An atomistic simulation of the effect of pressure on conductive polymers

Abstract

Two conductive polymers are selected for static lattice and molecular dynamics methods to determine the possibilities of `fine tuning' them in order to achieve desired bandgaps. These are poly-para-phenylene (PPP), consisting of a π-conjugated backbone only, and the thermochromic polymer poly(3-alkylthiophene) (P3AT), which additionally contains flexible side chains. Conformational changes in both polymers indicate that pressures of ~6-7 GPa planarize the main chains. With a sterically hindering atom F in the ortho site of PPP, conformations a few degrees from planarity may be achieved at about 20 GPa. The response of the C-H and C-F bonds to pressure is also described. In the P3AT polymer molecular dynamics predicts that above 10 GPa not only does planarization of the main chain occur but the spontaneous `tilting' observed in the alkyl side chains is also reduced.