Electrowetting is a means of driving microfluidic motion by modifying the surface tension [133]. Here, we determine the effect of an electrostatic potential difference Δφ  applied between the solid and liquid phases on the surface tension. Since the liquid is now electrically charged a double layer forms at the interface between the solid and the liquid phases. The capacitance per unit area c of this double layer is supposed to be known. Determine the electrically charged surface tension ¯γ_sℓin terms of the neutral surface tension γ_sℓ.