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2015: Relationship between the local piezoelectric response and the molecular mobility in ferroelectric polymers

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MSU physicists in collaboration with their colleagues from Karpov Institute of Physical Chemistry and National Univerisity of Science and Technology (MISIS) studied the relationship between the local piezoelectric response and the molecular mobility in ferroelectric polymers.

Organic ferroelectric polymers based on vinylidene fluoride (VDF) attract much attention because of their high piezo- and pyroactivity. The mentioned polymers are characterized by the presence of at least two phases: amorphous (disordered) and crystalline. As polymers belong to the class of flexible chain, the amorphous phase is characterized by low glass transition temperature (about −40 °C). This means that at room temperature and higher these polymers are characterized by strong dynamic heterogeneity: the molecular mobility in crystalline and amorphous phases is totally different.

In this paper, the topography of the surface, the local piezoelectric response and the dielectric relaxation processes, which characterize the molecular mobility, were studied for the films of ferroelectric copolymer of VDF with tetrafluoroethylene (TFE) of different composition. It has been shown that larger crystals of the polar phase are formed at the crystallization in the film with higher TFE content . At the same time they are characterized by higher values of piezoelectric response and markedly lower values of the activation energy of local and cooperative mobility.

The influence of the electric field leads to the formation of polarized regions (domains) with low stability. The features of the process of polarization and the characteristics of the local piezoeffect are controlled by several factors. On the one hand, it depends on the conformational structure of the copolymer chains. On the other hand, the domains responsible for the appearance of the local piezoeffect, must include both crystalline regions and the region-disordered phase.

Piezoelectric properties of the polymers under consideration make them good candidates for using as sensors in organic electronics.

The results of this work have been published in the paper: V.V. Kochervinskii, D.A. Kiselev, M.D. Malinkovich, A.S. Pavlov, I.A. Malyshkina "Local piezoelectric response, structural and dynamic properties of ferroelectric copolymers of vinylidene fluoride–tetrafluoroethylene”, Colloid and Polymer Science 293, 533543 (2015).