Hierarchical structure formation in inorganic (aero)gels: A computational approach

Kurzfassung

In contemporary times, there exists a growing need for sophisticated nanostructured materials that can be customized for highly specific applications. In this context, materials derived through sol-gel processes have garnered significant interest, with aerogels, in particular, drawing attention due to their remarkably high porosity, that renders them well-suited for diverse applications, including but not limited to insulation, sorbents, and catalyst support. Accurate modelling of aerogels requires acknowledging the hierarchical nature of their structure. The formation of the particle aggregates1 type of aerogel is a complex phenomenon, with polycondensation of monomers as a first step, followed by the formation of primary particles and their subsequent aggregation into the secondary particles. This complex process results in final nanostructured porous morphology of a product. However, the process does not have to be sequential. Furthermore, the condensation can proceed parallelly to phase separation. Thus, a comprehensive modelling approach is essential to reflect this process accurately. A widely utilised approach for modelling the sol-gel transition is diffusion- or reaction-limited cluster-cluster aggregation method (DLCA/RLCA)2-4. This type of numerical system can mimic the Brownian motion of primary/secondary particles and follow simultaneously the structure evolution as well as the kinetics of its formation. In this work, the above-mentioned approach was adapted to mimic the process of gel formation more accurately. Additionally, the impact of supercritical drying on the alcogel structure was simulated by the finite element method (FEM) and analysed to understand the pore shrinkage effects. The comparison of numerical and experimental results provides data for model validation and discussion whether the introduced model improvements bring us closer to reflecting the real materials and whether the computational approach indicates a potential for reverse engineering and product design.