Chain Entanglement Determining the Interlamellar Amorphous Thickness in Semicrystalline Polymers

Molecular dynamics simulations are employed to investigate how molecular topology governs the thickness of the interlamellar amorphous layer ( L a ) in semicrystalline polymers. Lamellar crystals with varying initial interlamellar spacing ( L a0 ) are seeded in the melt. When L a0 falls below twice the radius of gyration of the molecular chain (2 R g ), crystal stems exhibit uneven thickening, preferentially extending away from the adjacent lamellae. This leads to a progressive increase of L a as the crystal grows. Quantitative analysis reveals significant increases in local entanglement density ( N z ) and conformational entropy-derived free energy ( G con ) within the interlamellar amorphous layer, which collectively suppress crystal stem elongation into the constrained layer and direct growth toward the less entangled side. Regardless of the initial L a0, systems with identical chain length evolve toward a similar steady-state L a . A linear relationship between L a and N z emerges, whose slope corresponds to the entanglement density, which depends solely on the chain length. This reveals that the interlamellar amorphous layer self-adjusts its thickness to maintain a constant entanglement density, which is predetermined by molecular chain length. Our simulations provide molecular-level evidence for how topological entanglements govern the equilibrium morphology of semicrystalline polymers.