Droplet Behaviors on Substrates in Thin-Film Formation Using Ink-Jet Printing(<Special Issue>Micro Mechanical Engineering)

Physical phenomena associated with the dynamic spreading and dried shape of droplets on solid surfaces were demonstrated reviewing several models and discussed with regard to designing the most suitable thin-film formation processes using ink-jet printing. After droplets strike a substrate surface and expand for several microseconds, they spread semistatically for tens of seconds and asymptotically approach the final equilibrium shape determined by droplet volume and contact angle. The contact angle and the volume, number, and impact velocity of droplets for various ink-jet-deposition applications can be designed by using semi-empirical formulas. If the contact angle at the edge of droplet on the substrate is small, a large amount of solute might accumulate there during the drying process because the evaporation rate there is high. The evaporation rate distribution on droplet surfaces should therefore be controlled to be uniform in radial direction during drying.