Mass transfer as a proxy for hydrophobic coating durability

Durable hydrophobic coatings are essential in energy, corrosion protection, and barrier applications, but their long-term evaluation often requires months or years of testing. Here, we demonstrate a rapid, facile method for assessing hydrophobic coating durability using dissolvable substrates immersed in hot water as a surrogate for highly accelerated lifetime testing (HALT). Parylene C was deposited on sugar cubes of varying thicknesses, and the temporal evolution of sample mass was monitored to capture water diffusion, absorption, and subsequent dissolution dynamics. Analysis of the early-stage mass gain enabled extraction of diffusion coefficients, while dissolution onset provided a direct metric of coating performance. Comparisons with year-long condensation durability experiments revealed that dissolution time correlates strongly with coating lifetime, even when diffusion coefficients alone do not. These results highlight that substrate-dependent defects such as pinhole density, in conjunction with diffusion, govern long-term performance. The presented framework offers a generalizable, low-cost approach to rapidly screen hydrophobic polymer coatings and optimize thickness for applications requiring both water repellency and durability.