Nanoporous block copolymer films using highly selective solvents and non-solvent extraction

Area of Science:

• Materials Science
• Polymer Science
• Nanotechnology

Background:

• Block copolymer self-assembly is crucial for creating nanostructured materials.
• Controlling nanoporosity in thin films is challenging but essential for applications like optical coatings.

Purpose of the Study:

• To develop a facile and tunable method for fabricating robust nanoporous block copolymer thin films.
• To investigate the optical and mechanical properties of these films for potential applications.

Main Methods:

• Fabrication via selective solvent swelling and non-solvent extraction of poly(butylnorbornene)-block-poly(hydroxyhexafluoroisopropyl norbornene) (BuHFA).
• Tuning porosity using different primary alcohols and aqueous ethanol mixtures.
• Characterization of porosity, thermal stability, elastic modulus (via surface wrinkling), and optical transmittance.

Main Results:

• Achieved tunable porosity up to 69% by varying solvent quality and composition.
• Films demonstrated excellent thermal robustness, with porosity unchanged after heating at 160 °C.
• Elastic modulus scales with film density (E ∼ ρ(2.2)), similar to cellular solids.
• Transparent films with 55% porosity improved glass slide transmittance from 92% to 99.1%, acting as effective anti-reflective coatings.

Conclusions:

• The solvent-selective swelling and extraction method offers a simple, tunable route to nanoporous block copolymer films.
• These robust, transparent films show significant potential as high-performance anti-reflective coatings.
• The methodology is adaptable to other block copolymer systems with sufficient segment solubility contrast.