Control of droplet formation for low viscosity fluid by double waveforms applied to a piezoelectric inkjet nozzle

When dispensing liquid through a piezoelectric inkjet nozzle, a single droplet without a satellite is formed in the limited range of the Ohnesorge number. Especially, it is difficult to eject low viscosity fluids such as a silver nanoparticle suspension in the form of a single free drop using conventional single waveforms to drive the piezoelectric actuators. To overcome the lower limit of fluid viscosity, in the present study, double waveforms with two square pulses have been applied to control the droplet formation in the piezoelectric inkjet nozzle and its response has been observed. With regard to the double waveforms, the effect of the driving voltage and time separation between the pulses was investigated. The present nozzle shows that several satellites are produced by the successive ejection in a single pulse because the oscillating pressure wave is rarely damped out in the low viscosity fluid. On the other hand, a single droplet is easily formed in the double waveform and the droplet formation could be precisely controlled by changing the time separation between the pulses. The upper and lower limits of the time separation are discussed in view of the kinetic phenomena of a primary drop and a transient satellite for the low viscosity fluid. In addition, it is addressed how the time separation and driving voltage in the double waveform affect the droplet size and velocity.