Colloquia

Summary

Recent developments in foaming technology show the potential to produce foams with locally tuned properties, using additive manufacturing (AM), also known as 3D printing, with bubbles to produce foams, in a novel method called Direct Bubble Writing (DBW). In DBW, a core-shell nozzle that ejects bubbles is mounted on a 3 axis moveable stage, which allows the manufacturing of 3D foams. The bubbles are cured in-flight using Ultra Violet (UV) light. This core-shell nozzle ejects a liquid ink shell with a gas core, by varying these fluid ejection rates, the ejected combined flow can be tuned, from a pure liquid jet to monodisperse bubbles. This method allows the rapid production of polymer foams, with advanced mechanical, thermal, and acoustics properties compared to traditionally produced foams. Traditionally produced foams show broad cell size distributions and are not able to locally tune the foam properties. These advanced foams made with DBW could be used in multiple application fields, for example: in shoe soles, with tailored, customer-specific, dampening properties, in mattresses of Intensive Care Units of hospitals, to prevent decubitus ulcers, by having custom-tuned stiffness and density, or in acoustics, as highly monodisperse, small cell foams have uniform energy dissipation characteristics.

However, producing advanced materials brings advanced problems, for DBW those include the inconsistency of the bubble production method, controlling the bubble properties, and the dimensional accuracy of the 3D printed foam parts. Especially the bubble production from the core-shell nozzle with viscous ink is challenging. Up to now, printing with one liquid flow rate and gas pressure, for a giving nozzle geometry, is possible and used to print foams. However, when one of these parameters changes slightly, the monodisperse regime, used for printing, is not present anymore. It is desired that this bubble formation is more robust and by changing the liquid/gas flow rate or nozzle geometry, the bubble properties can be tuned instead of hindered. This brings us to the main research question of this thesis: To what extent can we control and optimize the bubble formation process from a core-shell nozzle?

The goal is to be able to print foams with a wider range of properties like the bubble size, for example, allowing us to print foams with gradients.