Material modeling of cellulose aerogels

Abstract

Aerogels are a unique class of highly porous materials that have been widely studied due to their distinctive properties such as low thermal conductivity, low bulk densities, and large specific surface areas [1, 2]. Recent aerogel research puts a growing focus on the exploration of bio-polymer aerogels. Cellulose aerogels present an environmentally sustainable alternative to their inorganic counterparts owing to their biodegradability, renewable nature, and the broad availability of raw materials for their production [3, 4].

The outstanding material properties of cellulose aerogels are commonly attributed to their porous fibrillar structure. The gelation step in the synthesis process is critical to the formation of the fibrillar gel structure. The central objective of this work is to enable comprehension of the network formation mechanisms in cellulose aerogels throughout the synthesis process. Although current material models for biopolymer aerogels provide precise predictions of structure-property relations, they typically do not account for the gelation and its subsequent impact on the material properties. [5, 6, 7]

The developed gelation model based on the discrete element method consists of an ensemble of a structural, polymer bond, diffusion and interaction model. The structural model abstracts the structure of the cellulose molecules through spherical approximation of their glucose repeating units connected with flexible bonds. The polymer bond model describes the local stiffness and curvature of the cellulose polymer chains. A Langevin dynamics based diffusion model and an interaction model defined by a Lennard-Jones potential capture the diffusion forces and intermolecular forces acting upon the cellulose molecules during gelation. A parameter sensitivity analysis studies the influence of the interaction model on the computational gelation kinetics and the microstructure of the cellulose network properties. Experimental data is utilized as model input and for validation of the developed model with respect to the structural properties.

In contrary to approaches, which regenerate a virtual twin of the aerogel materials based on experimental structural data, the gelation model developed in the scope of this work generates the desired virtual fibrillar network by simulating the cellulose aggregation process at a molecular level. This work represents a significant step forward in the property prediction of bio-polymer aerogels and sets the stage for improved optimization of their synthesis based on an established theoretical knowledge base.