Slip-link simulations of entangled polymers in planar extensional flow: Disentanglement modified extensional thinning

In the present work, we have extended a slip-link based model, originally proposed by Masubuchi et al. [J. Chem. Phys. 115, 4387 (2001)], to simulate planar extensional flow. The salient features of the extended model are (i) an unrestricted simulation time for planar extensional flow using Kraynik-Reinelt periodic boundary conditions, (ii) an implicit time stepping scheme to enhance numerical stability, and (iii) a mesh-free Lagrangian method for the evaluation of the osmotic force. With the new code, we have simulated both the static and dynamic responses of monodisperse linear worm-like and inverse Langevin chains and compared the simulations results with the experimental data reported by Bach et al. [J. Rheol. 47, 429 (2003)]. The simulations were run for monodisperse linear chains including up to 50 entanglements. The model is able to reasonably capture the rheological behavior of entangled systems in the nonlinear range. Based on our simulations, we also present an alternative explanation for the dynamics behind extensional thinning based on disentanglement and a physical explanation for the failure of standard models, i. e., Doi-Edwards (DE)/Doi-Edwards-Marrucci-Grizzuti (DEMG) (which predict a thinning exponent of -1) in predicting the extensional thinning exponent of near -0.5 (as seen in various experiments [Bach et al., J. Rheol. 47, 429 (2003); Luap et al., Rheol. Acta 45, 83 (2005)]). (C) 2011 The Society of Rheology. [DOI: 10.1122/1.3549296]