Consequently, the N/C ratio obtained at the PAN surface is lower (0.25) than the theoretical one (0.33). As expected, the basic hydrolysis of PAN (Figure ) resulted in an increase of the O/C ratio and in a decrease of the N/C due to the conversion of nitrile moieties into amides and carboxylates moieties (Table , entry 2). Addition of PEI by electrostatic adsorption at the HPAN surface (Figure ) logically led back to an increase of the surface N content.