Page 56 - Plastics News February 2019

teChnoLogy

Ferroelectric polymers made more versatile

cientists have developed a toolbox for the production Department of Polymer Science and co-first author of the
Sof different PVDF-based block copolymers with Nature Communications paper.Together with his fellow
tuneable properties. Scientists from the University of Ph.D. student Niels Meereboer and their supervisor,
Groningen have created block copolymers from PVDF Professor of Polymer Science Katja Loos, Terzic devised
that leave its ferroelectricity intact, but allow them a way to produce a copolymer of vinylidene fluoride and
to tune its characteristics. The ferroelectric polymer trifluoroethylene with a functionalized end group that can
PVDF (polyvinylidene fluoride) has interesting properties be linked to an insulating polymer chain to form a block
copolymer. Next, the scientists showed that the material
forms small domains at nanometre scales, through phase
separation between the blocks. These domains take
different shapes -- lamellar, cylindrical or spherical, for
instance -- depending on the ratio between the blocks.
Free-standing films- Terzic: 'Others have tried to prepare
PVDF block copolymers, but they could only produce blocks
with short polymer chains. In that case, the blocks mix
and show no phase separation.' By varying the type of
block and preparing block copolymers of sufficient length,
the scientists were able to tune the properties of the
material. An important part of this work was the ability to
make free-standing films of the polymer with satisfactory
mechanical properties. 'This allowed us to investigate the
properties of the material.'Terzic used block copolymers
to improve the interactions between PVDF and inorganic
nano-objects and to improve their dispersion of inside
the polymer. For example, magnetic nanoparticles can
and could be used to store information or energy. One be added to the PVDF to produce a multiferroic material
of the main drawbacks of PVDF is that if you add extra that has both ferroelectric and ferromagnetic properties,
functional groups to improve certain properties, this also which means it can be coupled. Furthermore, changing
interferes with its ferroelectricity. They wanted not only the behavior of PVDF could make energy retrieval more
to study how this polymer works but also to widen its use efficient. 'That would allow us to make a highly efficient
to include flexible organic electronics. PVDF polymers capacitator that could be used wherever stored energy
possess polar structures with dipoles that can be aligned needs to be released fast, like in defibrillators or to
with the application of an electric field. The orientation convert direct current from solar panels to alternating
of the dipoles can be reversed by changing the direction current.'
of the electric field. The material thus shows switchable
behavior, which means it could be used for information Toolbox-Overall, the authors have created a toolbox for
storage. The presence of dipoles in PVDF and its high the production of different PVDF-based block copolymers
dielectric constant means that energy storage in capacitors with tunable properties. 'We can use this to increase our
could also be an option, although its ferroelectricity would understanding of the ferroelectric and other properties
reduce the efficiency of such capacitors. of PVDF, but also for new applications', says Terzic. 'The
organic PVDF is flexible, lightweight and non-toxic, in
Phase separation- Modification of the material might solve contrast to some inorganic ferroelectrics that often
this issue. 'However, modifying the molecules by attaching contain lead. And it is bio-compatible, so medical
side chains affects their ferroelectric properties', explains applications are another interesting possibility.'
Ivan Terzic, a Ph.D. student at the University of Groningen's

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