Diffusion processes in the photo-oxidation of polymers

Plots of In(ro) versus the reciprocal of the absolute temperature yields the activation energy ( J, e.g. for polyethylene [353,922] and polystyrene [832, 833], 

The diffusion coefficient (D) is a function of the concentration of diffusant (penetration molecule) (Pick s second law) and for Cartesian coordinates is given by  

Polymers whose diffusion characteristics can be described by Pick s first and second laws are said to follow Fickian diffusion behaviour. 

Fickian diffusion behaviour is evidenced by a linear relationship between the sorption (or desorption) of penetrant and the square root of the time of diffusion ( )/(Fig. 2.5). 

Non-Fickian diffusion behaviour (also called case II diffusion) is an anomalous diffusion which cannot be described in terms of Fickian laws (cf. section 2.17). It can exist in polymers  

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