Electrostatic interactions and aqueous two-phase separation modes of aqueous mixed oppositely charged surfactants system.
Electrostatic interactions and aqueous two-phase separation modes of aqueous mixed oppositely charged surfactants system.
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DOI：
10.1021/jp303682d
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发表时间：
2012-08
期刊：
影响因子：
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通讯作者：
Lisheng Hao;Y. Gui;Yan-mei Chen;Shaoqing He;Yan-Qing Nan;Yi-lan You
中科院分区：
文献类型：
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作者：
Lisheng Hao;Y. Gui;Yan-mei Chen;Shaoqing He;Yan-Qing Nan;Yi-lan You
静电相互作用在确定带相反电荷的表面活性剂混合物的水两相分离行为中起着重要作用。十六烷基三甲基溴化铵（CTAB）和十二烷基磺酸钠（AS）的混合水溶液实际上是一个五组分体系，由CTAB、AS、复盐（十六烷基三甲基十二烷基磺酸铵，简称CTA（+）AS（-））、NaBr和水组成。在三维金字塔相图中，过量AS或过量CTAB的双水相区从非常靠近NaBr-H_2 O线的区域依次通过CTAB-AS-H_2 O常规混合平面延伸到CTA（+）AS（-）-AS-H_2 O侧平面或CTA（+）AS（-）-CTAB-H_2 O侧平面。位于金字塔的NaBr侧或CTA（+）AS（-）侧的带相反电荷的表面活性剂的抗衡离子与其相应的表面活性剂离子之间的大或小的摩尔比意味着强或弱的静电屏蔽。反离子的静电屏蔽改变了带相反电荷的头部基团之间的静电吸引力或过量的带相同电荷的头部基团之间的静电排斥力，并且聚集的静电自由能因此影响水两相分离模式。组成分析、流变性能研究和透射电镜图像表明，存在两种类型的双水相体系（ATPS）。在此基础上，根据Kaler的细胞模型，提出了两种不同的相分离模式。实验结果还表明，ATPS的顶相均为富表面活性剂相，底相均为贫表面活性剂相; ATPS的顶相和底相的密度差很小; ATPS的界面张力（σ）超低。
Electrostatic interactions play an important role in setting the aqueous two-phase separation behaviors of mixtures of oppositely charged surfactants. The aqueous mixture of cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfonate (AS) is actually a five-component system, comprised of CTAB, AS, complex salt (cetyltrimethylammonium dodecylsulfonate, abbreviated as CTA(+)AS(-)), NaBr, and water. In the three-dimensional pyramid phase diagram, the aqueous two-phase region with excess AS or with excess CTAB extends successively from the region very near to the NaBr-H2O line through the CTAB-AS-H2O conventional mixing plane to the CTA(+)AS(-)-AS-H2O side plane or to the CTA(+)AS(-)-CTAB-H2O side plane, respectively. Large or small molar ratios between the counterions and their corresponding surfactant ions for oppositely charged surfactants located in the NaBr side or the CTA(+)AS(-) side of the pyramid imply strong or weak electrostatic screening. Electrostatic screening of counterions alters the electrostatic attractions between the oppositely charged head groups or the electrostatic repulsions between the like-charged head groups in excess, and the electrostatic free energy of aggregation thus affects the aqueous two-phase separation modes. Composition analysis, rheological property investigation, and TEM images suggest that there are two kinds of aqueous two-phase systems (ATPSs). On the basis of these experimental results and Kaler's cell model, two kinds of phase separation modes were proposed. Experimental results also indicate that all of the top phases are surfactant-rich, and all of the bottom phases are surfactant-poor; the density difference between the top phase and the bottom phase in one ATPS is very small; the interfacial tension (σ) of the ATPS is ultralow.