Free Energy Trajectory and Transition State of Chain Expulsion from a Block Copolymer Micelle

Single chain exchange is the dominant relaxation process for block copolymer micelles close to equilibrium, and influences a variety of applications, including drug delivery, oil-based lubrication, and the formation of complex block polymer phases.Methods of studying chain exchange yield information about the system ensemble; however, the molecular-level details of the process are not well understood. We have implemented a simulation method to study the chain exchange process for diblock copolymer micelles in a small-molecule solvent, using dissipative particle dynamics. Our simulation framework utilizes umbrella sampling and the weighted histogram analysis method to compute the free energy profile of chain expulsion. We will present results for the effect of the block lengths of the expelled chain and the interaction energy between the core beads and the solvent, and their effect on the core block conformation at the transition state. Contrary to past models of chain exchange, we see evidence of core block stretching in the expelled chain at the transition state.