Polyaniline films electrodeposited on iron from oxalic acid solution: linear dichroism of X-ray absorption and molecular arrangement

The linear dichroism in the near-edge X-ray absorption fine structure (NEXAFS) spectra measured at the K edges of carbon and nitrogen was used to analyze the molecular orientation in the polyaniline films electrodeposited on iron from oxalic acid solutions under various conditions (cyclic/potentiostatic polarization, potential magnitude, duration, and quiescent/stirred solution). Most of smooth and chemically homogeneous films deposited from stirred solutions did not reveal any dichroism of X-ray absorption, which indicates no specific spatial arrangement of polyaniline molecules in them. Distinct dichroism in the spectra of both absorption edges was observed only for the films containing a great number of particles accumulating on the surface under deposition from quiescent solutions or long-term deposition. The changes observed in the spectra suggest predominant arrangement of most polyaniline chains in-plane the surface with aromatic rings oriented predominantly perpendicular to the surface. The features of molecular arrangement in electrodeposited polyaniline are compared with polypyrrole films. The influence of the observed molecular arrangement on the protective characteristics of the films is also discussed.