AMS Group Demonstrates Healing for Electronics

A conductive charge transfer salt is formed upon release of solutions of its precursors from microcapsule cores, bridging a crack in a gold line and restoring conductivity. Image courtesy Alex Jerez, Beckman Institute Imaging Technology Group.
A conductive charge transfer salt is formed upon release of solutions of its precursors from microcapsule cores, bridging a crack in a gold line and restoring conductivity. Image courtesy Alex Jerez, Beckman Institute Imaging Technology Group.

The Beckman Institute's Autonomous Materials Systems research group that pioneered self-healing materials has shown that the healing concept can also work for a critical small scale application: restoring lost conductivity in electronics.

The concept of self-healing materials has been successfully demonstrated for polymers and is being developed for applications such as coatings on large scale structures like bridges. Now, a Beckman Institute research group that pioneered this rapidly emerging field has shown that healing can also work for a critical small scale application: restoring lost conductivity in electronics.

Writing in Advanced Functional Materials, the researchers report on a twin-microcapsule method that is “the first microcapsule system for the restoration of conductivity in mechanically damaged electronic devices in which the repairing agent is not conductive until its release.” The paper, Restoration of Conductivity with TTF-TCNQ Charge-transfer Salts, is available online and will serve as a cover story for the journal.

Lead author of the paper is postdoctoral researcher Susan Odom, with faculty member Jeff Moore the corresponding author. They and their co-authors are members of the Autonomous Materials Systems (AMS) group at Illinois’s Beckman Institute.

Odom said that the system builds upon recent work in the group on a single capsule method for restoring conductivity, but with the added feature of being non-conductive until damage occurs and the conductivity agents are needed. The microcapsule shells of the twin microcapsules rupture in response to the damage and the component precursor materials are released as a liquid from the core, forming a solid charge-transfer salt that restores conductivity to the electronic device.

“We’ve been able to encapsulate this conductive salt on its own but we wanted to show that we could encapsulate something that was non-conductive,” Odom said. “We only want it to be conductive when it’s actually being used in repair.”

The precursor components are encapsulated in a solution in an organic solvent. An advantage of using non-conductive liquid precursors is improved flow of the healing agent, enabling improved delivery to a damage site.

The researchers write that these precursor solutions are “low viscosity liquids, avoiding delivery problems of viscous solutions or suspensions. This system has the potential to serve as a useful model for a two-part electronic self-healing system using liquid precursors by comparing the degree of restoration of conductivity of one- and two-part microcapsule systems.”

The AMS group has been a leader in developing self-healing materials that can restore functionality or extend the lifetime of structures by self-repairing cracks or damage, for example, in structural materials and in the coatings of bridges or automobiles.