Inkjet Printing onto Patterned Substrates

Abstract

The drying of picolitre droplets printed onto patterned substrates has been imaged. Organic solvents were printed in a drop-on-demand format into 200 µm × 200 µm square wells surrounded by walls of polymer resist which were 1.5 μm high and 20 μm wide. Particle tracking velocimetry (PTV) data revealed the velocity and direction of flows during drying, which could be understood in terms of differential rates of evaporation across the drop. Alongside PTV, interferometry was used to observe the profile of the drop during drying. The measurements revealed that variations in the evaporation rates across the drop were not the only cause of uneven deposits when printing onto patterned substrates. More important was the capillary suction caused by negative curvature in the drop once the level of the fluid dropped below the tops of the walls defining the wells, if the drying droplet was pinned at the tops of the walls. For fast evaporating drops, we observed the formation of a dimple in the centre of the well towards the end of drying.