Properties of Transient Azeotropic Condensates and Their Effects on Measuring Fog Residues

While working to develop a more reproducible fog testing method, an important revolatilization mechanism of the fog residue was discovered. Volatiles vaporize from the materials being tested as azeotropic mixtures and condense on the glass as such. When the glass is removed from the apparatus, some of the condensed volatiles vaporize again over a period of time causing reflectance values to change.

The components of a fog residue, dependent on the composition of the material being tested, determine how long or how rapidly the reflectance values will change. This explains why taking more than just a “one hour” reflectance reading is needed.