Electrowetting on dielectric-actuation of microdroplets of aqueous bismuth telluride nanoparticle suspensions

This work reports the actuation of droplets of nanofluid by the electrowetting on dielectric (EWOD) effect. The nanofluid is comprised of an aqueous (deionized water) suspension of 3 nm diameter bismuth telluride nanoparticles capped with thioglycolic acid (TGA). Microdroplets of nanofluid are cast on Si(001) wafers coated with 100 nm thick layers of silicon dioxide and AF Teflon. Applying an electric field between the substrate and an electrode immersed in the nanofluid droplet results in a strong change in the contact angle from 110 degrees to 84 degrees for a 0-60 V voltage range. The droplets of nanofluid exhibit enhanced stability and absence of contact angle saturation in the tested voltage range when compared with droplets of aqueous solutions of 0.01 M Na2SO4 or thioglycolic acid in deionized water. We propose that ion generation due to capping-agent desorption is a key factor determining the EWOD effect in the bismuth telluride nanofluid along with the nanoparticle contribution to charge transport. Our results open up new vistas for using nanofluids for microscale actuator device applications.