Characterization of electrohydrodynamic drop-on-demand injection of viscoelastic fluids in pulsed voltage

Abstract

Electrohydrodynamic drop-on-demand (DOD) injection in pulsed voltage is a very promising technique for fabricating nanostructures. However, it is still a challenge to achieve stable, high-precision, high-frequency DOD injection due to the lack of clarity on the mechanism of viscoelastic fluid injection. In this paper, a dimensionless parameter study based on the volume of fluid (VOF) method is used to systematically study the kinetic behavior of viscoelastic fluids in pulsed voltages. Four independent dimensionless parameters of voltage duration τ* pulse, electric Bond number BoE, electric Reynolds number ReE, and the ratio of charge relaxation time to fluid relaxation time δ are proposed to determine the operational phase diagrams in the dimensionless plane for the no jet mode, cone-jet mode, dripping mode, and reaching the substrate mode. The result shows that the voltage duration is negatively correlated with both the electric Bond number and the electric Reynolds number at the critical injection. The critical injection condition occurs over a wide range of voltage durations when the electric Reynolds number is <10. Cone-jet occurs in the region of δ < 1, with a jet frequency exceeding 2 kHz at its highest and the droplet diameter reaches 1/12 of the initial droplet diameter. Furthermore, the ability to print micron-scale patterns with precision in cone-jet mode fully demonstrates the promise of viscoelastic fluids in pulsed voltage for applications in micro/nano fabrication.