Electrowetting of weak polyelectrolyte solutions

Electrowetting occurs when an electric field is applied to a fluid interface, changing its equilibrium position. To date, most electrowetting studies used aqueous electrolyte solutions as the electrowetting liquid. The present work studies the phenomena of electrowetting on a hydrophobic dielectric solid (EWOD) of a semi-dilute anionic poly(acrylic acid) (PAA) aqueous solution. Changing the polyelectrolyte ionization degree by adjusting the solution pH provides insight into the wetting behavior. Droplets with strongly ionized PAA led to a greater increase in the wetting than the weakly charged PAA. Furthermore, contact angle hysteresis was higher for the droplet of completely ionized polyelectrolyte. The results demonstrate how charge-connectivity and polyelectrolyte architecture under an external electrical field can augment electrowetting gain and contact angle hysteresis. The present findings might help order and manipulate many biological polyelectrolytes, such as polypeptides, glycosaminoglycans, and DNA.