007. Simulated glass transition of poly(ethylene oxide) bulk and film: a comparative study
writer：Chaofu Wu
keywords：Glass transition; poly(ethylene oxide); polymer film
source：期刊
specific source：Journal of Physical Chemistry B 2011; 115(38): 11044-11052
Issue time：2011年
Stepwise cooling molecular dynamics (MD) simulations have been carried out on the bulk and film models for poly(ethylene oxide) (PEO) to understand glass transition of amorphous polymer films. Three types of properties—density, energy, and dynamics—are computed and plotted against the temperature for the two systems. It has been confirmed that all these properties can reveal glass transition in both PEO bulk and film systems. All the determined glass transition temperatures (Tgs) drop in the same order of magnitude to the experimental data available. Among various methods, the Tgs obtained from the density and energy data are close to each other if the same space regions are defined, which can suggest the same free volume theory, and dynamic Tgs obtained from mean-squared displacements (MSDs) are highest, which can suggest the kinetic theory for structural relaxation. Consistently, all these Tgs obtained using different methods show that the Tgs of PEO film are lower than those of PEO bulk. The free surface layers of polymer films dictate this offset.
http://pubs.acs.org/doi/abs/10.1021/jp205205x