Rate-Dependent Relaxation Spectra of Polymer Melt

Local Strain Relaxation Dictates Polymer Melt Viscosity

A remarkable manifestation of slow dynamics in dense polymeric systems is that their viscosity scales with their molecular weight as a power-law, with the “viscosity exponent” mη, experimentally measured to be 3.4 ± 0.2. Following De Gennes’ work in 1971, current understanding of this slow dynamics is based upon an effective single-polymer theory that pictures every polymer in such systems movi...

Polymer-specific effects of bulk relaxation and stringlike correlated motion in the dynamics of a supercooled polymer melt

We analyze dynamical heterogeneities in a simulated ‘‘bead-spring’’ model of a nonentangled, supercooled polymer melt. We explore the importance of chain connectivity on the spatially heterogeneous motion of the monomers. We find that when monomers move, they tend to follow each other in one-dimensional paths, forming strings as previously reported in atomic liquids and colloidal suspensions. T...

Polymer-specific effects of bulk relaxation and stringlike correlated motion in the dynamics of supercooled polymer melt

String-like collective motion in the α- and β-relaxation of a coarse-grained polymer melt.

Relaxation in glass-forming liquids occurs as a multi-stage hierarchical process involving cooperative molecular motion. First, there is a "fast" relaxation process dominated by the inertial motion of the molecules whose amplitude grows upon heating, followed by a longer time α-relaxation process involving both large-scale diffusive molecular motion and momentum diffusion. Our molecular dynamic...

Structural relaxation and dynamic heterogeneity in a polymer melt at attractive surfaces.

Molecular dynamics simulations of polymer melts at flat and structured surfaces reveal that, for the former, slow dynamics and increased dynamic heterogeneity for an adsorbed polymer is due to densification of the polymer in a surface layer, while, for the latter, the energy topography of the surface plays the dominant role in determining dynamics of interfacial polymer. The dramatic increase i...