High Resolution Transmission Electron Microscopy of Mixed Polymer Conductors

Pennsylvania State Univ University Park, University Park PA

Investigators

Abstract

Part 1. Non-technical summary Plastic mixed conductors, which are plastic materials capable of conducting ions and electrons, are poised to advance healthcare, energy storage and personal electronics. But, much remains unknown about the structure of these materials, in particular how constituent molecules pack and arrange themselves. This project will advance electron imaging approaches to reveal molecular organization of these materials. The work will leverage recent advances in electron microscope instrumentation to push the limits of what can be visualized. Visualization of frozen molecules will reveal how organization in solution affects molecular packing in solid films. Furthermore, the project will advance the three-dimensional characterization of plastic mixed conductors to reveal new aspects on how to tune conductivity. The project aims to study multiple materials using multiple approaches, which increases the likelihood of success and generation of knowledge. Advancing imaging of plastics could also advance a variety of other fields, including water purification, adhesives, and electronic materials. Educational and outreach efforts aim to support graduate student success and support retention of undergraduate students through pre-first-year summer programs and research experiences. Part 2. Technical summary Recent instrumentation advances in electron microscopy are transforming biology and material science. This project aims to leverage these recent developments to push the limits of polymer microscopy. Overall, this project will image mixed ionic-electronic polymer conductors at high resolution, to reveal chain packing and how morphology emerges after film casting. The project will use cryo-EM to image solution aggregates of polymers based on poly(ethylene dioxythiophene) and polystyrene sulfonate, e.g., PEDOT:PSS, and how these aggregates are perturbed with various additives, such as salts. The development of automated image acquisition enables collection of many high-resolution images, such that large data set analyses can reveal conductive pathways and correlations between crystalline domains. The project will also image swollen films of ladder-type mixed conductors such as poly(benzimid azobenzophenanthroline) (BBL) by vitrifying hydrated films, and reveal how ion uptake occurs. The work further aims to demonstrate how the 3D structure of mixed conductors can affect out-of-plane conductivity, and how structure is affected by swelling and salt uptake using electron tomography. Pushing the limits of resolution and techniques based on electron microscopy has the potential to advance many polymer-related fields, including charged polymers, membranes, actuators, gels, adhesives and electronic materials. This research is integrated with the proposed educational objectives. A partnership with the College of Engineering will advance professional development for graduate students and disseminate the excitement of polymer microscopy. 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.