Accurate measurement of diffusion rates of small molecules through polymers

The diffusion of methanol in PMMA and dodecane in PS has been studied by in situ dynamic observations using light microscopy. A specially constructed cell enabled accurate monitoring of the diffusion fronts as they advance in to the polymer matrices. It is shown that the diffusion rate at the early s tages of the process does not follow the rate predicted by square root from time behaviour and that swelling is also delayed. Analysis of the results indicated that the following equation gives an accurate correlation with th e experimental data: x = b(t(1/2) - (1 - e(-t1/2))). It was also observed t hat voids can be filled up by the penetrant, representing diffusion against the concentration gradient and thus indicating that concentration driven m echanisms are not applicable to the systems studied in this work. (C) 1999 Elsevier Science Ltd. All rights reserved.