Transport Studies of Conducting Polymers.
Abstract
Experimental results of transport in emeraldine form of polyaniline are reported for the first time in the thesis. Possible models of different transport mechanisms are proposed and examined. Polyaniline family has been proven to be an interesting system in that it provides a means of systematically studying the electronic structure of polymers as a function of both the number of electrons and the number of protons on the polymer chains. Emeraldine form of polyaniline differs substantially from earlier studied polymers in several respects. First, it is not charge conjugation symmetric. Second, it is a 'A-B' copolymer with nitrogen atoms and carbon rings in the same conjugation path. Third, it can be converted from insulating state to metallic state without change of the number of electrons on the chain. Experimental results in this thesis provides a direct evidence for insulator-to-metal transition of emeraldine with protonation. DC conductivity, AC conductivity, thermopower, and electric field dependent conductivity measurements demonstrate that there is a phase segregation of protonated emeraldine into a fully protonated and a unprotonated phase. In the metallic state, metal particles are embedded in the insulating matrix. Charge conduction is through charging energy limited tunneling between the metallic particles. In the semiconducting region, polarons and bipolarons are being formed due to protonation, and the charge conduction is via the variable range-type hopping between localized states. Together with some Preliminary work done on the new highly conducting poly-acetylene, it seems now possible that one can approach the intrinsic conductivity by decreasing the number of defect states to eliminate the barriers and increasing the size of metallic islands in the conducting polymers.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1988
- Bibcode:
- 1988PhDT........30Z
- Keywords:
-
- Physics: Condensed Matter