29 Juin – Thesis defense - Nicolas-Alexandre Goy

14 h Amphi D / building A29 (University of Bordeaux) - Partial videoconference

Evaporation, Marangoni effects and particles' deposition driven by laser heating.

Controlling the assembly and deposition of particles on substrates is essential for creating new materials and functionalizing surfaces. The use of so-called "bottom-up" methods such as selfassembly by "coffee stain" effect, resulting from the evaporation of a suspension of particles, seems promising. However, these methods often remain limited to relatively simple deposit geometries (lines, rings). The aim of this study is to overcome these limitations by proposing a new approach, versatil
and contactless, which would allow dynamic assembly and organization of micro / nano particles. In this thesis work, we use an infrared laser to locally heat a drop of an aqueous suspension deposited on a glass slide, in order to create a thermal gradient inducing a Marangoni effect. In addition to the dominant effects of evaporation at the edges of the drop, a recirculation zone appears and concentrates
the particles around the laser heating zone. We have experimentally analyzed the effects of several physicochemical parameters: composition of the solvent, geometry of the drop, laser parameters on the Marangoni recirculation zone and the size of the final deposit. We have also characterized, by an infrared thermography method, the amplitude and the evolution of the temperature field induced by the laser. Models linking the thermodynamic and hydrodynamic aspects of the system make it possible to account for the observed results. The use of more concentrated solutions also made it possible to demonstrate the formation of three-dimensional deposits induced by a buckling instability. Finally, we show that it is possible to structure the shape of the final deposit by modifying that of the laser beam. The use of laser heating therefore opens a new path towards the production of structured deposits of micro / nano particles at the submillimeter scale.

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