Responsive epoxy is healed and reshaped under illumination

Chinese chemists have created an epoxy that can be rapidly hardened and reshaped by shining a light on it. Unlike traditional epoxies which are cured using heat, this approach uses carbon nanotubes to translate light energy into localised heat to set the epoxy. Shining additional light on the set polymer initiates self-healing and reshaping.

Standard epoxies are epoxide containing polymers that form thermosets through a crosslinking reaction triggered by a curative agent. This study takes advantages of vitrimers, a recently developed form of epoxy that uses a thermally triggered transesterification reaction to form crosslinks, so the polymer can be reshaped without altering the number of bonds.

The team, led by Yen Wei and Yan Ji at Beijing University, integrated carbon nanotubes, which are known for their photothermal translation capacity, within a vitrimer with the aid of a polymer of intrinsic microporosity, called PIM 1, which acted as a dispersal agent. With sufficient light intensity, the carbon nanotubes provided sufficient heat energy to reach the toplogy-freezing transition temperature (the equivalent of the glass transition temperature) and allowed reshaping and restructuring of the epoxy in a matter of minutes or seconds.

An ester and a hydroxyl group react with each other, producing a new ester and a new hydroxyl group, which continue to react

Team member Yang Yang explains that flexible welding techniques could also be used as carbon nanotubes can translate non-visible light, enabling the use of the technique on opaque polymers. In addition, ‘thermoplastics and epoxies with different chemical compositions can also be welded together,’ a task which isn’t possible with current epoxies and crosslinking polymers. Yang also highlights that the same mechanism that allows reshaping and restructuring also enables light based healing as any damage is “dissolved”.

Materials chemist Jyothirmayee Aravind, from Rowan University in the US, acknowledges the difficulty involved in reprocessing and welding thermosets such as epoxy, and says the work is ‘highly significant as it paves the way to practical applications of carbon nanotubes and vitrimers.’ Yang agrees, and adds that the team are looking to expand their research into practical applications such as remote welding and welding of heat sensitive components.