ENTROPIC BARRIER MODEL FOR POLYMER DIFFUSION IN CONCENTRATED POLYMER-SOLUTIONS AND RANDOM-MEDIA

It is argued that the diffusion of a polymer chain in random media such as controlled pore glasses, entangled semiconcentrated polymer solutions, and swollen gels is determined dominantly by the entropic traps arising from the spatial inhomogeneities and lack of full topological correlations in the background. It is shown from scaling arguments and Monte Carlo simulations of model systems that the diffusion coefficient of a chain in such random media has a stronger molecular weight dependence than even the reptation law. The newly identified entropically activated dynamical regime appears as an intermediate regime between the Rouse and reptation regimes. Most of the experimental investigations in semidilute solutions and swollen gels and computer simulations are argued to actually belong to this regime and the current controversies regarding whether reptation is present or absent in these investigations are resolved by the non-universal features of this intermediate regime. The relevance of such entropically controlled chain dynamics in gel electrophoresis is also addressed.