Study effects of particle size in metal nanoink for electrohydrodynamic inkjet printing through analysis of droplet impact behaviors

Ink properties play a critical role in different printing techniques. However, it is not straightforward to correlate ink properties to the printing results. In this study, several parameters were identified and analyzed to evaluate the droplet behavior in electrohydrodynamic inkjet printing. More specifically, the effects of metallic nanoparticle sizes in the ink formulation were explored through the analysis of droplet impact behaviors. These parameters include droplet wetting diameter, height, initial impact velocity, and contact angle. With the assistance of machine vision, a high-speed camera captured a sequence of images, which were analyzed to extract the aforementioned parameters. Under fields of gravitational force with/without electric force, four phases of ink droplet behaviors were identified. Our data suggest that with an electric force field, particle size dominates the droplet behavior in respect to contact angle and wetting diameter. The increase of particle size decreased the droplet wetting diameter with an electric field, while increased the droplet wetting diameter without the electric field applied. Larger droplet size resulted in higher bouncing frequency and lower droplet height. Furthermore, under both gravitational and electrical fields, the droplet with medium particle size (average diameter of 276 nm) had a higher impact velocity than that with small (average diameter of 140 nm) and big (average diameter of 1517 nm) particle sizes. This study contributes to fundamental understanding of particle size effects. The results will help optimize ink formulations when designing new ink materials for electrohydrodynamic inkjet printing.