Drop-on-demand (DOD) inkjet dynamics of printing viscoelastic conductive ink

Abstract

Emerging applications of drop-on-demand (DOD) inkjet printing, such as printed electronics and bioprinting, are leading to an ever-increasing development of diverse functional inks with complex chemical and rheological properties, especially viscoelastic polymers. Forming droplets with desirable velocity and volume as well as excellent reliability is of great importance for successful printing. In this study, the dynamics and performance of droplet formation during DOD inkjet printing of viscoelastic ink were investigated by employing the piezoelectric inkjet technology to print a conductive polymer ink under various excitation waveform parameters. Four distinct droplet formation regimes were identified, namely, no droplet formation, a single droplet, one satellite droplet, and multiple satellite droplets. A process dynamics-related dimensionless number (Wj) was proposed to construct an operating phase diagram on droplet formation and quantify the transition of droplet formation regimes. The effects of bipolar waveform parameters on droplet formation were systematically examined in terms of Wj, droplet velocity, and droplet diameter. Moreover, the printing of conductive microlines and micropatterns was precisely controlled under well-formed droplets. This study could support fully understanding the droplet formation dynamics during DOD inkjet printing of viscoelastic inks to guide generating desirable droplets of functional ink and improve the performance and function of inkjet-printed devices.