Improving Elastic Properties of Polymer-Reinforced Aerogels

Abstract

Monolithic aerogels provide superior thermal insulation compared to other forms of aerogel (composites, particulate, etc.). It has also been demonstrated that monolithic aerogels can be made mechanically stronger and more durable by incorporating a conformal polymer coating on the skeletal nanostructure. However, for many applications it would be most desirable to have monolithic aerogels in a more flexible form, for example, as insulation in deployable and inflatable structures or space suits, or to wrap around a structure needing insulation. To this end, it has been found that by incorporating organic linking groups or alkyl trialkoxysilanes into the silica backbone, elastic recovery and/or flexibility is improved, while strength is maintained by the use of polymer reinforcement. IntroductionDue to their combination of low density, high porosity, high surface area, and nanoscale pore sizes, silica aerogels are of interest for many applications including thermal and acoustic insulation, optics, catalysis, and chromatographic systems [1-3] (Chap. 2). However, potential applications of aerogel monoliths in aerospace, industry, and daily life have been restricted due to their poor mechanical properties and their extreme fragility [4]. Hence, in aerospace, especially (Chaps. 32 and 33), aerogel monoliths have been limited to a few exotic applications such as collecting hypervelocity particles from the tail of the comet Wild 2 in the Stardust Program [5] and as thermal insulation on the Mars Rover [6].It has been shown that reinforcing silica aerogels by reacting polymer with the silanol surface to create a conformal coating over the silica skeleton is an effective way to increase mechanical strength by as much as two orders of magnitude while only doubling the density over those of native or nonreinforced aerogels [7][8][9] (Chap. 13). In addition, the mesoporosity of these polymer-reinforced aerogels, and hence, their superior insulation properties among other things, is maintained. Incorporating an amine onto the surface of the silica gel particles by coreacting the tetraalkoxysilane with 3-aminopropyltriethoxysilane (APTES), as shown in Scheme 15.1, allows for reinforcement with epoxy-terminated oligomers [10,11] or cyanoacrylates [12] and also improves the reactivity of the silica surface toward

Meta-Aerogels: Auxetic Shape-Memory Polyurethane Aerogels

“…The most well-studied class of aerogels is based on silica. ,, However, silica aerogels are notorious for their fragility, which limits the range of their applications. One way to address the fragility issue of oxide aerogels is to apply a conformal nanothin polymer coating over their entire skeletal framework. − These materials are referred to as X-aerogels, and their strength-to-mass ratio renders them suitable even for ballistic protection (armor). − The topology of the nanoscopic composition of X-aerogels directed the rational design and development of purely polymeric aerogels from all major classes of polymers ranging from polyolefins, and phenolic resins including polybenzoxazines, polyimides, polyamides, and polyureas to polyurethanes. − The latter class of aerogels includes recently reported rubber-like superelastic poly­(isocyanurate–urethane) (PIR–PUR) aerogels that show a strong nanostructure-dependent shape-memory effect triggered by a temperature swing around their glass transition temperature. − …”

Thermoresponsive Shape-Memory Aerogels from Thiol–Ene Networks

“…Aerogels are an intriguing class of materials which are formed by the extraction of the solvent from a gel while preserving the porous structure. This gives them a range of attractive properties such as low density, high surface area, low thermal conductivity, and low dielectric constant. − Some of the first aerogels were produced from silica and as a result were very brittle, requiring, for example, the addition of polymers to provide elasticity and mechanical toughness. − More recently, aerogels have been prepared entirely from organic materials such as polyimides, − polyamides, polyurethanes, , and polystyrene. , As the skeletal materials for aerogels have moved from inorganic to polymeric they have been shown to have increased toughness and deformability as well as an increased ability to recover from deformation. Such properties suggest the possibility of accessing shape-memory aerogels where the aerogel can be held in a compressed state and recover to its open porous structure upon demand.…”

From Fragile to Resilient Insulation: Synthesis and Characterization of Aramid-Honeycomb Reinforced Silica Aerogel Composite Materials

“…One other way to prevent the disintegration of silica aerogels was suggested by Capadona et al The authors could significantly increase the stiffness and strength by crosslinking with isocyanate [13]. Several methods to improve elastic properties are summarized by Meador [14]. In general, a polymer coating on the skeletal nanostructure makes aerogels mechanically stronger [14].…”

“…Several methods to improve elastic properties are summarized by Meador [14]. In general, a polymer coating on the skeletal nanostructure makes aerogels mechanically stronger [14]. To improve the mechanical properties of silica aerogels, other groups suggest a variety of other approaches, such as incorporation of tungsten disulfide nanotubes [15], chemical vapor deposition treatment with hexamethyldisilazane [16], or polymer-reinforcement allowing ambient drying of silica aerogels [17].…”