New Way To Alter Conductivity By Changing Ambient Temperature

Scholars at the Massachusetts Institute of Technology have devised a way to control the electrical and thermal conductivity of different materials by simply varying and controlling the external parameters such as surrounding temperature. The results of their initial experiments have been quiet encouraging. According to their experimental observations, they have concluded that the thermal conductivity can be tripled while the electrical conductivity can rise by multiplication factors well over 100! That’s a pretty big increase.

#-Link-Snipped-#A well documented paper on this topic was published in the online version of the Nature Communications dated 19th April and will be available in the printed format in the forthcoming issue. Gang Chen, MIT’s Carl Richard Soderberg Professor of Power Engineering and director of the Pappalardo Micro and Nano Engineering Laboratories, is a senior author of this paper. He told the press that they have implemented this technology for a particular category of materials popularly known as percolated composite materials. Their research was partially funded by the National Science Foundation. The list of team members and lead authors for this project includes many bright minds such as former MIT visiting students Jinwei Gao of South China Normal University and Ruiting Zheng of Beijing Normal University, along with current MIT science graduate scholar Jianjian Wang.

The system can be used for a lot of materials and has a wide range of applications in almost every engineering field. For example, this technique can be used in variable conducting fuses for protecting delicate electronic circuits from the harmful effects of overloading or heating. The fuse will conduct normally at the lower temperatures but with the increase in temperature, the resistance of the fuse will increase and conductivity will reduce. At a particular maximum temperature, the fuse will stop conducting and will act like a blown up fuse. However, it doesn’t need a replacement as it starts conducting once the temperature lowers down. It may even be used for storing thermal energy.

The approach taken by the scientists was that they formed a suspension or colloidal solution of tiny flakes of a conducting material like graphite in liquid hexadecane. The graphite flakes demonstrate a property of their crystals getting frozen at low temperatures. Hexadecane has a melting point close to room temperature. However, the research team clarified that many other material combinations can be used to arrive at the same results. This means that it is a generalized technique and not material specific.

The basic principle at work here is that the freezing liquid crystals tend to apply considerable pressure on the floating flakes of graphite. As a result, the graphite crystals are pushed closer to each other and the closer contact increases the material’s electrical and thermal conductivity. Similarly, as soon as the liquid starts melting, the pressure on the conductor reduces thereby lowering the conductivity. It sounds really simple but no one had thought about this obvious fact till date. The next question the skeptics will raise is about the stability of the suspension. Well, the scientists used a 0.2% mixture of graphite in hexadecane and found it just like that after a period of 3 months! Now, you can call that highly stable. By using distinctive fluids and different materials floating indefinitely in that liquid, the critical temperature for changing the properties can be adjusted as per the requirement of any application.

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