The Effect of Particle Necks on the Mechanical Properties of Aerogels

Abstract

Mechanical properties of open-porous materials are often described by constructing a cellular network with beams of constant cross sections as the struts of the cells. Such models have been applied to describe, for example, thermal and mechanical properties of aerogels. However, in many aerogels, the pore walls or the skeletal network is better described as a pearl-necklace, in which the particles making up the network appear as a string of pearls. In this paper, we investigate the effect of neck sizes on the mechanical properties of such pore walls. We present an analytical and a numerical solution by modeling these walls as corrugated beams and study the subsequent deviations from the classical scaling theory. Additionally, a full numerical model of such pearl-necklace-like walls with concave necks of varying sizes are simulated. The results of the numerical model are shown to be in good agreement with those resulting from the computational one.

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“…Coefficient “ b ” is the number of interparticle contacts per skeletal particle and is related to the overall connectivity of the network and therefore its mass fractal dimension. ,, Figure shows a linear relationship between E and the neck area per unit aerogel mass according to eq , assuming for simplicity b = 1. This relationship supports both the model of bicontinuous frameworks as strings of mostly merged spheres and the fact that the stiffness of aerogels consisting of interconnected spherical particles depends on the interparticle neck zone area, as predicted. , …”

“…(The corollary, of course, is that an assembly of interconnected spheres cannot be stronger than its weakest pointsthe interparticle links.) As it was discussed in Section , since all samples were made with the same amount of material (constant monomer concentration at 20% w/w throughout), large, well-separated spheres leave the least amount of material in the interparticle neck zones, and the stiffness of those structures is expected, and it was found low (Figure ). At the opposite end, smaller, merging skeletal particles with neck diameters close to the particle diameters can be thought of as coming from larger spheres by transferring material to the neck zones.…”

“…Finally, as it was discussed previously, 46 and modeled recently both analytically and numerically by Ratke et al, 47 the stiffness of aerogels consisting of assemblies of interconnected spherical particles depends on the size of the interparticle necks, which act as stress concentrators. (The corollary, of course, is that an assembly of interconnected spheres cannot be stronger than its weakest points�the interparticle links.)…”

“…merged spheres and the fact that the stiffness of aerogels consisting of interconnected spherical particles depends on the interparticle neck zone area, as predicted. 46,47…”