Mass transfer diffusion coefficient as a proxy for hydrophobic coating durability
Bakhshi, Alireza
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https://hdl.handle.net/2142/124711
Description
Title
Mass transfer diffusion coefficient as a proxy for hydrophobic coating durability
Author(s)
Bakhshi, Alireza
Issue Date
2024-05-01
Director of Research (if dissertation) or Advisor (if thesis)
Miljkovic, Nenad
Department of Study
Mechanical Sci & Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
M.S.
Degree Level
Thesis
Keyword(s)
Hydrophobic Coatings
Parylene C
Coating Thickness
Water Diffusion
Accelerated Testing
Durability
Dissolvable Substrate
Diffusion Coefficient
Temperature Dependence
Language
eng
Abstract
Hydrophobic coatings are designed to repel water. Durability increases with the thickness of these coatings, while thinner coatings are preferred for energy-related applications because they offer less thermal resistance. Therefore, there is an optimal thickness for such coatings. Durability tests, which expose the coatings to relevant operational conditions like steam condensation, can take years based on specific durability and qualification needs. To speed up these evaluations, it is crucial to develop accelerated methods for lifetime testing. In this study, we introduce a simple method for assessing the durability of hydrophobic coatings by using a dissolvable substrate and submerging the coated sample in hot water. We monitor the sample's mass to uncover detailed degradation patterns, which allows us to measure the water diffusion coefficient through the coating experimentally. We use Parylene C (poly-chloro-p-xylylene) as a prototype coating system to analyze absorption data and validate our findings against those from a year-long steam condensation test. Our findings indicate that the diffusion coefficient for Parylene C decreases as the coating thickness decreases, which suggests high durability for ultra-thin films (approximately 100 nm). Conversely, durability significantly improves in thicker films (around 5 μm), which can be attributed to various interconnected physical and chemical interactions at the coating interface.
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