Non-Gaussian effects in the cage dynamics of polymers

Abstract

The correlation between the fast cage dynamics and structural relaxation is investigated in a model polymer system. It is shown that the cage vibration amplitude, as expressed by the Debye–Waller factor, and the relaxation time τ_α collapse on a single universal curve with a simple analytic form when the temperature, the density, the chain length and the monomer–monomer interaction potential are changed. For the physical states with the same τ_α the coincidence of the mean-square displacement, the intermediate scattering function and the non-Gaussian parameter is observed in a wide time window spanning from the ballistic regime to the onset of the Rouse dynamics driven by the chain connectivity. The role of the non-Gaussian effects is discussed.

Keywords:

• glass transition
• polymers dynamics
• molecular dynamics simulation

Acknowledgements

Discussions with Dr. Luca Larini are acknowledged. Computational resources by ‘Laboratorio per il Calcolo Scientifico’ (Physics Department, University of Pisa), financial support from MUR within the PRIN project ‘Aging, fluctuation and response in out-of-equilibrium glassy systems’ and FIRB project ‘Nanopack’ are acknowledged.