Moving front phenomena in the switching of conductive polymers
Moving front phenomena in the switching of conductive polymers
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DOI：
10.1016/s0022-0728(97)00561-5
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发表时间：
1998-03-05
影响因子：
4.5
通讯作者：
Lacaze, PC
中科院分区：
文献类型：
--
作者：
Lacroix, JC;Fraoua, K;Lacaze, PC
对导电聚合物修饰电极中的传质现象进行了理论分析。在第一部分中，我们用两个不同的扩散系数来描述这类聚合物的电子输运性质：一个与导电态的电子迁移率有关，另一个与非导电态的电子输运有关。因此，这种方法假定电子扩散系数与薄膜中氧化态的局部浓度不连续。结果表明，这一假设引出了运动前沿的概念，它将薄膜处于导电状态的区域与处于绝缘状态的区域分开。当D随着氧化中心的浓度，即聚合物的掺杂水平急剧增加时，也得出了同样的结论。因此，移动前沿现象似乎与导电聚合物的特殊性内在地联系在一起，即在开关时电子导电性的急剧变化。对于计时安培实验，假设电化学过程受电子扩散控制，则前沿速度与t(-1/2)成正比，与电子在导电区的扩散系数成正比。当这个系数趋于无穷大时，就会出现与电子运动控制的过程假设相矛盾的情况。在这种情况下，电化学过程既可以由反离子运动控制，也可以由在移动边界发生的电化学反应速度控制；前沿的速度与t(-1/2)不成正比，计时安培响应可能偏离通常的Cottrell行为。在这项工作的第二部分，分析了反离子运动。认为该材料的导电性能可能导致薄膜内部结构内离子输运的迁移方面显著增强。结果表明，将离子输运描述为迁移现象而不是扩散现象，再次引出了移动前沿的概念。给出了几个传输方程：第一个方程描述了反离子的浓度分布，第二个方程描述了膜内的电势分布。这两个方程表明，浓度和电势在材料中以相同的速度传播。这一速度与驱动电场成正比，即在材料的导电/绝缘界面或绝缘区内发展的电势降，并随阴离子迁移率而变化。(C)1998 Elsevier Science S.A.保留所有权利。
A theoretical analysis of mass transport phenomena in conductive polymer-modified electrodes is presented. In the first part, the electronic transport properties of such polymers are described by two different diffusion coefficients: one relates to the electron mobility in the conductive state, the other describes electronic transport in the non-conductive state. Thus, this approach postulates a discontinuity for the electron diffusion coefficient with the local concentration of oxidized states within the film. It is shown that this hypothesis leads to the concept of a moving front which separates an area where the film is in its conductive state from one where it is in its insulating state. The same conclusions an drawn when D increases steeply with the concentration of oxidized sites, i.e. the doping level of the polymer. Thus, moving front phenomena appear to be intrinsically linked to the specificity of conductive polymers, i.e. the dramatic change in electronic conductivity upon switching. Assuming that the electrochemical process, for a chronoamperometric experiment, is controlled by electron diffusion leads to a front velocity proportional to t(-1/2) and to the diffusion coefficient of the electron in the conductive zone. When this coefficient tends towards infinity a contradiction to the assumption of a process controlled by electron movements occurs. In this case, the electrochemical process can be controlled either by counter-ion movements or by the rate of the electrochemical reaction that takes place at the moving boundary; the velocity of the front is not proportional to t(-1/2) and the chronoamperometric response can deviate from the usual Cottrell behaviour. In the second part of this work, the counter-ion movement is analysed. It is proposed that the conducting properties of the material might lead to a marked enhancement of the migrational aspect of ion transport within the internal structure of the film. It is then shown that describing ion transport as a migration phenomenon instead of a diffusion phenomenon leads again to the concept of a moving front. Several propagation equations are demonstrated: the first describes the concentration profile of counter-ions and the second describes the potential profile within the film. These two equations indicate that both concentration and electric potential propagate in the material at the same velocity. This velocity is proportional to the driving electric field, i.e. the potential drop that develops at the conductive\insulating interface or within the insulating zone of the material and varies with anion mobility. (C) 1998 Elsevier Science S.A. All rights reserved.