Mass transfer diffusion coefficient as a proxy for hydrophobic coating durability

Bakhshi, Alireza

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https://hdl.handle.net/2142/124711 Copy

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.

Graduation Semester

2024-05

Type of Resource

Text

Handle URL

https://hdl.handle.net/2142/124711

Copyright and License Information

Copyright 2024 Alireza Bakhshi

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