Electrowetting of a nano-suspension on a soft solid

TL;DR

This paper investigates how adding nanoparticles to a droplet can restore electro-spreading on soft surfaces by altering the interfacial dielectric properties, with a theoretical model explaining the observed phenomena.

Contribution

It introduces a novel mechanism where nano-particles enhance electro-spreading on soft solids by changing the dielectric constant, supported by experimental and theoretical analysis.

Findings

Nanoparticles recover electro-spreading on soft surfaces.

The mechanism is limited by particle volume fraction due to contact line pinning.

A theoretical model explains the experimental results.

Abstract

The wetting of solid surfaces can be manoeuvred by altering the energy balance at the interfacial region. While electric field acts favourably to spread a droplet on a rigid surface, this tendency may be significantly suppressed over soft surfaces, considering a part of the interfacial energy being utilized to deform the solid elastically by capillary forces. Here, we bring out a unique mechanism by virtue of which addition of nano-particles to the droplet brings in a favourable recovery of the electro-spreading characteristics of a soft surface, by realizing an alteration in the effective dielectric constant of the interfacial region. Our experiments further demonstrate that this mechanism ceases to be operative beyond a threshold volume fraction of the particle suspension, due to inevitable contact line pinning. We also develop a theory to explain our experimental observations. Our findings provide a non-contact mechanism for meniscus spreading and droplet control, bearing far-reaching implications in biology and engineering.