Employing Instabilities in Large Area Thin-Film Coating with Complex Fluids

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This project aims at understanding and employing the instability mechanisms that fundamentally limit rapid industrial uniform thin-film coating focusing on (1) blade coating and (2) slot-die coating techniques. These methods do not require high vacuum conditions and, therefore, are suitable for roll-to-roll production that is important for high-speed industrial surface processing. However, depending on fluid and substrate properties and process parameters, instabilities occur that result in coating defects and patterned coatings. For instance, a large coating velocity may induce breaking of the coating film if its thickness is below a critical one. We aim at understanding the various instability mechanisms and the resulting self-organised structures and patterns for simple non-volatile and volatile liquids as well as for complex liquids as polymer solutions and nanoparticle suspensions. We plan to analyse passive control strategies that allow one to fine tune the features of the resulting coating patterns by adjusting the control parameters of the system. Finally we will develop active control strategies that employ synchronisation effects to impose structure length by temporal modulaton of control parameters of the coating processes. In all stages, the project will be pursued in close cooperation between theory (Institut für Theoretische Physik, Westfälische Wilhelms-Universität Münster, WWU) and experiment (Lehrstuhl für Laseranwendungstechnik, Ruhr-Unversität Bochum, RUB).