Molecular dynamics simulation of slit rheometer for predicting shear thinning of short polyethylene chains.

This article focuses on using molecular dynamics (MD) simulations to investigate the isothermal contraction flow of short linear polyethylene (PE) chains in a nanoscale slit rheometer, aiming to understand the molecular basis of rheological properties. The study models a system where PE chains are extruded through a gold-atom slit, revealing phenomena such as die swelling, die wetting, and molecular chain stretching within the slit, with velocity profiles transitioning from uniform to parabolic as extrusion velocity increases. A critical extrusion velocity was identified at which die wetting ceases, coinciding with changes in slip velocity, shear stress, and shear rate inside the slit. The relationship between apparent shear viscosity and shear rate exhibits characteristic non-Newtonian behavior, including a first-Newtonian plateau and shear thinning slope, demonstrating that MD simulations can effectively capture macroscopic polymer fluid rheology from a molecular perspective.