Highly Permeable and Robust Responsive Nanoporous Membranes by Selective Swelling of Triblock Terpolymers with a Rubbery Block

The selective swelling of amphiphilic block copolymers has been demonstrated to be extremely facile and efficient in producing nanoporous membranes. However, all previous works are limited to diblock copolymers composed of two glassy blocks, suffering from inherent mechanical weakness. Here we elucidate the selective swelling-induced pore generation of triblock terpolymers with a rubbery polyisoprene (PIP) block, polyisoprene-<i>block</i>-polystyrene-<i>block</i>-poly­(2-vinylpyridine) (PIP-<i>b</i>-PS-<i>b</i>-P2VP). A short exposure to ethanol turns the initially dense films to nanoporous membranes with well-defined interconnected porosity. We fabricate composite membranes with the nanoporous terpolymer thin films as the selective layers deposited on macroporous substrates. Using PS-<i>b</i>-P2VP diblock copolymer without a rubbery third block for comparison, we identify the role of the rubbery PIP blocks in determining the mechanical properties as well as the swelling behaviors of the terpolymer. The rubbery PIP blocks enhance the mechanical robustness of the nanoporous membranes as revealed by nanoindentation tests on one hand and evidently accelerate the swelling process because of their softening effect to the PS matrix on the other hand, thus leading to 2–3-fold improved permeability. Moreover, the membranes exhibit a fast stimuli-responsive function as well as enhanced hydrophilicity because of the preferential aggregation of P2VP chains on the pore walls

Perpendicular Alignment and Selective Swelling-Induced Generation of Homopores of Polystyrene‑<i>b</i>‑poly(2-vinylpyridine)‑<i>b</i>‑poly(ethylene oxide) Triblock Terpolymer

Arrays of perpendicularly ordered nanopores with pore walls decorated by two or more functional polymer chains are of great importance in various applications. However, such porous structures have been rarely reported so far. Herein, lamellar-forming triblock terpolymer of polystyrene-<i>b</i>-poly­(2-vinylpyridine)-<i>b</i>-poly­(ethylene oxide) (PS-<i>b</i>-P2VP-<i>b</i>-PEO) is blended with PS homopolymers to fabricate a PS matrix embedded with perpendicular PEO@P2VP cylinders via solvent annealing. By further adjusting the annealing humidity and temperature, the perpendicular PEO@P2VP cylinders are capable of running through the entire films. The hydrophilic PEO@P2VP domains could be converted into cylindrical homopores by ethanol swelling, where the functional P2VP and PEO chains are distributed on the pore walls. Moreover, water is able to swell PEO and also produces homopores in such films. The pore sizes of the films are readily tuned in a relatively large range depending on the swelling temperatures and durations. The developed ordered nanostructures are expected to find important applications in the range from template synthesis to membrane separation and to nanofluidics

Homoporous Membranes with Tailored Pores by Soaking Block Copolymer/Homopolymer Blends in Selective Solvents: Dissolution versus Swelling

Extraction homopolymers premixed in aligned films of block copolymers by rinsing with selective solvents has long been used for the preparation of membranes with uniform straight pores (homoporous membranes). It is frequently assumed that only the dissolution of homopolymers contributes to the pore formation. However, in this work, we demonstrate that the effect of swelling plays a significant role in determining the pore sizes. We prepare blended films of block copolymers of polystyrene-<i>block</i>-poly­(2-vinyl­pyridine) (PS-<i>b</i>-P2VP) and P2VP homopolymers with low molecular weight and anneal the films to perpendicularly align the P2VP microdomains. Rinsing the aligned films in ethanol results in homoporous membranes, and the pore sizes can be tuned by the dosages of P2VP homopolymers. Interestingly, the pore sizes can also be effectively tailored by changing the rinsing temperatures and/or durations because of the significant contribution of the selective swelling of P2VP blocks under strong rinsing conditions in addition to the contribution of the dissolution of P2VP homopolymers. We identify the portion of the contribution from dissolution and from swelling and demonstrate that the pore sizes can be flexibly tuned within a wider range at no expense of pore ordering and uniformity by balancing the effect of dissolution and swelling