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Effect of Copolymer Sequence on Local Viscoelastic Properties near a Nanoparticle

Trazkovich, Alex J., Wendt, Mitchell F., Hall, Lisa M.
Macromolecules 2019 v.52 no.2 pp. 513-527
autocorrelation, composite polymers, hysteresis, interphase, loss modulus, nanocomposites, nanoparticles, viscoelasticity
We simulate a simple nanocomposite consisting of a single spherical nanoparticle surrounded by coarse-grained polymer chains that are composed of two monomer types differing only in their interactions with the nanoparticle. We measure the atomic stress fluctuations and use them to estimate the local stress autocorrelation as a function of distance from the nanoparticle. This local stress autocorrelation is substituted into the well-known relationship between the bulk stress autocorrelation and the bulk (frequency-dependent) dynamic modulus, and the result is treated as an estimate of the local dynamic modulus. This allows us to examine the effect of adjusting copolymer sequence on estimations of local storage and loss modulus as a function of distance from the nanoparticle. Notably, we find certain blocky copolymer sequences can lead to a higher tan(δ) (hysteresis) in the interphase than either homopolymer system, suggesting that tuning the copolymer sequence could allow for significant control over nanocomposite dynamics.