Dalstein Laetitia, Chiang Kuo-Yang, Wen Yu-Chieh
Institute of Physics, Academia Sinica, Taipei 11529, Taiwan, R. O. C.
J Phys Chem Lett. 2019 Sep 5;10(17):5200-5205. doi: 10.1021/acs.jpclett.9b02156. Epub 2019 Aug 23.
We developed and verified a phase-sensitive second harmonic generation spectroscopic scheme that allows for direct determination of the absolute surface charge density and surface potential of a water interface without the need for prior interfacial information. The method relies on selective probing of surface-field-induced reorientation order of water molecules in the electrical double layer and is, hence, independent of the interfacial molecular bonding structure. Application of this technique to a mixed surfactant monolayer on water suggests the manifest effect of the chain-chain interactions among the monolayer on adsorption of soluble ionic surfactants. We also deduce the third-order nonlinear susceptibility of bulk water and prove its applicability to analysis of charges of various water interfaces. In addition, we show that Debye-Hückle theory should be avoided in the spectroscopic analysis for its potential significant error, as evidenced experimentally and theoretically.
我们开发并验证了一种相敏二次谐波产生光谱方案，该方案无需先验界面信息即可直接测定水界面的绝对表面电荷密度和表面电势。该方法依赖于对双电层中水分子表面场诱导的重新取向顺序的选择性探测，因此与界面分子键合结构无关。将该技术应用于水表面的混合表面活性剂单层表明，单层中链-链相互作用对可溶性离子表面活性剂的吸附有明显影响。我们还推导了本体水的三阶非线性极化率，并证明了其在分析各种水界面电荷方面的适用性。此外，我们表明，在光谱分析中应避免使用德拜-休克尔理论，因为其实验和理论证明其可能存在重大误差。
