Inkophobic particles trigger nozzle failure: bubble nucleation, dynamics, and diffusive growth visualized in a MEMS-based piezo-acoustic printhead

The stability of piezo drop-on-demand inkjet printing is compromised through the stochastic entrainment of bubbles inside the ink channel. Here, bubble nucleation, translation, and growth in a micro-electro-mechanical printhead was studied using high-speed imaging triggered by changes in ink channel acoustics. It was found that inkophobic dirt particles trigger bubble nucleation upon their interaction with the oscillating meniscus. The jet length increase after bubble nucleation was shown to be a result of the bubble-induced decrease of the channel resonance frequency. Channel pressure profiles were measured from a fit of the measured radial bubble dynamics to the Rayleigh-Plesset equation. The acoustically driven bubble translates towards the ink channel wall due to acoustic radiation forces and convective ink flow. The ink velocity field was characterized using particle-tracking-velocimetry. The vortex flow above the oscillating meniscus was shown to trap dirt particles thereby increasing the particle-meniscus interaction probability.