Simulating Silica Aerogels with a Coarse-Grained Flexible Model and Langevin Dynamics

We use a simple coarse-grained model to investigate the formation and structural and mechanical properties of low-density silica aerogels. This model is fully flexible and can account for bond breaking and creation upon deformation of the gel structure. Model parametrization is discussed, and simulation protocols appropriate to the study of gelation, shrinkage, and bulk modulus are given. One key parameter of the model is the probability associated with bond creation, P . We show that for sufficiently low P the simulations achieve a scaling behavior in which the final gel structure is largely independent of P and so can be used to make contact with experimental results. Good agreement with gel fractal dimensions obtained by experiment is obtained under these conditions. We also investigate the effects of solvent viscosity on gel structure and find that gels grown in lower-viscosity solvents are more compact and better crosslinked than those grown at high viscosity. The gels simulated here all have bulk moduli somewhat lower than the corresponding experimental systems, but it appears that quantitative agreement on this measure is achievable.