Joint Stock Company Federal State Research and Design Institute of Rare Metal Industry Institute GIREDMET

Moscow, Russia

Joint Stock Company Federal State Research and Design Institute of Rare Metal Industry Institute GIREDMET

Moscow, Russia
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Kochervinskii V.V.,Karpov Institute of Physical Chemistry | Malyshkina I.A.,Moscow State University | Volkov V.V.,Russian Academy of Sciences | Shmakova N.A.,Karpov Institute of Physical Chemistry | And 2 more authors.
International Journal of Pharmacy and Technology | Year: 2016

By a method of broadband dielectric spectroscopy is studied the low-temperature molecular mobility in two uniaxially-stretched films of ferroelectric copolymer of vinylidene fluoride and tetrafluoroethylene obtained from isotropic samples with different morphology. One of the films was obtained by crystallization from a solution in acetone (I), and in the other case, from dimethyformamide (II). It is shown that film I is crystallizing in a mixture of β - and γ-phases. In contrast, in the film II are forming predominantly polar crystals of the β-modification. Using low angle x-ray diffraction it was shown that there are differences in the supramolecular structure. In the case of the film II it was formed stack lamellar crystals, while in the film I was not detected ones. Moreover, in sample II are forming the spherulites of micron size, which was not observed in sample I. These differences in the structure of the original films lead to the different morphology of these films after uniaxial drawing: film I is optically transparent, while in the film II there is a strong opalescence. The latter fact, together with data from small-angle x-ray scattering indicates the formation in its entirety a large number of microcracks. Indirectly this is confirmed by the lower values of the dielectric constant in the film II comparing with film I. For both films the temperature dependence of relaxation times αа- process is described by the Vogel –Fulcher equation, while for β-process (local mobility) obeys the Arrhenius one. It was found that the formation of a microporous structure in the film II leads to a small increase in the glass transition point (from 222 to 227 K). More significantly thus changing the parameter m (fragility), which characterize deviation of the law of relaxation from Arrhenius behavior. Thus, the formation of cellular (microporous) structure of the amorphous phase with excess free volume initiates its more significant reconstruction when approaching the glass transition point. The transition to the glassy state of sample II is not accompanied by a complete “collapse” of high free volume regions (micropores). This is evidenced by the fact that below the Tg values of dielectric permittivity appear to be lower than those in sample I. It was found that the micro porosity in the film II leads to higher activation parameters of local mobility (especially the entropy of activation) than those in sample I. © 2016, International Journal of Pharmacy and Technology. All rights reserved.


Kochervinskii V.V.,Karpov Institute of Physical Chemistry | Shoranova L.O.,Joint Stock Company Federal State Research and Design Institute of Rare Metal Industry Institute GIREDMET | Shakirzyanov R.I.,National University of Science and Technology "MISIS" | Korlukov A.A.,RAS Nesmeyanov Institute of Organoelement Compounds | And 2 more authors.
International Journal of Pharmacy and Technology | Year: 2016

Structural and electrical properties of elastomer based on ferroelectric poly(vinylidene difluoride) PVDF were studied. For the copolymer of VDF with chlorotrifluoroethylene (CTrFE), the content of the monomers, the composition of chain fragments containing up to five monomeric units, and the character of attachment of these units to each other were determined by high-resolution1D and 2D19F NMR. The mole fraction of CTrFE in the copolymer was evaluated at 0.3 It was also shown that the microstructure of the chains of the elastomer is characterized by a high content of defects of chemical attachments (head-to-head). From the data of IR spectroscopy we can see that in the film of the elastomer are missing parts of the VDF chains with long sequences in planar zigzag conformation. WAXS shows that the films obtained from a solution in ethylacetate are crystallizing in the paraelectric phase, which contains a large number of sections of chains in conformation T3GT3G-. A comparison of the electrical characteristics of the films of elastomer and copolymer of VDF/TFE with equal proportion of the VDF shows that both in low-field and in high-field the conductivity in the first one is at least considerably higher. This fact determines the unusual electrical response of an elastomer for the electric field of high voltage. © 2016, International Journal of Pharmacy and Technology. All rights reserved.


Kochervinskii V.V.,Karpov Institute of Physical Chemistry | Malyshkina I.A.,Moscow State University | Korlukov A.A.,RAS Nesmeyanov Institute of Organoelement Compounds | Shakirzyanov R.I.,National University of Science and Technology "MISIS" | Shoranova L.O.,Joint Stock Company Federal State Research and Design Institute of Rare Metal Industry Institute GIREDMET
International Journal of Pharmacy and Technology | Year: 2016

Low temperature crystallization of the vinylidene fluoride copolymer with trifluoroethylene on a glass substrate is followed by the formation of metastable paraelectric phase in the volume. Its proportion may be reduced by isothermal annealing at a temperature above the Curie point. The authors studied the characteristics of lowtemperature molecular mobility in the initial and annealed copolymer film above and below the glass transition temperature. It was shown that after annealing the parameters of micro-Brownian cooperative dynamics in the amorphous phase significantly changed. In particular, the amorphous phase obtains such microstructure when its change during glass transition becomes smaller than in the original sample. The relaxation processes at a temperature below the glass transition obey the Arrhenius equation. The activation energy of such mobility does not depend on the thermal history of the sample. Reducing the local mobility relaxation time in the sample after annealing is associated with the decrease in the activation entropy. © 2016, International Journal of Pharmacy and Technology. All rights reserved.

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