Coupling between intra- and inter-chain orderings in flow-induced crystallization of polyethylene: A non-equilibrium molecular dynamics simulation study
Non-equilibrium molecular dynamics simulations have been performed to study the molecular mechanism of flow-induced crystallization (FIC) of polyethylene (PE). The related work has been published in The Journal of Chemical Physics (2017, 146:014901).
NEMD simulations are performed to investigate the FIC of PE melt. Upon imposing the extension, intra-chain conformational ordering or gauche-trans transition occurs first, which further couples with the inter-chain ordering and results in a hexagonal order. The growth of the all-trans segments and hexagonal order finally leads to the formation of orthorhombic order. This process clearly demonstrates that FIC is a multi-stage ordering process involving the intra-chain and inter-chain orderings. Based on the simulation results, we propose that coupling between intra-chain conformational and inter-chain orientation and density orderings is the essential physics of FIC, in which the intra-chain conformational ordering is directly related to stress. In this intra-chain and inter-chain coupling mechanism, not only entropic reduction but also inter-energy, either due to gauche-trans transition or from inter-chain packing, contributes simultaneously in FIC.
The ideal hexagonal (a) and orthorhombic (b) crystal structures of PE. (c) The snapshot of spatial distributions of bond-orientational order (Q4) of the system at a strain of 4. The dark-blue and light-blue monomers correspond to the OM and HM crystal domains, respectively
