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