Formation of a Double Electric Layer on the Metal-Plastic Boundary
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FORMATION OF A DOUBLE ELECTRIC LAYER ON THE METAL–PLASTIC BOUNDARY W. Jarguliński and J. Szelka A double electric layer is formed on the boundaries of liquid solutions, of a solution and a metal, of a metal and air, and of a metal and a vacuum. Its structure resembles the structure of a plane capacitor. A layer formed on a metal–plastic boundary was experimentally detected in 1953 [1]. A specimen made of two copper plates with a plastic (dielectric) material between them is rapidly stretched. At the time of its rupture, a peak is observed in the screen of an oscillograph indicating the presence of electric current. The highest peaks are observed at the time of fracture of the plastic near the metallic plate or on its boundary. For different plastics, the oscillograph records the presence of currents of both directions. Thus, it is possible to conclude that a double electric layer (DEL) is formed on the metal–plastic boundary, [6]. Investigation of the DEL To study this phenomenon, we connected a charge amplifier, a tail recorder, and an acceleration gage to the measuring circuit used in [6]. The plates were made of 45 steel and a layer of polyvinylchloride (PVC) and Epidian-5 epoxy resin was placed between the plates (Fig. 1). We also tested an electric model of a specimen subjected to tensile fracture. The specimen is modeled by two capacitors connected in series and charged, in turn, by using a battery (Fig. 2). The discharge of a capacitor corresponds to changes in the DEL of the specimen. In the screen of the oscilloscope, we observe peaks similar to the peaks corresponding to the fracture of the specimen. As a result of the tests, we determined the signs (polarization) of the DEL for plastic materials. By using the charge amplifier, we tested numerous plastics in the form of films, including polyethylene, acetobutyrate, glass plates, and sheets of paper. The DEL was not detected only for glass and paper characterized by amorphous structures (the peaks were absent). The plastics for which the DEL was detected were characterized by partially crystalline structures. There exist two types of DEL with different locations of electric charges. In the PVC layer, we observe the accumulation of negative charges (excess electrons). At the same time, positive charges are accumulated in Epidian-5 resin (deficiency of electrons as compared with the electron density in metal plates) (Fig. 3). In the partially crystalline plastic responsible for the formation of the DEL on the boundary with the metal, we observe the appearance of regions with partially ordered structure characterized by the presence of conduction electrons. In these regions, we detect isolated islands (archipelagoes). The coatings of a plastic of this sort applied to metal specimens contain the indicated regions. Some of these islands are stuck to the metal surface. The density of the electron gas in the metal differs from its density in the islands. Electrons move from the metal to the islands and in the opposite direction equalizing (e
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