Recent simulation results of a moderately entangled linear polyethylene ${\mathrm{C}}_{700}{\mathrm{H}}_{1402}$ liquid have confirmed prior simulation and experimental evidence that individual polymer molecules experience periodic rotation and retraction cycles under steady shear flow at high Weissenberg number. With this insight, theoreticians have begun to grapple with this additional complicating physical phenomenon that needs to be incorporated into rheological models to help explain the data under conditions of high shear. In this paper we examine these recent efforts by using nonequilibrium molecular dynamics simulations to provide insight into the requisite theoretical variables and their assigned evolution equations to evaluate the capability of these tube-based models to predict accurately the simulated data sets. This analysis reveals that the primary variables used in tube models to impart a conceptual basis to the theory, namely, the tube orientation tensor and the tube stretch, remain fundamental system properties even far away from equilibrium; however, the theory describing their evolution under flow is not well suited to quantitative prediction. Furthermore, it is demonstrated that key system properties, such as the entanglement number and disengagement time, should play a more significant role in model development since these quantities can change dramatically under flow, particularly at high Weissenberg number where the chain rotation and retraction cycles dominate the system physics.

Close

PrevNext

View figure in article

• 
• 
• 
• 
• 
• 
• 
• 
• 
• 

• Complex fluids
• Polymer conformation & topology
• Polymer conformation changes
• Polymer entanglement
• Reptation
• Rheology
• Shear deformation