110th Anniversary: Solvent Exchange in the Processing of Biopolymer Aerogels: Current Status and Open Questions

In the past decade, the uses and applications of aerogels have garnered significant scientific curiosity in the aerogel community. Furthermore, renewed focus on the supercritical CO2 drying methodology of aerogels has expanded the material scope to several biopolymer systems that now offer new avenues for material, property, and application exploration. However, the principal challenge of the aerogel community is to balance the complexity and costs of aerogel processing with the enhanced material properties that the final aerogel presents. In the case of biopolymer aerogel processing by supercritical CO2 drying, an intermediate solvent exchange step is required in most cases as the biopolymers are gelled in water (hydrogels) and the supercritical CO2 drying cannot commence due to the miscibility gap in the water/CO2 system. Very limited information is available on exchanging water in a gel with organic solvents. The aim of this commentary paper is to introduce aerogel researchers to several aspects of the gel shrinkage during aerogel processing and invite the reader to address the open questions related to the basis for solvent selection in aerogel synthesis.