Numerical simulations of aerogel sintering

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Abstract
Following recent theoretical scaling ideas, numerical simulations for sintering of silica aerogels are performed starting from computer-generated gel structures obtained by diffusion-limited cluster-cluster aggregation on a cubic lattice. The sintering process is modeled in two steps: a ‘‘dressing’’ step in which all particles are replaced by overlapping larger particles and a ‘‘contraction’’ step in which an adequate length rescaling is performed in order to conserve the total mass. Several quantities are computed during sintering as a function of the aerogel density such as the two characteristic cutoff lengths (lower and upper limits of the fractal regime), the specific interface area and the small angle scattering intensity curve. Moreover the percolation transition between open and closed pores which occurs at a given stage of sintering is investigated. Comparison is made with results of similar off-lattice calculations when available. Some of the numerical results are compared with experiments on partially densified base-catalysed aerogels.