Determination of the local molecular structure in amorphous polyaniline

The short-range order within amorphous polyaniline (a-PANI) has been studied through use of a pair-distribution-function analysis of x-ray scattering data in combination with quantitative refinements of model structure functions. Both the emeraldine base and salt (ES) forms of a-PANI are less planar than their crystalline counterparts. Direct evidence for appreciable interchain hydrogen bonding is seen. A probable position of the dopant ions in hydrohalogenic-acid-doped ES has also been ascertained. The intrachain structure and the ion location are such that the effective π-conjugation length is lowered and the chain-to-chain packing is frustrated. These characteristics hinder charge transport through the polymer matrix and prevent evolution towards a metallic state.