How accurately can silica aerogels be computationally modelled?

Abstract

How accurately can silica aerogels be computationally modelled? Nina Borzęcka, Prakul Pandit, Ameya Rege Department of Aerogels and Aerogel Composites, Institute of Materials Research, German Aerospace Centre, Cologne, Germany Silica aerogel modelling 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 which result in their final nanostructured porous morphology (Fig. 1). However, the process does not have to be sequential - the steps can overlap or even occur simultaneously. Furthermore, the condensation can proceed parallelly to phase separation for organoalkoxysilane precursors. Thus, a comprehensive and multiscale approach is essential in order to reflect this process accurately. Fig. 1 Scheme of hierarchical structure of particle aggregates type of silica aerogel A widely utilised, although significantly simplified approach for modelling sol-gel transition is diffusion or reaction limited cluster aggregation method (DLCA/RLCA)2-4. This type of numerical system can mimic random motion of primary/secondary particles and follow simultaneously the structure evolution and the kinetics of its formation. But can we adapt this approach to reflect the reality more accurately? A significant aspect which is often omitted in these models is the polydispersity of particle sizes and its influence on the process rate and the structural and fractal properties. As a consequence, we introduce a modelling approach, that takes into the consideration the polydispersity effect, while also considering the numerical particle reactivity based on the experimental reaction rates. Furthermore, the impact of supercritical drying on the alcogel structure is analysed to understand the pore shrinkage effects. The comparison of numerical and experimental results provides data for model validation and discussion whether these improvements bring us closer to reflecting the real materials – silica aerogels. Which brings us to the question: Does such a modelling approach show potential for reverse engineering and product design? References 1. Nakanishi, K., and Kanamori, K. J. Mater. Chem. (2005), 15, 3776–3786 2. Hasmy, A., Anglaret, E., Foret, M., Pelous, J., and Jullien, R. Phys. Rev. B (1994), 50, 6006–6016. 3. Abdusalamov, R., Scherdel, C., Itskov, M., Milow, B., Reichenauer, G., and Rege, A. J. Phys. Chem. B, (2021), 125, 1944–1950 4. Borzęcka, N.H., Nowak, B., Pakuła, R., Przewodzki, R., and Gac, J.M. Int. J. Mol. Sci. (2023) 24