Molecular architecture of highly protective coatings of electrodeposited dodecyl sulfate-doped polypyrrole

Abstract The chemical structure and molecular arrangement in polypyrrole coatings electrodeposited in the presence of dodecyl sulfate has been studied using XPS, Raman spectroscopy and linear dichroism in the Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. The as-deposited polypyrrole has two-dimensional structure with a high proportion of dodecyl sulfate anions. This structure contains one dodecyl sulfate anion for each nitrogen atom involved in the formation of charge carrier or supposedly protonated. This corresponds to drastic changes in the N K NEXAFS spectra observed as complete disappearance of π*-related resonances. The dodecyl sulfate doped polypyrrole shows linear dichroism of the carbon edge NEXAFS spectra, indicating a predominantly flat laying orientation of the pyrrole rings and up-right orientation of the dodecyl sulfate ion tails relative to the substrate plane. Such molecular architecture of the electrodeposited dodecyl sulfate-doped polypyrrole provides its very high anticorrosive properties. The duration of the protection in the 3.5% NaCl solution was 850 h for dodecyl sulfate-doped polypyrrole coating, which is 17 times longer than for traditional polypyrrole coating doped with oxalate ions.