Abstract The nanoporous structure and the mechanical properties of silica aerogels are studied by molecular dynamics simulations on large samples. For the first time, atomistic simulations are able to reproduce a pore size distribution, centered on 10 nm, comparable to experimental values. Using an unprecedented combination for silica aerogels of large volumes, large strains, and relatively small strain-rates, direct evidence of their peculiar mechanical behavior at the nanoscale is provided, from elasticity to fracture. The surface stress that silica ligaments experience produces a significant tension-compression asymmetry and an unusual discontinuity in the Poisson effect. The ductility of highly porous silica aerogels arises from an interplay between surface stress and a significant amount of reorganization in ligaments. Taking advantage of the large volumes accessible here, the very heterogeneous nature of low-density silica aerogels is reproduced, with an impact both on their elasticity and on their strength. In particular, a clear dependence between tensile strength and sample volume is uncovered, which opens perspectives for the elaboration of multi-scale models.

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二氧化硅气凝胶的弹性和强度：大体积分子动力学研究

摘要 通过大样品的分子动力学模拟研究了二氧化硅气凝胶的纳米多孔结构和力学性能。原子模拟第一次能够重现以 10 nm 为中心的孔径分布，与实验值相当。对大体积、大应变和相对较小应变率的二氧化硅气凝胶使用前所未有的组合，提供了它们在纳米尺度上从弹性到断裂的特殊机械行为的直接证据。二氧化硅韧带所承受的表面应力会产生显着的张力-压缩不对称性和泊松效应的异常不连续性。高度多孔二氧化硅气凝胶的延展性源于表面应力和韧带中大量重组之间的相互作用。利用此处可访问的大体积，重现了低密度二氧化硅气凝胶的异质性，对其弹性和强度都有影响。特别是，揭示了拉伸强度和样品体积之间的明显依赖关系，这为多尺度模型的制作开辟了前景。