Simulation studies of polymer crystallization: Precursor-Phases, Reorganization and Self-Nucleation

• Antragsteller: Professor Dr. Jens-Uwe Sommer
• Fachliche Zuordnung: Experimentelle und Theoretische Polymerphysik
• Förderung: Förderung von 2008 bis 2015
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 107171127

• Erstellungsjahr: 2015

Zusammenfassung der Projektergebnisse

In this project we have carried our large scale MD simulations using a coarse grained polymer model for dense and entangled polymer systems. In the first part of the project we have studied nucleation and melting processes, in particular we were able to grow single lamellar crystals using a self-seeding protocol and to follow the dynamics of individual chains and chain parts during crystallization. Using a new order parameter we could define a kinetic precursor phase. In the second part of the project we have focused on the relation between the entanglement density and the properties of the polymer crystals using a variant of primitive path analysis. We found a direct correlation between the local entanglement length before crystallization and the stem length and crystallinity at the same place after crystallization. Moreover, cooling the amorphous melt leads to a shortening of the average entanglement length due to local stiffening. The entanglement length follows a similar behavior with respect to temperature as the crystalline stem length. This suggests a new approach to thickness selection by the entanglement density. We have shown that rapid cooling protocols which avoid adjusting of the entanglement density before crystallization proceeds leads to larger stem lengths and higher crystallinity. Also acceleration of the growth velocity can be observed for this protocols. We have further analyzed the the crystallization behavior in confined geometries and found again a correlation between the reduced entanglement density near impenetrable surfaces and enhanced, surface-induced crystallization underlying the key role of entanglements for the nucleation behavior. Also adding small amounts of solvent to the polymer can accelerate crystallization and increase the stem length. Finally, we have obtained preliminary results under non-equilibrium shear. Here, quite dramatic effects are known for nucleation and highly ordered structures can be obtained. Using primitive path analysis we have shown that in this case disentanglement takes place which can be a possible origin for flow-induced crystallization properties. To conclude, computer simulations allow for an direct analysis of the state of entanglement during crystallization and reveal a strong impact of entanglement properties on crystallization. Our results indicate en alternative explanation for the thickness-selection process at least under fast crystallization conditions. The project has yield new insights into polymer crystallization which can now be related more closely to experiments and suggests new types of experiments such as the crystallization of topologically non-entangled polymer rings which might be feasible soon.

Projektbezogene Publikationen (Auswahl)

• Coexistence of Melting and Growth during Heating of a Semicrystalline Polymer. Physical Review Letters 102, 147801 (2009)
  Chuanfu Luo and Jens-Uwe Sommer
  
• Molecular Dynamics Simulations of Semicrystalline Polymers: Crystallization, Melting, and Reorganization. Journal of Polymer Science: Part B: Polymer Physics 48, 2222 (2010)
  Jens-Uwe Sommer and Chuanfu Luo
  
• Growth Pathway and Precursor States in Single Lamellar Crystallization: MD Simulations. Macromolecules 44, 1523 (2011)
  Chuanfu Luo and Jens-Uwe Sommer
  
• Polymer Crystallization: Ordered Structures in ComplexSystems. DPG Frühjahrstagung Dresden, 24.-29. 06. 2011
  Jens-Uwe Sommer and Chuanfu Luo
  
• Polymer Crystallization: Ordered Structures in ComplexSystems. IUPAC World Polymer Congress, MACRO 2012 Blackburg, 24.-29. 06. 2012
  Jens-Uwe Sommer and Chuanfu Luo
  
• Disentanglement of Linear Polymer Chains Toward Unentangled Crystals. ACS Macro Letters 2, 31 (2013)
  Chuanfu Luo and Jens-Uwe Sommer
  
• Polymer Crystallization: Ordered Structures in ComplexSystems. Concluding conference of the collaborative research center From Single Molecules to Nanoscopically Structured Materials Mainz, 13.-16. 10. 2013
  Jens-Uwe Sommer and Chuanfu Luo
  
• Entanglement properties and polymer crystallization from melts. The 11th International Symposium on Polymer Physics (PP’2014) Nanjing, China, 09.06.2014
  Chuanfu Luo and Jens-uwe Sommer
  
• Frozen Topology: Entanglements Control Nucleation and Crystallization in Polymers. Physical Review Letters 112, 195701 (2014)
  Chuanfu Luo and Jens-Uwe Sommer