Partial phase mixing in solution-processed polyaniline-poly (methyl methacrylate) blends

Polyaniline protonated with camphor sulfonic acid is readily soluble in m-cresol. From appropriate solutions, blends of polyaniline with common insulating polymers can be cast as free-standing or ultra-thin films. Such blends exhibit non-standard conduction behaviour in that no conventional percolation threshold is observed, the conductivity rising smoothly from the insulating state with increasing polyaniline concentration. In this study, blends of polyaniline together with poly (methyl methacrylate) have been investigated by transmission electron microscopy to reveal the nature of the conductive pathways that are present at low filling fractions. The blends appear as a partially phase-separated structure with neither phase forming distinct domain boundaries. On removal of the insulating matrix, the polyaniline is observed to collapse into a complex network, in which spanning connections are present at all fractions above the conductive onset. Compatibilization of the polymers by the action of the surfactant counter ion and bound solvent is discussed as the means by which solubility and partial intimate mixing of the macromolecules are induced and from which conducting pathways arise.