Chemical Composition and Strain at Interfaces between Different Morphologies in Block Copolymer Thin Films.

Area of Science:

• Polymer Science
• Materials Science
• Nanotechnology

Background:

• Block copolymers self-assemble into diverse nanostructures crucial for advanced materials.
• Understanding the interfacial and subsurface composition of thin films is vital for controlling morphology.
• Polystyrene-block-poly(tert-butyl acrylate) (PS-b-PtBuA) is a model system for studying block copolymer behavior.

Purpose of the Study:

• To investigate the transitional composition between different thin-film morphologies of PS-b-PtBuA.
• To elucidate the sub-surface composition and block distribution at the nanoscale.
• To correlate observed morphologies with potential factors like block composition and substrate interactions.

Main Methods:

• Near-field infrared spectroscopy (SNIR) for nanoscale chemical identification.
• Atomic force microscopy (AFM) for mechanical property mapping and surface topography.
• Combined use of SNIR and AFM to determine block identification and sub-surface composition with high spatial resolution.

Main Results:

• Polystyrene (PS) formed coronae around poly(tert-butyl acrylate) (PtBuA) blocks in spherical valleys on flat film areas.
• PtBuA coronae were observed surrounding PS lamellae at the film edge, associated with parallel lamellae formation.
• Spectroscopic peak position and width variations indicated localized differences in block composition, chain tension, or substrate interaction.

Conclusions:

• The study reveals distinct nanoscale compositional arrangements in PS-b-PtBuA thin films.
• Morphological transitions are linked to specific topographical features (valleys, edges) and block arrangements.
• Local variations in chemical environment and physical stress influence the observed block copolymer nanostructures.