Dynamics of inkjet printing of shear thinning liquids

In this work, we investigate the drop formation dynamics of shear thinning liquids from a drop-on-demand piezoelectric inkjet printhead numerically using the volume-of-fluid (VOF) method. The influence of key liquid properties such as zero- and infinite shear-viscosity, power-law index, and surface tension on filament ejection and pinch-off, filament contraction, and drop formation are systematically explored. In the parameter range studied, we find that the early stages of ejection are unaffected by the liquid properties, and only surface tension critically governs the pinch-off length and pinch-off time during the late stages of ejection. The filament growth rate during ejection and its contraction post-pinch-off for shear thinning liquids match that of Newtonian fluids with viscosity equal to the infinite-shear viscosity, provided the power-law index remains below a threshold.