Liu Zhang, Fan Yaxun, Tian Maozhang, Wang Ruijuan, Han Yuchun, Wang Yilin
Key Laboratory of Colloid and Interface Science, Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, P.R. China.
Langmuir. 2014 Jul 15;30(27):7968-76. doi: 10.1021/la501656s. Epub 2014 Jun 27.
Cationic quaternary ammonium gemini surfactants C(n)H(2n+1)(CH3)2N(+)CH2CHCHCH2(CH3)2N(+)C(n)H(2n+1)2Br(-) (C(n)C4C(n), n = 12, 8, 6) with alkyl spacers, C(n)H(2n+1)(CH3)2N(+)CH2CHOHCHOHCH2(CH3)2N(+)C(n)H(2n+1)2Br(-) (C(n)C4(OH)2C(n), n = 12, 8, 6, 4) with two hydroxyl groups in alkyl spacers, and cationic ammonium single-chain surfactants C(n)H(2n+1)(CH3)2N(+)Br(-) (C(n)TAB, n = 12, 8, 6) have been chosen to fabricate oppositely charged surfactant mixtures with anionic sulfonate gemini surfactant C12H25N(CH2CH2CH2SO3(-))CH2CH2CH2(CH3)2N(CH2CH2CH2SO3(-))C12H252Na (C12C3C12(SO3)2). Surface tension, electrical conductivity, and isothermal titration microcalorimetry (ITC) were used to study their surface properties, aggregation behaviors, and intermolecular interactions. The mixtures of C12C3C12(SO3)2/C(n)C4(OH)2C(n) (n = 12, 8) and C12C3C12(SO3)2/C12C4C12 show anomalous larger critical micelle concentration (CMC) than C12C3C12(SO3)2, while the mixtures of C12C3C12(SO3)2/C(n)C4(OH)2C(n) (n = 6, 4), C12C3C12(SO3)2/C(n)C4(OH)2C(n) (n = 6, 4), and C12C3C12(SO3)2/C(n)TAB (n = 12, 8, 6) exhibit much lower CMC than C12C3C12(SO3)2. The results indicate that strong hydrophobic interactions between the alkyl chains assisted by strong electrostatic attractions between the headgroups and hydrogen bonds between the spacers lead to the formation of less surface active premicellar aggregates in bulk solution, resulting in the increase of CMC. If these interactions are weakened or inhibited, less surface active premicellar aggregates are no longer formed in the mixtures, and thus the CMC values are reduced. The work reveals that the combination of two surfactants with great self-assembling ability separately may have strong intermolecular binding interactions; however, their mixtures do not always generate superior synergism properties. Only moderate intermolecular interaction can generate the strongest synergism in CMC reduction.
已选用带有烷基间隔基的阳离子季铵盐双子表面活性剂C(n)H(2n + 1)(CH3)2N(+)CH2CHCHCH2(CH3)2N(+)C(n)H(2n + 1)2Br(-) (C(n)C4C(n), n = 12, 8, 6)、在烷基间隔基中带有两个羟基的C(n)H(2n + 1)(CH3)2N(+)CH2CHOHCHOHCH2(CH3)2N(+)C(n)H(2n + 1)2Br(-) (C(n)C4(OH)2C(n), n = 12, 8, 6, 4)以及阳离子铵单链表面活性剂C(n)H(2n + 1)(CH3)2N(+)Br(-) (C(n)TAB, n = 12, 8, 6)，来制备与阴离子磺酸盐双子表面活性剂C12H25N(CH2CH2CH2SO3(-))CH2CH2CH2(CH3)2N(CH2CH2CH2SO3(-))C12H252Na (C12C3C12(SO3)2)带相反电荷的表面活性剂混合物。使用表面张力、电导率和等温滴定量热法（ITC）来研究它们的表面性质、聚集行为和分子间相互作用。C12C3C12(SO3)2/C(n)C4(OH)2C(n)（n = 12, 8）和C1/C12C4C12的混合物显示出比C12C3C12(SO3)2异常更大的临界胶束浓度（CMC），而C12C3C12(SO3)2/C(n)C4(OH)2C(n)（n = 6, 4）、C12C3C12(SO3)2/C(n)C4(OH)2C(n)（n = 6, 4）以及C12C3C12(SO3)2/C(n)TAB（n = 12, 8, 6）的混合物表现出比C12C3C12(SO3)2低得多的CMC。结果表明，头基之间强烈的静电吸引以及间隔基之间的氢键辅助下烷基链之间的强疏水相互作用导致在本体溶液中形成表面活性较低的预胶束聚集体，从而导致CMC增加。如果这些相互作用被削弱或抑制，混合物中不再形成表面活性较低的预胶束聚集体，因此CMC值降低。这项工作表明，两种分别具有很强自组装能力的表面活性剂的组合可能具有很强的分子间结合相互作用；然而，它们的混合物并不总是产生优异的协同性能。只有适度的分子间相互作用才能在降低CMC方面产生最强的协同作用。
