Oral: Exploring molecular mechanisms underlying mechanical and rheological response of dispersed polymer melts from molecular dynamics simulations*

Motivated by the importance of interfacial properties of polymers in applications such as adhesion, there is a need to understand the molecular mechanisms which drives structure-property responses in the bulk. Due to their synthesis routes, commodity polymers have a large distribution of molecular weights, which is commonly characterized by dispersity (Ð). Recent studies have shown that dispersity can be used to tune polymer properties without the use of additives, or by changing the chemistry of the system. Here, using molecular dynamics simulation, we unravel molecular mechanisms that govern mechanical and rheological properties of entangled melts with dispersities ranging from 1.0 – 2.0. Specifically, we study the Schulz-Zimm distribution type, which models polymer samples synthesized by anionic and atom - transfer radical polymerization, across different average molecular weights (or chain lengths). We use the standard Kremer Grest bead – spring model which has been shown to capture the underlying physics of polymer melts.

 

First, we perform entanglement analysis on the basis of primitive paths to elucidate the topology of entangled melts. Next, we compute the stress relaxation of the melts from equilibrium simulations using the Green – Kubo relation. We also generate the frequency – dependent modulus of the melt and extract the storage and loss moduli. Finally, we perform uniaxial deformation to compute the stress-strain curve. All properties are compared with monodisperse systems. Future work includes simulating free standing films of these systems, to understand how dispersity affects interfacial melt properties.

 

 

Keywords: Polymer Melts, Dispersity, Viscoelastic Responses, Entanglements, Primitive Path Analysis, Stress Relaxation