The behavior of both inorganic and organic thin films and coatings in the electronics and pharmaceutical industries is influenced by the presence of moisture retained from the original drying and curing process or moisture absorbed from the surroundings while the product is stored or in use. By combining a quartz crystal microbalance/heat conduction calorimeter* with a relative humidity generator based on mass flow controllers, we have measured both the equilibrium water content (sorption isotherm) , the heat of sorption, and the water vapor diffusion coefficient in various thin films and coatings of thicknesses ranging from 0.1 to 10 micrometers: (a) Eudragit RS and Eudragit NE, acrylate copolymers used in enteric coatings in pharmaceutical products; and (b) composite polyethylene oxide/polyacrylic acid coatings prepared layer-by-layer and being studied for use in membranes. In this talk we present examples of these measurements and we assess the precision and accuracy obtained in determining thermodynamic and dynamic quantities used in characterizing the water vapor sorption process.

* Smith, A. L.; Shirazi, H. M. Thermochim. Acta. 2005, 432, 202-211. See also www.Masscal.com