Nanocomposite films used to keep thin electronics cool


Friday, 30 September, 2022


Nanocomposite films used to keep thin electronics cool

Heat dissipation is essential for maintaining the performance of electronic devices; however, efficient heat dissipation is a concern for thin-film electronics, as conventional heat sinks are bulky and cannot be integrated into them. Thus, there is a need for thermal diffusion materials that are thin and flexible and can be implemented in thin-film devices for efficient heat dissipation.

Researchers from Japan have found that using sea squirts or ascidians can help solve this problem. The researchers prepared flexible nanocomposite films using an ascidian-derived cellulose nanofibre matrix and carbon fibre fillers — the prepared films demonstrated “excellent” anisotropic in-plane heat conduction and the carbon fibre fillers inside are reusable.

Currently, several substrate materials can act as heat diffusers as thin films, but most diffuse heat in the in-plane direction isotropically. This could create thermal interference with the neighbouring components of a device. Junior Associate Professor Kojiro Uetani from the Tokyo University of Science (TUS) said that for substrates on which multiple devices are mounted in high density, it is necessary to control the direction of thermal diffusion and find an effective heat removal path while thermally insulating between the devices. “The development of substrate films with high anisotropy in in-plane thermal conductivity is, therefore, an important target,” said Uetani.

In a recent study published in ACS Applied Materials & Interfaces, Uetani and his team, comprising Assistant Professor Shota Tsuneyasu from the National Institute of Technology, Oita College, and Professor Toshifumi Satoh from Tokyo Polytechnic University, reported a newly developed nanocomposite film made of cellulose nanofibres and carbon fibre-fillers that demonstrated in-plane anisotropic thermal conductivity. Many polymer composites with thermally conductive fillers have been proposed to enhance thermal conductivity; however, there are few reports on materials with particulate or plate-like fillers that exhibit thermal conductivity anisotropy, which is important to prevent thermal interference between adjacent devices. Fibrous fillers such as carbon fibres (CF), however, can provide in-place anisotropy in two-dimensional materials due to their structural anisotropy.

It is important to select matrices with high thermal conductivity. Cellulose nanofibres (CNFs) extracted from the mantle of ascidians have been reported to exhibit higher thermal conductivity (about 2.5 W/mK) than conventional polymers, making it suitable for use as a heat-dissipating material. Cellulose has a high affinity for carbon materials and is easy to combine with CF fillers. For example, hydrophobic CF cannot be dispersed in water by itself, but in the presence of CNF, it is easily dispersed in water. Accordingly, the researchers chose bio-based ascidian derived CNFs as the matrix.

For material synthesis, the team prepared an aqueous suspension of CFs and CNFs and then used a technique called liquid 3D patterning. The process resulted in a nanocomposite consisting of a cellulose matrix with uniaxially aligned carbon fibres. To test the thermal conductivity of the films, the researchers used laser-spot periodic heating radiation thermometry and found that the material showed a high in-plane thermal conductivity anisotropy of 433% along with conductivity of 7.8 W/mK in the aligned direction and 1.8 W/mK in the in-plane orthogonal direction.

The researchers also installed a powder electroluminescent (EL) device on a CF/CNF film to demonstrate the effective heat dissipation. In addition, the nanocomposite film could cool two closely placed pseudo heat sources without any thermal interference. Another major advantage of the CF/CNF films is their recyclability. The researchers were able to extract the CFs by burning the cellulose matrix, allowing them to be reused.

Overall, these findings can act as a framework for designing 2D films with novel heat-dissipating patterns and can also encourage sustainability in the process. “The waste that we humans generate has a huge environmental impact. Heat transfer fillers, in particular, are often specialised and expensive materials. As a result, we wanted to create a material that does not go to waste after usage but can be recovered and reused for further applications,” Uetani said.

Image credit: iStock.com/scanrail

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