The purpose of the work is to find out dielectric characteristics of samples of polyvinyl alcohol and composites based on it in the frequency range below 100 Hz. In this work, films based on polyvinyl alcohol (PVA) with the addition of sodium chloride and fullerenol were fabricated, and the frequency dependences of dielectric permittivity, dielectric loss, and dissipation factor in the range of 0.01 – 100 Hz were measured and analyzed.

This work presents the results of comparison of optical properties at room temperature and electrical characteristics of films of polyvinyl alcohol (PVA) and nanocomposite based on PVA with small additives of fullerenol C60(OH)44 in a wide frequency range (25 Hz - 1 MHz) at temperatures from 294 to 398 K. The addition of 2 wt.% fullerenol leads to a significant absorption of light by such a film in the UV region of the spectrum (IR spectra of both film samples were identical), as well as to a decrease in dielectric permittivity c '. The c " frequency dependences of both films showed peaks in the low-frequency region, which shifted towards higher frequencies when the films were heated. The values of the activation energy of conduction at direct current for PVA and polymer nanocomposite were found to be about 1.5 eV. An explanation of the observed effects is proposed.

The paper presents the results of experimental study of the influence of the doping agent (acid) nature on the conductivity, Seebeck coefficient, and thermoelectric power factor of composite material based on multilayer carbon nanotubes coated with polyaniline. Polyaniline was deposited on carbon nanotube surfaces by heterophase synthesis (in-situ polymerization), by oxidative polymerization of aniline in the presence of nanotubes dispersed in the reaction medium. Hydrochloric, camphorsulfonic and dodecylbenzenesulfonic acids were used as doping agents. The effect of temperature on the conductivity, Seebeck coefficient and thermoelectric power factor of the investigated composite materials has been studied in the range from 300 to 410 K. Comparison of the influence of the acid volatility on the changes in these parameters in the heating-cooling cycle allowed us to conclude that the decrease in conductivity and increase in the Seebeck coefficient when heating composites doped with different acids is caused by the acid removal from the samples.

The optical and electrical properties of PVA films and PVA + C6o(OH)44 nanocomposite have been compared. It was found that even a small addition of fullerenol molecules to PVA leads to its coloration, and the nanocomposite films become opaque in the UV region of the spectrum. It is shown that at elevated temperatures, noticeable differences in the conductivity and low-frequency dielectric permittivity of PVA films and PVA+fullerenol composite films are observed. Their possible causes are analyzed.

The paper shows that it is possible to obtain reliable information on the dependence of the radial distribution of longitudinal birefringence in glass cylindrical elements with a radial distribution of refractive index (GRIN lenses) on the basis of transverse polarization tomography data on residual stresses. This does not require complicated procedures of sample preparation, as is necessary in the case of longitudinal translucency measurements. The approach developed was verified in the experiments with a set of different GRIN lenses formed with the ion exchange technique, and the closeness of the data obtained from transversal and conventional longitudinal transmission measurements was demonstrated.

The paper presents the results of an experimental study of the electric conductivity and thermoelectric properties of a new coordination polymer (CP) based on phenazine ligands (Phz) and silver (Ag) synthesized by a one-step method. This method produces phenazine by oxidative dimerization of aniline under the action of AgNO3 followed by release of metal nanoparticles and subsequent self-organization of Phz with excess AgNO3 into the CP. The used method of the Phz-Ag synthesis was found to make possible obtaining CP with conductivity of about 1300 S/cm commensurable with the modern record value for CPs. The obtained experimental data led to the conclusion that the studied CP Phz-Ag possesses a metallic type of conductivity. A physical mechanism of forming this property was put forward.

In the paper, the effect of temperature (range 22 - 140 degrees C) on the power factor (PF) of composite material made of multi-walled carbon nanotubes with a 10 run thick polyaniline coating applied to their surface has been studied. The conductivity value of the coating was varied by treating the composite with buffer solutions of different pH values. The nano-tubes were randomly oriented relative to each other in the composite samples under study. It was found that the composite material where polyaniline was in an oxidized conductive form had the highest PF value. In that sample, the PF values were about 0.5 mu W/(m.K-2) at room temperature and about 1 mu W/(m.K-2) at 140 degrees C.

We present the results of an experimental study of the pulse electrical strength of polyethylene terephthalate and polypropylene films when they are subjected to a single electric pulse. It has been found that the breakdown of these films is possible both at the front and at the plateau of the pulse, and the probability of breakdown at the front increases with pulse amplitude. We recorded a jump in the durability of the films at the transition from breakdown at the front to breakdown at the pulse plateau. It is shown that the processes that prepare the film electrical breakdown develop faster at the pulsefront than at the plateau. We discuss a possible physical mechanism to explain this effect. Keywords: polymers, polypropylene, polyethylene terephthalate, pulsed electrical breakdown, electroluminescence.

The process and salient features of modifying the structure of dielectric nanocrys-talline vanadium dioxide films by doping with Ni and W transition metals have been studied. The dielectric spectra obtained experimentally were interpreted in terms of Debye relaxation theory and the equivalent circuits method. The changes in the spectra of doped compounds were established to be due to the selective effect of the dopants on various morphological struc-tures of the film surfaces. It was shown that dielectric spectroscopy made it possible to obtain detailed information about parameters of relaxation response of different-sized morphological structures of films, and such information could not be extracted by other research methods

The dielectric and physical-mechanical properties of organophosphorus polyurethane ionomers based on the ethers and aminoethers of ortho-phosphoric acid have been investigated. The influence of the content of ionogenic groups and polyphosphate structures on the dielectric properties of polyurethanes has been analyzed. It is shown that the values of dielectric permittivity and tangent of dielectric loss in a wide frequency range increase with the content of ionogenic groups in polyurethanes studied. In this case, the increase in conductivity is diffusive in nature and is due to the mobility of protons within the phosphate anion clusters. The compositions of samples with a combination of high dielectric properties and excellent physical-mechanical and adhesion characteristics have been determined. These are samples in which polyphosphate structures are present in addition to phosphate anions.

The dielectric permittivity and loss factor of polyvinyl alcohol films in the frequency range of 100 Hz to 1 MHz at room temperature are studied. The laboratory manufacturing technology of polyvinyl alcohol films with thickness of 50–60 microns has been worked out. It has been shown that the dielectric characteristics of the films remain stable for a long time and do not depend on the thermal history of the samples. High values of dielectric permittivity ( $\varepsilon^{\prime}\sim 10$ ) and small losses ( $\text{tg}\delta\sim 0.09$ ) in the frequency range from 1 kHz to 10 kHz allow recommending polyvinyl alcohol as an OFET gate dielectric for devices operating in this frequency range.

We present the results of an experimental study of the pulse electrical strength of polyethylene terephthalate and polypropylene films when they are subjected to a single electric pulse. It has been found that the breakdown of these films is possible both at the front and at the plateau of the pulse, and the probability of breakdown at the front increases with pulse amplitude. We recorded a jump in the durability of the films at the transition from breakdown at the front to breakdown at the pulse plateau.It is shown that the processes that prepare the film electrical breakdown develop faster at the pulsefront than at the plateau. We discuss a possible physical mechanism to explain this effect.

The impedance spectra of composite nonwoven materials based on nano- and microfibers of polyvinylidene fluoride-trifluoroethylene copolymer modified by polypyrrole with different doping degree were studied in the frequency range 1000 Hz-5 MHz. It was found that an increase in the doping degree of polypyrrole coating of nanofibers leads to a decrease in the imaginary and real components of the electrical impedance. Regardless of their magnitude, the shape of the hodographs is close to circular arc resting on the ReZ axis, which allows us to consider the studied material as a nanocomposite polymer electrolyte whose dielectric characteristics can be reversibly changed.

—The impedance spectra of composite nonwoven materials based on nano- and microfibers of polyvinylidene fluoride copolymer with trifluoroethylene modified with polypyrrole with various degrees of doping are studied in the frequency range 1 × 10 3 –1.5 × 10 7 Hz. It is found that an increase in the degree of doping of the polypyrrole coating of nanofibers leads to a decrease in the imaginary and real components of the electrical impedance. Regardless of their size, the shape of the hodographs is close to the arc of a circle based on the axis of the real component, which allows considering the studied material as a nanocomposite polymer electrolyte, the dielectric characteristics of which can be reversibly changed.

Dielectric properties of polyvinylidene fluoride based thin films and electrospun mats have been studied. Frequency dependences of samples capacity and tangent of dielectric losses have been obtained. The influence of trifluoroethylene presence in copolymer on dielectric properties has been investigated. Efficiency of using deposited contacts instead of pressed contacts was considered.

Tissue engineering and cell-based therapy approaches require artificial scaffolds as extracellular matrix (ECM) and three-dimensional (3D) environment for clinically relevant cells to attach, be metabolically active and proliferate. Moreover, these constructs must possess mechanical and physical-chemical properties matched with certain implantation site. If all the required conditions are met, a tissue-engineered construct is considered as functional and will regenerate or replace the damaged tissue after implantation. In this work, we give a short overview of so-called electrohydrodynamic approach (EHD), e.g. with an application of electric field, to fabricate nano- and microstructured porous polymeric networks. This includes the application of electrospinning (networks) and electrospraying (micro- and macrospheres) to produce scaffolds and semipermeable hydrogel structures as a basis for tissue engineering and cell-based therapies.

Polyvinylidene fluoride and its co-polymer with trifluoroethylene are promising biomaterials for supporting nerve regeneration processes because of their proven biocompatibility and piezoelectric properties that could stimulate cell ingrowth due to electrical activity upon mechanical deformation. This study reports the piezoelectric effect of electrospun polyvinylidene fluoride scaffolds in response to mechanical loading. An impact test machine was used to evaluate the generation of electrical voltage upon application of an impact load. Scaffolds were produced via electrospinning from polyvinylidene fluoride and polyvinylidene fluoride-co-trifluoroethylene with concentrations of 10-20 wt% dissolved in N,N-dimethylformamide (DMF) and acetone (6:4). The structural and thermal properties of scaffolds were analyzed using Fourier Transform Infrared Spectroscopy and Differential Scanning Calorimetry, respectively. The piezoelectric response of the scaffolds was induced using a custom-made manual impact press machine. Impact forces between 0.4 and 14 N were applied. Fourier Transform Infrared Spectroscopy and Differential Scanning Calorimetry results demonstrated the piezoelectric effect of the electrospun polyvinylidene fluoride and polyvinylidene fluoride-co-trifluoroethylene scaffolds. All the scaffolds exhibited a piezoelectric polar beta-phase formation. Their thermal enthalpies were higher than the value of the initial materials and exhibited a better tendency of crystallization. The electrospun scaffolds exhibited piezoelectric responses in form of voltage by applying impact load. Polyvinylidene fluoride-co-trifluoroethylene scaffolds showed higher values in the range of 6-30 V as compared to pure polyvinylidene fluoride. Here, the mechanically induced electrical impulses measured were between 2.5 and 8 V. Increasing the impact forces did not increase the piezoelectric effect. The results demonstrate the possibility of producing electrospun polyvinylidene fluoride and polyvinylidene fluoride-co-trifluoroethylene scaffolds as nerve guidance with piezoelectric response. Further experiments must be carried out to analyze the piezoelectricity at dynamic conditions.

Комплексная природа термических фазовых превращений в растворах альбумина

The dielectric properties of MIM-structures with Al2O3 dielectric layers obtained by ALD method have been studied. The breakdown field strength of these structures has been determined to be about 4.4 MV/cm in the linear voltage increase mode and to have virtually no dependence on the voltage increase rate. The type of the frequency dependence of permittivity and dielectric loss of these structures has been established in the frequency range of 25 Hz — 1 MHz. Dielectric loss has been shown to increase upon sample exposure to gamma-quanta of caesium-137 proportionally to exposure time.