Abstract
We present results of electrowetting experiments employing droplets formed from aqueous suspensions of Au nanoparticles. A planar electrowetting system, consisting of a Pt wire electrode and a bottom Cu electrode with an insulating silicone layer, is used to observe changes in droplet contact angle when an external electric field is applied. The equilibrium contact angle at 0 V decreases with increasing nanoparticle concentration, dropping from 100.4° 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 15 V, contact angle decreases by 9% and 35% for droplets formed from pure water and a 0.5 μM 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 10 V 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.
Highlights
Numerous applications involving the actuation of fluids at miniaturized scales are enabled by the variable wettability of contact surfaces
We report the use of a planar electrowetting on dielectric (EWOD) set-up to actuate nanofluid droplets
Spreading of the droplet is attributed to a normal force, acting on the fluid surface near the edge, generated by an electric field due to excess charges distributed on the liquid surface [2]
Summary
Numerous applications involving the actuation of fluids at miniaturized scales are enabled by the variable wettability of contact surfaces. In electrowetting (EW), an established method for fluid manipulation, an applied electric field affects surface tension and modifies how a liquid spreads over a substrate [1,2,3,4]. With EW methods, wettability of a surface is modified without changing the chemical composition of the liquid or substrate. The basic design of a liquid droplet in contact with an appropriate substrate avoids issues involving microfabrication, with electrowetting on dielectric (EWOD) droplet systems performing as deformable optical elements that are cost-effective and disposable [11,12,13]. EWOD is currently the most common actuation method in digital microfluidic architectures [14]. We report the use of a planar EWOD set-up to actuate nanofluid droplets
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
