Brownian Dynamics Simulation of FENE Dumbbell Model for Dilute Polymer Solutions in Extensional Flow: Effect of Distribution of FENE Parameter and Relaxation Time.

Abstract

Brownian dynamics (BD) simulations of the steady and transient rheological behaviors of FENE dumbbell model for dilute polymer solutions in uniaxial extensional flow are reported. The simulations include examination of the effects of distributions of maximum allowable extension (FENE parameter b) and of relaxation time parameter α. Stretch-thickening and strain-hardening behaviors, which can be often observed in polymer solutions, are confirmed in the simulations either with or without the distribution of b or α. However, overshoot phenomenon in a start-up extensional flow can never be observed unlike the situation in a start-up shear flow. Curves of transient extensional viscosity vs. strain clearly show that the extensional viscosity is independent of the stretch rate in the regime of αλ0e>1~2 where polymer solutions exhibit significant strain-hardening. Furthermore, it is found that the distribution of b has little influence on extensional flow properties while the distribution of α can affect both the steady and transient extensional flow properties under the distribution condition used in the simulations. BD simulation can precisely predict the extensional viscosity even in the low stretch rate region.