Molecular simulations for the effect bidispersity and crystallization temperature on the initial stage of structural formation of polyethylene oligomers upon instantaneous deep quench from their melts

The early stage of structural formation induced by an instantaneous quench from the melts of mono- and binary (50:50) mixtures of polyethylene oligomers, short- and long-chain components represented by eicosane (C₂₀H₄₂) and tetracontane (C₄₀H₈₂) at different crystallization temperatures (Tc = 300 K, 320 K, 340 K and 360 K), were investigated by Monte Carlo (MC) simulation of the coarse-grained (CG) molecular models mapped on the second nearest neighbor diamond (2nnd) lattice. In this simulation, intramolecular interactions were represented by the rotational isomeric state (RIS) model, and intermolecular interactions were represented by the Lennard-Jones (LJ) potential energies. The scattering profiles, local dynamics at the monomer level, conformation properties, intra- and intermolecular interaction energies, bond order parameters and structural pair correlation function, were monitored to assess the development of the ordered structure quantitatively. Simulation results suggest that the formation of ordered structures tends to be optimal at Tc = 340 K among binary mixtures with the degree of supercooling (Tm - Tc) around 50–60 K. The structures of binary mixtures formed at Tc = 340 K are also more ordered in comparison to those of pure components. At this condition, although both chain components tend to have less amount of trans conformation than those in pure systems, short chains gain a higher degree of bond orientation, more segregation tendency for short-chain monomers, enhanced monomer dynamics, and the overall structures become more densely packed than their pure components, while long chain components exhibit the opposite characteristics.