Parametrization and simulation of blister-actuated laser-induced forward transfer (ba-lift) and lift for high-viscosity pastes
- Autores: Juan José Moreno Labella
- Directores de la Tesis: Miguel Morales Furió (dir. tes.)
- Lectura: En la Universidad Politécnica de Madrid ( España ) en 2021
- Idioma: español
- Materias:
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- Resumen
Laser-Induced Forward Transfer techniques are part of the additive direct-write processes fo-cused on the transference of a material, either solid or liquid, towards an acceptor substrate. The start-ing point of this work was the elaboration of an intensive bibliographic review to take the knowledge of the state of the art. Besides, the study of the Finite-Elements Method (FEM) was necessary to accom-plish the modeling of the LIFT processes. Two main techniques have been studied during the time of this thesis: Blister-Actuated LIFT (BA-LIFT), within the techniques that involve an intermediate layer, and LIFT for high-viscosity pastes, part of the direct-interaction LIFT techniques.
In Blister-Actuated Laser-Induced Forward Transfer (BA-LIFT), a laser pulse generates a blister in an intermediate polyimide layer to push away the fluid. The process is too quick and small to directly observe it, so a Phase Field model is proposed in COMSOL Multiphysics to study the transference mechanisms. The starting model was only able to reproduce the jet formation and its growth, but it was enough to understand the main dynamics of the process. The input parameters for the model are thought to match the operating experimental parameters. The energy pulse parameter rules the size of the formed blister, and it is needed some image calibration to assess its dependency on the laser pulse energy.
When the simulations and the experimental shadowgraphy images for BA-LIFT of water-glycerol mixtures were compared, the model did not explain some secondary effects in the jet expan-sion that had already been described in other LIFT techniques and associated with the cavitation of a thermally generated vapor bubble. The transference mechanism in BA-LIFT is ideally only mechanical –and not thermal– because of the characteristic times of each process and the presence of the interme-diate polyimide layer that avoids the direct interaction between the laser and the fluid.
The evolution of the blister over time makes the numerical model reproduce the expansion of the main jet. Assuming the existence of a cavitation bubble analogous to that one that appears in other LIFT techniques with direct interaction, and only introducing its effects in the model as a second push at 9 μs after the start of the transference, the model also reproduces the secondary effects. Four possi-ble causes of the second push have been studied: absorption of the laser pulse in the fluid, thermal conduction through the polyimide layer, a mechanical rebound of the elastically deformed blister, or pressure fall due to fluid velocity. After the analysis, the first three explanations have been rejected, and a hypothesis is proposed: the velocity field generated by the blister produces a cavitation bubble in the interface between the polyimide layer and the fluid, whose effects would be the same as the cavitation of the vapor bubble in other LIFT techniques.
Once the dynamics are reproduced by the model, the existence of the supposed bubble was sought. For that study, the BA-LIFT setup was modified to avoid the interface effects that distort the acquired images. Setting a much bigger fluid layer in front of the blister –considered infinite as no jet is created and only the dynamics in the interface are observed–, images of bubbles were taken within the water mass. These new images were studied to evaluate the hypothesis previously presented.
Secondly, the Laser-Induced Forward Transfer (LIFT) for high-viscosity –of Pa·s– pastes differ from standard LIFT processes in its dynamics. In most techniques, the transference after setting a great gap does not modify the shape acquired by the fluid, so it stretches until it breaks into droplets. In contrast, there is no transferred material when the gap is bigger than three times the paste thickness in LIFT for high-viscosity pastes, and only a spray is observed on the acceptor using this configuration. Through a new Phase-Field FEM-CFD model, the dynamics of the paste have been, and the behavior of the paste varying the gap between the donor and the acceptor substrates has been modeled. The paste bursts for great gaps, but it is confined when the acceptor is placed close enough. The obtained simulations have been compared with a previous work, in which the paste structures were photo-graphed. The analysis of the simulations in terms of speed allows for predicting the burst of the paste –spray regime– and the construction of a printability map regarding the gap between the substrates.
