Dielectric response of vinylidene fluoride-hexafluoropropylene copolymer, crystallized in different polymorph modifications, to a high-voltage electric field was studied. Polarization switching at high electric fields below coercive was detected. It was found that crystallization of the copolymer predominantly in nonpolar alpha-phase is accompanied by more intensive growth of electric displacement at polarization. For the sample with higher content of polar gamma-phase, the value of high-voltage conductivity "anomalously" decreased with increasing field at fields above coercive. The data on the field dependences of the remnant polarization showed that this should be attributed to an increase of the effective capture cross section of deep traps of gamma-phase polar planes for impurity and injected carriers. X-ray diffraction has revealed the field-induced transition of a part of the chains of the amorphous phase to the crystal.

Ferroelectric poly(vinylidene fluoride–hexafluoropropylene) films were prepared by low-temperature crystallization from the acetone and ethyl acetate solutions. Crystalline modifications of the obtained films were different (mixture of β- and γ-phases in case of acetone and predominantly α-phase in case of ethyl acetate). The dielectric spectroscopy studies showed that the relaxation strength of the main relaxation above the glass transition temperature (associated with the cooperative mobility in the amorphous phase) unusually increases with increasing temperature. Thermodynamic relationships suggest that this effect may be explained by assuming that there is a certain long-range order in the amorphous phase. This order may be due to the presence of the local field near the polar planes of the crystals, which form ferroelectric domains.

An effect of Rhodamine 6G dye introduced into vinylidenefluoride and tetrafluoroethylene copolymer on a number of its structural and electrical characteristics has been detected. It was shown that at film crystallization, the inserted dopant shifts the equilibrium distribution of isomers to the side of increasing concentrations of chains with the conformation of a planar zigzag. The dye introduced strongly increases ac conductivity, especially at high electric fields. The investigation of high voltage polarization under bipolar external field conditions shows slow switching of gigantic current which is observed at fields lower than coercive ones. The estimation of the charge density indicates the non-ferroelectric nature of the phenomenon observed. The analysis of the data shows that in the system, Maxwell–Wagner relaxation processes take place, which lead to the space charge formation in the polymer matrix. It is established that current switching observed must be attributed to the relaxation of the space charge field.

According to IR spectroscopy data, crystallization of polyvinylidenefluoride from dimethylformamide and dimethylsulfoxide solutions at 100 °C and 80 °С is accompanied in the last case by the formation of polymorph modification mixtures of γ and β phases. In the presence of a number of ionic liquids, the same crystallization is accompanied by conformation transition in polymer chains from T3GT3G− to the conformation of a planar zigzag. We think that it takes place due to ion-dipole interactions between cations of the imidazole ring with fluorine atoms of polymer chains in the amorphous phase. X-ray data show that polar crystals of the β phase of non-doped polymer contain many conformational defects in the form of T3GT3G− isomers. At polymer doping with ionic liquid, the number of such defects is lowering. Due to this, the density of crystals formed grows. Conformation changes noted affect the signal of electromechanical response fixed by piezoresponse force microscopy. In particular, it has been shown that in the film under conditions of crystallization chosen process of self-polarization, which is registered by the method of Kelvin mode, takes place.

Structural changes in isotropic films of ferroelectric vinylidene fluoride (VDF)/tetrafluoroethylene (TFE) 94/6 copolymers in the metastable state have been studied on heating. The metastable state was ascribed to -crystals. The dielectric relaxation spectroscopy was employed to study space charge relaxation processes. Two relaxations were observed at high temperatures. One of them was attributed to relaxation of space charge accumulated on the Al electrode which may be partially blocked due to new functional groups formed in the polymer surface. Recrystallization of the film from the melt is accompanied by small -crystals formation. This results in a decrease in activation energy of the space-charge relaxation process.

Electrical, electromechanical, and structural–optical properties of films of vinylidene fluoride copolymer with tetrafluoroethylene TFE, doped with Rhodamine 6G dye, have been investigated. It is found that the conductivity increases in doped films; at the same time, it “anomalously” decreases with an increase in the field. The hysteresis loop of local piezoelectric response has an asymmetric shape, which is related to the difference in the local field when its polarity changes. According to the data of absorption and luminescence spectra, the dye (at chosen concentrations) exists in form of, at least, monomers and dimers. It is shown by IR spectroscopy that hydrogen bonds can be formed between a dye molecule and vinylidene fluoride units located in amorphous regions. A model is formulated, which provides a correlation between the electrical and structural properties of the doped films.

The efficiency of ozone absorption by nonwoven polypropylene fibrous material prepared by industrial spunbond technology and changes of its chemical composition and structure after ozone treatment were studied. The effects of ozone treatment at low (250 μg/m3) and high (25 g/m3) ozone concentrations were compared. It was found that oxidative destruction in both instances was localized primarily on the fiber surface. The conditions under which the propylene nonwoven spunbond material was resistant to ozone were determined.

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.

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.

Abstract-Using the methods of X-ray microanalysis (XRMA), Auger electron spectroscopy (AES), highresolution scanning electron microscopy (HRSEM), atomic-force microscopy (AFM), IR specular reflection spectrometry (IRSRS), and quadrupole mass-spectrometry (QMS), the chemical and phase composition, as well as the morphology of the cleaved surfaces of sodium chloride crystals formed as a result of thermally stimulated surface autosegregation (TSAS), is studied. A super-stoichiometric increase in the sodium content in the surface nanolayers with an increase in temperature up to 600 K and a decrease in this content upon further heating is established experimentally. A decrease in the sodium content in the nanolayers virtually in the entire range of annealing temperatures for the reversible segregation process, as well as a decrease in this content on the surface with increasing annealing time under conditions of medium vacuum, is also been found. In addition, we observe the selective sublimation of sodium in the nanolayers at temperatures above 400 K and in the microlayers at temperatures above 600 K.

Composite polymer fibers with a composition of Si-C-O obtained by electrospinning of precursors solution containing polycarbosilane or phenol formaldehyde resins with an admix of organic-silicon compounds were synthesized in order to find efficient new electrode materials for lithium ion batteries. The composition and structure of pyrolized composite fibers were studied by means of X-ray dispersive analysis and X-ray diffraction, Raman spectroscopy, and by AFM and SEM. It was shown that the composite fibers (with a diameter of 0.5–1.5 μm) were nanostructured materials with carbon and silicon-oxy-carbide areas about 2–5 nm in size. A model of the nanostructure of a skeleton for composite fibers synthesized is proposed.