Electrification at water\u2013hydrophobe interfaces

Jamilya Nauruzbayeva,Zhonghao Sun,Adair Gallo,J Carlos Santamarina,Himanshu Mishra,Mahmoud Ibrahim

doi:10.1038/s41467-020-19054-8

Jamilya Nauruzbayeva, Zhonghao Sun + Show 4 more

Open Access

https://doi.org/10.1038/s41467-020-19054-8

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Abstract

The mechanisms leading to the electrification of water when it comes in contact with hydrophobic surfaces remains a research frontier in chemical science. A clear understanding of these mechanisms could, for instance, aid the rational design of triboelectric generators and micro- and nano-fluidic devices. Here, we investigate the origins of the excess positive charges incurred on water droplets that are dispensed from capillaries made of polypropylene, perfluorodecyltrichlorosilane-coated glass, and polytetrafluoroethylene. Results demonstrate that the magnitude and sign of electrical charges vary depending on: the hydrophobicity/hydrophilicity of the capillary; the presence/absence of a water reservoir inside the capillary; the chemical and physical properties of aqueous solutions such as pH, ionic strength, dielectric constant and dissolved CO2 content; and environmental conditions such as relative humidity. Based on these results, we deduce that common hydrophobic materials possess surface-bound negative charge. Thus, when these surfaces are submerged in water, hydrated cations form an electrical double layer. Furthermore, we demonstrate that the primary role of hydrophobicity is to facilitate water-substrate separation without leaving a significant amount of liquid behind. These results advance the fundamental understanding of water-hydrophobe interfaces and should translate into superior materials and technologies for energy transduction, electrowetting, and separation processes, among others.

Highlights

The mechanisms leading to the electrification of water when it comes in contact with hydrophobic surfaces remains a research frontier in chemical science
Electrification underlies various curious phenomena, such as the electrostatic manipulation of droplets placed on hydrophobic surfaces[1,2,3] and Kelvin generators[4,5,6]
With the exception of surface-bound electrons, these mechanisms assume that common hydrophobic surfaces such as polypropylene and perfluorocarbons are electrically neutral in air

Summary

Introduction

The mechanisms leading to the electrification of water when it comes in contact with hydrophobic surfaces remains a research frontier in chemical science. Results demonstrate that the magnitude and sign of electrical charges vary depending on: the hydrophobicity/hydrophilicity of the capillary; the presence/absence of a water reservoir inside the capillary; the chemical and physical properties of aqueous solutions such as pH, ionic strength, dielectric constant and dissolved CO2 content; and environmental conditions such as relative humidity. Based on these results, we deduce that common hydrophobic materials possess surface-bound negative charge. Could other liquids besides water become electrified when brought into contact with hydrophobic surfaces? What is the role of hydrophobicity in the context of electrification at water-hydrophobe interfaces?

Methods

Conclusion