The pinch-off regimes of confined interface vibration inkjet printing

This study combines experimental analysis with numerical simulation to systematically investigate the formation and pinch-off mechanisms of liquid columns in the process of confined interface vibration inkjet printing. Two typical droplet pinch-off regimes are identified: (i) the second-extrusion pinch-off regime and (ii) the second-retraction pinch-off regime. In the second-extrusion pinch-off regime, the interface forms a continuous liquid column during the second-retraction phase, which subsequently pinches off and generates droplets during the second-extrusion phase. In contrast, the second-retraction pinch-off regime involves the rapid formation and pinch-off of the liquid column during the second-retraction phase, resulting in earlier droplet generation. The results indicate that the occurrence of these two regimes is significantly influenced by the amplitude of the excitation waveform and the viscosity of the continuous phase. Furthermore, based on extensive experimental and numerical data, a parameter space diagram was constructed using the Weber number and the Ohnesorge number, which clearly delineates the controllable regions for different droplet formation regimes.