𝐅𝐫𝐨𝐦 𝐭𝐨𝐨𝐭𝐡𝐛𝐫𝐮𝐬𝐡𝐞𝐬 𝐭𝐨 𝐚𝐞𝐫𝐨𝐬𝐩𝐚𝐜𝐞: 𝐆𝐫𝐚𝐩𝐡𝐞𝐧𝐞 𝐫𝐞𝐬𝐞𝐚𝐫𝐜𝐡 𝐚𝐝𝐯𝐚𝐧𝐜𝐞𝐬 𝐟𝐢𝐛𝐞𝐫𝐬 𝐭𝐡𝐚𝐭 𝐜𝐨𝐧𝐝𝐮𝐜𝐭 𝐡𝐞𝐚𝐭 𝐞𝐟𝐟𝐢𝐜𝐢𝐞𝐧𝐭𝐥𝐲

KAIST's discovery of graphene oxide liquid crystals in 2011 laid the foundation for 15 years of research worldwide, leading to technologies for producing graphene fibers with high strength and thermal conductivity. The fundamental materials research that helped bring antibacterial toothbrushes and functional sportswear to market is now advancing into materials for thermal management.

Professor Sang Ouk Kim's team in the Department of Materials Science and Engineering has published a commentary in Nature Materials, examining recent advances in high-performance graphene fibers based on graphene oxide liquid crystals and their scientific significance.

Graphene oxide consists of graphene, a single layer of carbon atoms arranged in a honeycomb structure, with oxygen functional groups attached. Graphene is strong and conducts heat and electricity well, but its poor dispersibility in water makes it difficult to process in liquid form.

By contrast, the oxygen functional groups allow graphene oxide to disperse readily in water, making it easier to formulate into inks, apply as coatings or spin into fibers.

In 2011, Kim's team was the first in the world to report that graphene oxide dispersed in water above a certain concentration spontaneously forms a liquid-crystalline state in which its thin sheets align in a common direction.

Alignment enables fiber spinning

Under certain conditions, graphene oxide sheets floating randomly in water align like a scattered deck of cards arranged to face the same direction. This alignment allows graphene oxide to be drawn into long fibers while maintaining the sheets' orientation along the fiber axis.

Following this discovery, researchers worldwide have developed methods for producing graphene fibers from graphene oxide liquid crystals. Conventional methods, however, have faced problems such as breaks in the liquid filament during drawing and insufficiently aligned or loosely packed graphene sheets, which leave voids and defects within the fibers.

These problems have limited efforts to improve strength and thermal conductivity simultaneously.

In their commentary, Kim's team discussed recent research addressing these limitations and examined how research on graphene oxide liquid crystals has led to technologies for manufacturing high-performance fibers.

Stretching fibers into alignment

Researchers at Zhejiang University in China recently dispersed graphene oxide in highly viscous glycerol, giving the dispersion viscoelastic properties similar to those of a polymer solution. This enabled "ultrahigh-ratio drawing" during wet spinning, allowing the graphene oxide dispersion to be stretched much further than before.

During this process, the graphene oxide sheets become more closely aligned along the fiber axis, reducing internal voids and defects. Subsequent heat treatment at high temperatures promotes the growth of large, aligned graphitic crystallites, producing lightweight, strong graphene fibers with high thermal and electrical conductivity.

The graphene fibers produced in this recent study were reported to have a tensile strength of up to 5.9 gigapascals (GPa) and a thermal conductivity of up to 1,720 watts per meter per kelvin (W/(m·K)). In simple terms, the fibers resist breaking when pulled and transfer heat quickly. These results show how denser packing and better alignment of graphene oxide sheets can improve both strength and thermal conductivity.

In the commentary, Kim's team highlighted how research on graphene oxide liquid crystals, first discovered in 2011, has progressed from observing a fundamental phenomenon to processing a two-dimensional material through flow and stretching, much like a polymer solution.

The phenomenon of graphene oxide self-alignment, discovered by KAIST researchers 15 years ago, has, through continued follow-up research worldwide, expanded into technology for producing fibers that are both strong and highly conductive of heat.

source : Phys.org