Physical properties of silica gels and aerogels prepared with new polymeric precursors

“…Typically, aerogels made from TMOS in methanol can be obtained with an optical transmittance ratio up to 93% (for~1 cm thick aerogels) at a wavelength of 900 nm [140,141]. Silicon precursors prehydrolyzed with an acid catalyst and a substoichiometric water molar ratio w ¼ n H 2 O =n Si < 2 are available on the market [124,142] and make it possible to control a more uniform porous texture, as is needed for optical applications. Transparency ratio up to 90% together with specific extinction coefficient of the order of 15 m À1 [143] can be obtained with 1 cm thick aerogels synthesized with such prepolymerized precursors (Figure 2.14).…”

Section: Optical Propertiesmentioning

confidence: 99%

SiO2 Aerogels

Pierre

Rigacci

2011

Aerogels Handbook

View full text Add to dashboard Cite

International audienceThis chapter focuses on one of the most studied aerogel materials, silica aerogels. It aims at presenting a brief overview of the elaboration steps (sol-gel synthesis, aging, and drying), the textural and chemical characteristics (aggregation features, porosity, and surface chemistry), the main physical properties (from thermal, mechanical, acoustical, and optical, to biological, medical, etc.), and a rather broad panel of related potential applications of these fascinating nanostructured materials. It cannot be considered as an exhaustive synopsis but must be used as a simple tool to initiate further bibliographic studies on silica aerogels

show abstract

“…1. 9 ml of polyethoxydisiloxane (PEDS), a prepolymerized form of tetraethyl orthosilicate (TEOS) containing a water-to-TEOS molar ratio of 1.5 and a SiO 2 content of 20% w/w in ethanol (referred to as PEDS-P 750E20 ) was used as the silica source [60] and diluted with 21 ml of ethanol (F25-AF-MEK, absolute ethanol denatured with 2 vol% methyl ethyl ketone) and with 1 ml of distilled water under constant stirring conditions for 5e10 min at room temperature. Gelation occurred approximately 10 min after the addition of 0.36 ml of 5.5 M ammonium hydroxide solution (NH 4 OH in water).…”

Section: Aerogel Synthesismentioning

confidence: 99%

Effect of aging on silica aerogel properties

Iswar

Malfait

Balog

et al. 2017

Microporous and Mesoporous Materials

129

View full text Add to dashboard Cite

Silica aerogels' unique physical and chemical properties make them fascinating materials for a wide variety of applications. In addition to hydrophobization by silylation, aging is very important in the synthesis of silica aerogel by ambient pressure drying. Here we systematically study the effect of aging on the physico-chemical properties of silica aerogel with emphasis on ambient dried materials. Silica gels were aged for different times and at different temperatures in their gelation liquid (without solvent exchange), hydrophobized in hexamethyldisiloxane and subsequently dried either at ambient pressure or from supercritical CO 2 . Dynamic oscillatory rheological measurements demonstrate that aging reinforces the alcogels, particularly at high strain. The specific surface area decreases with increasing aging time and temperature as a consequence of Ostwald ripening processes during aging. With increasing aging time and temperature, the linear shrinkage and bulk density decrease and the pore size and pore volume increase for the ambient dried gels, but remain nearly constant for supercritically dried gels. Small-Angle X-ray scattering does not detect significant structural changes at length scales smaller than about hundred nanometers, but hints at systematic variations at larger length scales. The findings of this study highlight the importance of aging to increase the ability of the gel particle network to withstand irreversible pore collapse during ambient pressure drying.

show abstract

Physical properties of silica gels and aerogels prepared with new polymeric precursors

Cited by 65 publications

References 11 publications

Fast and one-pot synthesis of silica aerogels via a quasi-solvent-exchange-free ambient pressure drying process

Fast and one-pot synthesis of silica aerogels via a quasi-solvent-exchange-free ambient pressure drying process

SiO2 Aerogels

Effect of aging on silica aerogel properties

Contact Info

Product

Resources

About