Page 53 - Plastics News April 2017
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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.



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