Experimental and computational analysis of the forces acting on highly porous nanoparticle scaffolds/layers during liquid imbibition
Final Report Abstract
In this project, experimental and computational nanoparticle layers were generated successfully. The structural properties of the simulated layers were validated and agreed well with experimental data. Subsequently, these porous percolating nanoparticle layers were imbibed with non-reactive (common for electrode applications) and reactive liquids (formation of inverse nanoparticle-polymer-composites, NPCs). The capillary rise was investigated, as it determines the destabilizing forces during the process of liquid imbibition. The capillary rise differs from classical theories and a new model was developed that accounts for the crossflow from larger to smaller pores. With this new model, a prediction of the capillary rise in the porous nanoparticle structures is possible for arbitrary liquids. Based on model fits to experiments, the most relevant structural parameter, i.e. fractal dimension of tortuosity and equivalent pore diameter, for the liquid imbibition were identified and determined. With these values, an estimation of the destabilizing forces during liquid imbibition was feasible that provides a first criterion for mechanical stability to avoid detachment and restructuring of the layers. Methods for the wet chemical preparation of porous nanoparticle layers were also developed. For this sol-gel binder were combined with silica and metal oxide particles and solvents. The porosity can be adjusted by the composition and preparation technique. The layer quality is strongly determined by the solvent evaporation and additives in the composition as well as the application parameters. This includes the control of the sol-gel binder's crosslinking reaction, which was examined in detail as well as the morphology of the formed layers. The formed solid porous layers can be filled with a second component in an additional step to form a multimaterialnanocomposite or to adjust the remaining porosity. The porous layers formed by both preparation methods where imbibed with monomers leading to a distinct structural densification during polymerization. Polymerization was initiated photochemically and the cure shrinkage leads to improved particle-particle contacts. For the case of ITO particles this could be verified by changes of the electrical conductivity. A distinct improvement was obtained during pore imbibition with the electrically insulating monomer. During polymerization the conductivity increased by about a factor of 5. This strong increase might make the method applicable for the production of displays with a reduced amount of ITO compared to sputtered ITO coating according to the state of the art.
Publications
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Imbibition into Highly Porous Layers of Aggregated Particles. Transport in Porous Media, 2017. 119(1): p. 119-141
Schopf, S.O., Hartwig, A., Fritsching, U., Mädler, L.
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Determination of the Flat Band Potential of Nanoparticles in Porous Electrodes by Blocking the Substrate–Electrolyte Contact. The Journal of Physical Chemistry C, 2018. 122(5): p. 2796-2805
Naatz, H., Hoffmann, R., Hartwig, A., La Mantia, F., Pokhrel, S., Mädler, L.
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Verfahren zur Bestimmung des Flachbandpotenzials von Nanopartikeln in porösen Elektroden. Chemie Ingenieur Technik, 2018. 90 (9): p. 1212-1212
Naatz, H., Hoffmann, R., Hartwig, A., La Mantia, F., Pokhrel, S., Mädler, L.
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Compaction-Induced Restructuring of Aggregated Nanoparticle Films Using the Discrete Element Method. Powder Technology, 2019. 342: p. 773–779
Baric, V., Colombi Ciacchi L., Mädler, L.
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Inverse Nanocomposites Based on Indium Tin Oxide for Display Applications: Improved Electrical Conductivity via Polymer Addition. ACS Appl. Nano Mater, 2019. 2(4): p. 2273-2282
Hoffmann, R., Baric, V., Naatz, H., Schopf, S. O., Mädler, L., Hartwig, A.
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Inverse Nanocomposites – High Particle Percolation without Running into Viscosity Problems, Proc. Makromol. Col. Freiburg, 20.-22.2.2019
Hoffmann, R., Schopf, S.O., Naatz, H., Baric, V., Mädler, L., Hartwig, A.
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Preparation of Inverse Nanoparticle-Polymer Composites by Infiltrating Monomers in Indium Tin Oxide Layers, SBPMat Brazil-MRS, 2018-09-16 - 2019-09-20, Natal, RN, Brazil, pp. 1–3
Hoffmann, R., Baric, V., Naatz, H., Mädler, L., Hartwig, A.
