Mechanics of Organic Mixed Ionic-Electronic Conductors (OMIECs)

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This grant will focus on understanding the mechanical behavior of organic conductors in interaction with conduction of ions and electrons. Organic mixed ionic-electronic conductors are the core functional component of organic electrochemical devices such as organic electrochemical transistors, electrochromic devices, energy harvesters/storage, and light-emitting devices. While most efforts on mixed conductors are currently focused on the charge and ion dynamics, the strong coupling of the electronic/ionic conduction with structural changes and mechanical deformation is largely unknown. This project will formulate a theoretical framework and experimental protocols for the understanding, evaluation, and improvement of organic mixed conductors for mechanically reliable, high performance organic electronics. The research will create fundamental knowledge on the concurrent ionic-electronic transport and chemomechanical responses in polymeric conductors via a close integration of theoretical and experimental approaches. The interdisciplinary nature of the project provides unique training opportunities for students at different levels. The various outreach activities, in collaboration with the Women in Engineering Program at Purdue, will focus on the engagement of underrepresented minorities, and will promote the interest of undergraduate and K-12 students toward the engineering career pathway.The overarching goal of the research is to understand the interplay between electronic, ionic, and mechanical responses in organic conductors using coordinated multi-physics continuum theories, multi-scale computational modeling, and experimental validations. The project includes three specific tasks. (i) Formulate a continuum theoretical framework that describes the underlying physics of mass transport, electron/hole conduction, and mechanical stresses. Develop a finite element model to simulate the electrochemical/mechanical processes in organic comductors. Perform electrochemical/moving front experiments on the doping kinetics and stress-sensitive kinetics to feed the theory. (ii) Understand the mechanical constitutive behavior and the molecular-scale structure-property relationship through complementary tools of in-situ nanoindentation and molecular modeling on intermolecular interactions. (iii) Understand the mechanical damage using finite element analysis and experiments. Conduct mechanical tests to evaluate interfacial strength, perform cyclic voltammetry to evaluate the electrochemical performance, and employ optical microscope and absorbance spectroscopy to identify mechanical damage. Unravel the correlation between the mechanical reliability and device performance and determine the key material and geometrical parameters that govern the damage initiation and evolution in solid-state organic devices. The fundamental understanding on the mechanics of organic mixed conductors will shift the research paradigm towards a complete design spectrum of concurrent ionic and electronic conduction and mechanical reliability in electrochemical devices.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.