Block Polymer Membranes Functionalized with Nanoconfined Polyelectrolyte Brushes Achieve Sub-Nanometer Selectivity

Abstract

The well-defined nanostructure of membranes manufactured from self-assembled block polymers enables highly selective separations; however, recent efforts to push the pore size of block polymer-based membranes to the lower end of the size spectrum have only been moderately successful for a variety of reasons. For instance, the conformational changes of the stimuli-responsive functional groups lining the pore walls of some block polymer membranes result in varied pore sizes that limit their operational range. Here, we overcome this challenge through the directed design of the third moiety of an A-B-C triblock polymer. The use of this macromolecular design paradigm allows for the preparation of a 500 nm thick polyisoprene-b-polystyrene-b-poly­(2-acrylamido-ethane-1,1-disfulonic acid) (PI-PS-PADSA) coating atop a hollow fiber membrane support. This nanoporous test bed, which exhibits an average pore radius of 1 nm, demonstrates an extremely high solute selectivity by fully gating solutes that have only an 8 Å size difference, a separation that is based solely on a sieving mechanism. Furthermore, the nanoscale structural characteristics of the solvated PADSA pore walls are elucidated by quantifying the rejection of neutral solutes and calculating the hydraulic permeability values in solutions of high ionic strength (1 mM ≤ I ≤ 3 M) and over a broad range of solution pH (1 ≤ pH ≤ 13). These key results provide a solid foundation for defining structure–property–performance relationships in the emerging area of nanoporous triblock polymer thin films. Moreover, the successful demonstration of the test bed separation device offers a tangible means by which to manufacture next-generation nanofiltration membranes that require a robust performance profile over a dynamic range of conditions.

Functionalized Nanochannels from Self‐Assembled and Photomodified Poly(Styrene‐b‐Butadiene‐b‐Styrene)

“…In addition, the increased hydrophilicity of the membranes after modification can be beneficial to improve the antifouling properties of the membranes. Our approach can open the avenue to develop robust nanofiltration membranes, having a sharp selectivity in the sub‐nanometer range, in addition to another interesting approach using postpore functionalization, recently demonstrated by Zhang et al On the other hand, isoporous hydrophobic block copolymer membranes have been rarely reported before and therefore new applications can profit from this class of membranes. The hydrophobicity of the unmodified membranes as well as the high porosity and well‐defined nanochannels can be promising for applications such as membrane distillation, membrane crystallization, and thermo‐osmotic energy conversion …”

Chemically Tailored Multifunctional Asymmetric Isoporous Triblock Terpolymer Membranes for Selective Transport

“…The permeance of ultrapure water (pH 5.5, conductivity 0.055 µS cm −1 ) through I0, MM, and PM is 515, 11, and 9.5 L m −2 h −1 bar −1 , respectively (Figure f). It is worth noting that the water permeance of MM and PM is higher than reported for SNIPS BCP membranes with charged‐induced swelling of nanopores (0.6–4 L m −2 h −1 bar −1 ),13c,14a nanofiltration membranes formed by an amphiphilic random copolymer (1.4–7.3 L m −2 h −1 bar −1 )10a,25 and comparable to that of commercially available nanofiltration membranes (3.7–11.4 L m −2 h −1 bar −1 ) . Since at the dry state the pore sizes of I0, MM, and PM are close to each other, it can be seen that during the measurement of ultrapure water permeance (i.e., at pH 5.5) the chains of pore‐forming block of MM and PM are in a highly swelled state attributed to strong electrostatic repulsion of positive or negative polyelectrolytes while those of I0 are in a rather collapsed state.…”

High-performance asymmetric isoporous nanocomposite membranes with chemically-tailored amphiphilic nanochannels

“…A recent promising trend is to obtain so nanochannels by taking advantage of the swelling of the poreforming block at the hydrated state that are conned within the mesopores of SNIPS membrane. [36][37][38][39] The water permeance of the resulting SNIPS membranes with swelled so nanochannels reported so far is in a range of 0.6-15 L m À2 h À1 bar À1 . There is a critical need to prepare SNIPS membranes with a higher permeance and good selectivity in the nanoltration regime.…”