An MIT research team has unraveled a way to monitor the thermal and electrical conductivity of materials by altering the environment outside, including temperature.
The technique could alter electrical conductivity by factors exceeding 100, and heat conductivity exceeding the limit.
MIT's graphite flakes clump together to form a connected network as they are pushed into place by the crystals that form as the liquid hexadecane surrounding them begins to freeze.
MIT’s Carl Richard Soderberg Professor of Power Engineering and director of the Pappalardo Micro and Nano Engineering Laboratories Gang Chen has co-authored the research paper recently released online and to be published shortly in Nature Communications. Other authors include former MIT scholars Ruiting Zheng of Beijing Normal University and Jinwei Gao of South China Normal University, with graduate student Jianjian Wang. The program received some of the funds from the National Science Foundation.
The system could be applied either in thermal or electrical applications in varied materials. It could be used for a fuse that can safeguard electronic circuitry, in which electricity could be conducted with almost no resistance at room temperature. When the circuit begins to warm up, the extra heat would enhance the resistance of the material to a limit, at which it could behave like a blown fuse and block the current flow. When the circuit begins to cool down, the resistance reduces allowing the circuit to function normally once again. It could also be used to store heat including from a solar thermal collector. The saved heat could later heat water or residences, or produce electricity. The thermal conductivity of the system in the solid state enables it to transfer heat.
Graphite flakes were suspended in liquid hexadecane. The team showed that conductivity could be controlled in other materials too. The liquid hexadecane melts almost at room temperature, enabling operations in near ambient environments.
The pressure of the liquid turning into crystals as it freezes forces the floating nano-particles to come close to each other, enhancing their electrical and thermal conductivity. When the liquid melts, the pressure is relaxed decreasing the conductivity. A suspension comprising 0.2% graphite flakes in volume was used. The nano-particles could remain suspended in the liquid for long periods. The temperature, at which the alteration occurs can be monitored by using different liquids and suspension materials.