Correlation between structure and thermal conductivity of organic aerogels

Abstract

Organic aerogels are derived from the sol-gel polymerization of resorcinol with formaldehyde. While these materials are usually produced as monoliths, this paper describes a new method for the production of organic aerogel microsphere powders. Supercritical drying provides highly porous aerogels which have an open-cell structure consisting of interconnected solid particles with typical diameters of 10 nm. The structure is controlled by the sol-gel polymerization conditions. This paper addresses the correlation between structure and thermal conductivity of these novel materials. Thermal conductivity measurements have been performed on both monoliths and powders using a hot-wire device. The measurements under variation of gas pressure as well as spectral infrared transmission measurements allow the determination of the solid, gaseous and radiative thermal conductivity as a function of density and catalyst concentration. The results show that the thermal conductivity components are clearly correlated with the aerogel structure: porosity and connectivity between the particles determine the solid conductivity, while the pore size influences the gaseous conductivity and radiative transport depends on the mass specific infrared absorption of the building units.