Computer simulation of mechanical structure-property relationship of aerogels

Aerogel is a highly compliant material, whose elastic modulus scales with i ts relative density with an exponent between 3 and 4; however, the underlyi ng physics is not understood. The diffusion-limited cluster-cluster aggrega tion (DLCA) was combined with a 'dangling bond deflection' algorithm to gen erate aerogel models with extensive loop structure. Their linear elastic pr operties were examined by the finite element method. Although the network m odels contain negligible dangling mass, the simulation yields the same empi rical scaling relationship as aerogels, with an exponent of about 3.6. Ther efore the consensus that 'dead-ends' contribute to the compliance of aeroge ls is contradicted. The result shows that the fraction of bonds bearing the strain in the aerogel model decreases with decreasing density and this is why the network is so compliant. During gelation, particles aggregate to fo rm primary clusters with dense cores (which we call 'blobs'). Then the clus ters percolate by interconnecting with a few tenuous chains (links) to form a gel. Stress and strain localize mostly at the weak links when the gel ne twork is deformed, leaving the rigid blobs unloaded. (C) 2001 Elsevier Scie nce B.V. All rights reserved.