Free Energy Trajectory for Escape of a Single Chain from a Diblock Copolymer Micelle

SC Seeger and KD Dorfman and TP Lodge, ACS MACRO LETTERS, 10, 1570-1575 (2021).

DOI: 10.1021/acsmacrolett.1c00508

We use umbrella sampling to compute the free energy trajectory of a single chain undergoing expulsion from an isolated diblock copolymer micelle. This approach elucidates the experimentally unobservable transition state, identifies the spatial position of the maximum free energy, and reveals the chain conformation of a single chain as it undergoes expulsion. Combining umbrella sampling with dissipative particle dynamics simulations of A(4)B(8) micelles reveals that the core block (A) of the expelled chain remains partially stretched at the transition state, in contrast with the collapsed state assumed in some previous models. The free energy barrier increases linearly with the Flory-Huggins interaction parameter chi up to large interaction energies, where the structure of the otherwise spherical core apparently deforms near the transition state.

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