Effect of viscosity, electrical conductivity, and surface tension on direct-current-pulsed drop-on-demand electrohydrodynamic printing frequency

Experiments were conducted to measure the performance of direct-current-pulsed electrohydrodynamic drop formation as a function of liquid viscosity, electrical conductivity, and surface tension. While hydrodynamic and charge relaxation times and Taylor cone formation frequencies suggest theoretical drop-generation frequencies well in excess of 100 Hz, we show that it is impossible to produce more than 50 drops per second with performance decreasing as viscosity increased or electrical conductivity decreased (and not a significant function of surface tension). Instead of relying on relaxation-time calculations to predict the maximum, reliable drop-production frequency, a dimensionless coefficient that is a function of viscosity and electrical conductivity is proposed to estimate the fulcrum frequency.