Bof Bufon Carlos Cesar, Vollmer Judith, Heinzel Thomas, Espindola Pamela, John Hermann, Heinze Jürgen
Lehrstuhl für Festkörperphysik, Heinrich-Heine-Universität Düsseldorf, 40225 Düsseldorf, Germany.
J Phys Chem B. 2005 Oct 20;109(41):19191-9. doi: 10.1021/jp053516j.
The effects of the polymerization temperature and of voltammetric cycling on the chain length and the resistivity of polypyrrole films are investigated. The studies provide further proof for the existence of at least two different types of polypyrrole, the so-called PPy I and PPy II. As the electropolymerization of conjugated systems in contrast to normal polymerization reactions is a fully activated process, the generation of these different types of PPy depends on experimental parameters such as temperature or formation potentials. UV-vis measurements demonstrate that PPy II comprises significantly shorter chains than PPy I (8-12 vs 32-64 units); moreover, film conductivity is found to increase with the fraction of PPy II. This fraction is changed via the polymerization temperature as well as by cyclic voltammetry, both of which can induce a metal-insulator transition. The counter-intuitive relationship between resistivity and chain length is interpreted in terms of disorder-dominated transport, in which the shorter chains of PPy II support the formation of delocalized electronic states, thereby increasing the localization length. Thus, our results are in agreement with recent broadband reflectivity measurements.
研究了聚合温度和伏安循环对聚吡咯膜链长和电阻率的影响。这些研究进一步证明了至少存在两种不同类型的聚吡咯，即所谓的PPy I和PPy II。与正常聚合反应相比，共轭体系的电聚合是一个完全活化的过程，这些不同类型的PPy的生成取决于温度或形成电位等实验参数。紫外-可见光谱测量表明，PPy II的链明显比PPy I短（8 - 12个单元对32 - 64个单元）；此外，发现薄膜电导率随PPy II的比例增加而增加。该比例可通过聚合温度以及循环伏安法改变，这两者都能引发金属-绝缘体转变。电阻率与链长之间这种违反直觉的关系是根据无序主导的输运来解释的，其中PPy II的较短链支持离域电子态的形成，从而增加了局域化长度。因此，我们的结果与最近的宽带反射率测量结果一致。
