Multiscale simulations of star polymer melts

Depending on the architecture, polymers are observed to show different dynamical and rheological properties. The results obtained from this work will not only contribute to a fundamental understanding of the character of star polymeric systems, but also possibly help to design industrial architecturally complex polymer materials with specific macroscopic properties. Simulations are carried out with coarse-grained method at multiple levels. The Twentanglement algorithm for mesoscopic simulations of polymers is extended to study three armed polymers with various arm lengths. Firstly, a star with three moderately entangled linear arms is studied to test the method. The segmental diffusions are calculated, where it is found that the branch point diffuses the slowest and the free ends move the fastest. By increasing the arm length, the star polymers gradually show a slower diffusion than both matching linear chains, as well as a delayed relaxation. Furthermore, in this work the zero shear viscosities of star melts are calculated from their stress moduli. The observed exponential scaling law in the arm molecular mass of star polymer shows a reasonable agreement with experimental and theoretical investigations for very large star polymers presented in the literature. Besides, the asymmetric three-armed polymer melts have also been studied. The presence of the agile side chain allows for relatively fast local stress relaxations and dilates the tube constraining the backbone. The investigation of polymer systems at different time and length scales requires different coarse graining levels. We present a highly coarse grained model, Responsive Particle Dynamics (RaPiD). In this model, the coarse grained forces can be split into conservative interactions described by the extended Flory-Huggins potential, 'transient' forces depending on the contacts between polymers to represent entanglement effects, and random thermal forces. In this work, the parameterization is obtained in a bottom-up approach as well as considerations of polymer concepts in physics. The radial distribution function generated by RaPiD reproduces the small scale simulation data very well. The shear stress modulus as calculated in RaPiD is in reasonable agreement with the small scale simulations. This work proves that a many-body model is capable of describing the system dynamics very well.