Aerogels

Abstract

Aerogels are low‐density and high‐porosity materials that are most commonly prepared by removing the pore liquid from a wet gel with supercritical extraction. The most extensively studied and characterized are silica aerogels, which can be prepared in the density range of 3 to 500 kg/m 3 through a proper control of preparative variables. The unusual properties of these materials, such as high surface area and pore volume, low thermal conductivity, and low dielectric constant, make them attractive for applications in diverse areas including thermal insulation, detection of high energy particles, and catalysis. The challenge is to produce them in a cost‐competitive process, which means exploring options that do not involve supercritical drying. Recent results show that with surface modification, aerogel‐like materials can indeed be produced at ambient conditions. Other ongoing research has been directed at the preparation and characterization of nonsilicate aerogels, as well as organic and inorganic–organic hybrid materials in an attempt to define their properties and to identify potential applications.

Aerogels and Polymorphism of Isotactic Poly(4-methyl-pentene-1)

“…Then, the percentage of porosity P of the aerogel samples can be expressed as P = 100 ( 1 − normalρ app normalρ pol ) where ρ pol is the density of the polymer matrix (e.g., equal to 0.83 and 0.85 g/cm 3 for semicrystalline i-P4MP1 samples with a crystallinity of 50%, exhibiting form I and form II phases, respectively) and ρ app is the aerogel apparent density calculated from the mass/volume ratio of the monolithic aerogels.…”

Strain Hardening and Pore Size Harmonization by Uniaxial Densification: A Facile Approach toward Superinsulating Aerogels from Nematic Nanofibrillated 2,3-Dicarboxyl Cellulose

“…Cellulose aerogels of narrow pore size distribution in the mesopores range (<50 nm diameter) are potential superinsulating materials as heat conduction via the gas phase as the main transport mechanisms of heat in organic aerogels is largely hindered due to the Knudsen effect . Predominantly silica-based aerogels have been hitherto explored as thermal superinsulating materials (λ ≥ 14 mW m –1 K –1 ) since their porosity in terms of size and narrow distribution can be easily controlled in the required range by sol–gel chemistry. Recently, both synthetic and natural polymer based aerogels have increasingly moved into the focus of thermal insulation, such as polyurethanes (e.g., polyurethane aerogels from BASF; λ ≥ 19.8 mW m –1 K –1 ) or pectin (e.g., Aeropectin; λ ≥ 20 mW m –1 K –1 ) …”

Nanoporous Crystalline Composite Aerogels with Reduced Graphene Oxide

“…Then, the percentage of porosity ( P ) of the aerogel samples can be expressed as follows [ 60 ]: where ρ s is the aerogel skeletal density (i.e., polymer matrix or polymer/r-GO matrix) and ρ app is the aerogel apparent density calculated from the mass/volume ratio of the monolithic aerogels.…”