An overview on silica aerogels synthesis and different mechanical reinforcing strategies

Abstract

Silica aerogels are lightweight and highly porous materials, with a three-dimensional network of silica particles, which are obtained by extracting the liquid phase of silica gels under supercritical conditions. Due to their outstanding characteristics, such as extremely low thermal conductivity, low density, high porosity and high specific surface area, they have found excellent potential application for thermal insulation systems in aeronautical/aerospace and earthly domains, for environment clean up and protection, heat storage devices, transparent windows systems, thickening agents in paints, etc. However, native silica aerogels are fragile and sensitive at relatively low stresses, which limit their application. More durable aerogels, with higher strength and stiffness, can be obtained by proper selection of the silane precursors, and constructing the silica inorganic networks by compounding them with different organic polymers or different fiber networks. Recent studies showed that adding flexible organic polymers to the hydroxyl groups on the silica gel surface would be an effective mechanical reinforcing method of silica aerogels. More versatile polymer reinforcement approach can be readily achieved if proper functional groups are introduced on the surface of silica aerogels and then copolymerized with appropriate organic monomers. The mechanical reinforced silica aerogels, with their very open texture, can be an outstanding thermal insulator material for different industrial and aerospace applications. This paper presents a review of the literature on the methods for mechanical reinforcing of silica aerogels and discusses the recent achievements in improving the strength and elastic response of native silica aerogels along with cost effectiveness of each methodology.

Graphene oxide reinforced high surface area silica aerogels

“…Alternatively several studies have integrated the gel network with composite materials, such as crosslinking polymers, nanoparticles and/or ceramic fibres [36][37][38][39][40][41][42][43][44][45][46]. Conversely, it is often difficult to improve the mechanical properties of silica gels with the use of nanofillers or cross-linking reagents without altering or hampering additional properties such as the bulk density and surface area [36,47].…”

“…Conversely, it is often difficult to improve the mechanical properties of silica gels with the use of nanofillers or cross-linking reagents without altering or hampering additional properties such as the bulk density and surface area [36,47]. However, with effective control of each stage of aerogel synthesis and composite integration, the incorporation of additional materials between the weaker neck regions of the silica nanoparticles enhances the strength of the gel network and can also yield aerogels with improved or additional properties [30].…”

Silica Based Superhydrophobic Nanocoatings for Natural Rubber Surfaces

“…In addition, they demonstrate small pore sizes ranging between 1 and 100 nm. Low index of refraction (∼1.05) and high optical transmission (∼93%) impart transparent characteristics into silica aerogel materials [25][26][27][28][29]. In superhydrophobic applications, silica aerogel is generally modified with a suitable long-chain alkyl groups.…”

Study the Effect of Doping with Chromium Chloride on Silica Aerogel Properties Prepared with Ambient Pressure

“…Energy storage and heat, catalyst supports, battery electrodes, humidity sensors and gas, adsorbents, and drug delivery systems, etc. [5,[9][10][11][12]. The first report of aerogel by Kistler, published in Nature (1931), was enabled by the invention of supercritical drying (SCD) and appeared in a letter.…”