Asymmetric Polymersomes from an Oil-in-Oil Emulsion: A Computer Simulation Study

Area of Science:

• Polymer Science
• Soft Matter Physics
• Biomedical Engineering

Background:

• Asymmetric vesicles, or polymersomes, are crucial for cell mimicry and biomedical applications.
• Previous experimental methods for fabricating asymmetric polymersomes lacked detailed mechanistic understanding.
• Understanding the self-assembly mechanism is key to controlling polymersome structure and function.

Purpose of the Study:

• To elucidate the microscopic mechanism of asymmetric polymersome formation.
• To investigate the influence of block copolymer incompatibility and process parameters on self-assembly.
• To provide insights for designing and fabricating advanced asymmetric polymersomes.

Main Methods:

• Dissipative Particle Dynamics (DPD) simulations were employed to model the coassembly process.
• The simulation system mimicked the experimental setup involving polystyrene-b-poly(ethylene oxide) (PS-b-PEO) and polybutadiene-b-poly(ethylene oxide) (PB-b-PEO) block copolymers.
• Systematic investigation of copolymer addition order and PEO volume fraction effects.

Main Results:

• DPD simulations successfully reproduced the experimental formation of asymmetric polymersomes.
• The bilayer formation mechanism involves the folding and crossing of poly(ethylene oxide) (PEO) blocks.
• Three distinct stages were identified: micelle formation, interface diffusion, and interface rearrangement.
• Block copolymer incompatibility is the primary driving force for asymmetry.
• The order of copolymer addition significantly impacts bilayer perfection; initial addition of PS-b-PEO is beneficial.
• A PEO volume fraction (f_PEO) greater than 0.55 is necessary for forming perfect asymmetric polymersomes.

Conclusions:

• The study provides a detailed microscopic understanding of asymmetric polymersome self-assembly.
• Simulation results highlight the critical roles of block copolymer incompatibility and process parameters.
• Findings offer guidance for the rational design and synthesis of tailored asymmetric polymersomes for various applications.