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Interface polymer material conducts heat at 4.4W/mK

Posted: 03 Apr 2014 ?? ?Print Version ?Bookmark and Share

Keywords:interface? polymer? heat?

Researchers have developed a thermal interface material able to conduct heat 20 times better than the original polymer. The modified material can reliably operate at temperatures of up to 200C.

Amorphous polymer materials are poor thermal conductors because their disordered state limits the transfer of heat-conducting phonons. Creating aligned crystalline structures in the polymers through fibre drawing processes can improve the transfer, but those structures can leave the material brittle and easily fractured as devices expand and contract during heating and cooling cycles.

Virendra Singh

Research scientist Virendra Singh, from the George W. Woodruff School of Mechanical Engineering at Georgia Tech, holds a test sample used to measure thermal conductance and thermal cycle reliability in a new polymer material developed to remove heat from electronic devices. Source: Georgia Tech Photo, Candler Hobbs

Microscopic image of nanofibre array

This scanning electron microscope image shows vertical polythiophene nanofibre arrays grown on a metal substrate. The arrays contained either solid fibres or hollow tubes, depending on the diameter of the pores used to grow them. Source: Virendra Singh

The interface material is produced from a conjugated polymer, polythiophene, in which aligned polymer chains in nanofibres facilitate the transfer of phononsbut without the brittleness associated with crystalline structures, said Baratunde Cola, an assistant professor in the George W. Woodruff School of Mechanical Engineering at the Georgia Institute of Technology. Formation of the nanofibres produces an amorphous material with thermal conductivity of up to 4.4 watts per metre Kelvin (W/mK) at room temperature.

The structures are grown in a multi-step process that begins with an alumina template containing tiny pores covered by an electrolyte containing monomer precursors. When an electrical potential is applied to the template, electrodes at the base of each pore attract the monomers and begin forming hollow nanofibres. The amount of current applied and the growth time control the length of the fibres and the thickness of their walls, while the pore size controls the diameter. Fibre diameters range from 18nm to 300nm, depending on the pore template.

Hollow nanofibres

This transmission electron microscope image shows four polymer nanofibres with hollow structure. The thickness of the walls of the tubes ranged from 40 to 80nm, depending on the amount of current applied and the growth time. Source: Ye Cai

After formation of the monomer chains, the nanofibres are cross-linked with an electropolymerisation process, and the template removed. The resulting structure can be attached to electronic devices through the application of a liquid such as water or a solvent, which spreads the fibres and creates adhesion through capillary action and van der Waals forces.

The material has been tested up to 200C. It could be used to draw heat away from electronic devices in servers, automobiles, high-brightness LEDs and certain mobile devices. It is fabricated on heat sinks and heat spreaders and adheres well to devices, potentially avoiding the reliability challenges caused by differential expansion in other thermally-conducting materials.

A patent application has been filed on the material. Cola has formed a start-up company, Carbice Nanotechnologies, to commercialise thermal interface technologies. It is a member of Georgia Tech's VentureLab program.

Nanofibre Array

This image shows testing of a polythiophene nanofibre array grown on a copper heat sink and dried in contact with a silicon carbide RF device simulator. Source: Daniel P. Resler

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