Application of dynamic speckle interferometry to the drying of coatings

In this work a new tool to study the drying of paints, based on an optical technique known as dynamic speckle interferometry is presented. The basic c oncepts of the technique are described and applied to the drying process of white solvent-borne and white water-borne paints (latex paint) following t he time evolution of the activity of dynamic speckle patterns. For processi ng the data an alternative method based on the use of the second-order mome nt of the modified co-occurrence matrix of the time history of its intensit y was used. The experimental results obtained were compared with the gravim etric technique and the resulting curves from the speckle-time evolution co mpared favorably with gravimetric drying curves. The results were also disc ussed on the basis of the knowledge of the coating drying process and facto rs related with the surface properties. Dynamic speckle interferometry seem s to be a useful technique for assessing the time evolution of surfaces and , its sensitivity to refractive index changes helps to determine the start of different stages during the drying of latex paints. The dynamic speckle method tests mainly the activity on the surface and the measurements seem t o confirm that the initial stage of drying is like a pure solvent. Finally, the study of different aspects of the drying process using this technique is proposed. (C) 2001 Elsevier Science B.V. All rights reserved.