Electrowetting interfacial tension measurement system

It is reported that electrical monitoring of interfacial tension by the electrowetting on dielectric (EWOD). The contact angle of a sessile oil droplet in conducting liquid was calculated with an capacitance measurement on a single chip. Contact angle can be measured at different operational voltage and it is used to calculate the interfacial tension by the Young-Lippmann equation. The results were in agreement with an optical analysis. It was performed by a conducting liquid (Na₂SO₄) / oil (n-decane) system with a non-ionic surfactant (Tween 80) to change the interfacial tension. The deviation of the contact angle and interfacial tension from the values determined by the optical analysis were 2.8° and less than 1 mN/m, respectively.