Time–dependent geometrical changes in a ceramic ink droplet

Ceramic ink droplets have been deposited on two fundamentally different types of substrate and the evolution of contact angle, width of the ink–substrate interface and droplet height was measured as a function of time from digital images of the droplet captured on video. On substrate type I, with a lower surface free energy than the surface tension of the ceramic ink, after reaching stability in a few seconds, the contact angle decreased and the width of the ink–substrate interface remained stationary. Subsequently, the contact angle stayed constant and thereafter reduced again, while the width of the ink–substrate interface decreased and remained constant thereafter. On substrate type II, with a higher surface free energy than the surface tension of the ceramic ink, stability was achieved instantaneously and the contact angle decreased rapidly, while the width of the ink–substrate interface increased initially but thereafter remained constant. The corresponding variation of droplet height due to spreading and evaporation, and volume shrinkage rate were also found to be much faster on the type–II substrate.