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Method for Measuring Water Diffusion in a Coating Applied to a Substrate.

pdf icon Method for Measuring Water Diffusion in a Coating Applied to a Substrate. (1330 K)
Nguyen, T.; Bentz, D. P.; Byrd, W. E.

Journal of Coatings Technology, Vol. 67, No. 844, 37-46, 1995.


building technology; coatings; substrates; FT-IR; water


A method based on Fourier transform infrared-multiple internal reflection (FTIR-MIR) spectroscopy was developed for measuring the apparent diffusion coefficient of water in a coating applied to a substrate. The method requires an application of a coating of any thickness on an internal reflection element, which serves as the substrate, with the attachment of a water chamber to the coated specimen. Water is introduced to the chamber and FTIR-MIR spectra are collected automatically without disturbing the specimen or the instrument. The amount of water at the coating/substrate interface was determined using a model based on the theory of internal reflection spectroscopy. A mass-time curve for water at the interface is established, which provides the time-lag value, the time required for water to diffuse through the coating film and reach the interface. The diffusion coefficient (D) is then determined by the time-lag equation. For thick coating films (> 25 mm), D may be estimated from the FTIR-MIR in situ intensity data only. The sensitivity of FTIR-MIR spectroscopy and the strong FTIR absorption of water molecules make this an ideal method for measuring the diffusivity of liquid water through a coating applied to a substrate.