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Generation and Control of Electrohydrodynamic Flows in Aqueous Electrolyte Solutions

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Published on: September 7, 2018

Disparate External Electric Field Effect on the Adsorption and Shear Behavior of Monovalent and Trivalent Ions in

Ruiqi Zhao¹, Tianyi Han¹, Chenhui Zhang¹

¹State Key Laboratory of Tribology in Advanced Equipment, Tsinghua University, Beijing 100084, China.

|June 24, 2024

Abstract:

Reducing friction is of great interest, and an external potential applied to the friction pair can regulate lubricity. Electrochemical atomic force microscopy (EC-AFM) is used to study the tribological and adsorption behavior of monovalent and trivalent ionic solutions between charged surfaces. An opposite trend of coefficient of friction (COF) and normal force that varies with the applied electric potential is witnessed. Direct force measurements and theoretical models have disclosed that, for the NaCl solution, the negative electric field reduces the COF by increasing cation adsorption. As for LaCl₃ solution, the positive electric field promotes the primary adsorption of anions on HOPG, resulting in the disappearance of the attractive ion-ion correlation between the trivalent ions, thereby reducing the COF. The shear behavior of adsorbed ions in electrolyte solution is sensitive to their valence, because of their different surface force contribution. The study further provides a framework to optimize the design of hydration lubrication.

Keywords:

electrical field hydration lubrication ion adsorption ion valency stern layer

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