# Optimizing coating performance for diffusion under cyclic moisture exposure

## TL;DR

This study uses lattice Boltzmann simulations to analyze how cyclic moisture exposure affects diffusion in coatings, highlighting the impact of diffusivity variations on corrosion risk.

## Contribution

It introduces a numerical approach to model moisture diffusion under cyclic conditions, considering both constant and concentration-dependent diffusivity effects.

## Key findings

- Diffusivity type significantly influences moisture concentration at the substrate.
- Swelling-related diffusivity causes highly variable equilibrium moisture levels.
- Cyclic exposure impacts the effectiveness of barrier coatings against corrosion.

## Abstract

Fickian diffusion is often used to model moisture transport through barrier coatings, where the goal is to protect an underlying substrate from the onset of corrosion caused by buildup of water or other aggressive species. Such coatings are often exposed to cyclic moisture, either in laboratory testing or in service due to natural environmental fluctuations. In this paper, we use lattice Boltzmann numerical techniques to investigate the effects of reservoir cycling on moisture propagation and concentration at the substrate where corrosion onset occurs. We examine both the simple case of constant diffusivity, representing idealized Fickian diffusion, and diffusivity that depends on concentration via either a step or linear function, representing polymer network swelling. The use of a coating subject to swelling is shown to lead to highly variable equilibrium behavior. We show that the nature of the functional diffusivity has large effects on water concentration at the substrate, and has implications for material design and analysis to avoid corrosion.