Model description of contact angles in electrowetting on dielectric layers

The electrowetting on dielectric (EWOD) technique has considerable potential for microfluidic and biomedical applications. The Lippmann-Young model based on the force balance concept has long been used to predict the contact angles of droplets under electrowetting. However, recent experimental evidence has indicated that this model fails to provide accurate predictions of the lower contact angles associated with saturation conditions at higher electric potentials. Hence, the study simulates the internal flow in an actuated droplet and treats it as stagnation-point flow. This kinetic energy is then taken into consideration while calculating the contact angles using an energy balance model. The energy of an actuated droplet is contributed by the combination of the side surface tension energy, the base tension energy, the dielectric energy, and the kinetic energy when deriving the energy balance model. Consequently, the new energy balance model modifies the Lippmann-Young equation, thereby providing enhanced reasonable predictions of the droplet contact angle across the higher electric potential where the contact angles are close to the saturated condition. © 2006 American Chemical Society.