Salt-induced phase inversion in aqueous cationic/anionic surfactant two-phase systems.
Salt-induced phase inversion in aqueous cationic/anionic surfactant two-phase systems.
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DOI：
10.1021/jp805126j
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发表时间：
2008-09
期刊：
影响因子：
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通讯作者：
Yan-Qing Nan;Lisheng Hao
中科院分区：
文献类型：
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作者：
Yan-Qing Nan;Lisheng Hao
研究了1，3-丙二基双（十二烷基二甲基溴化铵）（简称12-3-12）与十二烷基磺酸钠（简称AS）在318.15 K下形成的含有过量阳离子表面活性剂（简称ATPS-C）的双水相体系的相转化。实验结果表明，NaF、NaCl、NaHCO 3、NaNO 3的加入可使12-3-12/AS体系形成的ATPS-C发生相反转，而NaBr的加入则不能使ATPS-C发生相反转。透射电镜实验表明，ATPS-C中浓相的微观结构与相转化没有直接关系。为了解释ATPS-C的相转化现象，研究了ATPS-C中的相组成、相密度和稀相与浓相之间的相体积比。相组成分析结果表明，对于由0. 10 mol.kg（-1）12-3-12/AS混合体系形成的ATPS-C，加入NaF、NaCl、NaHCO 3或NaNO 3后，ATPS-C稀相中Br（-）抗衡离子浓度增加。与此同时，ATPS-C浓相中F（-）（Cl（-），HCO 3（-），NO3（-））反离子与Br（-）反离子的摩尔比也增大。它说明了当向体系中加入额外的盐时，过量的表面活性剂12-3-12的天然抗衡离子溴抗衡离子的一部分被其他阴离子抗衡离子交换。研究表明，加入的F（-）、Cl（-）、HCO 3（-）和NO3（-）反离子的共同点是它们对ATPS C中混合正电荷聚集体的反离子结合能力比Br（-）反离子弱或强，但它们对密度的贡献都小于Br（-）反离子。密度实验表明，加入NaF、NaCl、NaHCO 3或NaNO 3后，ATPS-C中稀相的密度增加大于浓相的密度增加，从而发生相转化。加入的无机钠盐水溶液的密度和加入的无机阴离子相对于12-3-12离液头基的Hofmeister级数在ATPS-C的相转化中起重要作用。
Phase inversion of aqueous two-phase systems with excess cationic surfactant (abbreviated as ATPS-C) formed by aqueous mixtures of 1,3-propanediyl bis(dodecyl dimethylammonium bromide) (abbreviated as 12-3-12) and sodium dodecyl sulfonate (abbreviated as AS) at 318.15 K was investigated. The experimental results indicate that addition of NaF, NaCl, NaHCO 3, or NaNO 3 can result in phase inversion of ATPS-C formed by 12-3-12/AS systems; however, addition of NaBr cannot lead to phase inversion. TEM micrographic experiments illustrate that there is no direct relationship between the microstructures of the concentrated phase in ATPS-C and phase inversion. To interpret the phase-inversion phenomena of ATPS-C, the phase composition, phase density, and phase volume ratio between the dilute phase and the concentrated phase in ATPS-C were investigated. Phase composition analysis results illustrate that for the ATPS-C formed by 0.10 mol.kg (-1) 12-3-12/AS mixed system, the concentration of Br (-) counterions in the dilute phase of ATPS-C increases with addition of NaF, NaCl, NaHCO 3, or NaNO 3. At the same time, the molar ratio between the F (-) (Cl (-), HCO 3 (-), or NO 3 (-)) counterions and Br (-) counterions in the concentrated phase of ATPS-C increases also. It illustrates that part of the bromide counterions which are the natural counterions of the surfactant 12-3-12 in excess are exchanged by other anionic counterions when an additional salt is added to the system. The investigation indicates that the common ground of the added F (-), Cl (-), HCO 3 (-), or NO 3 (-) counterions is that they all make a smaller density contribution than that of Br (-) counterions, although they have a weaker or stronger counterion binding ability with the mixed positively charged aggregates in ATPS-C than that of Br (-) counterion. Density experiments illustrate that the density increase of the dilute phase is larger than that of the concentrated phase in the ATPS-C with addition of NaF, NaCl, NaHCO 3, or NaNO 3; thus, phase inversion occurs. The densities of the added inorganic sodium salt aqueous solution and the order of the Hofmeister series for the added inorganic anions with respect to the chaotropic headgroup of 12-3-12 play important roles in the phase inversion of ATPS-C.