Effect of copolymer sequence on local viscoelastic properties in spherical coordinates around a nanoparticle
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Date
2019-05
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Publisher
The Ohio State University
Abstract
A polymer nanocomposite consisting of a spherical nanoparticle surrounded by
coarse-grained polymer chains is simulated. Two monomer types make up the polymers,
differing only in their interactions with the nanoparticle. All atomic stress fluctuations
are measured, converted to spherical coordinates centered around the nanoparticle,
and used to estimate the local stress autocorrelation as a function of distance
from the nanoparticle. The local stress autocorrelation is substituted into the relationship
between the bulk stress autocorrelation and bulk dynamic modulus, analyzed in
both radial shear and tangential shear geometries. The result is then treated as an estimate
of the local dynamic modulus. This allows us to separate radial and tangential
effects on overall dynamic modulus as a function of distance from the nanoparticle for
multiple copolymer sequences. Unlike the direction-independent results, short block
length copolymer sequences exhibit a non-monotonic progression of the magnitude of
the tan( ) (hysteresis) peak over distance to the nanoparticle, suggesting that adjusting
copolymer sequence could significantly control observed nanocomposite dynamics.
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Keywords
polymers, nanoparticle, hysteresis, modulus, rubber