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Thursday, 20 June 2019

Controlling Thermal Conductivity of Polymers with Light

Under ambient conditions or visible light (left side), the polymer is crystalline and has a high thermal conductivity. Once exposed to ultraviolet (UV) light (right side), the bond becomes a liquid of low thermal conductivity - the crystalline phase appears bright and the liquid phase appears dark. [Image: University of Illinois Materials Research Lab]

Heat control with light

The plastics capable of conducting heat are a recent class of new materials used in electronics and promise lighter cars .

The newest member of this family is a plastic that has its thermal conductivity controlled by light: Light can function as an optical switch, turning on and off the plastic's ability to conduct heat.

This means that this polymer will allow to route the heat on demand, taking it to where it is needed or removing it from where it is harmful.

"As far as we know, this is the first observation of a light-reversible reversible crystal-liquid transition in any polymer material." The particularly notable finding in this study is the rapid and reversible three-fold change in thermal conductivity associated with phase transition, said Jungwoo Shin of the University of Illinois, USA.

This possibility of optical control of the thermophysical properties of the polymer is due to the photoresponsive effect of the azobenzene molecule , which can be optically energized by visible light or by ultraviolet light.

"By synthesizing it with visible and visible UV light, we can change the shape of the azobenzene group by modulating the bond strength between the chains and producing a reversible transition between crystal and liquid," he said. Jaeuk Sung, a member of the team.

The next step will be to study the resilience of the polymer under various operating conditions, to define its possible uses.


 Light-triggered thermal conductivity switching in azobenzene polymers
Jungwoo Shin, Sung Jaeuk, Minjee Kang, Xu Xie, Byeongdu Lee, Kyung Min Lee, Timothy J. White, Cecilia Leal, Nancy R. Sottos, Paul V. Braun, David G Cahill
 Proceedings of the National Academy of Sciences
 DOI: 10.1073 / pnas.1817082116

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