Resistivity of Conductive Polymers

Hao, Q. Kulikov, V. Mirsky, V. M. Investigation of contact and bulk resistance of conducting polymers by simultaneous two- and four-point technique. Sens. Actuators. 2003, B94, 352-357... 

An alternative in situ electrochemical method provides another piece of valuable information. Resistometry, a technique invented by Fletcher and coworkers, and first used for CEPs in our laboratories,146 enables changes in the resistance of conducting polymers to be monitored in situ. The increase in resistance of the polymer material as it is reduced is obvious (Figure 1.23c). The definite potential/time lag between the current flow and resistance change is also apparent. This lag is due to the finite time required for the chemical processes causing the resistance change to occur. 

Lange U, Mirsky VM. Separated analysis of bulk and contact resistance of conducting polymers comparison of simultaneous two-and four-point measurements with impedance measurements. J Electroanal Chem 2008 622 246-251. 

The arc resistance of a polymer is the length of time for which we can apply an electrical discharge to its surface before it breaks down and begins to conduct electricity. Breakdotvn typically takes the form of conductive carbonaceous tracks that are caused by oxidation due to locally high temperatures. Polymers -with lowpolarity typically fare better in this test than polar polymers. Arc resistance is reduced by dirt, moisture, and other surface contaminants. 

As discussed in Chapter 10, a wide variety of additives is used in the polymer industry. Stabilizers, waxes, and processing aids reduce degradation of the polymer during processing and use. Dyes and pigments provide the many hues that we observe in synthetic fabrics and molded articles, such as household containers and toys. Functional additives, such as glass fibers, carbon black, and metakaolins can improve dimensional stability, modulus, conductivity, or electrical resistivity of the polymer. Fillers can reduce the cost of the final part by replacing expensive resins with inexpensive materials such as wood flour and calcium carbonate. The additives chosen will depend on the properties desired. 

Lithium polymer electrolytes formed by dissolving a lithium salt LiX (where X is preferably a large soft anion) in poly(ethylene oxide) PEO can find useful application as separators in lithium rechargeable polymer batteries.Thin films must be used due to the relatively high ionic resistivity of these polymers. For example, the lithium-ion conductivity of PEO—Li salt complexes at 100 °C is still only about Viooth the conductivity of a typical aqueous solution. 

The internal resistance of a fuel cell includes the electric contact resistance among the fuel cell components, and the proton resistance of the proton-conducting membrane. In PEMFCs, the proton resistance of the polymer electrolyte membrane contributes the most to the total ohmic resistance. 

Figure 4.37. Equivalent circuit of conducting polymers [10]. (Albery WJ, Mount AR. Dual transmission line with charge-transfer resistance for conducting polymers. J Chem Soc Faraday Trans 1994 90 1115-9. Reproduced by permission of The Royal Society of...

The ionic resistance of a polymer electrolyte membrane is an important parameter in determining the mobility of protons through the membrane and the corresponding voltage loss across the membrane. Currently, the most commonly used membranes in PEM fuel cells are Nafion membranes produced by DuPont. However, these membranes are limited to low-temperature uses (usually below 80°C) because membrane dehydration at high temperatures can lead to reduced water content and then a lower proton transfer rate, resulting in a significant decrease in conductivity. The relationship between conductivity and the diffusion coefficient of protons can be expressed by the Nemst-Einstein equation ... 

FIGURE 1.23 Communicating with a conducting polymer PPy/Cl in solution (a) cyclic voltammetry—a plot of current flow versus the electrical (potential) stimulus applied (b) the electrochemical quartz crystal mircobalance readout—mass polymer versus electrical (potential) stimulus applied (c) the resistometry readout—resistance of the polymer versus the electrical (potential) stimulus applied. (Printed with permission from Materials Science Forum, Vol. 189-190, Characterization of conducting polymer-solution interfacial processes using a new electrochemical method, A. Talaie, G. G. Wallace, 1995, p. 188, Trans Tech Publications, Switzerland.)... 

Polymers are used in many applications especially for their ease of moulding in combination with a high electrical insulation resistance. There are also applications where a too high electrical resistance hampers the discharge of electrostatic charges which can build-up. It is often necessary then to decrease the polymer s original resistivity to lower values for safety reasons. Addition of conducting particles, for example carbon black, is one of the possibilities to decrease the resistivity of a polymer to an acceptable value. This acceptable value is set by rather simple rules ... 

Insufficient chemical resistance of a blend at times leads to its rejection for use in an aggressive chemical environment, although it possesses an excellent combination of mechanical properties. Thus chemical and solvent effects on polymer blends are important factors that frequently determine blends applicability. Attention has been given to chemical resistance of blends starting from the fundamental concept of the solubility parameters. Apart from the chemical and environmental restrictions, thermal resistance of a polymer blend is often a major criterion for its applicability. Thus, the thermal conductivity, heat capacity and heat deflection temperature of polymeric materials are discussed in separate sections. 

Electrical Reoulrements. The pottant should contain no plasticizer because plasticizer can reduce the volume resistivity of a polymer drastically. It reduces the resistivity of PVB by 5 orders of magnitude In some formulations. PVB with 40 dlester plasticizer measures only 10 ohm-cm In laminated form at room temperature whereas It measures 10 ohm-cm with the plasticizer driven out. Volume resistivities of 10 2 ohm-cm or less will conduct small amounts of current fairly readily, albeit slowly. (For example, a resolved 5 line palr/mm charge Image has been observed to blur within the first few seconds when placed on the surface of a film or Immersed In a llould of lO I-IO ohm-cm resistivity. The same Image on or In 101 ohm-cm material will not blur for several hours. On a ohm-cm material an Image will last unblurred from weeks to months.)... 

Bruschi R, Cacialli R, Nannini A., and Neri B., Gas and vapour effects on the resistance fluctuation spectra of conducting polymer thin-film resistors. Sens. Actuators B, 18-19, 421-425, 1994. 

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