Analysis of the radiative properties of insulating and conducting granular polymers and of their mixtures
Introduction
While olefins are traditionally used as electrical insulators, organic polymers having conjugated π electrons can show electrical conduction properties. These polymers have attracted much scientific interest since their conductivity can be increased from the insulator to the metal range upon doping. However, conductive polymers are far from having good mechanical properties unlike conventional polymers that exhibit mechanical properties suitable for applications in various fields. The idea was to overcome this limitation by producing composites prepared with a conductive polymer coating deposited on a host material such as a conventional polymer. As a result, the obtained composite combines the elasticity of polymers with the conductivity of the conductive polymer. Mixtures of the two types of polymers can also be made, thus permitting the synthesis of new materials presenting electrically conducting properties and preserving the mechanical properties of the polymers [1], [2], [3].
Polypyrrole (PPy) is one of the most widely used conducting polymers in antistatic coatings, heating and conducting textiles, electromagnetic radiation shielding, batteries, absorbing materials for missiles, the aircraft and space industry, rechargeable electrochemical cells, etc., owing to its conductivity, thermal stability and ageing behavior [1], [2], [3], [4], [5], [6].
Radiative properties take into account the energy transfer during the interaction of an incident electromagnetic wave on a surface. They are defined as the ratio of a sample flux to a relative flux. The knowledge of both the spectral and conducting properties of PPy is necessary in so far as numerous applications involve radiative and electrical transfers [7], [8], [9], [10], [11], [12]. Some of them concern, for instance, optical windows, light emitting diodes, camouflage in military domains, and also the conversion by a photocell of radiation such as solar radiation into electrical energy. The observed properties are related to chemical characteristics of the material, such as the nature and composition of the surface, and also to physical factors, such as granulometry, morphology and the surface state of the particles [1], [2], [13], [14], [15], [16], [17], [18], [19], [20].
The synthesis of polypyrrole can be made either by (1) chemical vapor deposition; (2) an electrochemical route (both are experimentally constraining and with a low yield); or (3) a chemical polymerization method, easy to handle and thereby chosen when larger quantities are required, because it can be usually done in water [1], [2], [3], [4], [5], [6], [7], [8], [13], [14], [21], [22], [23], [24]. A large variety of supports can be chemically coated with PPy; they include insulating materials such as plastics, metal oxides or glasses, or conducting materials such as metals. Materials presenting particular shapes such as porous membranes, honeycomb structures and micro- or nano-particles can also be chemically coated with PPy.
This paper reports the study of the particular radiative and conductive linked properties of polypyrrole, deposited on an insulating material, polyvinyl chloride (PVC), in granular form, and of their mixtures.
Section snippets
Chemical synthesis of polypyrrole
This synthesis is a reaction of oxidizing polymerization of pyrrole initiated by an oxidant. The polymerization is accompanied by the doping of the polymer matrix by inserting electron-furnishing species in the neighborhood of the chains. Ferric chloride corresponds perfectly to the experimental criteria; the ferric ion acts as an oxidant and is easily eliminated in its reduced form while the Cl− anion acts as a dopant [1], [2], [3], [4], [5], [6], [7], [8], [13], [14], [20], [21], [25], [26],
Results and analysis
If the complexity of the processes occurring during radiative and electrical transfers in a granular medium is considered, it is easily understood that the nature, the particle sizes and the composition of granular mixtures may affect both the spectral and electrical properties of the material [15]. Moreover, the preparation procedure chosen for the chemical synthesis of PPy was found to have a significant effect on the properties of the composite obtained [1], [2], [7], [13], [14], [21]; their
Conclusions
This study concerning granular polymers allowed us to show the correlation between the electrical and the radiative behaviors of powders. These powders were used as received or coated with a conducting polymer, polypyrrole. It was demonstrated that experimental parameters (temperature and duration of the polymerization) were prevailing factors influencing the radiative and electrical behaviors to a large extent. Experiments were carried out with mixtures between uncoated and coated powders and
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