Functionalised Aerogels for Thermoacoustic Emission
Polyimides are a mechanically and thermally stable, flexible class of engineering polymers that have gained wide interest over the course of the last century. Aerogels made of polyimides have been studied extensively in areas such as aerospace, electronics and insulation for their superior properties including very low thermal conductivities and low densities. The aim of this cooperative project with the Federal Institute for Materials Research and Testing (BAM), Berlin, is to systematically design experiments to minimise the thermal effusivity of aerogels to be used as substrates for coatings with thermoacoustic effect, such as ITO. Effusivity, the quantity at the core of the substrate’s influence on the thermoacoustic effect, is computed as the geometric mean of thermal conductivity and volumetric heat capacity. Thus, our experimental design is challenged to optimise thermal conductivity λ, density ρ, and heat capacity cp. The mechanical and thermal properties tied to poylimide aerogels make them an ideal first candidate of exploration for coating applications requiring low effusivity. While their properties have been said to mostly depend on the amide-anhydride backbone, many factors during the aerogel production can be considered regarding their effect on the properties of interest. These include solvent quantity, duration of solvent exchange, temperatures and flows during the supercritical drying process, etc. Using an active experimental design based on black-box Bayesian optimisation, the vast experimental space of polyimide aerogel production will be navigated to systematically identify synthesis factors that would help in optimising these thermal properties for the tailoring for thermoacoustic applications.
