Key Takeaways & Executive Findings
- •• A directional freezing technique using polyimide enables vertical alignment of graphene nanosheets, significantly enhancing through-plane thermal conductivity. • The PG/PDMS composite with 21.1% PG achieves a through-plane thermal conductivity of 14.56 W·m−1·K−1, 81 times that of pure PDMS. • The method recycles scraps of highly conductive graphene films, offering a sustainable approach for TIM fabrication. • The polyimide-assisted alignment improves the order and density of the foam, enhancing both mechanical strength and heat transfer performance.
Abstract
Graphene and its derivatives are often preferentially oriented horizontally during processing because of their two-dimensional (2D) layer structure. As a result, thermal interface materials (TIMs) composed of a polymer matrix and graphene-derived fillers often have a high in-plane (IP) thermal conductivity (K), however, the low through-plane (TP) K makes them unsuitable for practical use. We report the development of high-quality polyimide/graphite nanosheets (PG) perpendicular to the plane using a directional freezing technique that increase the TP K of polymer-based composites. Graphene-derived nanosheets (GNs) were obtained by the crushing of scraps of highly thermally conductive graphene films. A water-soluble polyamic acid salt solution was used to disperse the hydrophobic GNs filler to achieve directional freezing. The polyimide, which facilitated the directional alignment of the GNs, was then graphitized. The introduction of the GNs increases the order and density of the PG, thus improving the strength and heat transfer performance of its polydimethylsiloxane (PDMS) composite. The obtained PG/PDMS composite (21.1% PG, mass fraction) has an impressive TP K of 14.56 W·m−1·K−1, 81 times that of pure PDMS. This simple polyimide-assisted 2D hydrophobic fillers alignment method provides ideas for the widespread fabrication of anisotropic TIMs and enables the reuse of scraps of graphene films.
1. Introduction
The performance of integrated circuits often degrades significantly or fails to operate due to overheating. Consequently, effective thermal management materials are vital for the optimal operation of high-power electronic devices[1–3]. Polymer-based thermal interface materials (TIMs) are widely investigated for the heat dissipation of electronic devices due to their multiple merits of lightweight, chemical stability, easy processability, and cost-effectiveness[4–6]. However, polymers generally exhibit low thermal conductivity (K) (～0.5 W·m−1·K−1) due to the disordered structures and entanglements which cause considerable phonon scattering[7–8]. To improve the K of composites, thermally conductive fillers are often compounded with polymers for the goal of increasing the phonon transport path[9].
Graphene and its derivatives are considered to be the most promising candidates for thermal fillers because of their high in-plane (IP) K[10–14]. Lin et al. obtained polymer/graphene composites with K of 1.43 − 1.84 W·m−1·K−1 by first coating the polymer powder with graphene and then hot pressing, in which the graphene content was 10% (mass fraction)[15]. Fang et al. prepared polyvinyl butyral (PVB)/graphene composites by solution blending, and the K of the sample reached 4.52 W·m−1·K−1 with 30% (mass fraction) graphene nanoplates[16]. Nevertheless, even with high graphene concentration, the K of composites formed by directly mixing graphene sheets with polymer matrix did not rise as significantly as predicted. It is mostly owing to the disconnected phonon transport channel between the filler and polymer matrix and the large filler-filler interfacial thermal resistance, which can be mitigated by pre-establishing three-dimensional (3D) filler networks in the polymer matrix[17–22]. Bai et al. fabricated graphene foams with 3D inte...
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XIONG Ke, SUN Zhi-peng, HU Ji-chen, MA Cheng, WANG Ji-tong, GE Xiang, QIAO Wen-ming, LING Li-cheng (2025). Polyimide-assisted fabrication of highly oriented graphene-based all-carbon foams for increasing the thermal conductivity of polymer composites. SinoTechIntel Verified Research. https://doi.org/10.1016/S1872-5805(NCM2024-39-02-06)
Research & Educational Purpose Only:The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntel are intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
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Frequently Asked Questions
What is the main challenge in using graphene-based fillers for thermal interface materials?
Graphene fillers tend to align horizontally, leading to high in-plane but low through-plane thermal conductivity, which is unsuitable for practical TIM applications.
How does the polyimide-assisted directional freezing technique work?
A water-soluble polyamic acid salt solution disperses hydrophobic graphene nanosheets, and directional freezing aligns them vertically. The polyimide is then graphitized to form a highly oriented all-carbon foam.
What is the achieved through-plane thermal conductivity of the PG/PDMS composite?
The PG/PDMS composite with 21.1% PG achieves a through-plane thermal conductivity of 14.56 W·m−1·K−1, which is 81 times that of pure PDMS.
What are the environmental benefits of this method?
The method recycles scraps of highly thermally conductive graphene films, reducing waste and providing a sustainable approach for fabricating anisotropic thermal interface materials.
What are the potential applications of this anisotropic foam?
The highly oriented graphene-based all-carbon foams can be used as fillers in polymer composites for thermal management in high-power electronic devices, improving heat dissipation efficiency.
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