Researchers from the Institute of Metal Research (Chinese Academy of Sciences), the University of Science and Technology of China, and Xi'an Rare Metal Materials Institute Co., Ltd. have developed a new thermal interface material (TIM) that combines high thermal conductivity with the compressibility needed to fill microscopic air gaps between heat-generating components and heat sinks - a combination that has been difficult to achieve in a single material.
The team built a vertically oriented, porous skeleton from short pitch-based carbon fibers (CFs), which have an exceptional axial thermal conductivity of 900 W/m·K, and bridged the individual fibers together using a small amount of graphene oxide (GO). "Graphene oxide acts as an inorganic adhesive," said Dr. Han Wang, co-corresponding author of the study. "It effectively bonds individual carbon fibers together through π–π interactions, creating continuous thermal transport pathways while significantly reducing interfacial thermal resistance. This is a key advantage over traditional polymer binders like cellulose, which hinder heat flow."
The skeleton was formed using a directional freezing technique - casting a CF-GO slurry into a mold and cooling it from the bottom with liquid nitrogen so the fibers and GO are organized into long-range ordered architectures as the ice front advances - followed by freeze-drying and vacuum-assisted infiltration with polydimethylsiloxane (PDMS). "At a carbon fiber loading of just 25.2 wt%, the resulting CF-GO/PDMS composite achieved a through-plane thermal conductivity of 7.61 W/m·K - a 41-fold increase over neat PDMS and a 57.6% improvement over composites made with cellulose binders," said Wang. The thermal conductivity enhancement efficiency reached 162.9% per 1 wt% of filler added, which the researchers say outperforms previously reported CF/PDMS composites. Measured interfacial thermal resistance in the CF-GO skeleton was about 30% lower than in an equivalent cellulose-bonded skeleton, and in a heating test the CF-GO/PDMS composite reached a maximum surface temperature of 96.5°C - 5°C higher than the cellulose-bonded version - reflecting its faster heat transfer.
Despite the added carbon fiber, the porous architecture keeps the material soft. "The porous structure constructed from short-cut fibers allows the material to deform easily under pressure," said co-corresponding author Professor You Zeng. "The composite exhibited a low compressive modulus of only 6.91 MPa, ensuring it can conform to uneven surfaces and fill air gaps without damaging delicate electronic components." Cyclic compression testing over 50 cycles confirmed the composite's mechanical stability and resilience.
"Our findings demonstrate that using graphene oxide as a nanoscale bridge - rather than as a primary filler - can unlock the full potential of high-conductivity carbon fibers," added Zeng. "We believe this strategy offers a practical and scalable route to next-generation thermal interface materials for advanced electronics cooling."
The team plans to further optimize the structure and explore covalent bonding strategies to push thermal conductivity even higher for engineering applications.
