Investigation of the ion permeability of poly(p-xylylene) films

Abstract

The ion permeability of poly(p-xylylene) (PPX, parylene-N®) thin films was investigated using a cyclovoltammetric setup. Iron rods of different surface roughness were coated with PPX films of different thickness (140 - 700 nm) by vapour phase deposition (Gorham process). The presence of pinholes in PPX films deposited as described was analyzed by ion permeability according to cyclovoltammetric measurements. Current densities were directly related to the area of iron not covered by the polymer. It was found that films deposited on iron surfaces by the Gorham process showed significant ion permeability for film thicknesses below 500 nm and no permeability at all for films equal to or thicker than 700 nm, which indicated the absence of pinholes of PPX films of 700 nm thickness. Furthermore, films of 140 nm were deposited on iron surfaces of different roughness (the mean roughness was measured to be 102 nm, 103 nm and 105 nm). Current density increased by the increase in roughness, which confirmed that pinhole formation correlated with surface roughness.