CNT wires for wearable electronic devices from the existing fiber manufacturing process!

Dr. Han Joong Tark's team at KERI's Nano Hybrid Technology Research Center has successfully fabricated ‘functional wires’, which are the foundation of wearable electronic devices, by directly applying the existing synthetic fiber processing methods.

Wearable electronic devices, which can be attached to or worn on the body, such as on the wrist, ear, or eyes, have long become a part of our daily lives in various forms like smartwatches, glasses, and earphones. The key to these devices is that they must be lightweight while maintaining long-lasting performance. While there have been various efforts to achieve this, one of the most important elements is the conductive functional wire, which is a crucial material.

KERI's achievement is a high-energy, lightweight wire made using single-walled carbon nanotubes (CNT)¹⁾. CNT is a new material that is 100 times stronger than steel and has electrical conductivity comparable to copper. The carbon atoms in CNT are connected in hexagonal rings, forming a long cylindrical shape, which also gives it excellent flexibility. In particular, CNT has the advantage of significantly increasing energy density even with a small amount of addition, which allows for a substantial reduction in the amount of heavy copper used in electronic devices. However, CNT has a strong tendency to agglomerate, forming tangled structures and it is difficult to disperse CNTs using organic solvents and other methods. Therefore, applying CNT in the field of electronics and electrical devices requires highly advanced and sophisticated technology.
^{Carbon nanomaterials are conductive materials at the nanoscale, made of carbon atoms arranged in a hexagonal pattern. These include graphene, a two-dimensional planar structure often referred to as the ‘dream material’, and carbon nanotubes (CNT), which are structures formed by graphene spiraling into a cylindrical shape. Among them, CNTs are classified into multi-walled and single-walled varieties, with single-walled CNTs being thinner and more transparent, offering superior material properties and electrical conductivity.}

To address this, ▲ Dr. Han Joong Tark's team first introduced a small amount of strong acid and additives to the CNT powder to add ‘oxygen functional groups’ onto the surface that are compatible with solvents. They then kneaded the mixture and stored it at a low temperature (2°C) for a certain period. This method mimics the process used in making bread or noodles, where flour is mixed with water and additives to undergo maturation. By doing this, when CNTs are highly functionalized with less defective structures on the surface, maximizing its performance.

In addition, ▲ 'graphene oxide' with a size-controlled to around 100 nanometers (nm) was added, and then, ▲ following the same process as the conventional synthetic fiber manufacturing method, the CNT paste (dope) was spun through multiple small holes to form multi-filament in coagulation bath. In this process, the size-controlled graphene oxide enhanced the dispersion of the CNT dope and significantly reduced the nozzle clogging during spinning. Finally, the CNTs with oxygen functional groups, after undergoing the spinning process, ▲ are bonded into a single strand through hydrogen bonding, forming functional wires like a spiderweb.

KERI produced CNT wires in the form of textile supercapacitors through Dr. Kim Taehoon's team at the Korea Institute of Materials Science (KIMS) and evaluated their performance, confirming excellent energy storage capabilities. Additionally, through Professor Lee Wi Hyeong's research team at Konkuk University, it was confirmed that CNT wires with oxygen functional groups also exhibited excellent gas sensor performance for detecting the presence of harmful gases. This functionality could be greatly applied in smart clothing, such as for firefighters' fire suppression efforts or in defense fields.

The research results were recognized for their excellence and published in *ACS Nano*, a top-tier SCI journal in the field of nanoscience, published by the American Chemical Society. The journal's impact factor, evaluated by the JCR Impact Factor, is 15.8, placing it in the top 7.9% of its field.

KERI's Dr. Han Joong Tark said, "This is the world's first achievement of dispersing functionalized CNTs in organic solvents for solution spinning. It will drive the development of lightweight and long-lasting wearable electronic devices." He also mentioned, "Through continuous research, this technology could replace copper wires in future mobility fields, such as electric vehicles and drones, greatly improving both lightweight design and energy efficiency."

Meanwhile, KERI is a government-funded research institute under the National Research Council of Science & Technology (NST) of the Ministry of Science and ICT. This research was conducted as part of KERI's research projects, with support from the Creative Convergence Research Program of the National Research Council of Science & Technology (NST) and the Individual Research Program of the National Research Foundation of Korea (NRF). <KERI>