Process-Accessible States of Block Copolymers

Area of Science:

• Polymer Science
• Materials Chemistry
• Soft Matter Physics

Background:

• Block copolymers self-assemble into ordered mesostructures.
• Process-directed self-assembly utilizes thermodynamic control over kinetic pathways.
• Controlling kinetics allows access to metastable states beyond equilibrium.

Purpose of the Study:

• Investigate the kinetics of self-assembly in ACB triblock copolymers after transforming the middle C block to A.
• Determine which metastable mesostructures can be fabricated by varying block copolymer composition.
• Explore the relationship between initial and final mesostructure symmetries.

Main Methods:

• Utilized a prototypical process (e.g., photochemical transformation) to convert ABB triblock copolymers to AAB.
• Systematically varied block copolymer composition to map process-accessible states.
• Analyzed the resulting mesostructures, including equilibrium and metastable phases.

Main Results:

• Identified a diagram of process-accessible states for AAB copolymers, including 7 metastable periodic mesostructures.
• Discovered Schoen's F-RD periodic minimal surface as an accessible metastable structure.
• Observed that the final metastable mesostructure generally retains the symmetry of the initial ABB copolymer equilibrium mesophase.

Conclusions:

• Process-directed self-assembly offers a route to fabricate specific metastable mesostructures in block copolymers.
• The symmetry of the initial equilibrium phase serves as a predictor for the final metastable phase symmetry.
• This approach expands the range of accessible nanostructures for advanced material applications.