Differentiation of the drying time of paints by dynamic speckle interferometry

This work is part of studies of drying of paints using dynamic speckle interferometry (DSI), a technique based on the use of laser light. DSI is a non-invasive method that does not disturb the drying process. The sample is illuminated by a laser light from a source and the images corresponding to a phenomenon of interference called speckle are registered. If the surface shows activity, the interference pattern changes in time. Following this evolution, we can analyze the drying process by means of an image-processing algorithms. Therefore, it is possible to determine the temporal evolution of surfaces with different drying times. In this work the application of DSI to follow the drying process of paints with different drying times and drying velocities is presented. Different types of paints applied in different thicknesses of wet film and aerosol spray were analyzed. Quantitative measurements were obtained by analysis of the inertia moment of the co-occurrence matrix. Also, qualitative measurements were obtained by sample activity. A new approach for monitoring simultaneously zones with different drying times is discussed and applied. As in previous work, results were compared with those from conventional techniques such as gravimetric analysis providing a good correlation between both techniques.