Self-healing, flexible electronic material restores functions after multiple breaks

May 18, 2016

Penn State researchers have developed a flexible electronic material that self-heals to restore multiple functions, even after repeated breaks. (Top row) The material is cut in half, then reattached. After healing for 30 minutes, the material is still able to be stretched and hold weight. (credit: Qing Wang, Penn State)

A new electronic material created by an international team headed by Penn State scientists can heal all its functions automatically, even after breaking multiple times. The new material could improve the durability of wearable electronics.

Electronic materials have been a major stumbling block for the advance of flexible electronics because existing materials do not function well after breaking and healing.

“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, 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.”

In the past, researchers have been able to create self-healable materials (such as these, covered on KurzweilAI) that can restore a single function after breaking. But restoring a suite of functions is critical for creating effective wearable electronics. For example, if a dielectric material retains its electrical resistivity after self-healing but not its thermal conductivity, that could put electronics at risk of overheating.

The material that Wang and his team created restores all properties needed for use as a dielectric in wearable electronics — mechanical strength, breakdown strength to protect against surges, electrical resistivity, thermal conductivity, and dielectric (insulating) properties. They published their findings online in Advanced Functional Materials.

“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.” Most self-healable materials are also soft or “gum-like,” said Wang, but the material he and his colleagues created is very tough in comparison.

SEM images of healing process of polymer nanocomposite with 8% volume boron nitride nanosheets: (i) freshly cut, (ii) healing in 15 min, and (iii) completely healed in 30 min (credit: Lixin Xing et al./Advanced Functional Materials)

His team added boron nitride nanosheets to a base material of plastic polymer. The material is able to self-heal because boron nitride nanosheets connect to one another with hydrogen bonding groups functionalized onto their surface. When two pieces are placed in close proximity, the electrostatic attraction naturally occurring between both bonding elements draws them close together. When the hydrogen bond is 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 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.

Harbin Institute of Technology researches also collaborated on this research, which was supported by the China Scholarship Council.

Penn State Research Communications | Flexible Insulator

Abstract of Self-Healable Polymer Nanocomposites Capable of Simultaneously Recovering Multiple Functionalities

The continuous evolution toward electronics with high power densities and integrated circuits with smaller feature sizes and faster speeds places high demands on a set of material properties, namely, the electrical, thermal, and mechanical properties of polymer dielectrics. Herein, a supramolecular approach is described to self-healable polymer nanocomposites that are mechanically robust and capable of restoring simultaneously structural, electrical, dielectric, and thermal transport properties after multiple fractures. With the incorporation of surface-functionalized boron nitride nanosheets, the polymer nanocomposites exhibit many desirable features as dielectric materials such as higher breakdown strength, larger electrical resistivity, improved thermal conductivity, greater mechanical strength, and much stabilized dielectric properties when compared to the pristine polymer. It is found that the recovery condition has remained the same during sequential cycles of cutting and healing, therefore suggesting no aging of the polymer nanocomposites with mechanical breakdown. Moreover, moisture has a minimal effect on the healing and dielectric properties of the polymer nanocomposites, which is in stark contrast to what is typically observed in the hydrogen-bonded supramolecular structures.