Creating high-strength materials for flexible electronics

An international research team has developed a method that allows for a laser-driven integration of metals into polymers to form electrically conductive composites. The work was led by Tomsk Polytechnic University (TPU) in collaboration with the University of Electronic Science and Technology of China, Leibniz Institute of Polymer Research Dresden and University of Amsterdam, with findings published in the journal Advanced Functional Materials.

“Currently developing breakthrough technologies such as the Internet of Things, flexible electronics [and] brain–computer interfaces will have a great impact on society in the next few years,” said TPU Professor Raul David Rodriguez Contreras.

“The development of these technologies requires crucially new materials that exhibit superior mechanical, chemical and electric stability, [and] comparatively low cost to produce on a large scale, as well as biocompatibility for certain applications.

“In this context, polymers and a globally widespread polyethylene terephthalate (PET), in particular, are of special interest. However, conventional methods of polymers modification to add the required functionality, as a rule, change conductivity of the entire polymer volume, which significantly limits their application for complex topologies of 3-manifolds.”

In the TPU method, aluminium nanoparticles are deposited on PET substrates; then the samples are irradiated by laser pulses. A conductive composite is thus locally formed in the irradiated areas. The researchers chose aluminium because it is a cheap and readily available metal. Silver is frequently used as a conductor for flexible electronics; therefore, the obtained samples with aluminium nanoparticles were compared with a silver conductive paste and graphene-based materials.

“Mechanical stability tests (abrasion, impact and stripping tests) proved that composites based on aluminium nanoparticles surpass other materials. Moreover, the material structure itself turned out to be very interesting,” said TPU Professor Evgeniya Sheremet.

“During laser processing, aluminium carbide is formed on sample surfaces. Furthermore, polymers induce the formation of graphene-like carbon structures. We did not expect this effect. Besides, by adjusting laser power, we can control material conductivity. In practice, using a laser, it is possible to ‘draw’ almost any conductive structure on [a] polymer surface and make it locally conductive.”

According to the scientists, the laser integration of metals into polymers was used in flexible electronics for the first time. There are methods based on ‘metal explosion’ by laser and its application into polymers at a high speed, but they are more complicated in terms of technological implementation. The TPU method implies two basic technological steps: application of nanoparticles on polymer surface and laser processing. In addition, the method is applicable to a wide variety of materials.

“What can it be used for?” the study authors said. “First, it can be used for flexible electronics. One of the problems in this field is a low mechanical stability of products. There are many approaches to improve it. However, normally, the obtained materials would not have passed our tests. There is also photocatalysis, flexible sensors for robotics, light-emitting diodes and biomedical products among the potential fields of application.”

The research team is planning to test the new method on other materials such as silver, copper and carbon tubes, and to use various polymers.

Image caption: TPU Professors Raul David Rodriguez Contreras and Evgeniya Sheremet.

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