A new, smart fabric to control body temperature!

Title: Dynamic gating of infrared radiation in a textile

Authors: Xu A. Zhang, Shangjie Yu, Beibei Xu, Min Li, Zhiwei Peng, Yongxin Wang,

Shunliu Deng, Xiaojian Wu, Zupeng Wu, Min Ouyang, YuHuang Wang

Year: 2019

Journal: Science

DOI: 10.1126/science.aau1217

In a recent ChemBite, Elizabeth Joseph wrote about a wearable health monitoring device that is being studied for the diagnosis of cystic fibrosis, exploiting the properties of sweat, such as its salt concentration. On a similar note, a group from Maryland University has possibly broadened the range of applications with sweat as the medium.

They are developing a temperature-adaptable fabric that, responding to skin moisture (from sweat), exchanges or retains the heat. Sweat is the direct reaction of our body to warm conditions, thus this fabric is adaptable to different environmental conditions.

But, how does it work?

Yarns of triacetate cellulose, a common type of fibre, are covered with controlled quantities of carbon nanotubes (CNTs, Figure 1), a conductive material, which can interact with the infrared (IR, 10 μm) emission that the human body uses to dissipate heat.

Figure 1: 3D model of the inside of a carbon nanotube (CNT), by
Mstroeck da en.wikipedia.org, CC BY-SA 3.0

Carbon nanotubes are very small cylindrical tubes comprised of one -or more- sheet of graphene rolled to assume a tube-like shape. Like many objects of the “nano” world, their properties change drastically with their characteristics; such as size, number of layers, length, rolling angles and number of interacting nanotubes. Among so many interesting properties -mechanical, electrical, optical and thermal-, this paper focuses on their light emission!

CNTs emit light in the infrared range, but the exact wavelength can depend on the interaction between nanotubes, and thus on the distance between them. This phenomenon, called resonant electromagnetic coupling, is behind the working mechanism of the fabric.

In this way, when the nanotubes get close together, they emit the right wavelength to release the heat. On the contrary, this process is not activated if they are sufficiently separated.

But how does it happen?

This is where triacetate cellulose gets involved. It interacts with the sweat that is emitted from the skin in two opposing ways: the cellulose repels the water whilst the triacetate absorbs it, making the fibres twist and tighten. As a result, when sweat triggers this tightening mechanism, brings CNTs in adjacent fibres closer to each other and causes the emission of the 10 μm IR wavelength.

This fabric, made within CNT-covered triacetate cellulose, can modify its heat-exchange properties and has great potential as a tool for adapting to climate changes that are causing extreme weather conditions. Moreover, by reducing the need for external air conditioning -and thus energy consumption- it can support our fight against climate change.

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