(713h) Cosolvent Effects on Micellization of Diblock Copolymers in a Selective Solvent

Cosolvent is commonly used at various stages in preparing micelles from amphiphilic diblock copolymers (DBC). Yet 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 cosolvent (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 micelles may decrease or increase in a wide rage relative to the cosolvent-free state depending on interaction strength between cosolvent and the solvophilic block. A decrease in AG happens when cosolvent acts as a surfactant that helps to reduce the interfacial energy by residing at the micellar core-solvent interface. An increase in AG is observed, however, when cosolvent exhibits a sufficiently large excess affinity for the solvophilic block relative to primary solvent. The osmotic second virial coefficient calculated from the Flory-Huggins theory reveals that large excess affinity induces a net attraction between solvophilic segments (i.e., cononsolvency effect), that gives rise to an increased micellar AG as a result of reduced steric repulsion. The extent of increase is seen to be more significant as the sovophilic block composition increases. Beyond the context of DBC micellar formation, our study highlights the nontrivial effects of polymer-solvent-cosolvent interplay on polymer assemblies in solution phase. Understanding of such effect enables designs of new strategies for tuning microstructures from polymer assemblies.