title: Melting processes of oligomeric α and β isotactic polypropylene crystals at ultrafast heating rates.
abstract: The melting behaviors of α (stable) and β (metastable) isotactic polypropylene (iPP) crystals at ultrafast heating rates are simulated with atomistic molecular dynamics method. Quantitative information about the melting processes of α- and β-iPP crystals at atomistic level is achieved. The result shows that the melting process starts from the interfaces of lamellar crystal through random dislocation of iPP chains along the perpendicular direction of lamellar crystal structure. In the melting process, the lamellar crystal gradually expands but the corresponding thickness decreases. The analysis shows that the system expansion lags behind the crystallinity decreasing and the lagging extents for α- and β-iPP are significantly different. The apparent melting points of α- and β-iPP crystals rise with the increase of the heating rate and lamellar crystal thickness. The apparent melting point of α-iPP crystal is always higher than that of β-iPP at differently heating rates. Applying the Gibbs-Thomson rule and the scaling property of the melting kinetics, the equilibrium melting points of perfect α- and β-iPP crystals are finally predicted and it shows a good agreement with experimental result.
authors: School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, People's Republic of China.
authors: Xiaojing
authors: X
authors: Ji
authors: Department of Chemistry, School of Science, Tianjin University, and Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072, China.
authors: Xuehao
authors: X
authors: He
authors: School of Material, Tianjin University, Tianjin 300072, China.
authors: Shichun
authors: S
authors: Jiang