Mechanism of Escape of a Single Chain from a Diblock Copolymer Micelle

Abstract

We investigate the dependence of the free energy trajectory for chain expulsion from a diblock copolymer micelle in a selective solvent on core chain length through dissipative particle dynamics simulations and umbrella sampling. The free energy barrier scales linearly with the core block length of the expelled tracer chain for N core = 4−12, consistent with experiments. The simulations further reveal that the core chain undergoes a "hyperstretching" mechanism near the transition state, where the core block partially stretches through the corona to allow monomers further from the chain junction to remain shielded in the micelle core. As the junction extends past the transition state, it becomes more favorable for the chain to be fully expelled, and the monomer furthest from the junction exits the micelle core, allowing the core block to escape from the micelle and collapse upon entering the solvent. We propose a simple model to describe this process of chain expulsion, which provides an effective description of the simulation results.

Hydrogels of Amphiphilic Triblock Copolymers with Independently Tunable pH and Temperature-Controlled Exchange Dynamics

“…According to Halperin and Alexander, the hydrophobicity of the core-forming block has a major influence on the exchange dynamics. This hydrophobicity can be tuned by modifying the B-block length ,− or by changing the chemistry of the hydrophobic block itself. , One versatile strategy is to incorporate hydrophilic units into the hydrophobic blocks. This was illustrated by Bendejacq et al and Billon et al who demonstrated that frozen block copolymers containing hydrophobic polystyrene B-blocks became dynamic when acrylic acid (AA) units were incorporated through copolymerization within the B-blocks.…”

Editorial

“…More recent work has focused on the use of self-consistent field theory and coarse-grained molecular dynamics simulations of block polymer self-assembly and dynamics, including the origin of Frank−Kasper phases 5 and micellar chain exchange. 6 Finally, I want to give my sincere thank you to both Prof. Glenn Fredrickson and Prof. Hiroshi Watanabe, who have both stepped down as Associate Editors. The journal has benefitted tremendously from Glenn's keen insights, careful analysis, and steady hand.…”

“…In particular, he developed a definitive understanding of the thermodynamics and hydrodynamics of DNA confinement in nanochannels for genome mapping technologies. More recent work has focused on the use of self-consistent field theory and coarse-grained molecular dynamics simulations of block polymer self-assembly and dynamics, including the origin of Frank–Kasper phases and micellar chain exchange …”