Local Segmental Dynamics and Stresses in Polystyrene–C60 Mixtures
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- 作者：Georgios G. Vogiatzis ; Doros N. Theodorou
- 刊名：Macromolecules
- 出版年：2014
- 出版时间：January 14, 2014
- 年：2014
- 卷：47
- 期：1
- 页码：387-404
- 全文大小：943K
- ISSN：1520-5835
文摘
The polymer dynamics of homogeneous C60鈥損olystyrene mixtures in the molten state are studied via molecular simulations using two interconnected levels of representation for polystyrene nanocomposites: (a) A coarse-grained representation, in which each polystyrene repeat unit is mapped into a single 鈥渟uperatom鈥?and each fullerene is viewed as a spherical shell. Equilibration of coarse-grained polymer鈥搉anoparticle systems at all length scales is achieved via connectivity-altering Monte Carlo simulations. (b) An atomistic representation, where both nanoparticles and polymer chains are represented in terms of united-atom forcefields. Initial configurations for atomistic molecular dynamics (MD) simulations are obtained by reverse mapping well-equilibrated coarse-grained configurations. By analyzing MD trajectories under constant energy, the segmental dynamics of polystyrene (for neat and filled systems) is characterized in terms of bond orientation time autocorrelation functions. Nanocomposite systems are found to exhibit slightly slower segmental dynamics than the unfilled ones, in good agreement with available experimental data. Moreover, by employing Voronoi tessellation of the simulation box, the mean-squared displacement of backbone carbon atoms is quantified in the vicinity of each fullerene molecule. Fullerenes are found to suppress the average motion of polymeric chains, in agreement with neutron scattering data, while slightly increasing the dynamic and stress heterogeneity of the melt. Atomic-level and local (per Voronoi cell) stress distributions are reported for the pure and the filled systems.