Controllable droplet generation at a microfluidic T-junction using AC electric field

Abstract

We investigated the influence of an alternate current (AC) electric field on droplet generation in a T-junction device. We used sodium chloride solution with various conductivities to adjust the response time of the fluidic system. At constant flow rates of both continuous and dispersed phases, the critical parameters for the droplet formation process are the magnitude, the frequency of the applied voltage and the conductivity of the dispersed phase. The response of the droplet formation process to AC excitation is characterised by the relative area of the formed droplet. The relative response time of the fluidic system to the applied AC voltage is characterised by the relative response time that is proportional to the ratio of the AC frequency to the conductivity of the dispersed phase. An accurate prediction of the breakdown voltage for the walls also proved robustness of our model. Furthermore, experiments were repeated with 0.5 g/L and 1 g/L xanthan gum solutions as non-Newtonian fluids. The results reveal the negligible influence of viscoelasticity on the droplet formation process. On-demand size controllable generation of non-Newtonian droplets is subsequently demonstrated following the same trend of the Newtonian counterparts.