Synchronized molecular dynamics simulation using LAMMPS: application to pressure-driven flows of polymer melts

Abstract We investigate the effects of anisotropic thermal conductivity on the pressure-driven thermal flow of entangled polymer melts through a multiscale simulation that combines molecular dynamics (MDs) and computational fluid dynamics (i.e. a synchronized MDs method). We incorporate a linear relationship between the thermal conductivity tensor and the bond orientation tensor on the basis of network theory, which causes the thermal conductivity in the heat flux to be spatially distributed rather than uniform. We develop a simulation code using the LAMMPS package as the MD engine. Benefitting from LAMMPS, we can apply the method to a wide range of complex fluids with good parallel efficiency. Our results demonstrate that when the shear rate is very small and the Weissenberg number ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>W</mml:mi> <mml:mi>i</mml:mi> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> ) is less than approximately 100, the effect of the anisotropic thermal conductivity on the temperature and velocity profiles is minimal; thus, it can be ignored. However, when <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>W</mml:mi> <mml:mi>i</mml:mi> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> is greater than approximately 100, the anisotropic thermal conductivity has a significant effect on both the temperature and velocity profiles. This result indicates that in high-Weissenberg-number flows (e.g. <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>W</mml:mi> <mml:mi>i</mml:mi> </mml:msub> </mml:mrow> <mml:mo>&gt;</mml:mo> <mml:mn>100</mml:mn> </mml:mrow> </mml:math> ), anisotropic thermal conductivity can play a critical role in polymer processing in chemical engineering.