Aerogels are a class of solid materials that are created by drying wet gels – a product of polymer-solvent interactions – under supercritical conditions. Central to the formation of aerogels is the removal of a gel’s liquid component and replacing it with a gas. This substitution makes aerogels lightweight and maintains the structural integrity of the material’s three-dimensional network.
Figure 1 – Basic research scheme for aerogels.
Aerogels can be classified as a monolith, powder or film. And they characteristically exhibit high porosity, low apparent density, high surface area and low thermal conductivity. The combination of these properties makes aerogels a great material for a range of applications such as: thermal insulation in aerospace vehicles; electromagnetic interference (EMI) shielding in wearable electronic devices; acoustic insulation in motor vehicles; and oil spill cleanup.
In the past, the brittle nature of aerogels compounded with their high production costs made them impractical for large-scale usage. More recently, advancements in polymer-reinforced aerogels, optimizations in the supercritical process and an increased focus on heat dispersion across the electronics industry have increased the commercial viability of aerogels. IDTechEx – a UK-based independent market researcher – forecasts that the aerogel market will exceed $700 million by 2031, more than double its current valuation of $300 million.
As aerogels gain increased recognition for their utility as a robust, cost-effective and relatively sustainable material, understanding the thermal properties of aerogels will be paramount to effectively leveraging their extraordinary capabilities.
Figure 2 – Semi-transparent monolith aerogel sample.
In a paper published at the 11th SEATUC Symposium, Son et al created hydrophobic, rice-straw-based cellulose aerogels. The aerogels were produced using a sol-gel process with aqueous solutions of NaOH-polyethylene glycol (PEG) and the freeze-drying method. They observed the thermal conductivities of their samples using the C-Therm Thermal Conductivity Instrument. Results from their work can be seen below.
Figure 3 – Thermal conductivities of the surveyed aerogel samples compared to those of common heat insulation materials.
In a paper published in Colloids and Surfaces, Ba Thai et al successfully developed a novel rubber aerogel from recycled care tire fibers (RCTF). The rubber aerogels were synthesized using polyvinyl alcohol (PVA) and glutaraldehyde (GA) as crosslinkers and the freeze-drying method. The C-Therm Thermal Conductivity Instrument was used to determine the thermal conductivity of their aerogels. Results from their work can be seen below.
Figure 4 – Density, porosity and thermal conductivity of various rubber aerogels.
The two case studies above highlight not only the diverse compositions of aerogels that exist, but also the expertise that C-Therm Technologies has developed within the aerogel testing space; The continuous evolution of their instrumentation has kept pace with the testing requirements necessitated by the expanding applications for aerogels. At present, the Trident system paired with the MTPS sensor offers a competitive solution for determining the thermal properties of aerogels – from raw aerogel powder to bulk aerogels.
Figure 5 – Monolith Aerogel being tested on a MTPS thermal conductivity sensor.
While traditionally measured via steady-state, aerogels and their composites can now be measured much faster with C-Therm’s MTPS sensor, without sacrificing accuracy. For more information on C-Therm’s portfolio of tools for thermal conductivity characterization of aerogels please visit: https://ctherm.com/ or contact us directly at: +1 (506) 457-1515.