X-ray reflectivity and interfacial tension study of the structure and phase behavior of the interface between water and mixed surfactant solutions of CH3(CH2)19OH and CF3(CF2)7(CH2)2OH in hexane.
X-ray reflectivity and interfacial tension study of the structure and phase behavior of the interface between water and mixed surfactant solutions of CH3(CH2)19OH and CF3(CF2)7(CH2)2OH in hexane.
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X射线反射率和界面张力研究了水与CH3(CH2)19OH和CF3(CF2)7(CH2)2OH在己烷中的混合表面活性剂溶液之间界面的结构和相行为。
DOI：
10.1021/jp045887q
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
M. Schlossman
中科院分区：
文献类型：
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作者：
S. Pingali;T. Takiue;G. Luo;A. Tikhonov;N. Ikeda;M. Aratono;M. Schlossman
通过界面张力和X射线反射率测量研究了水与CH(3)(CH(2))(19)OH和CF(3)(CF(2))(7)(CH(2))(2)OH在己烷中的混合表面活性剂溶液之间的界面。对于一定范围的总本体表面活性剂浓度以及氟化物与总表面活性剂浓度的摩尔比的三个不同值（0.25、0.28和0.5），测量作为温度函数的张力，确定界面可以处于三种不同的单层相。对这些相测定的界面过量熵表明其中两个相是 CH(3)(CH(2))(19)OH 和 CF(3)(CF(2))(7)(CH(2))(2)OH 的缩合单表面活性剂单层。通过研究四种不同成分随温度的变化，X射线反射率被用来确定液-液界面所有三相中这些单分子层的结构。使用层模型分析 X 射线反射率测量结果，以确定头基层和尾基层的电子密度和厚度。反射率表明相 1 和相 2 对应于仅被一种表面活性剂完全覆盖的界面（相 1 中的 CH(3)(CH(2))(19)OH 液体单层和相 2 中的 CF(3)(CF(2))(7)(CH(2))(2)OH 固体稠合单层）。这是通过分析电子密度分布以及直接比较仅含有一种表面活性剂（加上己烷和水）的系统中液-液界面的反射率研究来确定的。随着温度的升高，CH(3)(CH(2))(19)OH的液体单层转变为CF(3)(CF(2))(7)(CH(2))(2)OH的固体单层。第 3 相以及第 1 相和第 2 相之间的过渡区域由界面处的混合单层组成，其中包含两种表面活性剂的区域。在第 3 阶段，界面还包含气体区域，随着温度升高，气体区域逐渐占据界面的更多区域。反射率决定了界面处表面活性剂域的覆盖范围。提出了一个简单的模型，该模型根据单一表面活性剂系统的行为预测混合表面活性剂系统的域覆盖率随温度变化的基本特征。
The interface between water and mixed surfactant solutions of CH(3)(CH(2))(19)OH and CF(3)(CF(2))(7)(CH(2))(2)OH in hexane was studied with interfacial tension and X-ray reflectivity measurements. Measurements of the tension as a function of temperature for a range of total bulk surfactant concentrations and for three different values of the molal ratio of fluorinated to total surfactant concentration (0.25, 0.28, and 0.5) determined that the interface can be in three different monolayer phases. The interfacial excess entropy determined for these phases suggests that two of the phases are condensed single surfactant monolayers of CH(3)(CH(2))(19)OH and CF(3)(CF(2))(7)(CH(2))(2)OH. By studying four different compositions as a function of temperature, X-ray reflectivity was used to determine the structure of these monolayers in all three phases at the liquid-liquid interface. The X-ray reflectivity measurements were analyzed with a layer model to determine the electron density and thickness of the headgroup and tailgroup layers. The reflectivity demonstrates that phases 1 and 2 correspond to an interface fully covered by only one of the surfactants (liquid monolayer of CH(3)(CH(2))(19)OH in phase 1 and a solid condensed monolayer of CF(3)(CF(2))(7)(CH(2))(2)OH in phase 2). This was determined by analysis of the electron density profile as well as by direct comparison to reflectivity studies of the liquid-liquid interface in systems containing only one of the surfactants (plus hexane and water). The liquid monolayer of CH(3)(CH(2))(19)OH undergoes a transition to the solid monolayer of CF(3)(CF(2))(7)(CH(2))(2)OH with increasing temperature. Phase 3 and the transition regions between phases 1 and 2 consist of a mixed monolayer at the interface that contains domains of the two surfactants. In phase 3 the interface also contains gaseous regions that occupy progressively more of the interface as the temperature is increased. The reflectivity determined the coverage of the surfactant domains at the interface. A simple model is presented that predicts the basic features of the domain coverage as a function of temperature for the mixed surfactant system from the behavior of the single surfactant systems.