Mechanical characterization techniques for practical application of flexible silica aerogels

Abstract

Aerogels are materials that are known for their high porosity, resulting in a number of exceptional properties, including low density and high surface area, as well as remarkable thermal and acoustic insulation capabilities [1]. This renders them suitable for a broad spectrum of applications, particularly those that demand multifunctionality [2]. However, in order to facilitate widespread practical application and the scaling up of processes, it is necessary to subject the materials to mechanical characterisation. The wide range of aerogel types and their mechanical properties, which can vary from highly brittle to flexible, poses a significant challenge in the establishment of universal solutions and standards. In this study, we will present a range of advanced mechanical characterisation techniques and methods for testing aerogel materials and their composites, including digital image correlation (DIC), dynamic mechanical analysis (DMA) and computer tomography (CT) for in situ analysis.

In order to synthesise aerogel specimens and to minimise post-processing, aerogels were fabricated using specific moulds, for example, 3D printed containers or syringes. Moreover, 3D scanning is employed to facilitate geometric analysis and volume estimation of the moulded aerogels, a process that can be challenging due to the brittle or flexible nature of certain aerogel types. The advantages of DIC are illustrated by correlating them with finite element simulations, resulting in the creation of a digital twin. Furthermore, DMA measurements are conducted on flexible silica, brittle silica and cellulose aerogels, with the objective of investigating the influence of density, temperature and frequency on different aerogel types. Finally, the utilisation of micro-CT is demonstrated on flexible silica aerogels to examine pore deformation and the integrity of the porous structure during cyclic deformation.

In the context of the need for efficient mechanical characterisation techniques for practical and scale-up applications, an overview of the strengths and weaknesses of techniques for certain aerogel types can play a crucial part in defining reproducible and efficient, or even standardized, methods for the future.

References [1] Fricke J. Aerogels — highly tenuous solids with fascinating properties. Journal of Non-Crystalline Solids. 1988;100:169-73. [2] Smirnova I, Gurikov P. Aerogels in Chemical Engineering: Strategies Toward Tailor-Made Aerogels. Annual Review of Chemical and Biomolecular Engineering. 2017;8:307-34.