Thermally conductive polymer composites consist of fillers oriented in certain directions that form pathways for heat flow. However, conventional methods to control the orientation of these fillers are energy-intensive and require surface modifications that can deteriorate the quality and properties of these materials. Now, researchers from South Korea have developed an energy-efficient method to control the orientation of the fillers without the need for surface modification, resulting in improvement in thermal conductivity.

Owing to their lightweight nature and flexibility, thermally conductive polymer composites are applied between a heat source and a sink in electronics to dissipate the generated heat to the surroundings. Efficient heat dissipation is achieved due to the use of fillers with certain orientations that facilitate heat flow. The conventional process of modifying the orientation of the filler material, however, is an energy-intensive process that requires the use of electric/magnetic fields and surface modifications that can compromise the filler’s quality and its thermal properties.

Now, in a new study, Professor Chae Bin Kim and his team at Pusan National University, Republic of Korea, have developed an energy-efficient process to change the orientation of the filler without the need for surface modifications.

This paper was made available online on 17 October 2022 and will be published in Volume 117 of the journal Polymer Testing on 1 January 2023.

The proposed method makes use of thermophoresis, a phenomenon in which a temperature gradient causes solid particles suspended in a fluid medium to move or rotate. To prepare the polymer composite, the researchers suspended thermally conductive hexagonal boron nitride (h-BN) filler particles in a UV-curable liquid and coated it between two glass plates. A temperature gradient was applied along the film thickness, causing the filler particles to rotate, and realign along the applied temperature gradient. On achieving the desired orientations, the composite was photocured, resulting in a solid composite with fixed filler orientations that form a heat transfer pathway.

“To our best knowledge, the current study is the first experimental demonstration of controlling anisotropic filler orientation using thermophoresis,” says Professor Kim.

Thermally conductive polymer composites such as thermal paste are used in phones, laptops, even in batteries. Considering the growing production of electronics and the expected transition to electric vehicles, the proposed method has the potential to lower the energy cost of manufacturing thermally conductive polymer composites. Furthermore, by avoiding the need for surface modifications, highly efficient thermally conductive polymer composites can be developed for improved heat dissipation and extend the life of electronics.

“Efficient heat dissipating materials can ensure best operating conditions for the device with improved reliability, lifespan, and user’s safety,” says Professor Kim.

Apart from improving thermal conductivity, fillers are also used to alter a composite’s optical, electrical, and mechanical properties. By offering a way to reorient the filler without any surface modifications, the proposed method can also be adopted to tune the properties of a wide range of polymer composites without deteriorating their quality.

Title of original paper: Thermally conductive 2D filler orientation control in polymer using thermophoresis.

Journal: Polymer Testing

Pusan National University, located in Busan, South Korea, was founded in 1946, and is now the no. 1 national university of South Korea in research and educational competency. The multi-campus university also has other smaller campuses in Yangsan, Miryang, and Ami. The university prides itself on the principles of truth, freedom, and service, and has approximately 30,000 students, 1,200 professors, and 750 faculty members. The university is composed of 14 colleges (schools) and one independent division, with 103 departments in all.

Website: https://www.pusan.ac.kr/eng/Main.do

Prof. Chae Bin Kim is an Assistant Professor of Polymer Science and Engineering at Pusan National University (PNU), South Korea. His current research interests are various interfacial phenomena in polymers for realizing practical applications including sustainable and recyclable networked polymers, functional polymer composites, adhesives, patterned thin films, and coatings. Before coming to PNU, he worked as a research scientist at Korea Institute of Science and Technology (KIST). In 2016, Chae Bin Kim received a PhD in Chemical Engineering from the University of Texas at Austin.