Other Influences on Properties

The relative stabilities of the oxidized oligo(thiophene)s and PTs depend on the oxidation state (i.e. the doping level) [177, 541]. The dependence is weakest for FeCla-doped PAT above 10 Scm Below that value the dedoping rate decreases with decreasing electrical conductivity, as is the case for organic acid anions. For the dopant I2 and the dopant anion PFg the decay rate is proportional to the electrical conductivity [189]. The deterioration of the electrical conductivity with time depending on the doping level is also found for PAT with n = 12 [542]. PBT in the neutral (dedoped) form is stable up to 300 °C and 

The low temperature results indicate that a metal-insulator (or semiconductor) transition takes place at 30 K for PT and 10 K for PMT [546]. The temperature dependence of the electrical conductivity corresponds to the three-dimensional variable range hopping mechanism [485]. The temperature dependence of charge mobilities in PATs (n = 4,6, 8, 12) exhibits a local maximum immediately after the end of the glass transition region, which can be attributed to the transition of soft conformons (conformational defects) in the disordered phase to localized conformons [494]. 

For the dopant I2 and the dopant anion PF the decay rate is inversely proportional to the square of the sample thickness. No thickness dependence can be found in FeCla-doped PAT (50-300 pm thick pressed films) [189]. The change of wettability of a PBT film (cf. Sect. 3.11) increases with increasing film thickness, and depends on the flow of charge during the electropolymerization. The maximum change is reached for PBT layers formed by 300 mC/cm [217,261]. 

Increasing humidity of the surrounding atmosphere induces a dedoping reaction in POT, probably because of a nucleophilic attack of water molecules, and therefore a decrease of radical cationic centers the electrical conductivity increases in dry air [324,547, 548], 

The conditions during the polymer synthesis (cf. also Sect. 5.3) [324,490]. 

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