Pre-charging polymer surfaces enhances droplet mobility and electrification

TL;DR

This study shows that pre-charging polymer surfaces can control droplet behavior and electrification, enabling manipulation of fluid motion through surface charge adjustments.

Contribution

It introduces a systematic method to control surface charge on polymers, revealing how pre-deposited ions influence droplet mobility and electrification effects.

Findings

Deposited surface charge correlates with transferred charge during wetting.

Surface charge affects contact angle and contact-line mobility.

High surface charge densities cause droplet instabilities.

Abstract

Surface-bound electric charge on polymer materials can strongly influence droplet behaviour and solid-liquid charge transfer, but the mechanisms and the means to control these effects remain unclear. In this work, we systematically controlled the surface charge on polymer surfaces, including polytetrafluoroethylene (PTFE) and Nylon-66, by first neutralising the surfaces with an anti-static ion blower and then applying charge using an ion gun. We find that droplets pick up pre-deposited surface ions during the first wetting of the surface, and that the transferred charge directly correlates with the deposited charge encountered by the wetted area for moderate deposited densities (|{\sigma}_d |<40 {\mu}C/m2) independent of material properties. We also demonstrate that the deposited charge reduces contact angle and increases contact-line mobility in a manner consistent with an increase in effective solid surface energy. For higher surface charge densities, we observe instabilities such as droplet splitting or detachment. This work demonstrates an effective approach to control solid-liquid electrification, enabling amplification or suppression of surface charge and the directed manipulation of fluid motion on surfaces.