Fractal Structure in Silica and Composites Aerogels

Abstract

Silica aerogels are known to be materials with exceptional characteristics, such as ultra-low density, high surface area, high porosity, high adsorption, and low-thermal conductivity. In addition, these unique properties are mainly related to their specific processing. Depending on the aerogel synthesis procedure, the aerogels texture can be tailored with meso and/or macroporosity. Fractal geometry has been observed and used to describe silica aerogels at nanoscales in certain conditions. In this review paper, we describe the fractal structure of silica aerogels that can develop depending on the synthesis conditions. X-ray and neutron scattering measurements allow to show that silica aerogels can exhibit a fractal structure over one or even more than two orders of magnitude in length. The fractal dimension does not depend directly on the material density but can vary with the synthesis conditions. It ranges typically between 1.6 and 2.4. The effect of the introduction of silica particles or of further thermal treatment or compression of the silica aerogels on their microstructure and their fractal characteristics is also resumed.

Porous glasses from aerogels: from organic liquid to mineral materials

“…We will test the Scherer model for composite aerogel and figure 4 shows the evolution of the density as a function of time for CA10 (fractal material [18,21]) and CA70 aerogel ( non-fractal material [18,21] ). The reduced lines k(t-t0) versus t is shown in Figure 5.…”

“…Composite aerogels are stronger, stiffer and tougher than classical aerogels because of the presence of the aerosil powder, which strengthens the porous material [20]. Moreover, the aggregation process is affected by the addition of the aerosil powder [18,21]: the porosity is changed (larger macroporosity ) [14] and fractal structure is in a higher length range [21]. So classical aerogel and composite aerogels have completely different networks and we could expect different sintering behavior.…”

Springback effect of ambient-pressure-dried silica aerogels: nanoscopic effects of silylation revealed by in situ synchrotron X-ray scattering

“…6,9–11 Furthermore, the preceding sol–gel process allows for tailoring many of the properties of this inorganic porous network, such as the bulk density, and the size of the elementary particles. 12…”

Auto-Continuous Synthesis of Robust and Hydrophobic Silica Aerogel Microspheres from Low-Cost Aqueous Sodium Silicate for Fast Dynamic Organics Removal

“…Silica aerogels have large specific surface areas, nanopore volumes, and porosities and show excellent performances in thermal insulation, adsorption, catalysis, and many other aspects [ 1 , 2 , 3 , 4 , 5 , 6 ]. Recently, it has caused wide public concern to remove organic contaminants from water with hydrophobic silica aerogels [ 7 , 8 ].…”