Cellular Automata Modeling of Silica Aerogel Condensation Kinetics.

Nina H Borzęcka,Robert Przewodzki,Rafał Pakuła,Jakub M Gac,Bartosz Nowak

doi:10.3390/gels7020050

Abstract

The formation of silica aerogels and the kinetics of condensation were investigated numerically. The influence of the reaction-limited to the diffusion-limited aggregation (RLA to DLA) transition on the reaction kinetics curves and the evolution of the aggregate size distribution during condensation were examined. The 2D cellular automaton was developed and applied to reflect the process of secondary particle aggregation. Several tendencies were observed due to the adjustment of the model parameters: the probability of condensation reaction and the particles’ concentration. The final wet-gel structures’ visualizations proves that the structure becomes more dense and compact due to entering the RLA regime. The simulation time (associated with the gelation time) decreased along with the increase in both model parameters. The lower the collision probability, the slower reaction becomes, and particles are more likely to penetrate the structure deeper until they finally join the aggregate. The developed model reflects the condensation process’s nature and its mechanisms properly and indicates a significant potential for further aerogel synthesis investigations and for the prediction of wet-gel properties according to condensation parameters.

Highlights

Silica aerogels have gained increasing attention since they were first synthesized in 1931 [1]
Simulations were conducted for three chosen concentration values: c ≈ 1%, 5% and 12.5% and four probability values: P = 0.001, 0.01, 0.1 (reactionlimited aggregation, reaction-limited aggregation (RLA)/reaction-limited cluster–cluster aggregation (RLCA)) and 1 (diffusion-limited aggregation, DLA/diffusionlimited cluster–cluster aggregation (DLCA))
The time of a simulation decreases as the system approaches the DLA/DLCA regime due to the higher probability of reaction between two adjacent particles/clusters

Summary

Introduction

Silica aerogels have gained increasing attention since they were first synthesized in 1931 [1]. Instead of silica oxides, provided control over the final material structure, which is the source of the aerogel’s unique properties. The formation of aerogel depends on plenty of parameters: temperature, silane/solvent/water molar ratio, catalyst type and its concentration [2,3,4,5,6], to name just a few. The sol-gel procedure conditions lead to changes in the final product features due to differences in the kinetics parameters. The influence of a specific set of parameters remains unclear, and often structures are obtained through trial and error by each group of authors separately. The sol-gel method’s complexity, together with numerous process variables, stems the need for further investigation to better understand aerogel formation’s nature

Methods

Results

Conclusion