Mixed ion-electron conduction

Mixed conducting polymers conduct both ions and electrons.  Developing the relevant deign parameters for optimal conduction of both charged species in a single system is a non-trivial task. Traditionally, these properties have been studied in separate materials classes, making the rational integration of both properties an interesting challenge. For example, many conjugated polymers have the ability to transport ions and electrons, but optimization typically focuses on semiconductor doping for electron transport, while ion transport optimization has been the focus of polyelectrolyte research. Additionally, these charged species follow different transport mechanisms across a variety of length scales as shown below, with electron conduction typically favoring crystalline regimes with long range order, and ion conduction favoring amorphous regimes.

We are interested in understanding how the structure on different length scales affects both ion and electron transport in polymeric materials.

We are interested in understanding how the structure on different length scales affects both ion and electron transport in polymeric materials.

Mixed conducting polymers research

Mixed conducting polymers have applications spanning areas from energy technology to bioelectronics, including organic photovoltaics, transistors, battery binders, biosensors, actuators, and ion pumps. Current areas of interest in our group include:

Stresses are internally developed in conjugated polymers owing to ion incorporation in crystalline regions during doping.

Stresses are internally developed in conjugated polymers owing to ion incorporation in crystalline regions during doping.

  1. Elucidating the relevant design parameters for mixed ion-electron conduction for polymeric battery binders

  2. Investigating fundamental mechanisms related to the next generation of charge carriers (polarons and bipolarons) from various classes of dopants

  3. Understanding the effect of water-induced changes in polymer conformation on ionic and electronic transport

  4. Engineering internal stresses and strains developed during electrochemical cycling of mixed conducting polymer systems

  5. Characterization of structure and transport in charge mediated, self-assembled mixed conducting polymer blends


Implantable electronics

Conjugated polymers are ideal for bioelectronics, owed in large part to their biocompatibility, ease of processing, and low modulus. However, it is necessary to first understand stability and function of these materials in operando before they can be widely adopted.

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For instance, a conjugated polymer transistor may transduce electric potential fluctuations (e.g., from cardiac tissue) into electronic signal. The migration of ionic charge carriers (anions and protons) induces electronic charge carriers (polarons); though, the reversibility of this reaction may be limited. When the transistor is cycled with the opposite bias, ions infiltrating crystalline stacks may introduce local strain that degrades the morphology over time. Similarly, the introduction of water may decrease the crystalline fraction of the polymer responsible for most of the electronic conduction.