material marvels

1. Conducting Polymer MOHAMMAD IMRAN AZIZ Assistant Professor PHYSICS DEPARTMENT SHIBLI NATIONAL COLLEGE, AZAMGARH (India).

7. Band structure in an electronically conducting polymer

9. Positively charged defects on poly(p-phenylene). A: polaron B: bipolaron

10. Oxidation of the polymer initially generates a radical cation with both spin and charge. Borrowing from solid state physics terminology, this species is referred to as a polaron and comprises both the hole site and the structural distortion which accompanies it. This condition is depicted in Figure A. The cation and radical form a bound species, since any increase in the distance between them would necessitate the creation of additional higher energy quinoid units. Theoretical treatments have demonstrated that two nearby polarons combine to form the lower energy bipolaron shown in Figure B. One bipolaron is more stable than two polarons despite the coulombic repulsion of the two ions. Since the defect is simply a boundary between two moieties of equal energy -- the infinite conjugation chain on either side -- it can migrate in either direction without affecting the energy of the backbone, provided that there is no significant energy barrier to the process. It is this charge carrier mobility that leads to the high conductivity of these polymers.