2026 Theses Doctoral

Advancing Block Copolymer Membrane Performance for Liquid Filtration through Directed Self-Assembly, Inorganic Infiltration, and Spray Processing

Bellini, Beatrice

Block copolymer (BCP) thin films are highly promising materials for liquid filtration because their self-assembly generates highly ordered nanoscale morphologies with well-defined pore size distributions, high pore densities, and chemically addressable domains. These attributes have made them an attractive platform for next-generation ultrafiltration membranes where control over both pore size and pore-wall chemistry is needed to tune properties towards simultaneously high permeability, strong selectivity, and minimized fouling. Despite significant progress in recent years, several critical challenges remain before these materials find widespread implementation in liquid filtration technologies including controlling the orientation of nanodomains in high-χ systems, limited mechanical robustness of ultrathin porous films, limited post-fabrication tunability of pore size/distances and chemistry, and a lack of scalable processing routes.

This dissertation addresses these challenges through the design, fabrication, characterization, and functionalization of pyridine-containing BCP thin films and related membrane architectures. To create isoporous film for size-selective transport, a general protocol for highly ordered arrays of vertical cylindrical nanopores in asymmetric poly(styrene-block-4-vinylpyridine) (PS-b-P4VP) diblock copolymer thin films mixed with P4VP homopolymer is developed. Vertical orientation is achieved through the combination of controlled acetone solvent vapor annealing (SVA) and substrate functionalization with a hydroxy-terminated poly(2-vinylpyridine) (P2VP-OH) brush.

Their resultant morphology and degree of ordering is characterized by grazing-incidence small-angle X-ray scattering (GISAXS), scanning electron microscopy (SEM). Translation of these nanostructures into functional filtration platforms was enabled by extending this study to isoporous composite membranes based on poly(4-vinylpyridine-block-styrene-block-4-vinylpyridine) (P4VP-b-PS-b-P4VP) triblock copolymer thin films self-assembled on a bifunctional polymer brush before being transferred onto porous support. These membranes exhibit both high permeability and high selectivity, while also showing improved mechanical durability enabled by the triblock architecture. Membrane structure and performance were evaluated by SEM, GISAXS, water permeation, nanoparticle rejection, UV–Vis spectroscopy, Dynamic light scattering DLS, and thin-film tensile testing.

To introduce post-fabrication control over pore size and pore-wall chemistry, porous BCP films were further modified by liquid-phase infiltration (LPI) of copper and iron nitrate salts followed by UV-induced oxide formation, and the resulting structural and chemical evolution was analyzed by SEM, GISAXS, and X-ray photoelectron spectroscopy (XPS). Finally, scalable fabrication of BCP films was investigated using ultrasonic spray deposition, revealing that the post-SVA orientation was significantly influenced by the evaporation rate during the spray deposition process. The resultant self-assembly pathways were studied by SEM, GISAXS, and in situ spectroscopic ellipsometry.

Together, this work demonstrates that precise nanoscale control in BCP thin films can be combined with high membrane performance, mechanical reinforcement, hybrid functionalization, and scalable processing techniques. Broadly, this work lays out a path forward for translating self-assembled BCP nanostructures out of model thin-film systems and into more pragmatic materials platforms with desired properties tailored towards liquid filtration applications.