arXiv subjects

D. V. Vlasov

Publications and source records attributed to D. V. Vlasov.

17 recordsLinked to original sources

arXiv2014

Self-organization of current channels percolation in polymer composite films with thermal nonlinearity of conductivity: comparison of experimental data and computer simulations

Numerical methods are developed to solve the problem of abnormal changes of current (conductivity) in polymer composite films which may be used as current, pressure or temperature sensors. General nonlinear model includes the heat equation, the nonlinear dependence of the resistivity of insulating composite intervals on temperature, taking into account the dehydrochlorination reaction, the appearance of conducting systems conjugated double bonds, and Ohm's law for full control circuit net. The property of thermal conductivity equation to smooth surges of source function allows to resolve the nonlinear closed system and carry out calculations by successive small time steps. As a result of numerical calculations we succeeded to explain and simulate virtually all previously seemed anomalous phenomena including spontaneous transitions in the highly conductive state, the conductivity jumps with temperature change, the dependence on sample thickness, etc.

cond-mat.mtrl-sci↗

arXiv2013

Investigation of the influence of temperature on the conductive properties of copolymer PVC -PolyAcetylene films

The temperature dependence of conductivity of partially dehydrochlorinated PVC films, containing in their macromolecules chains of polyene-conjugated bonds (PCB) and representing copolymer PVC-Polyacetylene. In samples with excess of some "threshold" concentration of PCB with increasing temperature it was found conductivity switching on 10 -11 orders of magnitude. Instability of states with high conductivity in the temperature range which depends on the concentration of PCB was detected. Qualitatively, the increase of concentration of PCB was monitored by fixing the fluorescent and absorption spectra.

cond-mat.soft↗

arXiv2013

An Approach to the interpretation of spontaneous transitions into a state of high conductivity in the PVC composite films

The results of experimental studies of conductivity anomalies in film samples of specially synthesized copolymer are analyzed, in which in PVC macromolecules the polyacetylene molecular fragments are embedded with a variable concentration. Previously, it has been experimentally found that in such samples spontaneous and stimulated conductivity jumps by 12 orders of magnitude occur, and the life of each of these states can be very large - minutes, hours and more. In this paper we propose a qualitative model describing the anomalous behavior of the conductivity of the PVC composite, comprising the mechanisms of stabilization of high conductivity state, the conditions of development of instability in the transitions between the states, as well as the reasons for long living state of high conductivity even when the applied voltage is switched off. Simple numerical estimates confirming the reality of the proposed mechanisms are considered too.

cond-mat.dis-nn↗

arXiv2013

PVC composite internal process of current-voltage time delay formation and conductivity levels lifetimes origin

In the previously described model of interpreting the numerous results in the switching states of the conduction in the films of PVC composites [1,2] was noted the need to involve hopping mechanism and percolation theory to explain the phenomenon of giant jumps conductivity, just as was done for the interpretation of such jumps for disordered semiconductor films. It was also shown that to explain the totality of spontaneous and stimulated transitions between states of the conduction in PVC composites requires the existence of an internal process that is able to produce a fixed observable current - voltage delay and switching electrical conductivity levels lifetime. In this paper one of the possible relaxation processes that lead to the emergence of the delay time, and the occurrence of spontaneous and stimulated transitions sample conductivity of nanocomposites PVC is presented. In particular, as a mechanism for determining time delay and lifetimes of the conduction states the reaction of dehydrochlorination is proposed, which should be reversible in case when HCl molecules separated from macromolecule physically can not "travel" far from "their place" in the macromolecule, as it just takes place within a local PVC free volume. In a frame of developed model all previously observed and called "anomalous" electrical phenomena receive a reasonable and predictable behavior.

cond-mat.mtrl-sci↗

arXiv2013

A short circuit in the electrical cables with polymer insulation: a new look at the cause of its occurrence and non-traditional ways of solving the problem

It is known that most of the electrical cables use as insulation compositions based on polyvinyl chloride. Like most polymers, the latter is quite sensitive to thermal aging, which is not without reason, to be one of the main causes of the various types of faults in the polymeric insulation, leading eventually to a short circuit and fire. On the example of the most common polymer insulator-PVC subjected to preliminary partial thermolysis, simulating the process of accelerated aging, we for the first time show that in this case as a result of the aging process, the electrical conductivity of PVC can acquire abnormal (not obeying Ohm's law) character. In this case, transitions from a state with normal (low) conductivity of PVC into the state with an ab-normally high conductivity was clearly observed, being spontaneous uncontrollable process. Es-pecially the large-scale nature of these changes allowing easily transferring polyvinylchloride from a state of typical dielectric (insulator) in a class of conductors attracts attention.). Thus, an-other one of the most important features of a short circuit in the PVC insulation is opened. It is noted that the reduction of fire hazards in this case (by the maximum possible elimination of the phenomenon of short circuit due to thermal aging of polymeric insulation) should be preventive in nature, as the most effective, simple and convenient way.

cond-mat.mtrl-sci↗

arXiv2013

Simple approach for detection and estimation of photoactivity of silver particles on graphene oxide in aqueous-organic dispersion

In the aqueous-organic (containing dimethylformamide) dispersion of graphene oxide flakes with deposited thereon Ag-particles, under the action of light in visible range, apparently for the first time, the effect of sediment flotation was observed with subsequent stabilization of the dispersion, which does not occur in the absence of Ag-particles. The main reason for such a laser light induced movement of sediment GO flakes may be explained with the appearance of small bubbles. The further development of this approach seem to be able to estimate photo activity of graphene flakes with different activation particles.

cond-mat.mes-hall↗

arXiv2013

Some features of anomalous conductivity of vinylene and vinyl chloride copolymer films

Manifestations of anomalous conductivity in polar dielectric films is demonstrated for the first time on samples of copolymer of vinylene and vinyl chloride, as was previously observed on modified PVC samples. On the base of these experimental results important new insights into the physical sense of traditionally used in these conditions specific resistivity indicators, both volume and surface, should be replaced by transverse and longitudinal resistance (according to polymer film surface) respectively, because the specific resistivity of polymer composite does not permits to calculate as usual the resistance of sample of arbitrary form..

cond-mat.mtrl-sci↗

arXiv2013

On the Depolarization Factors for Anisotropic Ellipsoids in Anisotropic Media

A definition of depolarization factors for anisotropic ellipsoid in an anisotropic medium is considered. The expressions for these factors are derived, which generalize some results known for special cases, and differences from the usual depolarization factors for ellipsoid in isotropic medium are described. The concept of "reduced" ellipsoid, allowing visually describe the effect of the medium anisotropy on depolarization is also introduced.

cond-mat.mtrl-sci↗

arXiv2013

On the specifics of the electrical conductivity anomalies in PVC nanocomposites

A qualitative model describing the "anomalous" features of the conductivity of polymer nanocomposites, in particular, switching to the conducting state in relatively thick (tens of microns or more) of flexible PVC films is considered. In previously published experimental results, change of conductivity by 10 or more orders of magnitude occurred both in the absence of external influences (spontaneously), and under the influence of an applied electric field, as well as other initiating factors (such as uniaxial pressure) . In a model of hopping conduction mechanism it is shown, that switching in the conduction states under the action of external field significantly (by orders of magnitude) below threshold can be associated with a high-resistance state instability that results from the sequence of "shorting" (reversible soft breakdown) of narrow insulating gaps between regions with relatively high conductivity. Increasing the field strength in the remaining insulating gaps ultimately leads to the formation of a conducting channel between the external electrodes and switching conductivity of the composite film sample in a state of high conductivity. This cascade model is essentially based on the transition from the usual description of the charge tunneling through single independent insulating gap to take into account correlations between adjacent gaps. In the frame of developed model other "anomalies" such as exponential dependence of the resistance on the sample thickness, pressure, and other influences can be qualitative explained. An analogy of the model with a cascading breakdown of avalanche transistors is also considered.

cond-mat.soft↗

arXiv2012

Anomalous effects in conductivity of thin film samples obtained by thermolysis of PVC in solution

It was stated earlier that in the samples of PVC films plasticized by a new type of plasticizer (modifier-A) abnormal transitions are possible from the state of low electrical conductivity to the state of high conductivity. For the first time a similar anomalous transition is demonstrated in thin-film samples of (partially dehydrochlorinated) PVC obtained by thermolysis in solution, without use of any special additives, plasticizers, ionizing radiation, etc. Anomalous effects of conductivity in the experimental data obtained clearly correlate with a concentration of conjugated double bonds (polyvinylen fragments) in the main chain of thermalized PVC macromolecules.

cond-mat.mtrl-sci↗

arXiv2012

Physical-chemical and chemical modification of PVC and their effect on the electrical properties of the polymer

The possibilities to increase the static conductivity of PVC compared to the initial antistatic level, for PVC plasticate obtained with effective plasticizer - a so called modifier of type A, and partial thermal dehydrochlorination for formation of a copolymer with a system of conjugated double bonds are investigated. To analyze the dependence of electrical conductivity from double conjugated bonds the doping method is proposed, in which a chemically active dopant is embedded between two thin films of the polymer sample, not touching, and, accordingly, not interacting with the metal electrodes. In this scheme it is found, that the for folding of two layers of partly dehydrochlorinated PVC on the border between them the barrier layer is formed, which can be eliminated by doping with iodine giving significant increase in electrical conductivity. This layer does not arise in the case of type A modifier plasticized PVC. The presence of such layer can be interpreted as a sign of the near-surface spatial heterogeneity associated with the presence of conduction mechanism of double conjugated bonds.

cond-mat.mes-hall↗

arXiv2011

Solution casting method for PVC nano-composites with functionalized single-walled carbon nanotubes1

Annotation A carbon nanotubes (CNT) filled polymer nanocomposites with their unique physical, mechanical and electro-optical properties has repeatedly discussed in the literature. The main part of this problem is to obtain high quality dispersion of CNTs. If for water-soluble polymers this problem can be considered as solved, it is not so for hydrophobic polymers, and PVC is an important example of this kind. This paper describes the methods of dispersion of SWNTs bundles in PVC, both by the use of specially synthesized surfactants, and by means of chemical surface modification of CNTs. The main criterion for an obtaining of a high degree of dispersion in our experiments is considered the sedimentation stability of non-aqueous organic colloidal solutions, which is essentially necessary for the polymer composites films preparation by solution casting method.

cond-mat.mes-hall↗

arXiv2011

Anomalous conductivity dependence of plasticized PVC for different modificator "A" concentrations and film thicknesses

The dependences of electrical conductivity of plasticized PVC films on mass fraction of plasticizer "A" and the film thickness are experimentally investigated. Non-monotonic dependence of conductivity on the concentration of plasticizer and strongly nonlinear dependence of the resistance of the film on its thickness are found. Possibility of construction of the models describing received results is shown and also discussed.

cond-mat.mes-hall↗

arXiv2010

Investigation of conductivity switching upon action of monoaxial pressure on plasticized PVC films

The effect of conductivity switching of wideband polymers -plasticized PVC films under the influence of mono axial pressure is experimentally investigated. For various plasticizers the value of monoaxial pressure, causing jumps of conductivity on four and more orders, changes from units to hundreds bars, and the effect remains at a thickness of films of an order of hundreds micron, that is on two orders more than critical thickness for others wideband polymers. In addition to the reasons stated earlier on the interpretation of anomalies of plastic compounds conductivity, the phenomenological electron-molecular model of dynamic traps is considered, in which local transfer of charges is carried out by mobile segments of the plasticized polymer molecules.

physics.chem-ph↗

arXiv2010

Conductivity states changes in plasticized PVC films near breakdown threshold voltages values

The near threshold "soft breakdown" measurements of PVC films conductivity are investigated. In a wide range of external electric field strength for various rather thick (>20 mkm) PVC films the resistance shows strong nonlinearity and seems to enter high conductive state close to the breakdown threshold. For our "thick" films boundary conditions electrode surface specifics should not be so important as in thin polymer films experiments. Both fast, instant mechanisms of nonlinearity, and effects of accumulation and delay responce were observed. The phenomena corresponding to reversible transitions in a state with rather high conductivity, seems to be similar to ones registered earlier in thin layers of some broad-bandgap polymers. In a range of relatively low field intensity, far from a threshold breakdown, as a result of reversible switches between normal and high resistivity states a polymer film in a standard measuring cell formed a relaxation generator giving a loud enough sound signal with frequency increasing with the increase of external field.

cond-mat.mtrl-sci↗

arXiv2010

On the mechanisms of switching between two steady states of electroconductivity in plasticized transparent PVC films

The results of experimental researches of electroconductivity of PVC films, plasticized by patented modifier, at fields below the breakdown level are described. A possibility of management of the repeated transitions between two states with high and relatively low conductivity with conservation of reversibility is found out. A simple qualitative model of abnormal conductivity based on representation of polymer film as a sequence p-n of transitions is offered. For samples of plasticized PVC films with thickness 30-50 microns specific volume resistance of steady states was of an order of 10E4 Om*m \times 10E6 Om*m, accordingly. A simple qualitative model describing abnormal character of conductivity of polymeric films is offered. The model considers the presence of known non-uniform plasticized polymer structure with discrete domains in which quasi-free moving of charges can occur. At imposing of an external field semi-condictive domains form sequence of p-n transitions which provides presence of two states of conductivity, in analogy with dinistors.

cond-mat.soft↗

arXiv2010

Nonlinear response and two stable electrical conductivity levels measured in plasticized PVC thin film samples

The electrical conductivity of PVC films prepared with a patented plasticizer of type "A" was measured with high precision automated setup, based on standard ring sell with a voltage range much less than breakdown voltage. Continual voltage-current measurements permit to take into account Debay relaxation process and clearly distinguish specific polymer film conductivity effects, connected with continuous current-stabilization behavior and transitions between two stable (long-living) states with several order magnitude different conductivities. Spontaneous reversible and non-destructive transitions of resistance levels was observed. For 30 mkm polymer films the values of sample resistance was measured equal to: high- 106 Ohm and low -103 Ohm.

cond-mat.mes-hall↗