Winter has arrived, the temperature has dropped sharply, and everyone is buying thicker and warmer winter clothes. The slogan "Made with aerogel, made of aerospace-grade materials" is increasingly appearing on some winter cold-proof and warm clothing, claiming to have super thermal performance and not cheap. So what kind of material is aerogel? Does airgel clothing really have miraculous effects in keeping cold and warm?
The picture is taken from an e-commerce platform
Let’s start with what exactly aerogel is.
What is aerogel?
Aerogel is a type of three-dimensional network structure material that envelops a large number of closed micropores. It can be made from inorganic materials or polymer macromolecules through a sol-gel transformation process and then through a special drying process.
Based on this definition, you can know that the concept of aerogel actually refers to a solid structure (rather than a certain chemical substance). The special feature of this structure is that it has a high porosity, with a porosity as high as 80.0%~99.8%, and a pore diameter ranging from 1 to 100 nanometers.
There is dispersed still air in the closed micropores of the aerogel structure, which determines that materials with an aerogel structure have the performance characteristics of low density and low thermal conductivity.
Airgel materials generally include inorganic aerogels and organic aerogels. Inorganic aerogels include silica aerogels, titanium dioxide aerogels, etc., and organic aerogels include polyimide aerogels, polyurethane aerogels, etc.
An airgel material. Picture provided by the author. The high thermal insulation properties of airgel materials make it widely used in aerospace, electronic communications, flame retardant and heat insulation and other fields.
For example, in the aerospace field, aerogel materials are used in aircraft heat shields, flexible thermal protection systems for reducers, cryotube insulation layers for space propulsion systems, space suits, etc. So from this perspective, aerogel is indeed a veritable "aerospace grade material."
How to make clothes from airgel?
So, since the thermal insulation performance of aerogel is so good, can this material be used in our daily human body warmth and cold protection scenarios? Textile science is indeed doing research in this area, and we can take a look at the current research results.
We usually wear clothes, and we have to stretch and rub them. This is a piece of cake for common textile fabrics. However, the current airgel structural material itself has poor mechanical properties, is easily broken and pulverized, lacks flexibility and drape, and is not suitable for direct use in daily textiles and clothing.
Bent airgel material Photo courtesy of the author
Textile scientists have also thought of many ways to improve this situation, hoping to use aerogels in textiles and clothing to improve cold protection and warmth retention properties.
For example, the airgel powder is adhered to the surface of the textile material by using an adhesive or the adhesion of the textile material itself to the airgel; the coating finishing agent containing airgel is evenly coated on the surface of the fabric; the solution for preparing the airgel is directly used to prepare airgel fibers through a specific processing technology; or airgel particles are added to the spinning solution to produce chemical fibers containing airgel. It sounds like there is some hope for the application of airgel in clothing, but in actual practice, there are still many problems.
Are current “airgel clothing” reliable?
Many attempts have been made to use airgel materials for clothing, but unfortunately there are still some problems with these technologies and processes.
For example, the manufacturing process of airgel fibers is very slow, and their mechanical properties are relatively poor, making it difficult to withstand the tension required in the later spinning and weaving processes. Although surface adhesion technology or airgel coating technology can improve the thermal insulation performance of treated fabrics, it is easy to cause the problem of the fabric being airtight and moisture-permeable.
There are also cases where airgel particles peel off. Some friends may be confused. Didn’t I mention that airgel materials are used in space suits? Why can't we make clothes?
In fact, the aerogel material used in space suits is a polyimide aerogel with high strength and good softness. This material is currently only used in some special fields such as space suits and protective clothing.
Although they are also called "clothing", space suits and protective clothing belong to a type of special personal equipment system rather than a simple piece of clothing. As a thermal insulation material, aerogel materials are only part of the system. Other materials and equipment are also required to achieve a moisture and heat balance between the human body and the external environment. It is a system completely different from daily clothing.
All in all, under the current technical conditions, the use of airgel materials for cold protection and heat preservation in daily clothing still has considerable limitations, and industrial large-scale production and commercialization are rare. It is recommended that consumers pay attention to check the materials and real effects of airgel used in related products, and do not place orders blindly.
References
[1] Zhao Guoliang, Li Guangwu, Xue Rong, etc. Current status of application technology of aerogels in the field of textile and clothing [J]. New Materials Industry, 2021, (02): 48-53. DOI: 10.19599/j.issn.1008-892x.2021.02.009
[2] Ma Xiaoyi, Hu Yanping, Wang Kai, et al. Research progress on the preparation, structure and properties of polyimide aerogels [J/OL]. Polymer Materials Science and Engineering, 1-12 [2023-11-13] https://doi.org/10.16865/j.cnki.1000-7555.2023.0221.
[3]NASA: NewUltra-Thin, FlexibleAerogelsCouldbeUsedtoMakeSuper-InsulatedClothinghttps://inhabitat.com/nasa-new-ultra-thin-flexible-aerogels-could-be-used-to-make-super-insulated-clothing/
[4]DurablePolyimideAerogels(LEW-TOPS-133)https://technology.nasa.gov/patent/LEW-TOPS-133