Solvent-mediated morphological transitions in polystyrene-block-poly (ethylene oxide) copolymer solutions

• Aggregation morphologies of PS-b-PEO in DMF/dioxane/water mixtures are investigated. • Self-assembly behaviors are modeled by coarse-grained molecular simulations. • Cylindrical and lamellar phases emerge as the concentration of PS-b-PEO increases. • Water can induce morphological transition from cylindrical phase to spherical phase. The self-assembly morphology of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) copolymers is significantly influenced by the selected solvents. The formation of various morphologies is driven by thermodynamic incompatibilities among the different components. In this study, the aggregation behavior of PS-b-PEO in mixed solvents comprising N, N’-dimethylformamide (DMF), dioxane, and water is investigated using a metastable coarse-grained model. The simulation results indicate that the morphology of the block copolymer (BCP) transitions from a spherical micellar (S) phase to cylindrical (C) and lamellar (L) phases as the BCP concentration increases. Additionally, varying water content is found to influence these phase states. For instance, at a BCP concentration of 20%, the BCP transitions from the C phase to the S phase as the water content increases. The number density statistics suggest that this transition is due to the thermodynamic incompatibility between water and the hydrophobic chain segments. Furthermore, simulation results for BCP with varying chain lengths demonstrate that the model can accurately predict the behavior of BCP with longer chain lengths. Our findings highlight that self-assembled materials with diverse morphologies can be achieved by adjusting the water content and the ratio of block copolymers, thereby providing valuable guidance for future related experiments.