Dear Mr. Nigam:
Fick's diffusion is the classical diffusion that controlled by thermodynamic forces (by gradient of chemical potential or differences of concentrations) with the constant (or even pseudo-constant) diffusion coefficients and relatively simple kinetic profiles of penetrant redistribution in polymer matrix as the consequence of 1st and 2nd Fick's lows.
In contrast to classical diffusion the nonfickian (anomalous) diffusion includes the other physical and physical-chemical processes especially when a polymer is in glassy-state. In this case the course of diffusion is complicated by molecular relaxation, segmental mobility retardation, functional interaction between penetrant and macromolecules, crystallization and others. Additionally for nonfickian diffusion we could recognize surface or/and volume anomalous processes. Especially you should pay attention on anomalous processes which occur in the nanocomposites where area for molecular movement too small to realize the classical diffusion. The latter is more typical for macro- bulk polymer area.
Regards,
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