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arXiv · 1906.10942

Direct Quantification of Water Surface Charge by Phase-Sensitive Second Harmonic Spectroscopy

Laetitia Dalstein·Kuo-Yang Chiang·Yu-Chieh Wen
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Abstract

We develop and verify 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 need of 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 the Debye-H\"uckle theory should be avoided in the spectroscopic analysis for its potential significant error, as evidenced experimentally and theoretically.

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Laetitia Dalstein, Kuo-Yang Chiang, Yu-Chieh Wen. 2019-06-26. Direct Quantification of Water Surface Charge by Phase-Sensitive Second Harmonic Spectroscopy. https://doi.org/10.1021/acs.jpclett.9b02156

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