Interaction of H2O, O2 and CO2 with the surface of polyphenylacetylene films: an XPS investigation

The interaction of small molecules (H2O, O2 and CO2) with polyphenylacetylene (PPA) thin films has been studied. The air-exposed PPA interacts with the atmosphere water vapour, leading to covalently bonded OH groups on the basis of X-ray photoelectron spectroscopy (XPS) core-level spectra of C 1s and O 1s. The surface-depth layer involved in the reaction is about 15 angstrom, as determined by Ar ion-sputtering measurements. The ion sputtering allows one also to obtain an oxygen-free PPA surface which in turn is exposed to H2O, O2 and CO2. The required gas pressure, in order to reach a detectable interaction, is greater-than-or-equal-to 760 Torr. Water vapour undergoes a dissociation reaction which gives OH moieties bonded to the polymer carbon atoms. O2 is only physisorbed at the PPA surface, while CO2 gives a chemical reaction which leads to the formation of weakly bonded C = O groups.