Multiphase flows of particles in thin film systems

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Note [] refers to journal publications in CCV.******The focus of this research is on the nature of flow of particle filled fluids, in multiphase thin films, in flows of industrial interest for the creation of functional devices or thin film coatings. The Applicant's group has considerable experience in dip coating and slot coating, as well as micro-injection molding - major processing technologies in the development of high value added devices where the coating is either functional (e.g. electrically conductive, light diffusion) or protective (e.g. oxygen or water barrier, damage protection). The size and complexity of devices such as batteries, organic photoconductors and microelectromechanical devices requires more precision at smaller length scales on the nano to microns length scale. The research objective is to better understand the mechanisms of particle flows in multiphase systems that may lead to particle deposition, adhesion, and agglomeration. The nature of the particle-solid interactions and particle-fluid interactions will be studied, taking into account the forces on the particles, and including two way coupling between the particles and the fluid. One of the challenging areas will be the incorporation of non-Newtonian fluid effects, as many coatings are particle dispersions in polymer matrices. Recent research has focused on dip coating [7,10] using fluid models that incorporate particle concentration, and in slot coating [2,8] using the discrete element method (DEM) to track individual particles. In both applications, using open source CFD software (OpenFOAM), there were serious difficulties in precisely determining the position of the interface of the coating film and in capturing the effects of particles within the flow. Questions still arise as to the competing forces due to flow, particle surface properties leading to particle-particle and particle wall interactions, and the role of free surfaces, which exist in all these applications. Simulation with experimental validation will provide a valuable tool in understanding the role of these competing effects and lead to better design and production of devices that use these manufacturing methods. There is also considerable scientific interest in discontinuous coating technologies (essentially printing) for applications such as printed electronics, battery coatings and high value functional materials on substrates. The precise location of the film edges are affected by the free surfaces: contact lines between liquid-solid, local surface tension, wettability of the surface and presence of particles. Simulation of such systems is an area of scientific interest to better understand the competing effects on the particle distribution, and necessary to design and produce devices - this research will contribute to better modeling tools for product design and process improvement.