(692g) Simulating Diblock Copolymer Micelles in Binary Explicit Solvents

Amphiphilic block copolymers form diverse nanoscale assemblies when dissolved in a selective solvent. Such self-assembled structures have wide-ranging applications as drug delivery vehicles, nanoreactors, and encapsulants. A powerful method to manipulate the assembled structure is to vary the composition of solvent mixtures. Unlike in single-solvent solutions, computational studies of amphiphilic block copolymers in solvent mixtures are rarely reported due to high computational cost associated with the necessity of treating solvents explicitly. Here, the recently developed Field-Accelerated Monte Carlo simulation [1] is employed in the expanded grand canonical ensemble to study the micelle formation of diblock copolymers (DBC) in binary solvent mixtures. With micellization in a single solvent as the reference, we investigate the effects of introducing a minor solvent into the solution on the critical micelle concentration (CMC), micelle morphology, and micelle size and aggregation number. We show that the effects of disparity in solvent selectivity are manifested through the change in effective surface tension, with the less selective minor solvent concentrating at micelle core-shell interface. As a result, the CMC increases and aggregation number decreases compared to the single-solvent case. With stronger interaction strength between the two solvents, the minor solvent redistributes within micelles, eventually leading to the formation of vesicles. When the two solvents form a cononsolvency pair with respect to the corona block, the micelle aggregation number significantly increases induced by the collapse of the corona. Our study reveals the sensitive dependence of micelle morphology on competing and cooperative interplays of the solvent pair, suggesting that a qualitatively correct understanding on micellization in solvent mixtures needs to go beyond the "effective single solvent" approach by considering solvents explicitly in simulations.

[1] Zong, J. and Meng, D. Performing Field-Accelerated Monte Carlo Simulations in nVT and nPT ensembles. submitted to Journal of Chemical Physics.