Journal
JOURNAL OF CHEMICAL PHYSICS
Volume 142, Issue 7, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.4908047
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Funding
- National Basic Research Program of China (973 Program) [2012CB821500]
- National Science Foundation of China [21025416, 21204029]
- Jilin Province Science and Technology Development Plan [20140519004JH, 20130101020JC]
- Wenner-Gren Center Foundation for Scientific Research
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The effect of confinement on the glass transition temperature T-g of polymeric glass formers with different side chain stiffness is investigated by coarse-grained molecular dynamics simulations. We find that polymer with stiffer side groups exhibits much more pronounced T-g variation in confinement compared to that with relatively flexible side groups, in good agreement with experiments. Our string analysis demonstrates that the polymer species dependence of dynamics can be described by an Adam-Gibbs like relation between the size of cooperatively rearranging regions and relaxation time. However, the primary effect of changing side-group stiffness is to alter the activation barrier for rearrangement, rather than string size. We clarify that free-surface perturbation is the primary factor in determining the magnitude of T-g variation for polymers in confinement: It is more significant for polymers having higher T-g and results in much more pronounced reduction of surface T-g and then the overall T-g of the polymers. (C) 2015 AIP Publishing LLC.
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