EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Star polymers have been used as model systems to study more complex architectures of industrial relevance. They exhibit rich dynamical response ranging from linear-like to coloidal-like behavior. The key characteristic determining their properties is their penetrability, which is related to their inner structure. Experimental evidence suggests that the penetrability and thus the softness of these materials may depend not only on the number of arms but also on their internal packing.
Computational design allows us to control the composition of the stars and thus eliminate experimental issues such as polydispersity.
In this work, we employ atomistic molecular dynamics simulations to study chemistry-dependent properties of selected star polymers. The used method captures all atomistic details, accounting for local packing and/or stiffness of the polymers. We study non-entangled poly(ethylene oxide) and polystyrene stars in melts, as two examples of dissimilar polymers, differing in flexibility and glass transition temperature. By varying the number of arms, we aim to tune their mutual penetration. We developed a specific protocol for the equilibration and the analysis of the polymeric melts. We quantified the shape and size characteristics and confronted them with widely used theoretical predictions. In addition, the differences in intramolecular and intermolecular packing for the two studied chemistries are discussed. Furthermore, a challenging algorithm for estimating the free volume in the system, is implemented. Results are related to the material's permeability.
To the best of our knowledge, our study of structural and dynamical properties represents the first attempt to describe the star polymer melts in atomistic detail. Our results, related to the packing and cooperative motion of the molecules, provide information complementary to the experimental techniques or coarse-grained models and can thus contribute to a better understanding of structure-dynamics relation in materials with branch-like architectures, such as those used in all-polymer nanocomposites or nanostructured electrolytes.