Structural efficiency and microstructural modeling of wet gels and aerogels

We present a microstructural model of aerogels that includes the effect of particle necks, tortuosity and dangling ends on the scaling of elastic modu li with density. Relative neck radii can be determined for sintering series of silica aerogels and for Resorcinol Formaldehyde (RF) aerogels produced with different catalyst concentrations. The density of elastically ineffect ive dangling ends and the tortuosity can be estimated using information fro m thermal conductivity and elastic modulus measurements in silica aerogels. Typical values for the load bearing mass range from >50% for high density and heat treated aerogels to <10% of the total mass for low density wet-gel s.