Modification of conducting polymers by low energy reactive ion beams and their chemical effects

Abstract

Usually polymers bombarded with high energetic ions degrade, carbonize, darken, become conducting and change their structure and solubility. In this work however, specific modifications of polymer surfaces were achieved by low energetic ion bombardment [G. Marletta, Nucl. Instr. and Meth. B46 (1990) 295; K.G. Jung and J.W. Schultze, Dechema Monographie, Band 125 (1992) p. 833]. The polymer systems investigated (polyaniline and poly-3-methylthiophene) are intrinsically conducting. On low energetic ion bombardment the electroactivity of the bulk is retained whereas the surface is distinctly modified dependent on the ionic species and its dose [K.G. Jung and J.W. Schultze, Dechema Monographie, Band 125 (1992) p. 833]. Surface analysis e.g. reveals an enrichment of N for N − bombardment whereas the oxygen content is depleted after O + bombardment due to a large sputter effect. Moreover, the various ion species applied (3 keV H 2 +, N 2 +, O 2 +, Ar +, He + and 30 keV Cu +) lead to different reaction products at the surface, especially with the reactive ions. Definite reaction sites within the polymer were investigated with electrochemical methods. Though the surface is activated in general, a further polymerization is hindered due to structural changes. The permeability for H + ions, however, remains constant up to high doses. Accordingly no bulk changes can be detected by cyclovoltammetry.