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1.6. CONDUCTING POLYMERIC MATERIALS

Conducting polymeric materials routinely receive by introduction in high-molecular dielectrics of substance with high conductivity (metals, conducting carbon black, black lead). Now in various areas of technics the polymeric compositions which electric conductivity reaches 1 - 104Ом ' 1 m ' 1 are used.

On the structure these materials are multiphase heterogeneous systems. Value of electric conductivity of the yielded systems depends both on properties of separate components, and from quantity and character of distribution in polimereyodielektrike conductive filler.

On character of distribution of components distinguish matrix systems, statistical mixes and the structured compositions (fig. 1.21). In matrix mixes one phase forms a continuous matrix at any concentration of this phase. For statistical mixes characteristicly chaotic distribution of components without formation of regular structures. At last to the structured compositions, in our opinion, it is possible to carry glass-reinforced plastics, laminates and other systems in which components form the ordered chained, flat or volume structures.

Fig. 1.21. Composites on the basis of polymers: and - laminated plastics; - glass-fiber materials; in - matrix mixes; g - statistical mixes [82].

Let's notice, that for real conducting compositions elements of matrix systems, statistical mixes and the structured compositions [97] are characteristic. For example, at compositions of a phenolic formaldehyde resin with carbon black by means of an electronic microscope observed both the sootflakes distributed in a polymeric matrix, and some aggregates from these particles. The structure of conducting compositions is characterised also by the sizes and the form of particles of filler.

In connection with the big practical value of the combined materials a number of authors executes the theoretical calculations devoted to an establishment of quantitative interrelation between a structure and composition of a composition, by properties of components, on the one hand, and properties of compositions, on the other hand. Odelevsky the design technique is offered «the generalised conductivity» heterogeneous compositions [98]. The parities received by these author for the generalised conductivity can be used for calculation of electric conductivity, thermal conductivity, magnetic and inductivity of a composition. This generalisation has appeared possible As the differential equations of scalar and vector fields for streams of heat, electric charges, a magnetic and electric induction are formally identical.

For matrix diphasic system in which polymer is a matrix, it is possible to present electric conductivity as follows

In case of a statistical bipropellant mix

Here θ - a volume fraction of a component. The index «1» falls into to polymer; an index «2» - to filler.

Fig. 1.22. Dependence of the relation νZ νι from volume content of filler for a matrix mix (1) and a static mix (2) at ν2Z νι = 1010 [82].

As fig. 1.22, size at for a statistical mix shows exceeds electric conductivity of matrix system approximately in 10 times at θ2 = 0,5. Still the big distinctions of size ν are observed at transferring to the structured compositions. For example, formation of system of continuous conductive chains of filler particles result ins to sharp increase of electric conductivity [97].

Let's notice, that at a conclusion of the equations (1.22) and (1.23) possibility of specific interactions on interfaces of components was not considered, also was taken over, that filler particles should be approximately izodiametrichny, i.e. Should not possess appreciable anisotropy

The sizes. Both these of the factor make essential impact on properties of the combined polymeric materials.

Thus, electric conductivity of compositions is structurally "sensitive" characteristic of conducting polymeric compositions, and measurements ν can be used for studying of character of distribution of components.

Electric conductivity of conductive polymeric compositions is connected with conduction of electric charges, both in areas of a conductive component, and through isolating layers of a polymeric dielectric. Now it is possible to consider, that electric conductivity in the yielded materials at the significant maintenance of conductive filler (θ2≥0,1÷0,2) has electronic character. Hall effect presence testifies to it, for example, at compositions of iron with polyisoprene. It is interesting, that to the compositions received by introduction of polyisoprene in a powder gland from 2 %-s' solutions in benzol, the Hall constant has positive value, and at the compositions received by polymerisation of monomer in the presence of metal in conditions vibropomola - is negative. In the second case at compositions values termo-e.d.s also are great. And electric conductivities. Authors of work connect these distinctions with more uniform distribution of particles of iron in the compositions received at vibrating beating [98].

As it was marked, value of electric conductivity of conductive polymeric materials reaches 104Om^1∙m ^ ∖ Stability of electric and other properties of such compositions would be impossible at the ionic mechanism of electric conductivity because of irreversible processes of electric purification and electrolysis.

Is of interest to use for the analysis of dependence of electric conductivity of conductive compositions, for example, from frequency of electric field the barrier model considered in works Oreshkina and others. According to this model the composition represents matrix system, particles of a conductive component are modelled by cubes with a rib,
Equal and. Filler cubes are divided by isolating layers in the thickness d.Электропроводность such composition in weak fields in the elementary case it is possible to present following expression

Where Xi and х2 - mobility; п\и п2 - concentration of carriers in making

Particles and isolating layers.

From the equation (1.24) follows, that prit. e.

Electric conductivity of matrix system in weak electric fields is completely defined by conductivity of isolating layers. However for real compositions elements of orderliness and structuring of particles of a conductive component are characteristic. Besides, at a thickness of isolating layers of order 1 micron at delivering on a sample of pressure 10-100 in electric field strength in layers can reach 107-108в/м. At such naprjazhennostjah fields issue of electrons from metal or carbon black in a dielectric is possible. It result ins all to sharp increase in value of g in comparison with expression (1.24).

For creation of conductive structure of a composition of ferromagnetic metals with polymers sometimes use a magnetic field. Under the influence of this field there is an orientation of the anisotropic particles of metal and electric conductivity increases. This increase at magnetic density increase aspires to saturation. Gul with employees have shown, that speed of orientation of particles of metal and electric conductivity increase essentially raises if to apply a pulsing magnetic field.

In the patent the effective way of reception of conducting compositions of polytetrafluoroethylene with carbon black is described. The named polymer is strongly electrized at contact to proceeding liquids. It complicates use of hose pipes from polytetrafluoroethylene for flowing through of dielectric liquids. Formulas and methods of reception of the compositions, electrifying providing elimination are resulted at introduction in polytetrafluoroethylene
Small amount (to 0,5 weight. %) micronex. It is reached by a covering of particles of polymer by sootflakes and the subsequent mixing with the polymer containing flying lubricant. After homogenization of a composition, moulding of an uncured blank of a hose pipe by extrusion and the subsequent batch of preparation it is possible to create developed enough chain structures of a conductive component in a product. Such by it is possible to receive conducting compositions with electric conductivity of order 1 Ом-1-1 at introduction in polymer of several percent of carbon black. It is necessary to notice, that moulding of conducting structures in polymers with use of flying lubricant with which carbon black is well combined and which in the course of manufacturing of products leaves from a composition, can be useful to working out of compositions with the maximum electric conductivity on the basis of polymers.

Now conducting polymeric materials allow to produce heating elements, microphones on their basis. The increase in electric conductivity of compositions of polystyrene with an aluminium bronze with growth of frequency of electric field gives the chance to use rods from this composition for a filtration of a high-frequency component of a current, protection of radio equipment and other appointments.

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A source: Danilov Anatoly Jurevich. OBTAINING POLYMERIC COMPOSITES WITH HIGH FERROELECTRIC AND THERMAL PROPERTIES. Thesis for the degree of candidate of chemical sciences. Tver - 2015. 2015

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  2. effects of dispersion in the filled polymeric materials
  3. the general problems of modelling of polymeric matrixes and nanostrukturirovannyh materials
  4. influence of the sizes and the form of particles of filler and pores on properties of polymeric materials
  5. 4.2. Definition of effective diameter of pores and their distribution in the sizes in porous polymeric materials
  6. Ekvivalentnostultratonkih polymeric films on solid surfaces and the filled polymeric matrixes
  7. reception of polymeric composites
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  9. 1.4.2. Polymeric composites
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  12. THERMAL PROPERTIES OF POLYMERIC COMPOSITES
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  15. reception of polymeric sponges
  16. construction of a polymeric matrix
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  18. 1.3 Properties of optical materials for field of a spectrum 10 microns. Measure for a select of optical materials of powerful lasers