Properties of ink-droplet formation in double-gate electrospray

Droplet ejection by an electrospray using a prototype inkjet head equipped with a ring-shaped gate electrode was demonstrated. The observation of droplet ejection with a high-speed camera revealed that ejection behavior can be categorized into two modes: a spindle-mode ejection and a multispindle-mode ejection. The former operation makes it more possible than the latter operation for the droplet to traverse the gate and travel toward the substrate where it produces a pattern. It was also found that the mode of ejection could be determined by the frequency of the applied voltage and the gap between the inkjet head and the gate electrode. Furthermore, droplet ejection orbit could be precisely controlled by a double-gate operation. A second gate electrode was important for realizing this. The ejection using a needle-type inkjet head was also investigated.