حسین اسلامی

We have constructed efficient coarse-grained (CG) models of poly(ethylene terephthalate) (PET), using three mapping schemes, in which a repeat unit is lumped into either three or four beads. The CG potentials are parameterized to reproduce target distributions of an underlying accurate atomistic model [H. Eslami and F. Müller-Plathe, Macromolecules 42, 8241–8250 (2009)]. The CG simulations allow equilibration of long PET chains at all length scales. The CG results on the density of PET in melt and glassy states, chain dimen- sion, local packing, and structure factor are in good agreement with experiment. We have established a link between the glass transition temperature and the local movements including conformational transitions and mean-square displacements of chain segments. Temper- ature transferabilities of the three proposed models were studied by comparing CG results on the static and thermodynamic properties of a polymer with atomistic and experimental findings. One of the three CG models has a good degree of transferability, following all inter- and intra-structural rearrangements of the atomistic model, over a broad range of temperature. Furthermore, as a distinct point of strength of CG, over atomistic, simulations, we have examined the dynamics of PET long chains, consisting of 100 repeat units, over a regime where entanglements dominate the dynamics. Performing long-time (550 ns) CG simulations, we have noticed the sig- nature of a crossover from Rouse to reptation dynamics. However, a clear separation between the Rouse and the reptation dynam- ics needs much longer time simulations, confirming the experimental findings that the crossover to full reptation dynamics is very protracted.