Method for Measuring Water Diffusion in a Coating Applied to a Substrate.
Method for Measuring Water Diffusion in a Coating
Applied to a Substrate.
Nguyen, T.; Bentz, D. P.; Byrd, W. E.
Journal of Coatings Technology, Vol. 67, No. 844,
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.