Mechanics in Organic Mixed Ionic-Electronic Conductors
This Dissertation aims at establishing an integrated framework of multimodal experiments and multiphysics theory to extend the understanding of the mechanics in electrochemically active materials using organic mixed ionic-electronic conductors (OMIECs) as a model system. OMIECs allow the transport of both ions and electrons, which is accompanied by the (electronic, micro-) structural reorganization. The electronic structural change in OMIECs induces transforms in the electrical conductivity and optical absorbance. The change in molecular packing invites the size change and evolution of mechanical properties. The multiphysics processes render OMIECs a fascinating platform for understanding the multi-physics coupling and advancing organic electrochemical devices. Despite significant progress, there are urgent needs in the experimental techniques and the subsequent mechanical characterization, theoretical understanding of the multiphysics processes, and mechanics-informed design principles for high-performance devices. Specifically, (i) an accurate and straightforward experimental method is in need to better understand the mechanical behaviors and kinetics such as swelling and softening of OMIECs upon electrochemical redox reactions; (ii) a theoretical framework is missing that describes the rich coupled multiphysics processes such as large deformation, charge and mass transport, electrostatics, and phase evolution in OMIECs; (iii) the rational design of the materials and structures based on mechanics principles are required for mechanically reliable, high-performance organic electrochemical devices. In this Dissertation, the mechanics of OMIECs are studied systematically. The basics of OMIECs, knowledge gaps, and the outline are introduced in Chapter 1. The in-situ environmental nanoindentation apparatus and the associating characterization techniques are presented in Chapter 2. In Chapter 3, a theoretical mechanics model is presented that elucidates the interfacial mechanical degradation of thin-film electrodes and outlines the design principles for mechanically reliable electrodes. In Chapter 4, the electrochemical doping kinetics and its stress dependency on conductive polymers are studied via a designed moving front device. Chapter 5 presents a thermodynamically consistent continuum theory of two-phase OMIECs undergoing large deformation, charge and mass transport, electrostatics, and phase separation, which forms the theoretical foundation for such conductive polymer systems. The conclusion and perspectives on future work are presented in Chapter 6.
Zhao, Purdue University.
Mechanics|Physical chemistry|Mechanical engineering
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