Deformation characteristics of a single droplet driven by a piezoelectric nozzle of the drop-on-demand inkjet system

In the drop-on-demand (DOD) inkjet system, deformation process and the direct relations between the droplet motions and the liquid properties have been seldom investigated, although they are very critical for the printing accuracy. In this study, experiments and computational simulations regarding deformation of a single droplet driven by a piezoelectric nozzle have been conducted to address the deformation characteristics of droplets. It is found that the droplet deformation is influenced by the pressure wave propagation in the ink channel related to the driven parameters and reflected in the subsequent droplet motions. The deformation extent oscillates with a certain period of T and a decreasing amplitude as the droplet moves downwards. The deformation extent is found strongly dependent on the capillary number (Ca), first ascending and then descending as the number increases. The maximum value of the deformation extent is surprisingly found to be within range of 0.068-0.082 of the Ca number regardless of other factors. Furthermore, the Rayleigh's linear relation of the oscillation frequency of the droplet to the parameter,root sigma/rho r(3) (where sigma is the surface tension coefficient, rho is the density and r is the droplet's radius), is updated with a smaller slope shown both by experiment and simulation.