Conformation and Aggregation Behavior of Homopolymers in Binary Mixed Solvents: Coarse-grained Molecular Dynamics Simulations

ZY Wang and XY Li and Z Wang and YH Yin and R Jiang and PF Zhang and BH Li, ACTA POLYMERICA SINICA, 56 (2025).

DOI: 10.11777/j.issn1000-3304.2025.25056

Stimuli-responsive polymers have broad application prospects because of their ability to exhibit reversible physical or chemical responses to external environmental changes (such as temperature and solvent composition,etc.). Such a response can manifest as changes in the chain conformation, solubility, and other related properties. However, a unified understanding of the chain conformations and aggregation behavior of polymers in mixed solvents is lacking. A well-known example is co-nonsolvency, a phenomenon in which the solubility of a polymer decreases in a mixture of two good solvents. In this study, we investigated the chain conformations and aggregation behavior of homopolymers in both single- and multi-chain systems in binary good solvent mixture systems using coarse-grained molecular dynamics simulations. The results show that in mixed solvents, chain conformations in a multi-chain system are significantly different from those in the corresponding single chain system. With increasing cosolvent fraction, polymers in multi-chain systems undergo a dispersion-aggregation-redispersion transition, where aggregation is induced by co-nonsolvency effects. In this case, the cosolvent undergoes liquid-liquid phase separation, where the polymer and cosolvent aggregate to form aggregates, constituting the cosolvent-rich phase. Furthermore, the total particle number density within an aggregate exceeded the average particle density of the system. In addition, the interaction strength between the polymer and cosolvent significantly affects the radial density distribution of the polymer. As the strength of this interaction increases, the total particle number density within an aggregate gradually increases. This study elucidates the mechanism of microstructural changes of polymers in mixed solvents and provides a theoretical foundation for understanding the behavior of polymers in mixed solvents, as well as for regulating the macroscopic properties of polymer solutions.

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