With the development of wearable devices and the Internet of Things, a sustainable solution for powering wireless devices and sensors is becoming important. Thermoelectric generators, which convert waste heat into electricity, can be one of them. A research team led by Masakazu Nakamura of the Nara Institute of Science and Technology (NAIST), Japan, is working on flexible, wearable thermoelectric generators. This is done by using carbon nanotubes (CNTs) that are sewn into fabric.
Effective thermoelectric materials generate voltage through temperature differences. Carbon nanotubes meet most of the necessary requirements. Their flexibility and high mechanical strength also make them a promising application. However, the high thermal conductivity of CNTs limits their thermoelectric performance. To reduce the thermal conductivity, the tubes are dispersed in a solution and combined with other materials. The resulting material is used to create filaments in a wet spinning process. However, conventional dispersion methods often entangle the nanometer-thick filaments, which reduces their electrical conductivity and thermoelectric performance.
In a study published in ACS Applied Nano MaterialsNakamura, together with graduate student Anh N. Nguyen and other NAIST representatives, developed a new method for dispersing CNTs. By using glycerin as a dispersant and polyoxyethylene(50) stearyl ether as a surfactant (used to improve the spreading and wetting properties of a liquid), the researchers fabricated a usable fabric.
«We are introducing a low-cost, fast, and environmentally friendly method for developing flexible, wearable fabric-type thermoelectric devices,» Nakamura says.
Glycerin has a high viscosity, which makes it an excellent medium for uniform dispersion, and the surfactant prevents the CNTs from clumping in the dispersion. Surfactants with oxyethylene groups also prevent heat transfer.
The concentration of the surfactant is crucial because it affects both the thermal and electrical conductivity of the dispersion. The process, which only took three hours and used environmentally friendly chemicals, produced a yarn of CNTs with well-aligned 8 nm diameter bundles with surfactant in between. Alignment of CNTs normally increases both electrical and thermal conductivity. However, by placing surfactant molecules between the bundles, the researchers were able to suppress heat transfer. Thus, the proposed new approach is promising for improving the thermoelectric performance of carbon nanotubes and materials made from them, from filaments to films and bulk structures.
Source: NAIST
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