Abstract: We use molecular simulations to examine the effects of small additive particles on dynamics in coarse-grained polymer systems. We model additives and monomers as spheres, and we use additives of diameters ranging from 60% of the monomer diameter to 200% of the monomer diameter. The effects of larger nanoparticles on polymer dynamics have been extensively studied, but the unique influence of these small additives is only just starting to be studied in detail. Due to the attractive interactions between monomers and additives, we find that the presence of additives generally slows down the system on long-timescales and restricts the dynamic free volume available to particles for movement. At low temperatures, we find that this long-timescale relaxation and dynamic free volume have qualitatively different dependencies on additive size. In order to understand this discrepancy, we connect these two measures of dynamics across temperatures using the “Localization Model”, successfully fitting our data for all additive sizes. We also examine the formation of “strings”, which are groups of mobile particles whose movements are correlated with each other. In accordance with previous studies, we find longer strings to be associated with slower long-timescale relaxation. Overall, this work shows the connection between the different ways we can examine the effects of additives on polymer dynamics, thereby bringing us one step closer to a more holistic view of these composite polymers.
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