Non-Fickian drying of binary polymeric coatings: Depth profiling study using confocal Raman spectroscopy

• Non-Fickian drying.
• Sigmoidal profiles.
• Glassy coatings.
• Depth profiling.
• Case-II diffusion.

Concentration profiles in two binary polymeric coatings of poly (styrene)–p-xylene and poly (methyl methacrylate)–ethylbenzene system have been measured using confocal laser Raman spectroscopy. Measured profiles are very different from as shown earlier for rubbery coatings. Sigmoidal profiles are observed in these polymeric coatings because they went through the glass transition temperature during the course of drying. These coating have reasonably very high concentration of polymer in the top as compared to the concentration in the deep of the coating near the substrate. The results follow the case-II diffusion trend in glassy coatings.