Department of Chemistry and ‡School of Engineering, Brown University , Providence, Rhode Island 02912, United States.
ACS Appl Mater Interfaces. 2016 Sep 14;8(36):24168-76. doi: 10.1021/acsami.6b06523. Epub 2016 Aug 31.
Minimization of stress-induced mechanical rupture and delamination of conducting polymer (CP) films is desirable to prevent failure of devices based on these materials. Thus, precise in situ measurement of voltage-induced stress within these films should provide insight into the cause of these failure mechanisms. The evolution of stress in films of polypyrrole (pPy), doped with indigo carmine (IC), was measured in different electrochemical environments using the multibeam optical stress sensor (MOSS) technique. The stress in these films gradually increases to a constant value during voltage cycling, revealing an initial break-in period for CP films. The nature of the ions involved in charge compensation of pPy[IC] during voltage cycling was determined from electrochemical quartz crystal microbalance (EQCM) data. The magnitude of the voltage-induced stress within pPy[IC] at neutral pH correlated with the radius of the hydrated mobile ion in the order Li(+) > Na(+) > K(+). At acidic pH, the IC dopant in pPy[IC] undergoes reversible oxidation and reduction within the range of potentials investigated, providing a secondary contribution to the observed voltage-induced stress. We report on the novel stress response of these polymers due to the presence of pH-dependent redox-active dopants and how it can affect material performance.
为了防止基于这些材料的器件失效，有必要最小化聚合物（CP）薄膜在机械应力下发生的力学断裂和分层。因此，对这些薄膜内的电压诱导应力进行精确的原位测量，应能深入了解这些失效机制的原因。使用多光束光学应力传感器（MOSS）技术，在不同的电化学环境中测量了掺杂靛红胭脂红（IC）的聚吡咯（pPy）薄膜的应力演变。在电压循环过程中，这些薄膜中的应力逐渐增加到一个恒定值，表明 CP 薄膜存在初始磨合阶段。从电化学石英晶体微天平（EQCM）数据确定了 pPy[IC]在电压循环过程中电荷补偿所涉及的离子的性质。在中性 pH 下，pPy[IC]内的电压诱导应力与水合移动离子的半径成正比，顺序为 Li(+) > Na(+) > K(+)。在酸性 pH 下，pPy[IC]中的 IC 掺杂剂在研究的电位范围内经历可逆氧化和还原，这为观察到的电压诱导应力提供了次要贡献。我们报告了这些聚合物由于存在依赖 pH 的氧化还原活性掺杂剂而产生的新型应力响应，以及它如何影响材料性能。
