Chemically Tailored Multifunctional Asymmetric Isoporous Triblock Terpolymer Membranes for Selective Transport

Membrane‐based separation of organic molecules with 1–2 nm lateral dimensions is a demanding but rather underdeveloped technology. The major challenge is to fabricate membranes having distinct nanochannels with desired functionality. Here, a bottom‐up strategy to produce such a membrane using a tailor‐made triblock terpolymer featuring miscible end blocks with two different functional groups is demonstrated. A scalable multifunctional integral asymmetric isoporous membrane is fabricated by the solvent evaporation‐induced self‐assembly of the block copolymer combined with nonsolvent‐induced phase separation. The membrane nanopores are readily functionalized using positively and negatively charged moieties by two straightforward gas–solid reactions. The pores of the post‐functionalized membranes act as target‐specific functional soft nanochannels due to swelling of the polyelectrolyte blocks in a hydrated state. The membranes show unprecedented separation selectivity of small molecules based on size and/or charge which demonstrates the potential of the proposed strategy to prepare next‐generation nanofiltration membranes.


DOI: 10.1002/adma.201907014
such separations. Fabrication of highperformance membranes for separation of such small molecules remains a grand challenge as it requires distinct nanochannels combined with target-specific functionality. To date, several approaches have been proposed to fabricate membranes having size-selective nanochannels decorated with specific functionalities. The electroless deposition of gold nanotubules within the pores of polycarbonate track-etched (PCTE) membrane followed by chemisorption of functionalized thiols has been extensively used to introduce different functions, e.g., pH responsiveness, [5] hydrophilicity, or hydrophobicity. [6] Chemical vapor deposition [7] and atomic layer deposition [8] on the PCTE or anodic alumina membranes were also widely explored to narrow down the channels and induce hydrophobicity. There is an ongoing research trend to design nanopores with specific function, e.g., polyelectrolytes deposited in nanochannels for molecular recognition, [1] apoenzyme immobilized in polymeric nanopores for separation of D-and L-amino acid enantiomers, [3] and antibody bounded on silica nanotubes for enantiomeric drug separation. [2] Membranes having vertically aligned 1 nm ionic channels have been fabricated by the alignment of self-assembled lyotropic liquid crystalline monomers using magnetic field and soft-confinement followed by crosslinking. [9] The interstices of the packed array of spherical silica colloidal crystals and random copolymer micelles have also been utilized as nanochannels with ionic or chiral moieties. [10] The periodic-ordered nanostructure of a block copolymer (BCP) can be translated into high-performance membranes employing the evaporation-induced self-assembly together with the nonsolvent-induced phase separation (SNIPS). [11] It is a straightforward and very fast one-step scalable method to fabricate mechanically robust membranes having high porosity and uniform pores at the surface. A typical diblock copolymerderived SNIPS membrane possesses a rather thin (<200 nm) selective layer with high number density (>10 14 pores m −2 ) of hexagonally packed vertically aligned cylindrical pores with a very narrow pore size distribution above a macroporous spongy sublayer. [11b,12] In the triblock terpolymer-derived SNIPS membranes, often a cubic lattice of pores is observed in the top layer. [13] The unique integral asymmetric isoporous structure can achieve relatively high selectivity while ensuring Membrane-based separation of organic molecules with 1-2 nm lateral dimensions is a demanding but rather underdeveloped technology. The major challenge is to fabricate membranes having distinct nanochannels with desired functionality. Here, a bottom-up strategy to produce such a membrane using a tailor-made triblock terpolymer featuring miscible end blocks with two different functional groups is demonstrated. A scalable multifunctional integral asymmetric isoporous membrane is fabricated by the solvent evaporation-induced self-assembly of the block copolymer combined with nonsolvent-induced phase separation. The membrane nanopores are readily functionalized using positively and negatively charged moieties by two straightforward gas-solid reactions. The pores of the post-functionalized membranes act as target-specific functional soft nanochannels due to swelling of the polyelectrolyte blocks in a hydrated state. The membranes show unprecedented separation selectivity of small molecules based on size and/or charge which demonstrates the potential of the proposed strategy to prepare next-generation nanofiltration membranes.
Membrane technology offers a scalable, green, and energy efficient solution for the separation of small chemical, [1] pharmaceutical, [2] and biological [3] molecules having dimensions of ≈0.5-5 nm. Many environmentally relevant emerging contaminants, e.g., plastic components, pesticides, textile dyes, and pharmaceutical pollutants have such dimensions which are notoriously difficult to separate from effluent water streams. [4] Although these separations recently became a center of attention, there is a lack of commercial membranes to perform good permeability. A recent promising trend to tune the SNIPS membrane from ultrafiltration toward nanofiltration is to take advantage of the swelling of the pore-forming blocks, [13c,14] e.g., Gu and Wiesner reported a combination of additive-driven pore expansion with P4VP chain stretching under acidic conditions to reduce the pore size down to 5 nm. [15] Besides, efforts have been made to introduce one end-functional group along the pore walls directly via SNIPS process for further chemical modification, e.g., triblock terpolymer poly(styrene)-block-poly(4vinylpyridine)-block-poly(propylene sulfide)-derived membrane for covalent molecule attachment. [13d] Herein, we present the fabrication of a novel SNIPS membrane with multifunctional nanopores using a tailor-made triblock terpolymer where miscible end blocks form the pores. The functional moieties within the pore walls were readily converted into positively and negatively charged polyelectrolytes via two simple in situ one-step functionalization reactions (Figure 1a). An unprecedented highly efficient separation of small molecules with lateral dimensions between 1 and 2 nm was achieved by taking advantage of the well-defined soft polyelectrolyte nanochannels.
To investigate the microphase separation PI-b-PS-b-P4VP, P1, P2, and P3 films were cast from two different solvent mixtures-CHCl 3 /N,N-dimethylformamide (DMF) 95:5 vol% and CHCl 3 /methanol 95:5 vol%. The solvents were evaporated slowly in a desiccator over a period of 2 weeks followed by thermal annealing in a vacuum oven at 170 °C to attain Adv. Mater. 2020, 32,1907014  morphologies to equilibrium as close as possible. The transmission electron microscope (TEM) images of Figure 2a illustrate a cylinder-sphere three-phase morphology [18] of a PI-b-PSb-P4VP film prepared from the CHCl 3 /DMF solvent mixture. The P4VP blocks form the cylinders and the PI blocks form the spheres in the PS matrix. The P4VP cylinders display a hexagonal symmetry with six cylinders at the corners of a hexagon and one cylinder at the center. The PI spheres are also arranged on a hexagonal lattice but the center of that hexagon is occupied by a P4VP cylinder (Figure 2a). The intrinsic incompatibility among the blocks and the volume fraction of the blocks change completely due to hydroxylation of the PI block. PS lamellae are observed in the P1, P2, and P3 films prepared from the CHCl 3 /DMF solvent mixture (Figure 2b-d).
The P1 film has a three-phase morphology as the P(HTMB-r-I) and P4VP domains are not miscible (Figure 2b). Two distinct phases of bright P(HTMB-r-I) and dark P4VP domains are visible between two successive PS lamellae in the I 2 stained P1 film ( Figure 2b). However, P2 and P3 films display a two-phase morphology where a PS domain and a mixed P(HTMB-r-I) and P4VP domain form alternating lamellae (Figure 2c,d). The miscibility is determined by the competing forces of self-association and intermolecular association of the P(HTMB-r-I) and P4VP blocks. [16c] The self-association of the P(HTMB-r-I) block is hindered due to the random distribution of the incompatible HTMB and I repeating units. The intermolecular association of the P(HTMB-r-I) and P4VP blocks is favored by the affinity of the hydroxyl moieties and opposed by the incompatibility of the isoprene moieties with the pyridine rings, respectively. The degree of hydroxylation of P1 is below the threshold to overcome the repulsion of isoprene and pyridine moieties. In P2 and P3, the affinity of the hydroxyl groups and pyridine Adv. Mater. 2020, 32,1907014  In the I 2 stained films, the P4VP domains appear dark in the bright PS matrix while the PI and P(HTMB-r-I) domains are not distinguishable from PS. In the double stained films with I 2 and OsO 4 , the P4VP, PI, and P(HTMB-r-I) domains are darker than the PS matrix. All the images have the some magnification. moiety dominates over the incompatibility of pyridine rings with the isoprene moieties, which results in domains of mixed P(HTMB-r-I) and P4VP blocks.
A three-phase morphology of PI-b-PS-b-P4VP is transformed into "banana-like" short PI cylinders and P4VP spheres dispersed in a PS matrix in the film prepared from the CHCl 3 / methanol 95:5 vol% solvent mixture ( Figure 2e and Figure S7a, Supporting Information). The vapor pressure of CHCl 3 , methanol, and DMF at 25 °C is 25.9, 16.96, and 0.49 kPa, respectively. Hence, the composition of the CHCl 3 /methanol solvent mixture was much less changed during the drying of the films than in case of the CHCl 3 /DMF solvent mixture. At a later stage of evaporation, PI-b-PS-b-P4VP micelles having a rather collapsed P4VP core and a relatively more swelled PS and PI corona were formed. Upon solidification, the P4VP formed spheres and PI formed short-range cylinder in the PS matrix. The PI-b-PS-b-P4VP film could not reach thermodynamic equilibrium as the CHCl 3 /methanol solvent mixture is not a good solvent for the P4VP block. However, for the films prepared from the CHCl 3 /DMF solvent mixture, the composition of the solvent changed gradually to a significantly higher DMF content. As a result the P4VP blocks were not kinetically trapped and the morphology reached thermodynamic equilibrium. Similarly, during preparation of P2 and P3 film from the CHCl 3 /methanol solvent mixture, the mixed P(HTMB-r-I) and P4VP blocks formed the collapsed core of the micelles and PS formed the swelled corona. Consequently, randomly distributed elongated spherical domains of the mixed P(HTMB-r-I) and P4VP blocks are formed in the PS matrix (Figure 2g,h). The P1 film shows a hexagonal array of lamellar-within-cylindrical [19] domains of immiscible P(HTMB-r-I) and P4VP in the background of a PS matrix (Figure 2f). A possible reason for the formation of symmetrical cylindrical domains with a lamellar substructure could be a gain of conformational entropy of the PS blocks, as they cannot only form bridges between different cylinders, but also fold back and have both PS block ends connected to the same cylinder. This could become possible due to a less repulsive interaction between the two end blocks compared to their repulsive interactions with the central block, in combination with an overall less selective solvent mixture compared to the CHCl 3 /DMF at the moment of freezing in the morphology. Thus, the composition of the chosen solvent mixtures dictates the morphology of the films but has no influence on the miscibility of the end blocks. The intriguing TEM images of the triblock terpolymers ( Figure 2) instigate future investigations with other techniques, e.g., small angle X-ray scattering in order to have more conclusive information on the bulk morphologies of the films.
In order to investigate the influence of evaporation speed on the miscibility of the P(HTMB-r-I) and P4VP blocks, nonporous P3 thin films were prepared by spin-coating using a CHCl 3 and methanol 98:2 (vol%) solvent mixture (Figure 3a). In this case, the evaporation was finished within 20 s. The P4VP blocks of the spin-coated film were selectively post-modified with methyl iodide which appeared as hexagonally packed domains in the atomic force microscope (AFM) adhesion map (Figure 3c). The film was subsequently treated with trimethylchlorosilane to post-modify the P(HTMB-r-I) blocks. As no new (additional) microdomain appears in the AFM adhesion map (Figure 3d), it is rather likely that the discrete domains consist of both P(HTMB-r-I) and P4VP blocks. Hence, the fast evaporation of the solvent induces a hexagonal symmetry of the microdomains without affecting the miscibility of the end blocks. The formation of an integral asymmetric isoporous membrane via SNIPS also relies on an evaporation-induced self-assembly of the BCP domains perpendicular to the surface before immersion in the nonsolvent. P3 was used to fabricate the desired isoporous membranes having multifunctional channels via SNIPS.
Adv. Mater. 2020, 32,1907014  The formation of SNIPS membranes requires the right choice of a considerable number of parameters, e.g., polymer concentration of the casting solution, solvent system and its composition, evaporation time and the additives, etc. [11b] Some efforts have been made to predetermine the casting parameters from a guiding trend line obtained from an analysis of the segregation strength of the polymer-solvent mixtures using Hansen solubility parameter and Flory-Huggins interaction parameter. [20] In practice, however, these corresponding parameters have to be optimized for a new BCP system empirically. A 22 wt% P3 solution in a ternary solvent mixture of THF, DMF, and 1,4-dioxane (50:25:25 wt%) containing 1.5 wt% magnesium acetate with respect to the weight of P3 is the optimum casting solution (Supporting Information, Section S2.4). The viscous solution was doctor bladed on a nonwoven polyester support and after a few seconds of evaporation time precipitated in a water bath (Figure 3e). The top surface and cross-section of a representative membrane are depicted in Figure 3f,g, respectively. After doctor blading the viscous layer, the volatile THF evaporated and directed the self-assembly of the BCP domains perpendicular to the surface while DMF selectively kept the polar pore-forming block in a relatively higher swollen state compared to the matrix-forming block. Before precipitation in the water bath, a gradient of polymer concentration was built up along the cross-section of the layer. Upon precipitation, the formation of an isoporous top layer on a macroporous spongy sublayer took place. The pore walls of the isoporous layer are composed of miscible P(HTMB-r-I) and P4VP blocks (Supporting Information, Section S2.5).
The membrane was post-functionalized with methyl iodide and 1,3-propane sultone by straightforward in situ one-step gas-solid interface reaction to obtain positively and negatively charged pores, respectively. In the Fourier-transform infrared spectroscopy (FTIR) spectrum of the methyl iodide-treated membrane (MM), a new characteristic peak of the CN + stretching vibration appears at 1640 cm −1 due to quaternization of the nitrogen moieties of the pyridine rings, while the intensity of the characteristic stretching vibration of CN and CC of the aromatic rings at ≈1600 cm −1 decreases dramatically (Figure 4c, blue curve). As the CC stretching of aromatic rings of PS block also contributes to the peak at ≈1600 cm −1 , even after complete quaternization of the pyridine rings this peak does not disappear completely. [21] In the case of the 1,3-propane sultone-treated membrane (PM), two new characteristic vibrations at ≈1036 and ≈1181 cm −1 appear in the FTIR spectrum (Figure 4c, green curve) owing to the stretching vibration of sulfonate groups. This proves the ring opening of 1,3-propane sultone and the covalent attachment of the sulfonic acid moieties on the membrane. [22] From scanning electron microscope (SEM) images, it is confirmed that MM (Figure 4a) and PM (Figure 4b) retain the kinetically trapped porous morphology of the pristine membrane (I0; Figure 3f,g). Due to the covalent attachment of the functional moieties, MM and PM show slightly lower surface pore sizes and relatively thicker pore walls along the cross-section compared to those of I0. The average surface pore sizes at the dry state (calculated from SEM images) of I0, MM, and PM are 32, 30, and 30 nm, respectively. The surface zeta potential (ζ) of I0 is negative at a basic pH which becomes positive below pH 6.5 due to protonation of the P4VP block. Owing to the quaternization of the nitrogen moieties of P4VP block, MM does not show such pH responsiveness, instead a slightly positive ζ is observed in the whole pH range of 2.5-10. Compared to I0, PM displays a remarkable shift of isoelectric point toward a lower pH and a plateau of higher negative ζ in the pH range of 6-10 which is attributed to the presence of acidic groups (sulfonic acid groups) and their corresponding dissociation (Figure 4d). [23] The pH responsiveness of the P4VP block of I0 has a strong influence on the water permeance. At pH 7, the water permeance through I0 is 598 L m −2 h −1 bar −1 which gradually decreases to 22 L m −2 h −1 bar −1 at pH 3 (Figure 4e). It is a distinct signature of swelling of the protonated P4VP blocks in response to pH. [24] At pH 7, the P4VP blocks exist in a collapsed conformation as the nitrogen moieties are in a deprotonated and thus hydrophobic state. The P4VP blocks gradually adopt an extended conformation due to increasing degree of protonation of the nitrogen moieties with the decrease of pH. Consequently, the pores of the membranes become narrow and the water permeance drops. As such pH responsive behavior is not undermined by the mixed P(HTMB-r-I) pore-forming block, it is clear that at low pH the nitrogen moieties of the P4VP blocks have a higher tendency to be in the protonated state compared to the hydrogen bond formation with the hydroxyl moieties of the P(HTMB-r-I) blocks.
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 4f). It is worth noting that the water permeance of MM and PM is higher than reported for SNIPS BCP membranes with chargedinduced 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 ). [26] 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.
To demonstrate the charge selective nature of MM, we employed aqueous solutions of three model molecules having comparable molecular weight (319-377 g mol −1 ) but different electrostatic charges-a cationic dye methylene blue (MB+), an anionic dye orange II (OR−), and a neutral vitamin riboflavin (RB0). According to MM2 force field energy minimization model calculation (in vacuum), the lateral dimensions of MB+, RB0, and OR− are rather similar, i.e., 1.1, 1.0, and 1.3 nm, respectively. [27] The permeability and selectivity of membranes can be investigated via two methods: concentration-driven diffusion [1,2,[5][6][7]28] and pressure-driven flow. We determined the retention and selectivity of the model molecules from pressuredriven flow of aqueous solutions containing single solutes and mixed solutes as it is more relevant to a realistic application compared to a diffusion cell experiment. Additionally, under applied pressure, some polymers self-regulate to change their conformation, leading to significant changes in the effective pore size and rejection behavior of the membranes. [29] The aqueous solutions of MB+, RB0, and OR− were passed through I0 with no rejection of MB+ and RB0 while only 2% rejection of OR− (Figure 5a-c). When aqueous solution of MB+ was used as a feed solution for MM, a substantial reduction of color was observed in the permeate solution. 95.3% of MB+ was retained from the aqueous solution by MM ( Figure 5a). Remarkably, neutral RB0 permeated through MM completely without any rejection (Figure 5b)   adsorption on the MM membrane (Table S3, Supporting Information). It is obvious that OR− was adsorbed at the positively charged moieties of the MM due to the attraction of two opposite charges. Such adsorption of molecules on the membrane is undesirable as the polyelectrolyte pore-forming block would lose its ability to swell due to neutralization. To confirm this assumption, we investigated the retention of OR− using a freshly prepared MM ( Figure S19, Supporting Information) and MM close to saturated adsorption by immersing in a 0.1 × 10 −3 m OR− solution for 30 days (Figure 5c). In the first case, the membrane retained 62% of the OR− from the feed solution while the latter allowed complete passage of feed solution without any retention of OR−. It corroborates that the pore walls of MM are decorated with rather strong positive charges which repel the MB+ and adsorb the OR− from their aqueous solutions. However, the surface zeta potential of MM is only slightly above zero (0.5-1.1 mV) in the pH range 5-10 ( Figure 4d). The discrepancy between the true value of surface zeta potential and the apparent value of the surface zeta potential from streaming current or streaming potential measurement has been pointed out in several studies. [30] Positive charges at the membrane pore wall can influence the retention of MB+ only when the nanochannel is narrow enough. The pH of 0.1 × 10 −3 m MB+ solution is 5.7 (Table S4, Supporting Information). At pH 5.7 the pores of I0 also carry a positive charge (Figure 4d) while the pore-forming block is slightly swelled (Figure 4e). However, the pores of I0 are too big to retain MB+ from aqueous solution.
Such enhancement of the real selectivity compared to the ideal selectivity was reported in a few studies of nonbiological systems. [5,10a] In the single-solute retention measurement, 100% Adv. Mater. 2020, 32,1907014  of neutral RB0 permeated through MM while only 4.7% of cationic MB+ could permeate through the membrane. MB+ lagged far behind RB0 to enter the positively charged nanochannels of MM as it had to overcome an additional energy barrier (due to electrostatic repulsion) compared to RB0. Therefore, during the mixed-solute retention study the nanochannels of MM constantly allowed the favorable entrance of RB0 molecules rather than unfavorable MB+ from the background of a mixture of MB+ and RB0. However, RB0 still had to compete with MB+ to reach the entrance of the nanochannels from the bulk of the solution. [31] As a result 85% of RB0 and 3% of MB+ permeated through MM during the mixed-solute retention measurement (ψ r RB0/MB+ = 28.3). A possibility of back diffusion after the entrance of MB+ and RB0 in the nanochannels of MM could be ruled out due to the transmembrane pressure. Overall, these results demonstrate the competition-induced enhancement of selectivity and strong capability of the prepared MM to perform charge-based separation of organic molecules having a lateral molecular dimension of ≈1 nm.
To investigate the separation efficiency of the negatively charged membrane PM, three anionic dyes having sulfonate functional groups and different molecular weights (350.32, 878.45, 1418.93 g mol −1 , respectively) were used as model compounds-monovalent orange II (OR−), trivalent naphthol green B (NG3−), and hexavalent reactive green 19 (RG6−). The pH of 0.1 × 10 −3 m aqueous solutions of OR−, NG3−, and RG6− is 6.4, 6.5, and 4.6, respectively (Table S4, Supporting Information). Single-solute aqueous solutions of OR− and NG3− permeated through I0 with only 1-2% rejection of the solutes (Figure 6a,b). At pH 4.6 the P4VP blocks of I0 swell ( Figure 4e) and acquire positive charges due to protonation (Figure 4d). 55% of RG6− was retained from the aqueous solution presumably due to a strong tendency of adsorption of RG6− on I0 (Table S3, Supporting Information). The pores of PM have strong negative charges in the range of pH 6.4-6.5 (Figure 4d). In the singlesolute retention measurement, 29.3% OR− was retained from the aqueous solution by PM (Figure 6a). In spite of the electrostatic repulsion between the like charges, the nanochannels of PM are big enough to allow 70.7% of OR− to permeate through the membrane. But the pores of PM are narrow enough for the bigger NG3− molecules to exert strong electrostatic repulsion, rejecting 95.2% NG3− (Figure 6b). As PM exhibited a very slight adsorption of OR− and NG3− after soaking in the aqueous solution even for 24 h (Table S3, Supporting Information), the solute adsorption might have a very small contribution on the rejection. Although pH 4.6 is pretty close to the isoelectric point of PM, 98.9% of RG6− was retained from the aqueous solution by PM (Figure 6c). RG6− showed a much stronger adsorption on PM compared to OR− and NG3−, which would form a negatively charged surface from adsorbed RG6− molecules and consequently repel the anionic RG6−. [32] Such high rejection of RG6− is presumably ascribed to the combination of charge/size-based separation and also small portion of the adsorption. Notably, the ideal selectivities ψ i OR-/NG3and ψ i OR-/RG6-are 14.7 and 64.3, respectively ( Table 2). As the pH of NG3− and OR− aqueous solutions are close to each other, we have used this pair of mixed solutes to investigate the competitive permeation through PM. PM retained 33.1% of OR− and 98.5% of NG3− from a 0.1 × 10 −3 m aqueous solution of a 50:50 (molar ratio) mixture of OR− and NG3− which resulted in the real selectivity ψ r OR-/NG3-= 44.6 ( Figure 6d and Table 2). OR− and NG3− repelled each other while competing to reach the entrance of the pores from the bulk of the solution. Both OR− and NG3− solutes had to overcome the energy barrier of electrostatic repulsion to enter the pores of the membrane which was larger for the trivalent NG3− compared to the monovalent OR−. The entry of NG3− was further hindered due to higher molecular dimensions in an aqueous solution compared to OR−. The monovalent OR− was likely to orient in a way so that the noncharged end enters the pore of the membrane first which was an additional advantage to overcome the energy barrier. Such orientation was not possible for the trivalent NG3− as each of three arms had a charged end. More strikingly, due to these competing factors, the real selectivity ψ r OR-/NG3-is threefold higher compared to the ideal selectivity ψ i OR-/NG3-. The prepared membrane PM can indeed be used to efficiently separate organic molecules with molecular dimension of 1-2 nm by taking advantage of small differences in size and charge number.
In summary, we report a novel asymmetric isoporous membrane with embedded multifunctional groups on the interior of the pore walls, i.e., -OH and 4VP groups, which is derived from a well-designed amphiphilic triblock terpolymer, P(HTMB-r-I)b-PS-b-P4VP, via SNIPS. We have demonstrated that the formation of nanochannels with multifunctional groups arises from the miscible domain consisting of two end blocks via hydrogen bonding. These highly accessible functional groups within the pore walls can readily allow straightforward scalable gas-solid interface post-functionalizations to integrate the positively or negatively charged moieties along the pore walls. The diameter of the well-defined soft nanochannels in a hydrated state is within the nanofiltration regime due to swelling of the polyelectrolyte pore-forming blocks. The single-and mixed-solute retention studies demonstrate the ability of the membranes to efficiently retain dye molecules from aqueous solutions as well as an unprecedented separation of small organic molecules (1-2 nm) from each other (other reported studies for the separation of small organic molecules (1-2 nm) are listed in Table S7, Supporting Information). This concept of integration of the multifunctionalities into the membrane by a bottomup design of a triblock terpolymer provides a new platform to fabricate next-generation nanofiltration membranes to solve the on-demand separation problems of several sectors, e.g., chemical and pharmaceutical separations, biomolecules purifications, etc.

Supporting Information
Supporting Information is available from the Wiley Online Library or from the author.