Phase Change Rapid Prototyping with Aqueous Inks

We present the first results of a new rapid prototyping technique that has been developed, which can produce structures with high aspect ratios (44:1) and freeform overhangs. The technique uses a piezoelectric printhead to precisely deposit material drop by drop at predetermined positions on a substrate. The temperature of the printhead can be varied so as to adjust the ink's viscosity, in order to improve its printability. The substrate on the other hand is kept below the ink's freezing point. For a normal water-based ink this means that the printhead is kept at room temperature and the substrate is kept at -20°C. When a droplet hits the surface its small thermal volume is almost instantly cooled. As a result of this fast freezing, the droplet does not spread but retains the shape of a half sphere. The next falling droplet lands on top of the first and covers it; heat is removed to the substrate through this contact area. Successive droplets result in the formation of a pillar with a rounded top. Finally, by moving the translational stage during printing simple, freestanding step structures can be fabricated.