Abstract:
We present results of electrowetting experiments employing droplets formed from aqueous suspensions of gold nanoparticles. A planar electrowetting system, consisting of a platinum wire electrode and a bottom copper electrode with an insulating silicone (polydimethylsiloxane) layer, is used to observe changes in droplet contact angle when an external electric field is applied. The equilibrium contact angle at 0V decreases with increasing nanoparticle concentration, dropping from100.4∘ for pure deionized water to 94.7∘ for a 0.5 μM nanofluid.
Increasing the nanoparticle content also lowers the required voltage for effective actuation. With actuation at 15V, contact angle decreases by 9% and 35% for droplets formed from pure water and a
0.5μM nanoparticle suspension, respectively. Contact angle saturation is observed with nanofluid droplets, with the threshold voltage decreasing as nanoparticle concentration rises. Maximum droplet actuation before contact angle saturation is achieved at only 10V for a concentration of 0.5 μM. A proposed mechanism for the enhanced electrowetting response of a nanofluid droplet involves a reduction in surface tension of the droplet as nanoparticles accumulate at the liquid-vapor interface.
