Nanocontraction flows of short-chain polyethylene via molecular dynamics simulations

Abstract

Nanocontraction flows of liquid short-chain polyethylene ([CH 2 ] 50 ) that were uniformly extruded by a constant-speed piston into a surrounding vacuum from a reservoir through an abrupt contraction nozzle were performed by employing molecular dynamics simulations. The extrudate exhibits a similar die swell phenomenon around the exit of the nozzle. In addition, numerous molecular chains are strongly adsorbed on the external surface of the nozzle. At high extrusion speeds, the velocity and temperature profiles in the nozzle show convex and concave parabolic curves, respectively, whereas the profiles are relatively flat at lower speeds. Near the internal boundary of the nozzle, the wall slip is inspected. Significantly, during the flow, the molecular chains undergo structural deformation, including compressed, stretched and shrunk motions. Comparisons with related experimental observations show that the simulated probability distributions of the bending and dihedral angles, and variations of the squared radius of gyration and orientations, are in reasonable agreement.

Master curves and radial distribution functions for shear dilatancy of liquid n-hexadecane via nonequilibrium molecular dynamics simulations

“…The functions and parameters of those potentials for the CM model are the same as the ones we apply to model n-hexadecane molecule. 16 This model has been adopted previously in the steady state shear flow, 16,36,[43][44][45] oscillatory shear flow, 46 and contraction flow 47 portions of molecular dynamics simulations.…”

Linear viscoelasticity and thermorheological simplicity of n-hexadecane fluids under oscillatory shear via non-equilibrium molecular dynamics simulations

“…This model is superior to the transferable potential for phase equilibria (TraPPE) model, which we previously used to examine n-hexadecane, when predicting rheological properties. 27 Such a model has been applied in the shear flow 27,55-57 and contraction flow 58 portions of MD simulations. In descriptions of the molecular chains below, the CM model is dominated by van der Waals (vdW) and covalent bonding interactions:…”

Molecular Dynamics Investigation of the Effect of Shear during Extrusion on the Permeation Behavior of CH4 in High-Density Polyethylene

“…On the other hand, friction between the melt and the die wall causes the wall slip, which forms a molten film. Since the inner and outer melts move at different speeds, shearing action is generated Under these shear effects, the microstructure of polymer molecules changes, which leads to big changes in the flow state, viscoelasticity, crystallinity, and density of polymers [18]; the mechanisms by which these microscopic changes lead to macroscopic property changes are not adequately comprehended. Therefore, it is imperative to investigate the effects of screw speed and wall friction on material properties from a shear action perspective.…”