High-Resolution Printing of Complex Fluids Using Blister-Actuated Laser-Induced Forward Transfer

Abstract

Blister-actuated laser-induced forward transfer (BA-LIFT) is a nozzle-less, layer-by-layer, additive printing technique capable of printing chemically and mechanically sensitive materials. In this process, a laser pulse is focused on a solid polymer film, which is coated with the liquid material to be transferred. This solid film absorbs the laser pulse energy and forms a rapidly locally expanding blister that deforms the liquid film and leads to jet formation. If the laser pulse energy is sufficient, the formed jet breaks up into one or more droplets through Rayleigh-Plateau instability and result with material transfer. As BA-LIFT can be used to print materials, it also offers a unique setup to study physics of liquid jets.

This thesis examines in detail the fluid mechanics of jet formation from viscoelastic liquids using BA-LIFT as a tool to generate jets that undergo high rates of deformation. An analytical model is presented to include the rheology of complex fluids into consideration to predict the printing regime, a priori. In the next chapters, a numerical model is developed to capture the physics of viscoelastic filament thinning and resolve the flow parameters. In addition, a numerical model is developed to simulate BA-LIFT, and this model is validated with previous experiments. Supported by experiments, these two models are combined to reveal the effects of viscoelastic parameters on droplet formation with BA-LIFT.

The last part of the thesis explores two separate experimental techniques to increase the resolution of the BA-LIFT technique using the phenomenon called flow-focusing. One method focuses on the formation of steady, meniscus-shaped liquid-air interface inside microfabricated holes on the polymer layer. The other technique creates transient, meniscus-shaped liquid-air interface through the creation of Faraday waves. Both methods enable jetting at subthreshold laser pulse energies, and the resulting jets break up into smaller droplets, which increase the resolution of the BA-LIFT process.