Synthetic Principles for Bandgap Control in Linear pi-Conjugated Systems.

π-Conjugated polymers that are electrochemically cycled in ionic liquids have enhanced lifetimes without failure (up to 1 million cycles) and fast cycle switching speeds (100 ms). We report results for electrochemical mechanical actuators, electrochromic windows, and numeric displays made from three types of π-conjugated polymers: polyaniline, polypyrrole, and polythiophene. Experiments were performed under ambient conditions, yet the polymers showed negligible loss in electroactivity. These performance advantages were obtained by using environmentally stable, room-temperature ionic liquids composed of 1-butyl-3-methyl imidazolium cations together with anions such as tetrafluoroborate or hexafluorophosphate.

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Use of Ionic Liquids for π-Conjugated Polymer Electrochemical Devices

Engineering applications of synthetic polymers are widespread due to their availability, processability, low density, and diversity of mechanical properties (Figure 1a). Despite their ubiquitous nature, modern polymers are evolving into multifunctional systems with highly sophisticated behavior. These emergent functions are commonly described as “smart” characteristics whereby “intelligence” is rooted in a specific response elicited from a particular stimulus. Materials that exhibit stimuli-responsive functions thus achieve a desired output (O, the response) upon being subjected to a specific input (I, the stimulus). Given that mechanical loading is inevitable, coupled with the wide range of mechanical properties for synthetic polymers, it is not surprising that mechanoresponsive polymers are an especially attractive class of smart materials. To design materials with stimuli-responsive functions, it is helpful to consider the I-O relationship as an energy transduction process. Achieving the desired I-O linkage thus becomes a problem in finding how to transform energy from the stimulus into energy that executes the desired response. The underlying mechanism that forms this I-O coupling need not be a direct, one-step transduction event; rather, the overall process may proceed through a sequence of energy transduction steps. In this regard, the network of energy transduction pathways is a useful roadmap for designing stimuli-responsive materials (Figure 1b). It is the purpose of this review to broadly survey the mechanical to chemical * To whom correspondence should be addressed. Phone: 217-244-4024. Fax: 217-244-8024. E-mail: jsmoore@illinois.edu. † Department of Chemistry and Beckman Institute. ‡ Department of Materials Science and Engineering and Beckman Institute. § Department of Aerospace Engineering and Beckman Institute. Chem. Rev. XXXX, xxx, 000–000 A

Mechanically-induced chemical changes in polymeric materials

Over the past twenty years, polypyrrole has appeared as the
most extensively studied conducting polymer. However, despite the volume of
work already done in this area, there has been little focus put on the
mechanism of polypyrrole synthesis, especially concerning the most
efficient method, electropolymerization. Numerous analytical techniques
have been used to study polypyrrole electrodeposition and/or doping.
However, the mechanism itself is still a controversial subject as there is
not one mechanism which is universally accepted. The mechanism proposed by
Diaz is the one most commonly referred to in the literature although
several other mechanisms are not lacking in support. The controversy lies
in the initiation step as each mechanism proposes a different way of
beginning the reaction, varying between electron transfer, proton transfer
and direct radical pyrrole formation. Without considering the initiation
step, there are many other factors including electrolyte, solvent,
temperature and pH which can influence the reaction mechanism during the
electropolymerization of pyrrole, thus impacting the characteristics of the
polymer formed at the electrode.

Renyuan Qian

Papers

Protonation and deprotonation of polypyrrole chain in aqueous solutions

Conducting polypyrrole electrochemically prepared from aqueous solutions

Studies on the chemical compensation of conducting polypyrrole by NaOH solution

Studies on iodine doped thiophene oligomers

Electrode potentials of electronically conducting polymer polypyrrole