Structural Evolution of Nanophase Separated Block Copolymer Patterns in Supercritical CO₂

Area of Science:

• Materials Science
• Polymer Science
• Nanotechnology

Background:

• Traditional block copolymer (BCP) nanopatterning often uses organic solvents, posing environmental and industrial challenges.
• Developing sustainable and efficient methods for creating ordered nanostructures is crucial for advanced material applications.

Purpose of the Study:

• To present a simple, environmentally friendly method for fabricating periodically ordered nanoscale phase-separated BCP structures.
• To investigate the structural and dimensional evolution of nanopatterns in various BCP systems using supercritical carbon dioxide (scCO2) annealing.

Main Methods:

• Annealing of asymmetric polystyrene-block-poly(ethylene oxide) (PS-b-PEO) thin films in supercritical carbon dioxide (scCO2).
• Systematic variation of scCO2 annealing parameters including temperature, pressure, time, and depressurization rates.
• Exploration of different BCP systems (PS-b-PEO, PEO-b-PS, PS-b-PDMS, PS-b-PLA) and their patterning on graphoepitaxial substrates.

Main Results:

• Achieved periodic, well-defined, hexagonally ordered nanohole and line/space patterns in PS-b-PEO films at low temperatures (35-40 °C) and pressures (1200-1300 psi).
• Demonstrated control over morphology, ordering, and feature sizes by adjusting scCO2 annealing parameters for different BCP molecular weights and film thicknesses.
• Successfully patterned various BCP systems using scCO2 annealing, including applications on graphoepitaxial substrates.

Conclusions:

• Supercritical carbon dioxide annealing offers a viable, green alternative for BCP nanopatterning.
• The scCO2 method provides precise control over nanostructure formation, enabling tailored material properties.
• This approach holds promise for scalable and sustainable manufacturing of nanostructured materials for device applications.