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April 20th 2019

There is a growing number of new applications for inkjet printing, including 3D printing and the printing of functional materials such as medicines or metals. These new forms of printing use liquids with very diverse characteristics. A thorough understanding of how drops form is therefore important for the development of these new technologies. The researchers from this FOM programme have developed a method to very accurately study the movement of ink drops.

Photo series
The study of ink drops is very challenging. The drops are miniscule – about 10 billionth of a litre. In addition they fly at speeds of up to 10 metres per second through the air. Nevertheless researchers can still make microscopic images of the drops. They prevent movement blur on these photos by using light pulses of just 8 nanoseconds (8 billionths of a second). The time interval between two photos is just 600 nanoseconds.

Using the photos, the physicists first of all determine where the liquid is located in the air. Subsequently they calculate the volume of the drops per pixel on the photo, as a result of which they can calculate the total volume with an accuracy of 0.1 billionths of a litre. Finally the speed of the ink drop is determined from the displacement of the fluid and the time interval between two photos.

The method developed in this programme was validated by comparing measurements with theoretical calculations. For these calculations an approach is needed which assumes that all liquid in the drop flows in the same direction. The measured drop profile and drop speed are taken as the initial situation in the theoretical model. Next the model characterises how the drop develops over the course of time. The experiment and the theory were found to be in good agreement with each other. This new method can therefore be used to study a flying ink drop in detail.

According to the researchers the method can be extended to include non-Newtonian liquids: liquids that behave differently from water when subjected to shear stresses.