Water Transport in Organic Coatings

Abstract

Abstract The electrochemical impedance spectroscopy (EIS) technique was used to evaluate the water transport (diffusion and equilibrium water uptake) and the dielectric properties of freestanding polyimide (Kapton® and PMDA-ODA) and polyethyleneterephthalate (PET) membranes at 25 and 40°C, respectively, and in supported PMDA-ODA-coated metals. Permeability and diffusion coefficients of freestanding films were also obtained by using the Payne cup method and the MacBain quartz spring balance in order to assess the reliability of the EIS method when compared to other techniques. Results from this work show that the diffusivity of water in polyimide films varies from 1.42 × 10−9 to 3.53 × 10−9 cm2 s−1 for thickness between 2.4 and 125 μm, while the equilibrium water uptake varies from 2.31 to 4.63% by weight for the same range of thickness. The average calculated dielectric constant of the freestanding Kapton® films is 4.5. Water diffusion coefficient in PET varies from 2.11 × 10−9 to 12.61 × 10−9 cm2 s−1 for...