Single chain expulsion from diblock copolymer micelles with dense corona

Area of Science:

• Polymer physics
• Soft matter science
• Theoretical chemistry

Background:

• Diblock copolymer micelles form complex structures in solution.
• Understanding single-chain behavior within these micelles is crucial for materials science.
• Chain exchange dynamics influence micelle stability and function.

Purpose of the Study:

• Investigate the free energy landscape of single-chain expulsion from dense corona diblock copolymer micelles.
• Determine the factors governing chain exchange barriers.
• Elucidate the theoretical foundation of the hyperstretching mechanism.

Main Methods:

• Employed self-consistent field theory (SCFT) to model the system.
• Utilized the distance from the micelle center-of-mass to the junction as a primary reaction coordinate.
• Introduced a second reaction coordinate (junction to hydrophobic end distance) to construct a 2D free energy surface.
• Applied the string method to identify minimum energy pathways.

Main Results:

• Computed the free energy landscape for chain exchange.
• Found expulsion free energy barriers scale linearly with hydrophobic block length and solvent selectivity.
• Identified a nearly degenerate reaction channel where pathways converge.
• Observed a broad distribution in hydrophobic block end-to-end distance within this channel.

Conclusions:

• Established a continuum-level theoretical framework for micellar chain exchange.
• Provided insights into the hyperstretching mechanism and transition state ensemble.
• Results are consistent with recent experimental findings on chain expulsion.