Electrohydrodynamic droplet formation in a T-junction microfluidic device

An experimental investigation of droplet formation induced by an external electric field in a T-shaped microfluidic device is presented. The effect of electric field is reported for scenarios where the hydrodynamics is known to be governed by the cumulative effect of hydrodynamic pressure and interfacial tension acting on the liquid–liquid interface. Experiments reveal that the electrohydrodynamic phenomena transforms the droplet formation mechanism by inducing pinning of the dispersed phase to the channel wall, leading to a significant decrease in the droplet filling time and hence a decrease in the size of droplets generated. The experimental observations are used to formulate a correlation between the droplet size, applied electric field, fluid properties and flow parameters. A mechanistic explanation of droplet formation process using a mathematical model is also presented. Simulations reveal that the droplets are formed primarily due to normal electric stress acting on the liquid–liquid interface. The electric stress results in a distinct feature of pinning and early onset of neck formation of the emerging dispersed phase, leading to a reduction in the size of the droplet formed for the same hydrodynamic conditions. The findings reported demonstrate that an applied electric field has the potential to produce relatively smaller-sized droplets than that possible through hydrodynamics alone.