کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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1402519 | 984767 | 2010 | 12 صفحه PDF | دانلود رایگان |
Absorption into polymers is frequently described by the terms Fickian, sigmoidal (S-shaped), Case II, or Super Case II. This terminology is used to describe absorption that is respectively, linear with the square root of time, has a slight delay or S-shape with the square root of time, is linear with linear time, or increases more rapidly than with linear time. Solutions to the diffusion equation, Fick’s second law, that include a potentially significant surface condition are shown to reproduce all of these. Sigmoidal absorption results when the surface condition is moderately significant for either a constant diffusion coefficient or exponential diffusion coefficients. Exponential diffusion coefficients and a lower surface mass transfer coefficient result in Case II type behavior, with Super Case II behavior resulting when the surface condition becomes still more significant. The results reported here are supported by extensive experimental data with reasonable and verifiable values for the diffusion coefficients and surface mass transfer coefficients.
The diffusion equation solved with a progressively significant surface condition successfully simulates sigmoidal absorption, Case II diffusion (shown in figure) and Super Case II, respectively. The straight line absorption curve with linear time at the lower right is typical of Case II diffusion.Figure optionsDownload as PowerPoint slide
Journal: European Polymer Journal - Volume 46, Issue 4, April 2010, Pages 651–662