Statics, linear, and nonlinear dynamics of entangled polystyrene melts simulated through the primitive chain network model.

Simulation results of the primitive chain network (PCN) model for entangled polymers are compared here to existing data of diffusion coefficient, linear and nonlinear shear and elongational rheology of monodisperse polystyrene melts. Since the plateau modulus of polystyrene is well known from the literature, the quantitative comparison between the whole set of data and simulations only requires a single adjustable parameter, namely, a basic time. The latter, however, must be consistent with the known rheology of unentangled polystyrene melts, i.e., with Rouse behavior, and is therefore not really an adjustable parameter. The PCN model adopted here is a refined version of the original model, incorporating among other things a more accurate description of chain end dynamics as well as finite extensibility effects. In the new version, we find good agreement with linear rheology, virtually without adjustable parameters. It is also shown that, at equilibrium, Gaussian statistics are well obeyed in the simulated network. In the nonlinear range, excellent agreement with data is found in shear, whereas discrepancies and possible inadequacies of the model emerge in fast uniaxial elongational flows, even when accounting for finite extensibility of the network strands.