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 (R) 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 degrees and less than 1 mN/m, respectively. (C) 2014 AIP Publishing LLC.