In this thesis we investigated three different aspects of polymer dynamics using molecular dynamics simulations: orientation relaxation in equilibrium, shear flows and possible ways of coarse-graining. In the first part, we studied the orientation relaxation function of monodisperse and bidisperse melts of linear polymers. A universal time- dependent coupling parameter was derived to build the bridge between the monodisperse and bidisperse melts, which facilitates application of the theory of mono disperse melts to polydisperse samples. In the second part, non-equilibrium molecular dynamics simulations were used to investigate start-up shear of polymer melts. Shear stress, first and second normal stresses were measured in both transient and steady states. A possible shear banding was observed in mildly entangled system, which is in contradiction with experimental observation. We also tried to map our simulation results to PI experimental results according to the same number of entanglements and a qualitative agreement was obtained. In the last part, a systematic method was developed to derive the effective interaction forces between polymer chains in the melts. If we apply the pair-wise interaction obtained from vacuum to the melts, a reasonable agreement between the original MD simulations and the coarse- grained simulations can be achieved. However, if many-body effects were introduced, the agreement became worse.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:553653 |
| Date | January 2011 |
| Creators | Cao, Jing |
| Publisher | University of Reading |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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