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** Experimental system parameters **

First, with no exception, in all classical diffusion models one or more adjustable parameters enter in the formula of D. To calculate the magnitude of this/these param-eter/s a number of diffusion experiments must be performed with the very penetrant polymer system which one intends to simulate theoretically. In practice such experiments most often require quite sophisticated equipment to obtain the experimental data, and often non-trivial theoretical schemes to evaluate them. The attempt to save experimental work by using the adjustable parameters determined for a certain penetrant polymer system in order to estimate/predict Ds in a related system is generally not recomendable. Hence, in a first step, in order to use one or other of the classical diffusion models, one is forced to replace migration experiments with diffusion ones. [Pg.152]

** Experimental system parameters **

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