Flow-induced polymer crystallization is a critical aspect of the film casting process for functional polymer films. It refers to the cooling and solidification of polymer melts or solutions upon exiting the extrusion die, and plays a significant role in understanding the nonequilibrium physics of functional films and guiding practical industrial production. During this process, flow-induced chain segment conformations evolve into crystalline structures through intermediate ordered states—a concept that is increasingly gaining acceptance among experimental scientists. However, key questions remain unresolved, including whether such intermediate states are universal, what crystal forms they adopt, and how these states depend on temperature and flow conditions.
1. Multi-Step Process of Flow-Induced Crystallization and Its Nonequilibrium Phase Diagram
(a) Nonequilibrium Crystallization Phase Diagram of PE Melt under Flow Fields; (b) Nonequilibrium Crystallization Phase Diagrams of Polypropylene Melt under Flow Fields at Different Temperatures and Strain Rates.
2. Multi-Step Molecular Picture of Flow-Induced Crystallization
(a) and (b) depict chain conformations at different simulation times under quiescent (static) crystallization conditions, showing only the ordered structures identified using the local order parameter OCB.
(c) shows the variation of structural entropy and density along the simulation trajectory for atoms that eventually participate in nucleation.
(d) presents the nucleating atoms in the simulation system at 10.05 ns under shear conditions.
(e) and (f) display the density and conformation distribution maps of the same system at 10 ns. In (f), atomic colors indicate the values of the CO parameter, representing the degree of chain orientation and the length of conformationally ordered segments.
At 10 ns, high-density regions correspond to the aggregation of conformationally ordered chain segments, revealing that density fluctuations originate from such aggregation. The fact that the nucleation regions precisely coincide with high-density zones confirms the inductive role of density in flow-induced crystallization.
