Swelling of block copolymers by selective solvents has emerged as a simple and efficient process to produce nanoporous materials with well-controlled porosities. It has been demonstrated that a number of parameters including the compositions of the copolymers, the swelling temperatures and durations strongly influence the swelling behaviors and consequently the porous morphologies of the copolymers. However, it remains unclear on the role of the swelling agents in this selective swelling-induced pore generation. Here we investigate the evolution of morphology, thickness, and surface chemistry of thin films of polystyrene-block-poly (2-vinyl pyridine) (PS-b-P2VP) soaked in a series of alcohols with changing carbon atoms and hydroxyl groups in their molecules. It is found that, in addition to a strong affinity to the dispersed P2VP microdomains, the swelling agents should also have a moderate swelling effect to PS to allow an appropriate plastic deformation of the PS matrix. Scanning electron microscopy demonstrates that monohydric alcohols with longer alphatic chains exhibit larger ability to induce the pore formation, and ellipsometry reveals that a remarkable increase in film thickness is associated with the pore formation. High-carbon alcohols including n-propanol, n-butanol, and n-hexanol provide strong ability to induce the pore formation and produce cylindrical micelles upon prolonged exposure for their strong affinity toward the PS matrix. In contrast, methanol and polyhydric alcohols including glycol and glycerol show very limited effect to swell the copolymer films as their affinity to the PS matrix is low; however, characterizations by water contact angles and x-ray photoelectron spectroscopy reveal that they evidently induce the surface segregation of P2VP blocks for the rich presence of hydroxyl groups in their molecules and consequently highest possibility to form hydrogen bonds with P2VP blocks.

Mesoporous polymers by selective swelling of block copolymers with different alcohols

251st National Meeting (2016)

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