Reversible switch between the nanoporous and the nonporous state of amphiphilic block copolymer films regulated by selective swelling

Abstract

Switchable nanoporous films, which can repeatedly alternate their porosities, are of great interest in a diversity of fields. Currently these intelligent materials are mostly based on polyelectrolytes and their porosities can change only in relatively narrow ranges, typically under wet conditions, severely limiting their applications. Here we develop a new system, which is capable of reversibly switching between a highly porous state and a nonporous state dozens of times regulated simply by exposure to selective solvents. In this system nanopores are created or reversibly eliminated in films of a block copolymer, polystyrene-block-poly(2-vinyl pyridine) (PS-b-P2VP), by exposing the films to P2VP-selective or PS-selective solvents, respectively. The mechanism of the switch is based on the selective swelling of the constituent blocks in corresponding solvents, which is a nondestructive and easily controllable process enabling the repeatable and ample switch between the open and the closed state. Systematic microscopic and ellipsometric characterization methods are performed to elucidate the pore-closing course induced by nonsolvents and the cycling between the pore-open and the pore-closed state up to 20 times. The affinity of the solvent for PS blocks is found to play a dominating role in determining the pore-closing process and the porosities of the pore-open films increase with the cycling numbers as a result of loose packing conditions of the polymer chains. We finally demonstrate the potential applications of these films as intelligent antireflection coatings and drug carriers.

Fast Evaporation Enabled Ultrathin Polymer Coatings on Nanoporous Substrates for Highly Permeable Membranes

“…Increasing the temperature during selective swelling leads to more pronounced cavitation of the mUPCFs and in turn to increased water permeance. 35 When the swelling temperature increases from 65 C to 75 C, the water permeance increases from $915 to $1,099 L m À2 h À1 bar À1 . Moreover, the swelling duration causes negligible influence on the water permeance.…”

Design of gradient nanopores in phenolics for ultrafast water permeation

“…For instance, the thickness is increased to 4.7 and 12.0 μm at a molar ratio of 70 and 280, respectively. Considering that the increase in thickness is caused by the formation of pores in the phenolic structure with the introduction of ZnCl 2 , we can easily estimate the porosity of the phenolic membranes by comparing their thicknesses with that of the phenolic structure produced in the absence of ZnCl 2 36. The porosity of the phenolic membranes prepared at a molar ratio of 70, 140, and 280 was thus estimated to be 38.3, 71.0, and 75.8% (ESI S10 and Fig.…”

Designing Robust, Breathable, and Antibacterial Multifunctional Porous Membranes by a Nanofluids Templated Strategy

“…Water uptake was estimated using a weighed membrane that had previously been immersed in deionized water. Then, this membrane was carefully blotted with a filter paper and weighed after 5,10,15,25,35,45,60,75, and 90 min. For testing the tensility, the prepared membranes were cut into 20 mm wide samples.…”

“…Because the selective solvent is easy to remove additives under relatively mild conditions, this strategy is often used to fabricate different porous membrane. However, the control of surface chemistry and function of pore formation in nanoporous polymers is limited to a few block copolymers, such as functional poly(2-vinylpyridine), [10] poly(ethylene oxide), [11] and poly(methyl methacrylate). [12] In addition, it is still required to obtain the desired porous structure under longer processing times.…”