The Cosolvent Effects on Micellization of Diblock Copolymers in a Selective Solvent

Cosolvents are commonly used at various stages in preparing micelles from amphiphilic diblock copolymers (DBC). Yet the cosolvent effects on the micellization has been rarely investigated. In this study, the Field-Accelerated Monte Carlo simulation and the self-consistent field calculations are employed in the grand canonical ensemble to examine the influence of adding a mutual solvent (a good solvent for both polymer blocks) on the DBC micelles formed in a selective solvent. It is found that the aggregation number (AG) of the micelles can decrease or increase within a wide range relative to the cosolvent-free state. The decrease in AG happens when the cosolvent acts as a surfactant that helps to reduce the interfacial energy by residing at the core-corona interface. The increase in AG is observed, however, when the corona block favors being in more contact with the cosolvent than with the solvent. This cononsolvency behavior of the corona block becomes more pronounced at higher molecular weight, leading to greater AG. Our study reveals the intriguing interplay of solvent and cosolvent in controlling the micellization of DBC, and highlights the importance of understanding polymer behaviors in solvent mixtures toward modulating polymer assemblies in the solution phase.