Characteristics of LiClO4/TTG and LiClO4/DMF electrolytes at different salt concentrations have been experimentally determined by conductometry, Li-7, H-1, C-13 NMR. It has been demonstrated that the influence of these parameters on the oxygen reaction is due to solvation and electrical conductivity, which, determine the transport characteristics of the reaction participants. In DMF the formation of Li2O2 proceeds predominantly through the solution bulk. In TTG the reaction proceeds predominantly on the electrode surface and does not depend on LiClO4 concentration, which is likely due to the formation of Li2O2 on the electrode surface without passing into the solution bulk with a weak concentration dependence of LiClO4 dissociation in TTG. It cannot be ruled out that the LiClO4 concentration in TTG has an effect on the oxygen reduction mechanism at higher concentrations (> 2 M) because of the complex formation. At any LiClO4 concentration in TTG, the amount of electricity in the cathodic process is lower and the reaction reversibility is higher than in DMF solutions. The key factor responsible for the change in the characteristics of the oxygen reaction in TTG is the decrease in the electrical conductivity and diffusion coefficients of O-2 and Li+ with increasing concentration, due to the viscosity of the solution and low dielectric constant. (c) 2021 Elsevier Ltd. All rights reserved.

The crystallization of a copolymer from a solution at room temperature is found to lead to the formation of a metastable structure, characterized by the coexistence of ferroelectric and paraelectric phases. The fraction of the latter decreases after annealing above the Curie point. Atomic force microscopy (AFM) has revealed a difference in the surface topographies between the films contacting with air and the films contacting with a glass substrate. The microstructure of copolymer chains has been investigated by 19 F NMR spectroscopy. The chain fragments with “defect” attached monomeric units are ejected to the surface. The character of the ferroelectric domains formed during crystallization and their size distribution are analyzed.

The processes of molecular mobility in vinylidene fluoride–tetrafluoroethylene ferroelectric copolymer–based films textured via uniaxial drawing are studied. It is found that the cooperative mobility in the amorphous regions of the copolymer is described by the Vogel–Fulcher equation, whose parameters are sensitive to the drawing conditions. It is shown that a decrease in the drawing temperature causes a reduction in the effective activation energy of the above-mentioned motion. In accordance with the X-ray diffraction data, this circumstance may be explained by an increase in the packing density of chains in interlamellar spaces. This effect is partially provided by deformation-induced processes of formation of small and defective crystals of the paraelectric or antiferroelectric phase in spaces between neighboring lamellar crystals at the primary stage of crystallization. The relationship between the value of the orientational polarization in oriented films and the topology of structure formation in microfibrils is discussed. It is observed that enlargement of the interlamellar space (filled with a liquidlike amorphous phase) between neighboring crystals in microfibrils promotes an increase in the orientational polarization of chains in the amorphous phase.

The low-temperature molecular mobility has been studied by dielectric relaxation spectroscopy on the bulk films of statistic copolymers of vinylidene fluoride (VDF) with tetra- (TFE) and trifluoroethylene obtained by crystallization from a solution in acetone. The results show that activation energy of the kinetic units in the glassy state depends significantly on the concentration of polar groups. The cooperative mobility above the glass transition temperature is described by Vogel-Tamman-Fulcher equation; the lowest value of the effective activation energy was found in the copolymer with highest amount of non-polar TFE content. It has been shown that the parameters of the dynamics are related to the structural parameters obtained by infrared spectroscopy, wide-angle X-ray Spectroscopy, and small-angle X-ray scattering. In particular, the largest crystals and the highest value of the “large” period have been detected in VDF/TFE copolymer with lowest activation parameters of microbrownian and local mobility. Number of lamellar crystals in stacks is determined by the concentration of VDF polar groups in copolymer chain.

Processes of relaxation of space charges formed by impurities carriers in isotropic films of vinylidene fluoride and tetrafluoroethylene copolymers of the composition 71/29 and 94/6 were studied. Al and Au symmetric electrodes deposited by evaporation in vacuum have been used. In the case of Al electrodes at temperatures above 100 °C, giant low frequency dielectric dispersion was observed, while it is absent in films with Au electrodes. Causes of this phenomenon were studied by the X-ray photoelectron spectroscopy. It was shown that at Al deposition, new functional groups, such as Al-C, Al-F, and Al2O3, which are not characteristic of the copolymer film surface, formed. They were supposed to be traps for impurity carriers and because of this the electrode became partially blocked. This led to appearance of the giant electrode polarization on the metal-polymer boundary, which did not take place in the case of Au electrodes. Parameters of the Au4f line for the copolymer with different contents of fluorine atoms in the chain were analyzed. An increase in the number of these atoms was shown to result in the line shift to higher energies. This phenomenon was associated with an increase in the shift of the electron density from Au atoms to the F ones which has a high affinity to electrons.

The phenomena of high-voltage polarization and conductivity in oriented vinylidenefluoride and tetrafluoroethylene copolymer films have been investigated. It was shown that under certain electric fields, injection of carriers from the material of electrodes appearsThe barrier for holes injection in the copolymer was found to be lower than that for electrons. It results in more effective screening of the external field near the anode than near cathode. Electrones, ejected from cathode, creating negative charge by trapping on the surface.It is shown that the electrons injected from cathodes create a negative homocharge on the copolymer surface and then become captured on the surface shallow traps. Their nature has been studied by the x-ray photoelectron spectroscopy. It was shown that these traps may consist of chemical defects in the form of new functional groups formed by reactions of surface macromolecules with sputtered atoms of aluminum. The asymmetric shape of hysteresis curves was explained by the difference in mobility of injected holes and electrons. These factors caused appearance of "non-closed" hysteresis curves for fluorine-containing polymer ferroelectrics. Hysteresis phenomena observed at low electric fields (below coercive ones) are to associate with the behavior of the domains localized in the ordered regions formed during secondary crystallization of copolymers.

Dielectric, IR spectroscopy and DSC measurements were made over a wide range of temperatures and frequencies in copolymers of vinylidene fluoride (VDF) with tetra- (TFE) and trifluoroethylene (TrFE) of different composition. Experimental results show that decrease of VDF content in VDF/TFE copolymers is accompanied by decrease of activation energy of kinetic units in the glassy state, though relaxation times of cooperative mobility in amorphous phase differ insignificantly. Substitution of TFE with TrFE in copolymers with the same VDF content increases activation energy values for the local mobility. The results of IR spectroscopy suggest that VDF/TFE copolymers with low VDF content have lower crystallinity, which may be explained by the secondary crystallization processes and absence of long isomers in planar zigzag conformation.

The polarization of oriented films of the ferroelectric copolymer of vinylidene fluoride and tetrafluoroethylene in a sinusoidal electric field is studied. In low fields, the copolymer behaves as a linear dielectric whose permittivity nonlinearly increases with the amplitude of the alternating field. This behavior is related to the preferential orientation of the dipole moment of the chain along the normal to the surface and to the monocrystal-structure formation. In higher fields, the hysteresis behaves formally coincidently with the behavior of an antiferroelectric. The important role of through stressed chains in the amorphous phase in the initiation of domains of a new direction in polar crystals is observed. Increased adsorption of water molecules on the surface of a polarized film is found and is attributed to the formation of the final density of the stable polarization charge on it.

The poling and local piezoresponse mechanism has been investigated in ferroelectric polymers. Isotropic 94/6 composition vinylidenefluoride and tetraflouroethylene copolymer films is formed from acetone at room temperature by slow evaporation of solvent. The copolymer crystallization results in metastability (nonequilibre) form at high overcooling temperatures. IR spectroscopy shows occurrence of isomers with conformation TGTG-, T3GT3G- and (TT)n. The local piezoresponse shows that ferroelectric domains include crystals areas as well as nonordered phase. After annealing by heating to 150 oC was found conformation changes in polymer chain: T3GT3G- TGTG- and T3GT3G- (TT)n. It is show that the regular conformation chains length rising after annealing. Polarization value decreasing kinetic was investigated by piezoresponse force microscopy method.

The surface topography and characteristics of a local piezoelectric-response signal in isotropic films of a ferroelectric vinylidene fluoride-tetrafluoroethylene copolymer with a composition of 94: 6 are studied via scanning probe microscopy. The X-ray diffraction and IR spectroscopy data indicate that crystallization occurs in a mixture of β and γ polymorphic modifications. The exposure of the original film to a dc field bipolar leads to the formation of polarized regions exhibiting low stability. Recrystallization is followed by structural transformations accompanied by conformational transitions. As a result, there is a decrease in the concentration of chain segments in the T3GT3G− conformation and, conversely, an increase in the concentration of isomers in the planar zigzag conformation. In addition, the characteristics of the local piezoelectric response after polarization become more stable, while the signal undergoes phase reversal. A second-harmonic piezoelectric response signal induced by the electrostriction effect is detected for the studied ferroelectric polymer samples. It is found that the original film has two types of regions that contribute to the measured signal. A change in the pattern of the second-harmonic piezoelectric-response signal in the recrystallized film is attributed to a change in the contribution of the electrostriction effect to the macroscopic piezoelectric response.

Permittivity and conductivity low-voltage temperature dependences of a ferroelectric copolymer of vinylidenefluoride VDF with tetrafluoroethylene TFE in the ferroelectric to paraelectric phase transition range were investigated.The as received films obtained by crystallization from a solution had the metastable structure shown in particular in coexistence of ferroelectric and paraelectric phases below a Curie point.Temperature dependences of electrical characteristics in the first and second cycles of heating differ.Low glass transition (-40 ºC) facilitate intensive micro-Brownian chains mobility in the amorphous phase at ambient temperatures and above.As per the x-ray and spectroscopic data, the first heating cycle will result in a recrystallization process for molecular structure improvement.Asymmetry of temperature dependence of a dielectric susceptibility in a vicinity of "order-disorder" phase change is found out.For the first time paid attention to the fact that for crystalline polymer ferroelectrics interpretation of the parameters of the temperature dependences of the dielectric susceptibility in the cycle of heating near the phase transition point should take into account the possibility of the premelt processes.First the method of IR spectroscopy shows that the melting of ordered structures, emerging secondary crystallization is accompanied by a change of the basic parameters (frequency position, the integral intensity and half-width) component of the doublet of valence vibrations of С-Н groups.Such structural changes lead to the emergence of "anomalies" on the temperature dependences of conductivity.

The low-temperature chemical crosslinking of a copolymer of vinylidene fluoride and tetrafluoroethylene was studied through various physicochemical methods. The reaction was conducted in solution in the presence of diethylenetriamine as a crosslinking agent. The penetration of the mixture molecules and the crosslinking agent only in the amorphous phase of the copolymer was provided via selection of the ratio between a good solvent (dimethylformamide) and a poor solvent (ethanol). Owing to this, the crosslinking reaction occurred in the amorphous phase and hardly involved the crystals. This outcome was confirmed by wide-angle X-ray diffraction data. The structural and chemical changes in the amorphous phase during crosslinking were recorded with the use of IR spectroscopy and differential scanning calorimetry. It is shown that crosslinking is accompanied by the formation of C=C bonds in the copolymer chains. The study of high-voltage polarization and conductivity during exposure to bipolar rectangular pulses suggested that crosslinking leads to an increase in the carrier concentration. It was found that the surface potentials in the films increase with an increase in the number of high-voltage pulses applied to the sample. This circumstance is attributed to the fact that the double bonds formed in the copolymer chains can effectively trap negatively charged carriers.