Diffusion in nanoporous materials made from block copolymers

Abstract

The production of monoliths containing aligned nano-pores by selective etching of a poly(styrene)/poly(lactide) block copolymer (P(S-b-LA) is examined. Small angle X-ray scattering (SAXS) is employed to characterize block copolymer (BCP) phase structure and orientation, and is used to observe the progress of poly(lactide) (PLA) hydrolysis through a section 5 mm long. Orientation is found to be good, and complete etching of the PLA phase is observed and confirmed by weight loss. Diffusion of hydroxide ions through etched pores is tested using a diffusion cell, and found to obey the qualitative behaviour expected in a porous membrane. Breakthrough times are shown to be extended by the requirement of surface wetting. It is confirmed that nanoporous monoliths can be made from block copolymers, suggesting potential applications in membrane and chromatography applications.

Nanoporous Membranes Derived from Block Copolymers: From Drug Delivery to Water Filtration

“…In 2006, Cooney et al studied the diffusion of water through a 2 mm thick nanoporous monolith they prepared from a PLAetched, channel-die aligned polystyrene-block-polylactide (PS-PLA) diblock copolymer. 18 Unlike Liu et al, they observed good orientation of PLA cylindrical domains and complete etching of the PLA phase. After wetting of the pores, the expected steady state flux was observed.…”

“…They noted that the permeability of their films was comparable to that of PAA-grafted, track-etched membranes and suggested higher permeabilities would have been possible if all channels had been oriented perpendicular to the film surface. In 2006, Cooney et al studied the diffusion of water through a 2 mm thick nanoporous monolith they prepared from a PLA-etched, channel-die aligned polystyrene- block- polylactide (PS-PLA) diblock copolymer . Unlike Liu et al , they observed good orientation of PLA cylindrical domains and complete etching of the PLA phase.…”

Tuning Structure and Properties of Graded Triblock Terpolymer-Based Mesoporous and Hybrid Films

“…Membranes based on diblock copolymer and triblock terpolymer self-assembly have been generated through bulk casting, but these nongraded materials suffer from low permeabilities due to relatively thick selective layers, and hybrids were not investigated. − Mesoporous thin films from diblock copolymers have been fabricated by spin coating onto solid substrates; however, this method requires long annealing times and the tedious transfer of a fragile thin film from the primary substrate to a secondary support membrane. − A third approach combines the self-assembly of diblock copolymers with nonsolvent-induced phase separation; however, a thorough performance evaluation of the resulting membranes has not yet been attempted, and the use of glassy diblock copolymers in this system reduces the opportunity for chemical and mechanical tunability. , …”

Stimuli responsive nanostructured porous network from triblock copolymer self-assemblies

“…10 Block copolymers offer great opportunities for the design of porous films with selective permeation through their regular structure. Previously, films have been fabricated from block copolymers using spin-coating, 7,[11][12][13] extrusion, 14,15 and bulk evaporation [16][17][18] techniques, yet the porous films produced from these methods typically require post-fabrication modifications to convey porosity into the films and are not based on sturdy industrial processes. Recently the relevance of block copolymer micelle assembly in the fabrication of isoporous asymmetric membranes by solution casting and immersion in a non-solvent bath has been demonstrated.…”