Title: Tuning Diblock Copolymer Micelles by Cosolvent Effects: A Simulation Study

A powerful method to manipulate the micellar structures formed by amphiphilic diblock copolymers (DBC) in a selective solvent is by addition of a cosolvent. Unlike the single-solvent case, few simulation studies on DBC micellization in solvent mixtures has been reported due to high computational cost associated with the necessity of treating solvents explicitly. Here, the Field-Accelerated Monte Carlo simulation is employed for the task under the expanded grand canonical ensemble. We investigate the effects of introducing a cosolvent on the critical micelle concentration, micellar morphology, and aggregation number. Specifically, we consider two types of solvent pair: interacting-solvent and cononsolvent pairs. It is found that the interacting-solvent pair promotes morphology transition from micelles to vesicles. In the case of cononsolvent pair with respect to the corona block, aggregation number of micelles increases significantly as the result of maximizing contact between polymers and the minor amount of cosolvent. Our study reveals the competing and cooperative interplays of solvent pairs in determining the DBC micellar structures, pointing out the necessity of considering solvent explicitly in simulations as oppose to the conventional "effective-single-solvent" approach.