Generation of neutral droplets via waveform optimization for stable electrohydrodynamic drop-on-demand printing

Electrohydrodynamic (EHD) drop-on-demand (DOD) printing is a highly promising additive manufacturing technology, particularly for micro- and nanoscale applications, owing to its exceptional printing resolution. However, a significant challenge for EHD DOD to achieve stable printing is the accumulation of residual charge, particularly on highly insulated substrates where the charge cannot be discharged. A novel voltage-driven waveform is proposed to generate neutral droplets in EHD DOD printing, aiming to completely solve the problem of residual charge accumulation. The proposed voltage-driven waveform consists of two waveforms with opposite polarity and equal amplitude. The waveforms of opposite polarity generate two droplets with opposite charges. Overlapping these two droplets causes the charges to be neutralized, therefore generating neutral droplets. The correctness of the proposed method is verified through simulations and experiments, and the printing parameters were optimized accordingly. Notably, silver nanowires with a line width of 5.3 μm were successfully printed on insulating substrates using this technique, and large-area on-demand patterns were stably printed. This outcome underscores the capability of the proposed high-voltage driving waveform to generate charge-neutral droplets, thereby significantly enhancing the stability of EHD DOD printing and facilitating its implementation in high-resolution manufacturing processes.