These photos show how the novel material can self-heal to restore many different functions, even after multiple breaks. Photos: Qing Wang, Penn State.
These photos show how the novel material can self-heal to restore many different functions, even after multiple breaks. Photos: Qing Wang, Penn State.

A major stumbling block in the advance of flexible, wearable electronics has been the fact that existing electronic materials do not function well after breaking and healing. An international team of scientists has now overcome this stumbling block by developing a new electronic material that can heal all its functions automatically even after breaking multiple times.

"Wearable and bendable electronics are subject to mechanical deformation over time, which could destroy or break them," said Qing Wang, professor of materials science and engineering at Penn State. "We wanted to find an electronic material that would repair itself to restore all of its functionality, and do so after multiple breaks."

Self-healable materials are naturally able to repair themselves with little to no external influence after subjected to physical deformation such as being cut in half. In the past, researchers have been able to create self-healable materials that can restore one function after breaking, but restoring a suite of functions is critical for creating effective wearable electronics. For example, if an insulating dielectric material retains its electrical resistivity after self-healing but not its thermal conductivity, it could be at risk of overheating.

The novel dielectric material that Wang and his team created can restore all the properties needed in wearable electronics – mechanical strength, breakdown strength to protect against surges, electrical resistivity, thermal conductivity and insulating properties. The researchers report this novel material in a paper in Advanced Functional Materials.

Most self-healable materials are soft or ‘gum-like’, said Wang, but the material he and his colleagues created is very tough in comparison. They produced the material by adding boron nitride nanosheets to a base polymer. Like graphene, boron nitride nanosheets are two dimensional, but instead of conducting electricity like graphene they resist and insulate against it.

"Most research into self-healable electronic materials has focused on electrical conductivity but dielectrics have been overlooked," said Wang. "We need conducting elements in circuits but we also need insulation and protection for microelectronics."

The novel material is able to self-heal because boron nitride nanosheets connect to one another using hydrogen bonding groups functionalized onto their surface. When two nanosheets are placed in close proximity to each other, the electrostatic attraction naturally occurring between both bonding elements draws them close together. When the hydrogen bonds are restored, the two pieces are ‘healed’. Depending on the percentage of boron nitride nanosheets added to the polymer, this self-healing may require additional heat or pressure, but some forms of the new material can self-heal at room temperature when placed next to each other.

Unlike other self-healable materials that use hydrogen bonds, boron nitride nanosheets are impermeable to moisture. This means that devices using this dielectric material can operate effectively within high humidity contexts such as in a shower or at a beach. "This is the first time that a self-healable material has been created that can restore multiple properties over multiple breaks, and we see this being useful across many applications," said Wang.

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