Cross-section scanning electron microscope images of pure graphene fiber (left) and graphene fiber after two-stage defect control using polydopamine (middle and right). Image: KAIST.
Cross-section scanning electron microscope images of pure graphene fiber (left) and graphene fiber after two-stage defect control using polydopamine (middle and right). Image: KAIST.

Researchers in Korea have shown that graphene fibers can be reinforced with a mussel-inspired polymer. A research group led by Sang Ouk Kim at the Korea Advanced Institute of Science and Technology (KAIST) has utilized polydopamine as an effective infiltrate binder to produce graphene-based liquid crystalline fibers with impressive mechanical and electrical properties. The group reports its work in a paper in Advanced Materials.

This bio-inspired defect engineering approach is clearly distinguishable from previous attempts at employing insulating binders and offers great potential for producing materials for use in flexible and wearable devices, as well as low-cost structural materials. The two-step defect engineering approach addresses the intrinsic limitation of graphene fibers, which arises from their folding and wrinkling during the fiber-spinning process.

Bio-inspired graphene-based fiber holds great promise for a wide range of applications, including flexible electronics, multifunctional textiles and wearable sensors. In 2009, Kim’s research group discovered graphene oxide liquid crystals in aqueous media while developing an effective purification process for removing ionic impurities. Graphene fibers, typically wet-spun from aqueous graphene oxide liquid crystal dispersions, are expected to demonstrate superior thermal and electrical conductivities, as well as outstanding mechanical performance.

However, owing to the inherent formation of defects and voids caused by the bending and wrinkling of the graphene oxide layer within graphene fibers, their mechanical strength and electrical/thermal conductivities are still far below the desired ideal values. Finding an efficient method for producing densely packed graphene fibers with a strong interaction between the layers is thus a critical challenge.

Kim's research group focused on the adhesion properties of polydopamine, a polymer inspired by the natural adhesive used by mussels, to solve the problem. This functional polymer, which is studied in various fields, can increase the adhesion between the graphene layers and prevent structural defects.

Using polydopamine as a binder, the group succeeded in fabricating high-strength graphene liquid crystalline fibers with controlled structural defects. They were also able to fabricate fibers with improved electrical conductivity by carbonizing the polydopamine.

Based on the theory that the high temperature annealing of polydopamine gives it a similar structure to graphene, the team optimized the dopamine polymerization conditions and showed that polydopamine could solve the inherent defect control problems of graphene fibers. They also confirmed that, compared with conventional polymers, polydopamine has improved electrical conductivity due to the influence of nitrogen in the dopamine molecules.

"Despite its technological potential, carbon fiber using graphene liquid crystals still has limits in terms of its structural limitations," said Kim. "This technology will be applied to composite fiber fabrication and various wearable textile-based application devices."

This story is adapted from material from KAIST, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.