From toothbrushes to space: KAIST's graphene technology keeps evolving

- Graphene oxide liquid crystal first discovered worldwide in 2011

- Research expands into high-strength, high-thermal-conductivity fibers

Professor Kim Sang-uk holds a graphene fiber. [Provided by KAIST]

A homegrown graphene technology already used in toothbrushes and sportswear is advancing into cutting-edge materials research for electric vehicles and aerospace applications. A graphene oxide liquid crystal technology that KAIST first discovered 15 years ago has evolved — through follow-up research around the world — into a manufacturing process for high-performance graphene fibers that are light, strong and highly thermally conductive.

KAIST announced Friday that a research team led by Professor Kim Sang-uk of the Department of Materials Science and Engineering had published a commentary in the "News & Views" section of the international journal Nature Materials, analyzing the development and academic significance of high-performance graphene fiber research based on graphene oxide liquid crystals.

Graphene is an ultrathin material in which carbon atoms are arranged in a honeycomb lattice. It offers high strength and excellent electrical and thermal conductivity, but its poor dispersibility in water makes it difficult to process.

Graphene oxide, produced by bonding oxygen to graphene, disperses easily in water and can be processed into a wide range of forms, including inks, coatings and fibers.

In 2011, Kim's team became the first in the world to discover that graphene oxide forms a liquid crystal state — in which thin, plate-like sheets align in a single direction — once its concentration in water exceeds a certain threshold. This property allows graphene oxide to be drawn out into long, thread-like fibers with a consistent orientation.

Researchers around the world subsequently entered the graphene fiber manufacturing race, but struggled to improve both strength and thermal conductivity simultaneously, as the spinning process often caused the solution to break or left internal voids and defects in the fibers.

Researchers at Zhejiang University in China recently overcame these limitations by dispersing graphene oxide in high-viscosity glycerol. Applying an ultra-high-draw-ratio spinning technique — which stretches the solution intensely to form fibers — they improved the alignment of graphene sheets and reduced internal defects.

Adding high-temperature heat treatment further densified the graphene structure, boosting both strength and thermal conductivity at the same time.

Graphene oxide liquid crystal technology (AI-generated image). [Provided by KAIST]

Graphene fibers developed in subsequent research achieved a tensile strength of up to 5.9 gigapascals (GPa) and a thermal conductivity of up to 1,720 watts per meter-kelvin (W/m·K), demonstrating that a high-performance fiber capable of resisting breakage while rapidly transferring heat had been successfully realized.

KAIST's foundational technology has also led to the commercialization of consumer products.

A graphene antibacterial toothbrush incorporating technology from Sojaechanjo — a faculty startup founded by Kim — has sold more than 14 million units since its 2023 launch. Functional fibers using Graphentex materials were used in the uniforms of the taekwondo demonstration team at the 2024 Paris Olympics, and their applications are expanding into golf wear, sportswear and bedding.

High-performance graphene fibers are expected to find future use in thermal management materials for controlling heat in electronic devices, lightweight components for electric vehicles and aerospace, and wearable electronics and smart clothing.

"The graphene oxide liquid crystal we discovered in 2011 has now advanced, through follow-up research by teams around the world, into high-performance graphene fibers with exceptional strength and thermal conductivity," Kim said. "It is significant that a single piece of basic research is expanding its reach — from everyday consumer products to advanced materials for electronics, mobility and aerospace."

nbgkoo@heraldcorp.com