scientists at the university of michigan (ann arbor, mich.) have developed a new, inexpensive, and scalable technique that changes the molecular structure of plastic to improve its thermal conductivity, according to a report on the university website.
a sample of heat - conducting polymer is tested for thickness in u-m’s lurie
nanofabrication facility. (joseph xu, michigan engineering)
engineers used a chemical process to straighten the molecular chain of a polymer, which allowed a more direct path for heat to move through the material. the researchers believe that this could lead to more energy-efficient, lighter, and cheaper components in electronics, vehicles, and led.
the process started with a common polymer being dissolved in water then electrolytes were added to raise the ph of the solution and make it alkaline. the monomers in the polymer chan took on a negative charge and repelled each other causing the chain to unfurl.
the final step was spraying the water and polymer solution onto plates with spin casting, which turned the solution into a solid plastic film.
“the process is a major departure from previous approaches, which have focused on adding metallic or ceramic fillers to plastics,” the article explained. “this has met with limited success; a large amount of fillers must be added, which is expensive and can change the properties of the plastic in undesirable ways. instead, the new technique uses a process that engineers the structure of the material itself.”
in tests, the engineers found that the polymer sheets were as conductive as glass, six times better than the same plastic prior to treatment. they also saw that the uncoiled chains became stiffer and packed together easier, which enhanced the thermal conductivity of the material.
“the team is now looking at making composites that combine the new technique with several other heat dissipating strategies to further increase thermal conductivity,” the article continued. “they're also working to apply the concept to other types of polymers beyond those used in this research. a commercial product is likely several years away.”
the research was recently published in science advances. the abstract stated:
“high thermal conductivity is critical for many applications of polymers (for example, packaging of light-emitting diodes), in which heat must be dissipated efficiently to maintain the functionality and reliability of a system.
“whereas uniaxially extended chain morphology has been shown to significantly enhance thermal conductivity in individual polymer chains and fibers, bulk polymers with coiled and entangled chains have low thermal conductivities (0.1 to 0.4 w m−1 k−1). we demonstrate that systematic ionization of a weak anionic polyelectrolyte, polyacrylic acid (paa), resulting in extended and stiffened polymer chains with superior packing, can significantly enhance its thermal conductivity.
“cross-plane thermal conductivity in spin-cast amorphous films steadily grows with paa degree of ionization, reaching up to ~1.2 w m−1 k−1, which is on par with that of glass and about six times higher than that of most amorphous polymers, suggesting a new unexplored molecular engineering strategy to achieve high thermal conductivities in amorphous bulk polymers.”