(81b) Computational Mechanics of Aerogels and Aggregation-Based Nanocomposite Materials

Aerogels are materials with very low densities and high surface areas prepared through sol-gel processing.  Aerogels are amorphous materials formed by in-solution aggregation processes, with fractal structure at scales from near-atomic to greater than the mean pore size. They can have extremely high surface area and porosity, low thermal conductivity, and impressive specific strength.  We have previously introduced (J. Phys. Chem. C 111 (2007) 15792) a coarse-grained flexible model where Langevin dynamics are used to mimic the gelation process of the aerogel primary particles; this model also naturally includes the effects of relaxation and fluctuation on the gel structure.  The work described in this study consists of two parts.  In the first, simulation methods for determination of the Young's modulus and Poisson ratio of model aerogels are introduced, and results obtained in good agreement with experiment.  In a second area, we study a selection of novel material structures obtainable from sol-gel-like aggregation processes.  These include (a) bidisperse and nanocomposite aerogel-like materials, consisting of a mixture of small and large particles; (b) interpenetrated aerogels, consisting of multiple independent gel networks; and (c) hierarchically-structured materials, formed by the (random) aggregation of regular nanoparticle assemblies.  These material models are mechanically and structurally characterized, and the results analyzed in order to establish structure-property-synthesis correlations for nanocomposite aerogels and related aggregation-based materials.