With the guidance of Prof. Li and Dr. Chen, Tang has performed molecular dynamics simulation to comparatively study the nucleation process of polyethylene melt under quiescent and high-temperature shear conditions. The related work has been published in The Journal of Chemical Physics.
Two order parameters were introduced in this work, and one is the local order parameter OCB, which is used to identify the local ordered structures from the melt, the other one is density represented by Voronoi Volume. The nucleation process under different conditions was analyzed by tracking the evolution of these two order parameters. At quiescent condition, it was observed that the local ordered structures emerge prior to the density and nucleation, thus the nucleation phenomenon was defined as “Local ordered structure fluctuation assisted nucleation”. On the other hand, the molecular chains were forced to transform their conformation as well as orientation, which incubates the high-density domains in the melt state, and the nucleation takes place within high-density domains after cooling. Therefore, a scenario “density fluctuation assisted nucleation” was defined under high-temperature shearing. These results could help to further understand the mechanism of flow-induced nucleation, and the accelerating of nucleation and growth rates under flow may associate with this new kinetics pathway.
This work is funded by the National Natural Science Foundation of China (51633009).
Related links: https://aip.scitation.org/doi/abs/10.1063/1.5054273
