(708f) Porous Thin Films with Hierarchical Structures Formed By Self-Assembly of Zwitterionic Comb Copolymers

Amphiphilic copolymers comprising a hydrophobic backbone with polar zwitterionic side groups are inclined to microphase separation due to molecular dissimilarity between the constituents, which stimulates interesting self-assembly in bulk. The drive for microphase separation is further enhanced in comb-shaped copolymers with this combination of constituents because of the architectural distinction between the backbone and zwitterionic side chains. We developed selective thin films whose morphology and function arise from the self-assembled nanostructure of the zwitterionic comb copolymer (ZCC). First, we established a correlation between polymer chemistry, film preparation method, self-assembled domain size, and thin film morphology. To achieve that, we synthesized a series of ZCCs with varying zwitterionic side chain frequency and length, and applied each of these copolymers as a thin film on glass substrate using different deposition methods including spin coating and non-solvent induced phase inversion (NIPS). Vastly varying self-assembled surface morphologies were observed, from relatively featureless flat films to highly porous network-type structures. We also applied one of the ZCCs as a thin selective layer on a porous membrane support to create a mechanically supported thin film (MSTF). Interestingly, the presence of the porous support resulted in a distinctly different film morphology, featuring hierarchical features including 17 ± 5 nm spherical micelles along with larger nanopores of 85 ± 45. In addition, the feature sizes in the MSTFs could be further tuned simply by using a zwitterionic homopolymer additive. The films proved ionic strength responsive permeation in ultrafiltration range with a pore density as high as 10¹³ pores/m².