Deposit pattern of inkjet printed pico-liter droplet

Abstract

The deposit pattern of an evaporating picoliter droplet is studied changing the solvents (water, diethylene glycol, and formamide), mixing composition of the solvents and substrate temperature. When depinning occurs in the early stage of the evaporation period, concentrated solute (or partially deposited solute, if any) also retracts with the receding droplet, resulting in dome shaped deposit patterns. When pinning is maintained during most of the evaporation period, either a ring deposit or a relatively uniform deposit is obtained depending on the type of solvent and heating condition. These results are explained by interplay of (1) radial outward flow due to the strong evaporation flux at the contact line of a sessile droplet, (2) inward Marangoni flow due to evaporative cooling and solvent concentration gradient, and (3) solute mixing by diffusion in liquid.