Electric Field and Humidity Trigger Contact Electrification

TL;DR

This paper investigates how electric fields and humidity influence contact electrification of insulators, revealing that water adsorption and ion separation under electric fields cause charge transfer, explaining phenomena like sand discharges near thunderstorms.

Contribution

It introduces a new mechanism where electric fields and humidity induce charge transfer between identical insulators via water-mediated ion separation.

Findings

Charge transfer occurs under electric fields in humid conditions.

Water adsorption on insulators facilitates ion separation and charge transfer.

Explains natural phenomena like sand discharges during thunderstorms.

Abstract

Here, we study the old problem of why identical insulators can charge one another on contact. We perform several experiments showing that, if driven by a preexisting electric field, charge is transferred between contacting insulators. This happens because the insulator surfaces adsorb small amounts of water from a humid atmosphere. We believe the electric field then separates positively from negatively charged ions prevailing within the water, which we believe to be hydronium and hydroxide ions, such that at the point of contact, positive ions of one insulator neutralize negative ions of the other one, charging both of them. This mechanism can explain for the first time the observation made four decades ago that wind-blown sand discharges in sparks if and only if a thunderstorm is nearby.