Liquid–gas surface tension voltage dependence during electrowetting on dielectric testing of water and 5–90 nm gold nanofluids

Abstract

This article investigates the effective liquid–gas surface tension changes of water and 5–90nm gold nanofluids measured during electrowetting on dielectric experiments. The Young–Laplace equation for sessile droplets in air was solved to fit the experimental droplet shape and determine the effective liquid–gas surface tension at each applied voltage. A good agreement between experimental droplet shapes and the predictions was observed for all the liquids investigated in applied range of 0–30V. The measured liquid–gas effective surface tensions of water and gold nanofluid decreased with voltage. At a given voltage, the effective liquid–gas surface tension of gold nanofluids initially decreased as the size of gold nanoparticles increased from 5nm to 50nm. Then, for 70nm and 90nm particle gold nanofluids, the effective liquid–gas surface tension started increasing too. The size of nanoparticles, and the applied voltage have a significant effect on variation of the effective liquid–gas surface tension with variations as much as 93% induced by voltage at a given particle size and 80% induced by particle size at a given voltage.