Page 53 - Plastics News April 2017

TECHNOLOGY

Conductive polymer can make ‘self-healing’ smart phones

esearchers in the United States have developed a self- improve the material's properties. They are testing the
Rhealing polymeric material for electronics and soft material in harsh conditions, such as high humidity.Wang
robotics that can auto-repair. The material is stretchable added: “Previous self-healing polymers haven't worked well
and transparent, conducts ions to generate current and in high humidity. Water gets in there and messes things up.
make self-repairing phones. Chao Wang, lead researcher, It can change the mechanical properties. We are currently
said: "When I was young, my idol was Wolverine from the tweaking the covalent bonds within the polymer itself to
X-Men. He could save the world, but only because he get these materials ready for real-world applications."
could heal himself. A self-healing material, when carved
into two parts, can go back together like nothing has Technology for writing electronic
happened, just like our human skin. I've been researching
making a self-healing lithium ion battery, so when you drop circuits directly onto polymers
your cell phone, it could fix itself and last much longer."
Wang's team at the University of California, Riverside, A new technology for writing electronic circuits directly
turned instead to a different type of non-covalent bond onto polymers by modifying surface properties with a
called an ion-dipole interaction, a force between charged laser has been developed as part of the European Appolo
ions and polar molecules.The key to self-repair is in the project. The technique reduces processing costs by at least
chemical bonding. Wang three times compared with the current technology used
said: “Most self-healing in industry, according to the researchers. The Selective
polymers form hydrogen Surface Activation Induced by Laser (SSAIL) technique
bonds or metal-ligand was developed at the Centre for Physical Sciences
coordination, but these and Technology (FTMC) in Vilnius, Lithuania. Moulded
aren't suitable for ionic interconnect devices (MID) – an injection-moulded
conductors.” “Ion-dipole thermoplastic part with integrated electronics – offers
interactions have never material, weight and cost savings by integrating electronic
been used for designing a self-healing polymer, but it circuits directly into polymeric components. The parts
turns out that they're particularly suitable for ionic are used in automotive and consumer products. Lasers
conductors.”The key design idea in the development of can write the circuits directly by modifying the surface
the material was to use a polar, stretchable polymer, of polymers followed by an electroless metal plating.
poly/vinylidene fluoride-co-hexafluoropropylene, plus a Fabrication of circuit traces is the most challenging task
mobile, ionic salt. The polymer chains are linked to each in MID production, being both technically difficult to
other by ion-dipole interactions between the polar groups achieve and difficult to make cost effectively. During
in the polymer and the ionic salt. the project at FTMC in Vilnius, demonstrators have been
built by partners from CRF, BioAge and Elas. The new
The resulting material could stretch up to 50 times technique for selective surface plating can be applied to
its usual size. After being torn in two, the material conventional plastics without any special additives, an
automatically stitched itself back together completely advantage over the current state-of-the-art technology,
within one day. laser direct structuring, which uses additives mixed within

As a test, the researchers generated an ‘artificial muscle’ the polymers. The additives increase the price of the raw
by placing a non-conductive membrane between two plastic material by three to five times, meaning the SSAIL
layers of the ionic conductor. The new material responded technology lowers processing costs by at least three-fold.
to electrical signals, bringing motion to these artificial SSAIL is a three-step process: the first is surface
muscles, so named because biological muscles similarly modification by laser; second is chemical activation of
move in response to electrical signals. For the next step, modified areas; and the last step is metal deposition by
the researchers are working on altering the polymer to electroless plating.

53 April 2017 | Plastics News