Primitive chain network simulations for H-polymers under fast shear.

Branchpoint Withdrawal (BPW) has been recognized as one of the important molecular mechanisms for the description of the dynamics of entangled branched polymers under fast flows. However, the relation to the other known molecular mechanisms has not been fully elucidated yet. In this study we performed primitive chain network (i.

Do Repeated Shear Startup Runs of Polymeric Liquids Reveal Structural Changes?

Using the integral equation of the Doi-Edwards theory that only accounts for tube orientation of entangled linear polymers, we explore the behavior of the stress maximum typically observed in shear startup as a function of the waiting time between repeated startup runs. Depending on whether the first run is interrupted before the maximum, or sufficiently beyond it, the magnitude of the peak in the second run comes out nonmonotonic with or else monotonically increasing, respectively. A similar behavior has been observed in several experiments and commonly attributed to structural changes of the entangled network.

Structure of entangled polymer network from primitive chain network simulations.

The primitive chain network (PCN) model successfully employed to simulate the rheology of entangled polymers is here tested versus less coarse-grained (lattice or atomistic) models for what concerns the structure of the network at equilibrium (i.e., in the absence of flow).

Primitive chain network simulations for entangled DNA solutions.

Molecular theories for polymer rheology are based on conformational dynamics of the polymeric chain. Hence, measurements directly related to molecular conformations appear more appealing than indirect ones obtained from rheology. In this study, primitive chain network simulations are compared to experimental data of entangled DNA solutions [Teixeira et al.

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.

Highly entangled polymer primitive chain network simulations based on dynamic tube dilation.

The concept of dynamic tube dilation (DTD) is here used to formulate a new simulation scheme to obtain the linear viscoelastic response of long chains with a large number of entanglements. The new scheme is based on the primitive chain network model previously proposed by some of the authors, and successfully employed to simulate linear and nonlinear behavior of moderately entangled polymers. Scaling laws are generated by the DTD concept, and allow for prediction of the linear response of very long chains on the basis of suitable simulations performed on shorter ones, without introducing adjustable parameters.

Flow-induced orientation and stretching of entangled polymers.

A single-mode constitutive equation is proposed which accounts, in a very simple way, for the most important feature of the molecular theory for entangled polymers based on the 'tube' concept, i.e. that the orientation of the tubes and the stretching of the chain within them relax over different time-scales.