Direct measurement of the viscoelectric effect in water

Abstract

Significance The viscosity of polar liquids increases in an electric field because of its interaction with the dipolar molecules. This viscoelectric effect was measured for organic liquids, but for water, the most important polar liquid, where it is crucial in areas from surface potential determination to nanofluidic applications, this is very challenging, and no direct measurements have been carried out to date. Consequently, estimates of its magnitude in water vary by more than a thousandfold. Here, we use a surface force balance to measure the dynamic approach of two molecularly smooth surfaces with a uniform, controlled electric field between them across water; this is modulated by the water viscosity and hence the viscoelectric effect, enabling its magnitude to be directly determined.