Coarse-Grained Molecular Dynamics Simulation of Elongational Flow of Polymer Melts

Abstract

Elongational flows in polymer melt are important for polymer processing. For fiber processes, uniaxial elongational flow stretches polymer chains and enhance the strength of the fibers. Biaxial elongational flow makes thin films during film extruding processes. Molecular dynamics (MD) simulation can be useful to understand the microscopic mechanics of polymer chains in elongational flow fields. However, it has been difficult to treat elongational flows in MD for a long time. Extending the Kraynik-Reinelt boundary condition [1] for planar elongational flow, uniaxial and biaxial elongational flow have been succeeded in MD and applied to Lenard-Jones fluid [2,3] and crystallization process of an n-eicosane melt [4]. We have investigated elongational flows of a weakly entangled polymer melt [5]. The highly entangled polymer melt in experiments shows extensional thinning [6] while our previous results show extensional thickening [5]. We investigate a mildly entangled polymer melt and discuss whether the non-linearity of elongational viscosity enhances or not. Moreover, we investigate the elongational viscosities of branched polymer melts. [1] A. M. Kraynik and D. A. Reinelt, Int. J. Multiphase Flow 18, 1045 (1992).[2] M. Dobson, J. Chem. Phys. 141, 184103 (2014).[3] T. A. Hunt, Mol. Sim. 42, 347 (2016).[4] D. A. Nicholson and G. C. Rutledge, J. Chem. Phys. 145, 244903 (2016).[5] T. Murashima, K. Hagita, and T. Kawakatsu, arXiv: 1803.01517.[6] A. Bach, K. Almdal, H. K. Rasmussen, and O. Hassager, Macromol. 36, 5174 (2003).