A University of Illinois Urbana-Champaign Materials Science and Engineering team has uncovered liquid crystalline epoxy resins with high thermal conductivity that is up to 5 times that of common polymers.
The research was spearheaded by UIUC’s Professor David Cahill (Grainger Distinguished Chair in Engineering, co-director of the IBM-Illinois Discovery Accelerator Institute, and IQUIST affiliate), along with Associate Professor Christopher Evans, Dr. Guangxin Lv (recent UIUC graduate and current MIT postdoc), and Dr. Chengtian Shen (recent UIUC graduate). The team worked closely with ALTANA’s ELANTAS division, a leading manufacturer of insulating and protective materials focusing on the global electrical and electronic industry. This work for the industrial application of epoxy resin as thermal management materials was supported by ALTANA Institute.
Polymers are made of large molecules composed by multiples of repeating subunits and they are everywhere! With applications that range from adhesives, to packaging materials, to electronic devices and even medicine, polymers are omnipresent and can be naturally or synthetically made. Liquid crystalline polymers are another class of polymers with properties between that of glassy polymers (with no long-range order in molecular structure) and crystalline polymers (with molecular order).
Despite their pervasiveness, polymers tend to have low thermal conductivities and recent research has focused on controlling the structure of materials to enhance or suppress thermal conductivity. One way of doing this is by precisely controlling the lengths of ethylene repeat units (like beads on a necklace) along a polymer. Changes in molecular structure can cause variations in the properties of the polymer and new materials can be designed using this information.
To study the thermal conductivities of epoxy resins (a common polymer), the team changed the linker length one unit at a time. Cahill explains a major result of this study was “pronounced odd-even effects of ethylene linker length found on liquid crystal formation and thermal conductivity of epoxy resin. Liquid crystalline structure and high thermal conductivity only exists in the epoxy resins with even-numbered linker lengths.”
The odd-even effect is an interesting phenomenon that describes the change in properties of materials depending on the odd or even number of repeating structural units in a molecule. The epoxy resin studied showed even values of the ethylene linker length have high thermal conductivity and liquid crystalline structure, while odd values of the ethylene linker length have low thermal conductivity (comparable to that of conventional epoxy) and lack liquid crystalline order. Cahill emphasized that “liquid crystalline order strongly enhances thermal conductivity and we were able to isolate that effect with very minor changes to the chemical structure of the polymer.”
Compared to common polymers, Lv reports that epoxy resins have higher thermal conductivity up to 5 times greater, thus making them highly attractive as thermal management materials. However, Cahill mentions that “these particular molecules are very difficult to synthesize” due to the large number of steps in the synthesis of the resin and the low yield the synthesis produces. Despite this, “the findings of this research indicate that controlling precise linker length is a powerful route to molecular design of thermally conductive polymers,” Lv says hopefully.
To read more about this research, check out the paper recently published in Proceedings of the National Academy of Sciences (PNAS).
About The Grainger College of Engineering
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ELANTAS produces protection and electrical insulating materials for the electrical and electronics industry. They are used in electric motors, household appliances, cars, generators, windmills, solar units, batteries, transformers, capacitors, computers, lamps, and sensors and support product design engineers to construct ever smaller and more powerful electrical and electronic devices, thus saving materials and energy. At the same time the products enhance the life cycle of such electrical and electronic devices. The ALTANA division, which is managed by a holding company headquartered in Wesel/Germany, has eight manufacturing companies in all major regions worldwide. In 2021, ELANTAS employed a total workforce of 1.061 people.
Proceedings of the National Academy of Sciences
Odd–even effect on the thermal conductivity of liquid crystalline epoxy resins