Question

What are solitons, polarons and bipolarons? Discuss-why polypyrrole can have polarons and bipolarons (p-type). while polyacetytene can only have solitons (assume that all these materials are p-type)

Answer 1

A soliton is a self reinforcing solitary wave (a wave packet or plus) that maintains its shape while it propagates at a constant velocity when a charge carrier (an electron or a hole) is placed in to a solid, the surrounding ions can interact with it. The ions can adjust its position slightly, balancing their interaction with the charge carrier and the force that hold the ions in their regular places. This adjustment of positions leads to a polarization locally centered on the charge carrier. The combination of the carrier plus the surrounding polarization is a Polaron. A Bipolaron is a bound pair of two polarons. When two polarons are close together, they can lower their energy by sharing the same distortion, which leads to an effective attraction between the polarons. Polaron and Bipolaron states are associated to the intermediary energy levels that arise with in the electronic energy gap region of the polymer due to oxidation.