Experimental and computational analysis of the forces acting on highly porous nanoparticle scaffolds/layers during liquid imbibition

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Recently, we developed a new two-step layer transfer process for the fabrication of highly porous nanoparticle layers on various substrates. First, the nanoparticles are synthesized in a Flame-Spray-Pyrolysis and accumulated on a filter paper. Subsequently, this filter cake is transferred to a second substrate via low pressure lamination. The resulting pore structure of the layer can be adjusted by the applied pressure. Submersion experiments in several liquids with different imbibition velocities were performed. They revealed a dependence of the particle loss from the layer in the liquid environment on the imbibition velocity, liquid properties (e.g. surface tension) and the properties of the layer (e.g. porosity and pore structure). By adjusting the pore structure through the lamination pressure, we were able to fabricate stable layers withstanding liquid environments. Previous studies mostly concentrate on the imbibition velocity in highly porous layers and their permeability. The occurring forces on the structure during imbibition are not studied in detail, yet. Within this project, we seek fundamental understanding of the mechanisms of liquid imbibition in highly porous particulate layers to quantify these occurring forces. This enables a prediction of the conditions needed to avoid restructuring or particle removal during imbibition. For this purpose, the imbibition properties of different liquids in nanoparticle layers will be analyzed in an experimental study. Additionally, the layer structure will be modelled and the forces acting on each nanoparticle within the layer will be simulated. The combination of experimental and theoretical investigations shall lead to a fundamental understanding of the occurring mechanisms during imbibition. This understanding will be applied in the last part of the project. Here, composite materials synthesized with percolating nanoparticle scaffolds in polymer matrices will be investigated. The properties of the nanoparticle layer will be adjusted to achieve a sufficient stability for the imbibition of the monomer. Furthermore, the cure shrinkage in nanoparticle layers and its influence on the particle-particle contacts will be studied. These studies enable the synthesis of polymer-nanoparticle composite materials with significantly lower particle contents compared to conventional composites having various applications as e.g. conductive or magnetic materials with polymer properties.