Insights into modelling the gelation process in cellulose aerogels

Abstract

With rapidly increasing demand for advanced materials that can be tailored for very specific applications, aerogels have attracted attention due to their outstanding properties, such as high porosity, well developed surface area and very low density. Due to this interesting combination of properties, aerogels provide solutions for various applications such as insulation, sorbents, support for catalysts, kinetic energy absorbers etc. Moreover, certain type of aerogels (biopolymer-based) are biodegradable, their synthesis requires less harmful substrates and aligns with principles of sustainable development. The focus of this presentation is cellulose aerogels. Their structure is formed due to the polycondensation of cellulose chains consisting of D-glucose molecules as a repeating unit. The process of the structure formation – gelation - is computationally designed with coarse-grained molecular dynamics. The Hooke’s law was applied for implementation of the linear elasticity of the chains. During simulation, cellulose polymer chains exhibit the Langevin dynamics which mimics the stochastic Brownian motion. They diffuse randomly, while parallelly an interaction between monomers (within the same or separate chains) occurs, due to Lennard-Jones potential, which leads to aggregation of the chains and forming the final, cellulose fiber-based gel structure. The computational system generation, relaxation, equilibration and gelation was followed by the next steps of the synthesis: solvent exchange and washing. These treatment steps are necessary for the supercritical drying – the final step providing a dried aerogel without a significant volume shrinkage. The developed approach and computational results indicate good agreement with the experiments. Obtained computationally microstructures were characterized in terms of pore structure and gelation kinetics. Combining experimental and numerical research creates an opportunity for deeper understanding the fundamentals of synthesis of these novel, promising materials.