Alternating currents, polymer electricity

By contrast, the technique of DETA is based on electrical measurements. In this technique polymers are exposed to an alternating current and changes... 

The most important dielectric properties are the dielectric constant, e, and the dielectric loss factor, tan 8. These properties are of interest for alternating currents indicates the polarizability in an electric field, and, therefore, it governs the magnitude of the alternating current transmitted through the material when used in a capacitor. For most polymers e is between 2 and 5, but it may reach values up to 10 for filled systems. 

The electrical properties of polyelectrolyte complexes are more closely related to those of biologically produced solids. The extremely high relative dielectric constants at low frequencies and the dispersion properties of salt-containing polyelectrolyte complexes have not been reported for other synthetic polymers. Neutral polyelectrolyte complexes immersed in dilute salt solution undergo marked changes in alternating current capacitance and resistance upon small variations in the electrolyte concentration. In addition, their frequency-dependence is governed by the nature of the microions. As shown in... 

Electrical Measurements. The electrical properties of polymers have much in common with mechanical properties. They can be divided into static properties equivalent to direct current properties and dynamic properties resulting from alternating current measurements. The most used parameter is the volume or bulk resistivity (ASTM-D257-75b) which is the resistance in ohms of a material 1 cm thick and 1 cm2 area. Bulk resistivity is one of only a few properties that vary nearly 1025 in typical use (materials with values above 10 ohm-cm for polystyrene to 10 5 ohm-cm for copper). 

Alternating currents of variable frequency are commonly used to measure the total electrical resistance i t of polymer coatings. On increasing the frequency to 2-25 kHz the ohmic constituent Rq of the total resistance can be estimated accurately enough. At low frequencies (400-1000 Hz) the recorded resistance value characterizes the polarizing resistance Rp of the coating. 

It is seen that adhesion increases from 1 (very poor) up to 5 relative units (good), value 3 corresponds to a valid level. The similar outcomes manage to be received, skipping a film of polymer between two metal electrodes, to what the alternating current by power 8-20 kV is brought. The schema of installation for treatment by electric discharge is given at a fig. 12. 

In EA experiments, the electric field in the polymer layer, arising fi-om the application of a sinusoidal voltage of the form V = V dc + cos(wt), consists of the superposition of a direct current (DC) component (Fq) and an alternating current (AC) component (Fac) ... 

Kilbride B E, Coleman J N, Fraysse J, Fournet P, Cadek M, Drury A, Hutzler S, Roth S and Blau W J (2002) Experimental observation of scaling laws for alternating current and direct current conductivity in polymer-carbon nanotube composite thin films, J Appl Phys 92 4024-4030. Sandler J K W, Kirk J E, Kinloch I A, Shaffer MSP and Windle A H (2003) Ultra-low electrical percolation threshold in carbon-nanotube-epoxy composites. Polymer 44 5893-5899. 

In implant resistance welding, an electrically resistive element that is placed at the joint interface is heating by either direct or alternating current [2], The resistive implant may be as simple as a nichrome or stainless steel wire or mesh. More complex implants can be tapes of braided metallic wire with thermoplastic monofilaments or a composite of polymer matrix with electrically conductive particles or fibers. As shown in Fig. 26.26, during implant induction welding, the resistive implant is placed between the two parts. Electric current is then passed for a preset time through the resistance implant while the parts are under pressure. Then the current flow stops and the parts are kept under pressure while the weld cools, and the implant remains at the joint interface. 

The effect of doping on electrical properties such as (1) direct current conductivity ouc (dc conductivity), (2) thermoelectric power characterized by the Seebeck coefficient 5, and (3) alternating current conductivity cTac (ac conductivity) has until recently essentially been studied in the case of electroactive polymers doped by chemical or electrochemical processes. 

---