Influence of humid atmosphere on phase separation in polyaniline-polystyrene thin films

Thin films composed of polystyrene (PS) and polyaniline (PANI) of different molecular weights doped with camphorsulfonic acid (CSA) prepared by spin-casting onto a gold substrate from chloroform in dry and humid atmosphere, were examined by secondary ion mass spectrometry (SIMS) using both depth profiling and mapping modes. In dry atmosphere, strong PANI segregation to the substrate was observed. Humidity inhibited this segregation and led to the separation of PANI and CSA, and the dopant segregated independently to the free surface. This effect was stronger for PANI with lower molecular weight. Dots, lines and seaweed patterns were observed after spin-casting in humid atmosphere.