropy is al- ways positive. This behavior indicates that an enthalpy-entropy compensation effect is the governing factor for micellization. Key words alkyltrimethylammonium bromide; EG and water binary mixture; critical micelle concentration; micellar thermodynamic在混合溶剂中研究表面活性剂的热力学性途径:1)与表面活性剂分子的相互作用,2)改变溶质,有助于理解溶质溶质和溶质溶剂的相互作剂的特性。改变溶液本体相性质最方便的办法就用。表面活性剂胶束性质主要由复杂的亲水是添加有机溶剂。有机溶剂主要进入本体相而不和僧水间平衡所决定。而溶剂因素的影响有两条参与胶团的形成,这些有机添加剂通常要求具有收稿日期:2010-11-28修回日期:2011-10-27联系人简介:凌锦龙(1964-),男,副教授,主要从事溶液热力学和界面化学研究-mail: lingjinlong hute.c第2期凌锦龙等:乙二醇对烷基三甲基溴化铵胶团化行为的影响323很高的内聚能和介电常数,以及较高的氢键形成40%的水溶液中的电导率;在20%E溶液中,测能力。二元醇具有两个羟基,既能形成分子内氢定了三种表面活性剂在298.15K~318.15K时的键,也能与水形成氢键而构成三维网状结构。其电导率。图1是298.15K时CTAB电导率随EG对表面活性剂胶团形成的影响,已引起基础研究浓度的变化关系(其他未列出)。可以看出,电导者的广泛兴趣 PalepuTriton6等研究了率在胶团形成前后有一个突变,两条直线的交点100在二元醇(乙二醇,三甘醇,四甘醇)水溶液中即为cmc,而胶团形成之后的直线斜率与之前的直的自聚行为及胶团热力学性质。 Eastoe等研究线斜率之比即为反离子解离度a表1和表2列了在水乙二醇和水-1,3丙二醇混合溶剂中表面出了三种表面活性剂的cmc和反离子解离度a活性剂头基对聚集行为的影响。这些研究指出了125非离子或离子表面活性剂在有二元醇存在时的不1同的胶团行为,说明了本体相在胶团形成过程中 EG(v/v]的重要性,揭示了通过改变本体相性质来控制胶20%团聚集的可能性本文选择不同疏水链长的烷基三甲基溴化铵(CTAB,n=12,14,16),研究了在不同乙二醇含量水溶液中的胶团化行为,分析了温度对胶团形成图1298.15K时不同体积分数的乙二醇水溶液中的影响,探讨了极性有机溶剂的加入对胶团形成CTAB电导率随浓度变化关系的影响规律。 Fig 1 Conductivity versus concentration of CTAB in EG+H2O mixtures at 298. 15K1实验部分由表1可以看到,cmc随EG的增加而增加。.1试剂这主要由两个因素引起:1)EG的加入,降低了本十二烷基三甲基溴化铵(DTAB),十四烷基三体相的内聚能密度,因而增加了表面活性剂单体甲基溴化铵(TTAB),十六烷基三甲基溴化铵的溶解性,使cmc升高;2)助溶剂引起水的介电常(CTAB),AR,用丙酮-乙醚混合溶剂重结晶5次;数下,导致离子头基间的相互斥力增加,使cm乙二醇(EG),AR;水为去离子水经石英亚沸重蒸升高。处理,电导率为1.0us·cm-1。所用试剂经测定表温度对临界胶团浓度的影响,可以从表2看面张力曲线均无最低点,表明无高活性杂质存在。出。固定溶剂比例时,表面活性剂的cmc随温1.2电导实验度升高而升高。这里存在两个对立的影响因素:DDS-11A型电导率仪,上海精密科学仪器有1)升高温度,表面活性剂亲水基团的水合能力下限公司雷磁仪器厂。电导测定在带有恒温水夹套降,这有助于胶团的形成;2)升高温度同时也导致的容器中进行。温度控制精度为±0.1K。测得表面活性剂疏水基周围水结构的破坏,这不利于298.15K时水中CTAB临界胶束浓度(cmc)9.3×胶团形成。从结果来看,第二个因素起了主导作10mol-,与文献值相符。用。同时由表1和表2看出,对胶团溶液的反离2结果与讨论子解离度a,增加EG含量与升高温度的效应是一致的都是增大。部分原因可能由于胶团聚集数2.1临界胶团浓度cmc下降从而导致胶团表面电荷密度下降而造成测定了298.15K时DTAB,TTAB和CTAB在的乙二醇体积分数分别为0%,10%,20%,30%和324化学研究与应用第24卷表1298.15K时烷基三甲基溴化铵在乙二醇水溶液中的cmca,C和△C Table The cme, degree of counterion dissociation( a), Gibbs energy of micellization( G. and Gibbs energy of transfer( for alkyltrimethylammonium bromides in EG aqueous solution at 298.15 K PEd/%cmc/10-3mol·l--ckmol△kmol DTAB014.540.25335.721016.910.26034.920.792019.010.28134.001.713022.380.32032.553.164028.490.38530.325.39 TTAB03.810.24141.80104.190.25241.130.67204.650.26540.371.43306.080.28738.723.08408.860.31636.495.30 CTAB0.930.25547.5711.180.26746.221.35201.390.27045.442.13301.890.28143.843.73402.960.30541.346.23表2不同温度下烷基三甲基溴化铵在20%E水溶液中的cmca及胶团热力学参数 Table 2 The emc, degree of counterion dissociation( a) and thermodynamic parameters of micellization for alkyltrimethylammonium bromides in 20%EG aqueous solution at various temperatures T/Kcmc/10-3mol·l- -AC/.mol"-AH/. mol-" TAS/. mol- DTAB298.1519.010.28134.0019.4414.57303.1520.440.30633.7619.8013.96308.1522.060.33033.5120.173.33313.1523.850.35433.2320.5312.69318.1525.800.37932.9120.8712.04298.154.650.26540.3829.8810.50303.155.150.27640.3530.699.66308.155.770.28740.2531.518.74313.156.520.29840.1032.337.77318.157.400.31239.8433.106.74 CTAB298.151.390.27045.4430.0515.39303.151.560.27845.4830.9214.57308.151.750.28745.4931.7813.7113.151.980.29545.4632.6712.80318.152.220.30345.4633.5611.92.2胶团热力学 Gibbs自由能△,混合△及混合熵△由相分离模型可得到胶团形成的标准摩尔△=(2-a)RTInX(1)第2期凌锦龙等:乙二醇对烷基三甲基溴化铵胶团化行为的影响325△H=-(2-a)()(2)基从本体相向胶团的迁移更为困难。△C越大, aTcmc也越高。表2数据表明,在同一EG浓度下,混合自由 TAS=AH-AG(3)能随温度的变化很小,几乎不变.随烷基链碳原式中a是反离子解离度,是用摩尔分数表示子数目的增加,变得更负,即胶团形成的自发的cmc浓度。从cmc随温度的变化关系可以求出性增大,所以相应的cmc也降低。胶团混合都△H。图2为各表面活性剂nXm随温度的变化是负值,随温度增加而降低,混合熵都是正值,也关系,均为线性关系,这与文献2的结论一致。随温度增加而降低。这说明了在20%EG水溶液为考察共溶剂对胶团化过程的影响,引入了中,烷基三甲基溴化铵的胶团化行为并不是熵驱迁移自由能△G动,而是熵补偿效应的结果。 Callaghan在研究EG水溶液中溴代十六烷基吡啶聚集行为时,认 DTAR为在高浓度的EG水溶液中(富醇区),随温度升 TTAR -CTAE高混合△H变小,而变△S从正变为负,因此△H是胶团形成的驱动力。Ruiz研究了在20%(wt)EG水溶液中(富水区),认为胶团化过程仍然是在与水结构性质类似的环境中进行的,EG的加295300305310315320入仅仅产生很小的溶质溶剂相互作用,胶团形成 T/K图2在20%E水溶液中烷基三甲基澳化主要是焓熵补偿效应。Lee2在研究EG水溶液ln随温度的变化关系中SDS的聚集行为时也有相似的结论。温度的升 Fig Plot of InX versus temperature for高,主要是弱化了氢键形成能力和液体的结构化, alkyltrimethylammonium bromides in 20% EG aqueous solution导致溶液的极性降低,疏溶剂作用减弱,使表面活性剂离子头基间的斥力增加,延缓胶团的形成,△=(ec+2-2(4)cmc增大。计算结果一并列于表1和表2中。由表1的胶团热力学参数来看,C都为负3结论值,说明胶团的形成是自发的。随EG浓度的增加,△C也呈增加趋势,因此EG的加入不利于胶烷基三甲基溴化铵的cmc和反离子解离度a团的形成。胶团cmc随本体相组成的变化原则上都随混合溶剂中EG浓度的增加而增大。升高温由迁移自由能△G决定,从水到乙二醇+水混合度的影响与添加乙二醇的效应一致。在EG水溶物的迁移自由能的大小取决于水、有机溶剂以及液中,胶团形成的驱动力是熵补偿效应。随着水有机溶剂的相互作用都是正值,是温度升高,混合溶液极性降低,疏水作用减弱,延因为EG的加入,导致疏水链溶解性增大,致使尾缓胶团形成。参考文献: [1 Binana-Limbele W, Zana R. 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