New nano composite film enhances heat dissipation of thin electronic materials

It is reported that in the past decades, with the development of thinner, lighter, more flexible and stronger equipment, electronic technology has made great progress. However, as the equipment becomes thinner and thinner, the space to accommodate internal working components becomes smaller and smaller. This has caused the problem of improper heat dissipation of thin-film devices, because traditional radiator materials are bulky and cannot be integrated into them. Therefore, thin and flexible thermal diffusing materials are required and can be realized in thin film devices to achieve effective heat dissipation.

In a new study, scientists from Japan designed a flexible thermal diffusion film made of cellulose nanofiber matrix and carbon fiber filler using a three-dimensional liquid model. The prepared films have large anisotropy of thermal conductivity in the plane direction, which promotes heat dissipation and avoids thermal interference between heat sources to film electronic devices.

Source:Kojiro Uetani from TUS, Japan

They synthesized CF/CNF composite films with uniaxial arrangement through the three-dimensional liquid model of CFs and CNF water suspension derived from sea squirts, and proved the thermal conductivity anisotropy of the film plane. The top emitting powder electroluminescence device was installed on the film, and its heat dissipation performance was tested. Fit two approximate heat sources, and evaluate the heat insulation performance and heat dissipation performance in different directions between the two heat sources. In addition, CF was extracted from the composite membrane by heat treatment at a specific temperature, and its reusability as a thermal conductive filler was studied.

"For a substrate with multiple devices installed at high density, it is necessary to control the direction of thermal diffusion and find an effective heat dissipation path while insulating the devices. Therefore, it is an important goal to develop a substrate film with high anisotropy in the in-plane thermal conductivity." Kojiro Uetani, a junior associate professor at Tokyo University of Science (TUS), Japan, explained.

Directional CF/CNF composite membrane. (a) Liquid 3D pattern setup and pattern program used in (b). (c) The appearance of the gel is shaped when the clot is gently removed after setting. (d) The aligned CF10 film is formed by drying the patterned gel. (e) Calibrate CF alignment angle distribution in CF10 and Random-CF10 films. (f) Height profile on each film filter side. (g) Thermal conductivity of CF/CNF films in all directions. (h) In plane thermal conductivity and (i) in-plane anisotropy of thermal conductivity and filler content of different 2D materials.

Their research was published in ACS. In the research, a newly developed nanocomposite film made of cellulose nanofibers and carbon fiber fillers was reported, which showed excellent in-plane anisotropic thermal conductivity.

It is also important to select a matrix with high thermal conductivity. It is reported that cellulose nanofibers (CNF) extracted from mantle worms have higher thermal conductivity (about 2.5 W/mK) than traditional polymers, making them suitable for use as heat dissipation materials. As demonstrated by the ability to write on paper with a pencil, cellulose has a high affinity for carbon materials and is easy to combine with CF fillers. For example, hydrophobic CF itself cannot be dispersed in water, but in the presence of CNF, it is easily dispersed in water. Therefore, the team chose CNF derived from ascidian as the matrix.

Heat dissipation test of top emitting powder EL devices formed on CF/CNF films.

For material synthesis, the team prepared aqueous suspensions of CF and CNF, and then used a technology called liquid 3D patterning. This process produces a nanocomposite consisting of a cellulose matrix with carbon fibers aligned with carbon monoxide. To test the thermal conductivity of the film, the team used the laser point periodic heating radiation temperature measurement method. They found that the material exhibited high in-plane thermal conductivity anisotropy of 433%, the conductivity in the aligned direction was 7.8 W/mK, and the conductivity in the in-plane orthogonal direction was 1.8 W/mK. They also installed powder electroluminescent (EL) devices on CF/CNF films to demonstrate effective heat dissipation. In addition, the nanocomposite film can cool two closely placed pseudo heat sources without any thermal interference.

Two heat dissipation tests close to the heat source.

In addition to excellent thermal properties, another major advantage of CF/CNF films is their recyclability. The researchers were able to extract CF by burning cellulose matrix, which can be reused. In general, these findings can not only serve as a framework for designing 2D films with novel heat dissipation modes, but also promote the sustainability of the process.

Source:Thermal Diffusion Films with In-Plane Anisotropy by Aligning Carbon Fibers in a Cellulose Nanofiber Matrix, ACS Applied Materials & Interfaces (2022). DOI: 10.1021/acsami.2c09332