Electrowetting-based measurement of interfacial tension

We report all-electrical monitoring of interfacial tension, enabled by the electrowetting on dielectric (EWOD) technique. The contact angle of a sessile oil droplet in water was obtained via an in-situ capacitive measurement of the EWOD area on a single chip. Contact angle data measured at different operating voltage values were used to calculate the interfacial tension using the Young-Lippmann equation. The results were in good agreement with the results of an image-based analysis, which was performed by using an electrolyte liquid (Na2SO4)/oil (n-decane) system with a surfactant (Tween® 80) to alter the interfacial tension. The maximum deviation of the contact angle and interfacial tension values determined using EWOD from the values determined using the image analysis were 2.8° and less than 1 mN/m, respectively.