Evidence for ‘bottom up’ growth during vapor phase polymerization of conducting polymers

Elemental analysis of sequentially formed PPy/PEDOT polymer blends using liquid-like oxidant layers by vapor phase polymerization (VPP) has provided conclusive evidence for a ‘bottom up’ growth mechanism during polymerization. Chemical analysis by XPS of the top surface of the polymer thin film formed by sequential polymerization of pyrrole monomer, followed by EDOT monomer, revealed the outer most layer to be PEDOT. ToF-SIMS depth profiling confirmed this result, indicating the diminishing presence of PEDOT fragments with concomitant increasing PPy fragments as a function of depth from the top surface, an indication that PEDOT was stationed above PPy. When the polymerization process was reversed (i.e. EDOT followed by pyrrole) the opposite was observed. By extension we propose that the same growth mechanism exists for any VPP conducting polymer where a (viscous) liquid-like oxidant layer is utilized.