Victoriya M. Kapralova

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 shows that it is possible to obtain reliable information on the dependence of radial distribution of longitudinal birefringence in glass cylindrical elements with radial distribution of refractive index (GRIN lenses) on the basis of transverse polarization tomography data of 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 ion exchange technique, and the closeness of the data obtained from transversal and conventional longitudinal transmission measurements was demonstrated.

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.

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 paper presents the results of a study of the electric strength of a polypropylene film with a thickness of 2 μm. The breakdown voltage of the film was determined under the influence of electric pulses and with a slowly increasing voltage. The rate of increase in voltage at the pulse front varied from 1.8 to 78 GV/s, and with a slowly increasing voltage it varied from 28 to 1100 V/s. A statistical analysis of the breakdown voltage data was performed. For both modes of electrical testing and at all rates of voltage increase, the most probable breakdown voltages F_br.exp were calculated. The effect of the voltage rise rate on the value of F_br.exp was not detected. The obtained values F_br.exp were approximately the same for both test modes and amounted to 550 MV/m for DC and 570 MV/m for pulses.

Fibrous materials based on polyvinylidene fluoride and trifluoroethylene copolymers have been obtained by blend electrospinning and modified with polyconjugated polymer polypyrrole. The composite structure formed is a dielectric fiber in a conductive shell. The results indicate that by varying the degree of polypyrrole doping-up it is possible to change the character of the conductivity of the composite reversibly from inductive to capacitive.

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.

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.