Primary Nucleation of Polymer Crystal via Particles Fluctuation with Non-Markovian Effect

The debate surrounding preorders in the primary nucleation of polymer crystals has captivated scientists for decades. By constructing a cylindrical order parameter (COP), we observe a preordering-crystallization two-step nucleation process in a molecular dynamics simulation of polymer crystallization. Instead of the sharp interface between amorphous and crystalline regions assumed by classical nucleation theory (CNT), we observe a gradient COP profile that shifts toward higher COP values as the nucleus size increases. In nucleation dynamics, we depart from the Markov process described in the CNT, where single particles attach to and detach from nuclei without memory. Instead, we find that nucleation occurs through particle fluctuations with a memory effect, which is enhanced as the nucleus size increases, leading to positive feedback. This mechanism of nucleation via particle fluctuations with memory effect fundamentally diverges from CNT and previous nonclassical nucleation models, offering a new perspective on understanding the nucleation of polymers.