Abstract

When neutral water drops impact and rebound from superhydrophobic surfaces, they acquire a positive electrical charge. To measure the charge, we analyzed the trajectory of rebounding drops in an external electric field by high-speed video imaging. Although this charging phenomenon has been observed in the past, little is known about the controlling parameters for the amount of drop charging. Here we investigate the relative importance of five of these potential variables: impact speed, drop contact area, contact line retraction speed, drop size, and type of surface. We additionally apply our previously reported model for sliding drop electrification to the case of impacting drops, suggesting that the two cases contain the same charge separation mechanism at the contact line. Both our experimental results and our theoretical model indicate that maximum contact area is the dominant control parameter for charge separation.

Highlights

  • Drop impact has been extensively studied for more than 100 years, including collision of drops with other liquids and different solid surfaces [1,2]

  • We will analyze the experimental results of drops that rebound and are deflected by a horizontal electric field

  • When an electric field was applied, rebounding drops followed a trajectory including lateral movement (x-direction) in the direction of the electric field (Figs. 2c, 2d). This indicates that drops acquired a positive charge when rebounding from the surface

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Summary

Introduction

Drop impact has been extensively studied for more than 100 years, including collision of drops with other liquids and different solid surfaces [1,2]. This phenomenon is present in nature [3,4] and is important for a variety of industrial applications [5,6,7]. Water drops that condense and coalesce on a superhydrophobic surface jump-off with a positive charge 31 Applications using such charging include designing surface charge gradients to transport drops on superamphiphobic surfaces 20

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