Re-examination of the effect of the stretch/orientation-induced reduction of friction under equi-biaxial elongational flow via primitive chain network simulation using two definitions of orientation anisotropy

Abstract

In this study, we examined the effect of the stretch/orientation-induced reduction of friction (SORF) between under uniaxial and equi-biaxial elongational flows using the primitive chain network (PCN) simulation with two definitions of orientation anisotropy under equi-biaxial elongational flow. We used two types of the orientation parameter S (S1 and S1/2) under equi-biaxial elongational flow, giving rise to different values 1 and 1/2 of S, as the limiting values for S1 and S1/2 along the elongational direction, respectively. We calculated the steady-state elongational viscosity of monodisperse polystyrene melts to observe the SORF, which should be effected at large strain rate by PCN simulation. Furthermore, we attempted molecular level analysis utilizing decoupling approximation. The difference between S1 and S1/2 was the critical strain rate of the SORF effect when using S1/2. The friction decreased at the critical strain rate, which was comparable with the inverse of the Rouse relaxation time under uniaxial and equi-biaxial elongational viscosities. On the other hand, the friction under equi-biaxial elongational flow using S1 decreased at earlier than that.