Conducting Polymers-Covalent Bond Type

Our story about polymer materials would not be complete if we did not mention here that some of them may be electric conductors. In Section 3.1 we touched upon the difference between covalent bonds of a- and 7r-types. Within the context of electrical conductivity, further difference is that a-electrons (i.e., participating in a a-bond) are strongly localized between the two connected atoms, they cannot move, and thus do not contribute to the electrical conductivity of the material. On the other hand, in the case of TT-bonds the electrons are much more delocalized and therefore may exhibit much higher ability to move from place to place. 

As discussed previously in the section on primary batteries, an acrylate is often used as a crosslinkable monomer to form a polymer matrix for a nonaqueous electrolyte. The salt-in-polymer type polymer electrolyte made by dissolving trifluoroethylene glycol methacrylate into methoxy poly(ethylene glycol methacrylate) forms a comb-like network structure at the covalently bonded portion. The ethylene oxide chain consists of 22 monomer units, and the ionic conductivity at room temperature is reported to be 10 S/cm. If sodium thiocyanate is used [30] instead of lithium trifluoromethane sulfonate, the ionic conductivity reduced to 10 S/cm. However, by adding 50 wt% of PC as a plasticizer, the ionic conductivity reaches 10 " S/cm. 

Similarly, the aspect ratio of the filler will have an effect on the sensitivity of the composite to various dispersion states. Thus, the effectiveness of comparisons made across studies can be compromised further if aspect ratio is not well characterized, even when the same filler type and polymer matrix are considered. This effect is compounded by the faa that high-aspect ratio fillers are typically more difficult to be dispersed effectively. Finally, correlations between dispersion and composite conductivity are ambiguous when covalently or noncovalently bonded chemical additives are used to enhance dispersion, but which may also inhibit electron transport. 

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