Crossover from Unentangled to Entangled Dynamics in a Systematically Coarse-Grained Polystyrene Melt

Abstract

We develop a mesoscale polystyrene model based on atomistic simulations of oligomers using the iterative Boltzmann inversion method. The potential is optimized against the atomistic simulation until the radial distribution function generated from the mesoscale model is consistent with the atomistic simulation. The mesoscale model allows to elucidate the polymer dynamics of long chains. The dynamics of polystyrene melts are investigated at various chain lengths between 15 and 240 monomers. Mean-squared displacements are analyzed to capture the dynamics changing from the Rouse to the reptation behavior. The reorientation behavior of segmental vectors is investigated to identify the heterogeneity along the chain. Diffusion constants of various systems are calculated to verify the crossover from the unentangled to entangled dynamics. Rouse mode analysis shows that the Rouse model is applicable from chain length between 50 and 100 monomers. The entanglement length of this polystyrene model is around 85 monomers at 450 K, in fair agreement with experiments.

Challenges in Multiscale Modeling of Polymer Dynamics

“…However, the obtained isothermal compressibility is far from the experimental value, which indicates poor transferability of the developed potential to pressures different from the one used in the all-atomistic simulation. Sun and Faller systematically developed a coarse-grained model for isotactic PS melts from the unentangled to the entangled regime using the super atom definition shown in Figure 11b [185,200]. The obtained entanglement length at 450 K is found to be in agreement with experimental observations.…”

“…From these studies, it is important to know that although there are different ways to define the super atom in deriving a coarse-grained model, the static, dynamic or thermodynamic properties of the coarse-grained model should be tested and validated before it is further applied [42]. [195][196][197]; (b) [185,200]; (c) [69]; and (d) [188,201]. Superatom Center…”

“…As such, S AA−CG can be estimated as MSD CG /MSD AA . Although such a dynamic rescaling method does not have rigorous theoretical foundations, it has been used successfully for low degrees of coarse graining [92,183,184,197,200,201,[221][222][223][224][225][226][227]. Using this mapping method, Harmandaris and Kremer [204,205] successfully mapped the dynamic behavior of PS melts from the all-atomistic scale to the coarse-grained level, as shown in Figure 12a,b.…”

Deforming glassy polystyrene: Influence of pressure, thermal history, and deformation mode on yielding and hardening

“…This is below the entanglement length N e of PS ͑simulations 45 at T = 450 K: N e = 83 monomers; experiments 46 at T = 413 K: N e = 128 monomers and 47 at T = 490 K: N e = 139 monomers, determined by measuring the rubberlike plateau modulus G N of an entangled PS melt above the glass transition and using this value to calculate the molecular weight between entanglements M e by means of 48 M e = 4 5 RT / G N , with R as the universal gas constant͒. Usually deformation would be affine for large length scales; for very long chains the ends do not feel immediately the connectivity constraint of each other as they are separated by many segments.…”

Biological and synthetic membranes: What can be learned from a coarse-grained description?

“…This scheme provides a systematic, yet approximate, approach for constructing the effective pair interactions. In polymer physics, one often employs a numerical method -iterative Boltzmann inversion [ 246,247,231,230,232]. One starts with an initial guess for the pair interactions, V 0 .…”