(2jz) Elucidating the role of network topology dynamics on the coil-stretch transitionhysteresis in extensional flow of entangled polymer melts

Research Interests:
•First principal modeling, mathematical modeling, multi-scale modeling and simulation of
complex systems, and molecular dynamics.
•Bio-inspired materials, material discovery, Polymers, and drug discovery.
•Structure, dynamics and Rheology of complex fluids, Micro-fluids and soft-matter.
•Processing and experimental characterization of Micro- and Nano-structured material.
•Applied machine learning in material discovery, bio-science, and bio-informatics.

Teaching Intrests:
•Multiscale modeling and simulation of materials
•Thermodynamics
•Rheology of complex fluids and soft-matter

Abstract
Dissipative particle dynamics (DPD) simulations are performed on coarse-grained replicas of
linear, monodisperse entangled polyethylene melts C1000H2002 and C3000H6002 undergoing both
steady-state and transient planar elongational flow (PEF). The fidelity of the DPD simulations is
verified by direct comparison of flow topological and rheological properties of a 334-particle chain
liquid against the united-atom C1000H2002 liquid, simulated using nonequilibrium molecular dynamics
(NEMD). These DPD simulations demonstrate that a flow-induced coil-stretch transition
(CST) and its associated hysteresis caused by configurational microphase separation, as observed
in previous NEMD simulations of PEF, can be replicated using a more computationally efficient
coarse-grained system. Results indicate that the breadth of the CST hysteresis loop is enlarged for
the longer molecule liquid relative to the shorter one. Furthermore, relaxation simulations reveal
that reducing the applied flow Deborah number (De) from a high value corresponding to a homogeneous
phase of highly stretched molecules to a De within the biphasic region results in a two-stage
relaxation process. There is a fast initial stratification of the kinetically trapped highly stretched
chains into regions of highly extended and less extended chains, which displays similar behavior to
a system undergoing a spinodal decomposition caused by spatial configurational free energy fluctuations.
After a short induction period of apparently random duration, the less extended chain
regions experience a stochastic nucleation event that induces configurational relaxation to domains
composed of coiled molecules over a much longer time scale, leaving the more highly extended
chains in surrounding sheet-like domains. The time scales of these two relaxation processes are of
the same order of magnitude as the Rouse and disengagement times of the equilibrium liquids.