Interplay of Coil-Globule Transitions and Aggregation in Homopolymer Aqueous Solutions: Simulation and Topological Insights

Abstract

We investigate the structural and topological properties of hydrophobic homopolymer chains in aqueous solutions using molecular dynamics simulations and circuit topology (CT) analysis. By combining geometric observables, such as radius of gyration and degree of aggregation, with CT data, we capture the relationship between coil-globule and aggregation transitions, resolving the system's structural changes with temperature. Our results reveal a temperature-driven collective transition from isolated coiled chains to globular aggregates. At a characteristic transition temperature $T_c$, each chain in multichain systems undergoes a rapid coil-globule collapse, coinciding with aggregation, in contrast to the gradual collapse observed in single-chain systems at infinite dilution. This collective transition is reflected in geometric descriptors and a reorganization of CT motifs, shifting from intrachain-dominated motifs at low temperatures to a diverse ensemble of multichain motifs at higher temperatures. CT motif enumeration provides contact statistics while offering a topologically detailed view of polymer organization. These findings highlight CT's utility as a structural descriptor for polymer systems and suggest applications to biopolymer aggregation and folding.