Pulsed coaxial drop-on-demand electrohydrodynamic printing

This research demonstrates pulsed electrohydrodynamic drop-on-demand (DoD) printing as a novel technique for synthesizing core–shell microparticles in a controlled manner. In this regard, a multiphase and multiphysics model is presented for coaxial electrohydrodynamic printing. The governing partial differential equations of the model are discretized using the finite element method, and a suitable numerical scheme is adopted to solve the system of discretized equations. The experimental results in the literature are used to validate the numerical model. Utilizing the validated model, the effects of continuous-direct current (DC) voltage and pulsed-DC voltage are examined on the behavior of a compound meniscus (composed of ethylene glycol core and olive oil shell) and the droplet formation process. According to the results obtained, the onset voltage of the compound meniscus is 3330 V, which agrees with the scale analysis. Furthermore, increasing continuous-DC voltage results in longer breakup length, shorter breakup time, faster droplet velocity, and shorter jetting start time. In addition, increasing pulsed-DC voltage duration leads to an increase in the breakup length and droplet velocity. Most importantly, it is possible to control the inertia of the coaxial spindle by controlling the pulsed-DC voltage magnitude and duration to ensure that a core–shell droplet separates from the meniscus in every pulse with the shortest breakup length and the minimum satellite droplets possible. It is generally recommended to keep the pulse duration and amplitude low enough to prevent the long breakup length and irregularities in the printed pattern; however, they must be sufficiently large to sustain the micro-dripping mode.