A transparent toaster, clothing that heats up when it is worn, and a hand warmer that never turns off have become a reality.
A three-dimensional, flexible, transparent material that can stretch 300% and can emit heat of 300°C is developed.
Korea University Professor Sukgoo Yoon’s research team’s results are published in NPG Asia Materials. 

▲ From the left, First Authors: Korea University researcher Hongseok Jo (doctorate program) and researcher Seongpul An (combined master’s and doctorate program), Corresponding Author: Professor Sukgoo Yoon, School of Mechanical Engineering 

Recently, with Korean researchers leading the way, copper fibers were used to fabricate a transparent heat-emitting heater that could be shaped into a 3D structure and is capable of stretching 300% and emitting heat up to 300°C.

Nanocarbon material, such as CNT (carbon nanotube) and graphene, is most commonly used in the heat-emitting heaters, but has weaknesses due to low flexibility and low heat-emission efficiency. Although silver nanowire (AgNW) has been lauded as a high-performance, transparent heat-emitting element for its excellent ductility and electrical conductivity, in addition to its diameter, which can be as small as a nanometer (nm, one billionth of a meter), the small size has several drawbacks, such as low electric conductivity caused by wire contact resistance and low heat durability.

In order to overcome the drawbacks of Indum Tin Oxide and silver nanowires, Professor Yoon’s research team first fabricated a polymer copper fiber a couple hundred nanometers (close to 1/M nm the thickness of a human hair) in size, and then electrically plated the surface with copper into the form of a net. By combining it with a high-elasticity polymer, Silicon rubber (ECO flex), they were able to develop a high-stretch, transparent heat-emitting element.

Accordingly, the research team confirmed that by utilizing the exceptional electric conductivity characteristic of copper and adding a net-shaped network structure, the copper fiber heat-emitting element’s electric conductivity proved to be ten times better than the current silver nanowire technology. When applying as little voltage as 1.5V, the research team reported high-performance operability even with high heat emittance of up to 328°C while registering 300% against a elasticity test.

Professor Yoon stated, “This transparent heat-emitting element can not only be bent to below 1mm in bending radius, but also could maintain its heat-emitting performance when stretched to 300% and above. Considering it is a low-power, transparent heat-emitting element, we have obtained the technology to apply to home appliances including electric heaters, next generation wearable applications, and personal heat management fields.”

The research results were published in the globally prestigious Nature Journal’s sister publication, NPG Asia Materials. Korea University Professor “Sam” Sukgoo Yoon contributed as a corresponding author with Korea University researchers Hongseok Jo (doctorate program) and Seongpil An (combined master’s and doctorate program) contributing as co-first authors.