A continuum theory of organic mixed ionic-electronic conductors of phase separation
A continuum theory of organic mixed ionic-electronic conductors of phase separation
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DOI：
10.1016/j.jmps.2022.105178
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发表时间：
2022-12
影响因子：
5.3
通讯作者：
Xiaokang Wang;K. Zhao
中科院分区：
文献类型：
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作者：
Xiaokang Wang;K. Zhao
有机混合离子-电子导体（OMIECs）由于其独特的混合导电能力，在新兴的柔性、生物和光电子领域中是核心功能元件。在所有类型中，两相OMIEC由于其高拉伸性和平衡的离子电子传导而表现出优异的性能。然而，在两相OMIEC中，电子传导相可能与离子传导相分离，改变传导路径并最终导致器件的性能下降和功能障碍。在这项工作中，我们制定了一个连续理论的热力学框架下的两相OMIEC进行相分离。自由能由聚合物链的变形、聚合物与盐和溶剂的混合、静电场和两相界面的贡献组成。在质量守恒、热力学定律和静电学的约束下，推导了反应的平衡条件和动力学方程。我们将该理论应用到有限元模型中，并研究了电解质门控有机电化学晶体管（OECT）器件中OMIEC通道的力学和电化学。计算模型捕获的电荷载流子，机械溶胀，并在OMIEC相分离的并发传输和复制的OECT的传输曲线，同意与实验。更具体地说，我们揭示了起源的体积电容的电荷载流子在两相界面的积累。我们研究的参数空间，以阐明实验观察，如分子大小依赖的电导率和基板依赖的相分离。比较了OECTs在拉伸、自由和约束状态下的溶胀行为和传输曲线，揭示了形变对相动力学和电子传导行为的影响。我们发现，对于体积膨胀和电化学传递曲线，应力-传输耦合的影响占主导地位，而麦克斯韦应力的影响可以忽略不计。本工作为两相OMIECs的力学和电化学研究提供了理论基础。
Organic mixed ionic-electronic conductors (OMIECs) are the core functioning component in the emerging flexible, bio-, and optoelectronics owning to their unique capability of mixed conduction. Of all types, two-phase OMIECs exhibit exceptional performance due to their high stretchability and balanced ionic-electronic conduction. However, the electron-conducting phase may segregate from the ion-conducting phase in a two-phase OMIEC, changing the conducting path and eventually leading to degraded performance and dysfunction of the devices. In this work, we formulate a continuum theory following the thermodynamics framework of a two-phase OMIEC undergoing phase separation. The free energy consists of contributions from the deformation of the polymer chains, the mixing of the polymer with salts and solvents, the electrostatic field, and the two-phase interfaces. The equilibrium conditions and kinetics equations are derived with the constraint of mass conservation, thermodynamics laws, and electrostatics. We implement the theory into a finite element model and study the mechanics and electrochemistry of the OMIEC channel in an electrolyte-gated organic electrochemical transistor (OECT) device. The computational model captures the concurrent transport of charge carriers, mechanical swelling, and phase separation in the OMIEC and replicates the transfer curves of an OECT which agree well with the experiments. More specifically, we reveal the origin of the volumetric capacitance as the accumulation of charge carriers at the two-phase interfaces. We examine the parametric space to elucidate experimental observations such as molecular size-dependent conductivity and substrate-dependent phase separation. The swelling behavior and the transfer curves of OECTs under stretched, free, and constrained states are compared, demonstrating the effects of deformation on the phase dynamics and the electron-conducting behavior. We show that, for volumetric swelling and the electrochemical transfer curves, the effect of stress-transport coupling dominates while the effect of the Maxwell stress is negligible. This work provides a theoretical basis for the mechanics and electrochemistry of two-phase OMIECs.