The influence of temperature on the intrinsic transport properties of water in inorganic and polymeric coatings

Highlights: • Temperature dependent quasi-stationary approximations were derived and validated. • Theoretical approximation reveals effect of temperature and pressure on permeation. • Temperature dependency of steady-state permeation is determined by silicon oxide. • Silicon oxide doubles the activation energy for permeation of the substrate film. • Lag time is mainly influenced by heat of sorption of polymeric intermediate layer. Barrier layers are often used to protect sensitive organic devices from the detrimental effects of oxygen and water vapor. We investigated the effect of temperature on the time-dependent behavior of water vapor permeation in multilayer barrier films, focusing on the water vapor solubility, diffusion and permeability coefficients of individual layers and layer sequences. Activation energy measurements helped to explain the permeation mechanisms and showed the possible interactions between water and silicon oxide (${\text{SiO}}_x$). The activation energy for permeation ($E_P$) through a two-layer film of polyethylene terephthalate (PET) coated with ${\text{SiO}}_x$ was 5.7 kJmol${}^{-1},$ about twice the $E_P$ value of the uncoated PET substrate. An intermediate ORMOCER® layer, providing a smooth surface for a second ${\text{SiO}}_x$ layer in an alternating structure, had only a negligible effect on the $E_P$. Temperature dependent quasi-stationary approximations were derived for permeation through films with at least one inorganic/polymer/inorganic triplet, and were validated according to experimentally determined values. These equations showed the temperature and pressure dependencies of steady-state permeation and lag time in multilayered structures. Accordingly, the temperature dependency of steady-state permeation is determined by the $E_P$ of ${\text{SiO}}_x,$ whereas the lag time was mainly influenced by the heat of sorption of the intermediate polymeric layer. Furthermore, the increase in water vapor transmission rate was dominated by the partial pressure change with increasing temperature. Using these equations and experimentally determined parameters, we can predict the influence of temperature and humidity on the barrier performance of multilayered barrier structures.