Solvent Diffusion and Drying of Coatings
A model for the drying of coatings has been developed based upon solvent evaporation at the surface (as determined by the solvent volatility), and transport through the film (as determined by solvent diffusion). A computer program based on this model has been written which uses these factors to predict the solvent loss as a function of time. Solvent volatility was based upon the standard evaporation rates (for the pure solvent) and the solvent activity given by the Flory-Huggins treatment. Diffusion within the film was simulated by the Crank-Nicolson implicit method, and the solvent self-diffusion coefficients used were measured by the pulsed-gradient, spin-echo (PGSE) NMR method. The results clearly show the major features found experimentally, namely regions of volatility and diffusion controlled drying. A comparison of experimental data with an actual drying curve shows excellent agreement with those predicted from this program for the polystyrene-toluene system. In addition, the program provides a unique look at the concentration profile within the coating.
R. A. Waggoner and F. D. Blum, "Solvent Diffusion and Drying of Coatings," Journal of Coatings Technology, Springer Verlag, Jan 1989.
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