Charge switchable filtration membrane, polymeric additive, polymer blend, and kit for manufacturing same, methods of manufacturing and of use

Abstract

A filtration membrane comprising a hydrophobic host polymer and a polymeric additive dispersed within the host polymer is provided. The membrane and the polymeric additive undergo reversible transitions of their charge from positive to neutral to negative. The polymeric additive is an amphiphilic block copolymer comprising a hydrophobic block and a hydrophilic block comprising repeat units bearing positively ionizable weak base and negatively ionizable weak acid functional groups. A polymer blend, a kit, and a method for manufacturing the membrane relying on phase inversion via immersion precipitation are provided. Use of the membrane for filtering a feed is also provided. It advantageously uses membranes that have an isoelectric point that is about that of a contaminant and / or foulant to be removed, which involves tuning the isoelectric point of the membrane by adjusting the ratio of repeat units bearing positively ionizable weak base and negatively ionizable weak acid functional groups.

Description

CHARGE SWITCHABLE FILTRATION MEMBRANE, POLYMERIC ADDITIVE, POLYMER BLEND, AND KIT FOR MANUFACTURING SAME, METHODS OF MANUFACTURING AND OF USE CROSS REFERENCE TO RELATED APPLICATIONSThis application claims benefit, under 35 U.S.C. § 119(e), of U.S. provisional application Serial No. 63 / 710,118, filed on October 22, 2024. All documents above are incorporated herein in their entirety by reference.FIELD OF THE INVENTION

[0001] The present invention relates to a charge switchable polymeric additive as well as a polymer blend comprising this additive and a kit that can be used for manufacturing such a membrane. Methods of manufacturing and using such membranes are also provided. More specifically, the present invention is concerned with charge switchable polymeric additive that can undergo reversible transitions of its charge from positive to neutral to negative. A membrane having an isoelectric point that is about that of a contaminant and / or foulant to be removed from a feed is advantageously manufactured / selected for use.BACKGROUND OF THE INVENTION

[0002] Membranes are selective barriers used to separate components with different physical or chemical properties1. They offer significant advantages over conventional separation methods, such as reduced secondary pollution, low energy consumption, compact design, and economic feasibility2-4. Due to these benefits, membrane research has advanced rapidly in recent decades, addressing energy and environmental challenges effectively.

[0003] The performance of membranes is primarily determined by their permeability and selectivity. Permeability is indicated by trans-membrane flux, while selectivity refers to the membrane's ability to reject or permeate specific substances56. However, membrane performance will decrease naturally over time due to undesirable membrane fouling.

[0004] Membrane fouling remains a persistent challenge in membrane separation, due to the accumulation of contaminants or foulant such as inorganic, organic, or biological substances on the surface or within the membrane7’8. Inorganic foulants primarily consist of substances like aluminum silicate minerals, ferric oxide / hydroxide colloids, and silica. Biofoulants include various microorganisms, such as bacterial cells. Organic foulants mainly comprise natural organic matter (NOM), oils, and biomacromolecules. Proteins are biomacromolecules that can interact with hydrophobic membranes such as poly (ether sulfone) (PES), which can eventually cause biological fouling. The accumulation of foulants leads to flux decline, operation pressure increase, frequent physical and chemical cleaning, reduction in separation efficiency, and membrane lifetime9.

[0005] As the fouling phenomenon is closely related to the membrane surface properties such as its surface hydrophilicity10’11, roughness12’13, and charge, many studies have been conducted on the development of foulingresistant membrane by modifying the membrane surface properties1415. Furthermore, since most organic foulants are hydrophobic, applying an ultra-thin hydrophilic layer to the membrane surface would create a barrier that preventsdeposition, contamination, and aggregation1011.

[0006] Charging the surface represents a promising approach to simultaneously enhance the hydrophilicity and create repulsive forces acting between the charged surface and the co-ions in the feed solution thus hindering the solute deposition on the membrane surface. Various methods can be employed to make charged membrane surface, such as surface modification with polyethyleneimine (PEI) and zwitterionic polymers. For example, Okoro et al. modified PES membranes with hyperbranched polyethyleneimine (HPEI) with a high cationic charge density to enhance their ultrafiltration, antibacterial, and antifouling properties16. However, this class of membranes often faces a limitation associated with the constant charge of the same sign on the membrane surface, which not only causes the accumulation of the counter ions but also makes it harder to clean. Additionally, conventional static membranes cannot adjust to different operational conditions. Recent studies indicate that incorporating zwitterionic materials can enhance antifouling performance more effectively than conventional positively or negatively charged membranes. Zwitterionic polymers feature both anionic and cationic groups in each repeating unit, maintaining an overall neutral charge, and include pendant groups like phosphobetaine, sulfobetaine, and carboxybetaine.17-19. Zhao et al. reported the fabrication of polysulfone (PSF) ultrafiltration (UF) membranes modified by surface zwitterionization from a PSF-based block copolymer, in which the PDMAEMA block was quaternized, using 3-bromopropionic acid (3-BPA), into zwitterionic poly (carboxybetaine methacrylate) (PCBMA); and the surface zwitterionization was found to greatly enhance the hydrophilicity and fouling resistance of PSF membranes20. However, despite these outstanding antifouling properties, it is generally challenging to immobilize zwitterionic polymers on hydrophobic membranes due to their extreme hydrophilicity and high water solubility21. In addition, they have constant charges and the lack of charge switchability limits their performance in some applications with hydrophilic foulants.

[0007] To address these issues, pH-responsive membranes are designed using charge-switchable polyelectrolytes that contain ionizable groups, which can act as either polyacids or polybases by adjusting the pH, since the ionizable groups can become protonated or deprotonated by accepting or releasing H+ions. This response to pH change can induce changes in the ionic interactions, hydrogen bonding, and hydrophobic interactions, resulting in alterations to the structure and properties of these polymers (e.g., solubility, chain conformation, hydrodynamic volume, and surface activity)22-25. Therefore, pH-responsive membranes possess self-regulating surface properties that help remove contaminants and / or foulants adhered to the surface, providing them with a self-cleaning ability.

[0008] These polymers are classified into two types based on their ionizable groups, which are positively pH-responsive membranes26-28and negatively pH-responsive membranes29-31. Positively pH-responsive membranes are made by cationic polymers with weakly basic groups, such as (PDMAEMA). In the acidic environment, tertiary amine groups switch from neutral to cationic state when reacting with H+which leads to a change in the ionization degree and net charge on the polymer chains. As the net charge on the chains increases, the electrostatic repulsion of the generated charges induces the transition of the chains from collapsed to an expanded state. Conversely, a reduction in the chain's net charge aggravates their transition from expanded to collapsed conformation32. Ye et al. investigated protein adsorption and desorption behavior for a pH-responsive PDMAEMA-grafted ethylene vinyl alcohol copolymer (EVAL) membrane with an interconnected porous structure. The transition of electrostatic behavior and conformationchange of the PDMAEMA chain contributed to the pH-responsive protein adsorption and desorption33.

[0009] In contrast, negatively pH-responsive membranes are fabricated by anionic polymers possessing weak acidic groups, e.g., poly (acrylic acid) (PAA). In a basic environment, carboxylic acids switch from the neutral to anionic form by donating H+, leading to extended chain conformation. Contrarily, the acceptance of H+causes intermolecular hydrogen bonding between COOH groups and polymer chain shrinkage. Ndlwana et al. fabricated pH-responsive membranes exhibiting low adhesion and high rejection of protein. In this case, the heterogeneous AIBN-initiated functionalization of PES powder with MAA was reported for the first time. The membranes were found to possess low protein adhesion and low fouling properties34.

[0010] Among the current methods, pH-responsive membranes are commonly prepared using surface coating, surface grafting, and surface segregation1435. Surface coating significantly increases the hydrophilicity of membrane surfaces; however, it can severely block membrane pores, and the coating layer may be washed off after prolonged use. Surface grafting, one of the common approaches for obtaining stable and fouling-resistant membrane surfaces, is hindered by harsh reaction conditions, pore blockage, and the inability to modify internal pore surfaces, limiting its efficiency and applicability. Additionally, both surface coating and surface grafting are post-treatment techniques and add extra steps and costs to membrane manufacturing14’3536.SUMMARY OF THE INVENTION

[0011] In accordance with the present invention, there is provided:1. A charge switchable filtration membrane comprising a porous layer comprising a hydrophobic host polymer and a charge switchable polymeric additive, wherein the charge switchable polymeric additive is dispersed within the host polymer, and wherein the charge switchable polymeric additive is an amphiphilic block copolymer comprising a hydrophobic block and a hydrophilic block, wherein the hydrophilic block comprises repeat units bearing a positively ionizable weak base functional group and repeat units bearing a negatively ionizable weak acid functional group.2. The membrane of embodiment 1 , exhibiting a finger-like structure.3. The membrane of embodiment 1 or 2, comprising a surface layer on top of a foundation layer, wherein the surface layer is thinner than the foundation layer, wherein the surface layer and the foundation layer each comprises pores, and wherein the pores of the surface layer are smaller than the pores of the foundation layer.4. The membrane of embodiment 3, wherein the surface layer represents about 1 % to 20%, preferably about 2% to 10%, and more preferably about 3% to about 7%, of the total thickness of the membrane.5. The membrane of embodiment 3 or 4, wherein the surface layer has an average thickness of about 2 pm to about 10 pm, preferably about 3 pm to about 7 pm.6. The membrane of any one of embodiments 3 to 5, wherein the foundation layer has an average thickness of about 50 pm to about 150 pm, preferably about 70 pm to about 100 pm.7. The membrane of any one of embodiments 3 to 6, wherein the pores of the foundation layer are elongated and arranged approximately perpendicularly to the surface of the membrane.8. The membrane of any one of embodiments 3 to 7, wherein the pores of the foundation layer have an average length of at least 20 pm.9. The membrane of any one of embodiments 3 to 8, wherein the surface layer is enriched in amphiphilic block copolymer.10. The membrane of any one of embodiments 1 to 9, being supported on a porous support to increase the mechanical strength of the membrane.11. The membrane of embodiment 10, wherein the porous support is a non-woven mat, preferably of polyethylene, polypropylene, or polyethylene terephthalate.12. The membrane of embodiment 10 or 11, wherein the porous support has an average thickness of about 0.06 mm to about 1 mm, preferably about 0.2mm, such as about 0.18 mm.13. The membrane of any one of embodiments 1 to 12, wherein the hydrophobic host polymer is polyether sulfone (PES), polystyrene (PS), polyvinylidene difluoride (PVDF), or polyacrylonitrile (PAN), preferably PES.14. The membrane of any one of embodiments 1 to 13, wherein the hydrophobic block of the amphiphilic block copolymer has a molecular weight (Mw) between about 5000 Da and about 20000 Da.15. The membrane of any one of embodiments 1 to 14, wherein the hydrophilic block of the amphiphilic block copolymer has a molecular weight (Mw) between about 5000 Da and about 20000 Da.16. The membrane of any one of embodiments 1 to 15, wherein the hydrophobic block of the amphiphilic block copolymer comprises polyacrylonitrile (PAN), polyether sulfone (PES), polypropylene (PP), polysulfide (PS), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or cellulose acetate, preferably PES or PVDF, and more preferably PES.17. The membrane of any one of embodiments 1 to 16, wherein the negatively ionizable weak acid functional groups are carboxylic acids, sulfonic acids, and / or phosphoric acids.18. The membrane of any one of embodiments 1 to 17, wherein the positively ionizable weak base functional groups are amidines, guanidines, amines, imidazoles, and / or pyridines.The membrane of any one of embodiments 1 to 18, wherein the hydrophilic block comprises repeat units bearing both the positively ionizable weak base functional group and the negatively ionizable weak acid functional group.The membrane of any one of embodiments 1 to 18, wherein the repeat units bearing the positively ionizable weak base functional group and the repeat units bearing a negatively ionizable weak acid functional group are different from one another.The membrane of any one of embodiments 1 to 18 and 20, wherein the repeat unit bearing negatively ionizable weak acid functional group are repeat unit of poly (acrylic acid), poly(ethyl acrylic acid), a polymethacrylic acid, poly(vinyl sulfate) PVS, poly (styrene sulfonate), polyphosphoric acid, or poly(vinylphosphonic acid), preferably polymethacrylic acid.The membrane of any one of embodiments 1 to 18, 20 and 21, wherein the repeat units bearing positively ionizable weak base functional groups are repeat units of• poly(N-methyltetrahydropyrimidine) (PMTHP),• poly(p-azidomethylstyrene-co-styrene),• poly[2-methyl-1 -(4-vinylbenzyl)-1 ,4,5,6-tetrahydropyrimidine],• poly(dimethyl acrylamide-co-(N-amidino)ethyl acrylamide) (P(DMA-co-NAEAA)), and• polyethylene oxide)-b-poly((N-amidino)dodecyl acrylamide).• poly[(2-dimethylamino) ethyl methacrylate] (PDMAEMA),• poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA), and• poly(3-N',N'-dimethylaminopropyl acrylamide) (PDMAPMA), orpoly(L-arginine methyl ester acrylamide-co-N-cyclopropyl acrylamide) (poly(AME-co-CPAM), preferably repeat units of PDMAEMA, PMTHP or PDMAPMA.23. The membrane of any one of embodiments 1 to 18 and 20 to 22, wherein the charge switchable polymericranHO additive is of formula: wherein R represents -NH(CH2)3N(CH3)2or O(CH2)2N(CH3)2, preferably -NH(CH2)3N(CH3)224. The membrane of any one of embodiments 1 to 23, wherein the charge switchable polymeric additive is present at a concentration between about 1 and about 15 wt.%, preferably between about 4 and about 8 wt.%, based on the weight of the hydrophobic host polymer.25. The membrane of any one of embodiments 1 to 24, wherein the isoelectric point of the membrane is between about 3 and about 10.26. The membrane of any one of embodiments 1 to 25, being a microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), or reverse osmosis (RO) membrane.27. The membrane of any one of embodiments 1 to 26, being in the form of a flat sheet or a hollow fiber.28. A charge switchable polymeric additive, wherein the charge switchable polymeric additive is an amphiphilic block copolymer comprising a hydrophobic block and a hydrophilic block, wherein the hydrophilic block comprises repeat units bearing a positively ionizable weak base functional group and repeat units bearing a negatively ionizable weak acid functional group29. The polymeric additive of embodiment 28, being as defined in any one of embodiments 1 to 27.30. The polymeric additive of embodiment 28 or 29, being for manufacturing a charge switchable filtration membrane, preferably wherein the charge switchable filtration membrane is as defined in any one of embodiments 1 to 27 .31 . A polymer blend comprising a hydrophobic host polymer and a charge switchable polymeric additive, wherein the charge switchable polymeric additive is an amphiphilic block copolymer comprising a hydrophobic block and a hydrophilic block, wherein the hydrophilic block comprises repeat units bearing a positively ionizable weak base functional group and repeat units bearing a negatively ionizable weak acid functional group.32. The polymer blend of embodiment 31, wherein the hydrophobic host polymer is as defined in any one of embodiments 1 to 27 and / or wherein the charge switchable polymeric additive is as defined in any one of embodiments 1 to 27 .33. The polymer blend of embodiment 31 or 32, being for manufacturing a charge switchable filtration membrane, preferably wherein the charge switchable filtration membrane is as defined in any one of embodiments 1 to 2734. A kit for manufacturing a charge switchable filtration membrane, the kit comprising a hydrophobic host polymer and a charge switchable polymeric additive, wherein the charge switchable polymeric additive is an amphiphilic block copolymer comprising a hydrophobic block and a hydrophilic block, wherein the hydrophilic block comprises repeat units bearing a positively ionizable weak base functional group and repeat units bearing a negatively ionizable weak acid functional group.35. The kit of embodiment 34, wherein the hydrophobic host polymer is as defined in any one of embodiments 1 to 27 and / or wherein the charge switchable polymeric additive is as defined in any one of embodiments 1 to 27.36. The kit of embodiment 34 or 35, wherein the charge switchable filtration membrane is as defined in any one of embodiments 1 to 27 .37. The kit of any one of embodiments 34 to 36, further comprising instructions for manufacturing and / or using the charge switchable filtration membrane.38. The membrane of any one of embodiments 1 to 27, the polymer blend of any one of embodiments 31 to 33, or the kit of any one of embodiments 34 to 37, further comprising a pore-forming agent.39. The membrane, the polymer blend, or the kit of embodiment 38, wherein the pore-forming agent is polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), an inorganic additive such as LiCI and TiC>2, or a surfactants such as Tween®-80.40. The membrane, the polymer blend, or the kit of embodiment 38 or 39, wherein the pore-forming agent is present at a concentration between about 0.5 and about 15 wt.%, preferably between about 2 and about 8 wt.%, based on the weight of the hydrophobic host polymer.41. The membrane of any one of embodiments 1 to 27, the polymer blend of any one of embodiments 31 to 33, or the kit of any one of embodiments 34 to 37, being free of a pore-forming agent.42. A method of manufacturing a charge switchable filtration membrane, the method comprising• providing a casting solution by dissolving a hydrophobic host polymer, a charge switchable polymeric additive, and a pore-forming agent in a solvent,• casting the casting solution onto a substrate,• submerging the substrate bearing the casting solution in a coagulation bath containing a non-solvent, thereby causing precipitation of the hydrophobic host polymer, the charge switchable polymeric additive, and the pore-forming agent to form the membrane.43. The method of embodiment 42, wherein the charge switchable filtration membrane is as defined in any one of embodiments 1 to 27, wherein the hydrophobic host polymer is as defined in any one of embodiments 1 to 27 and / or wherein the charge switchable polymeric additive is as defined in any one of embodiments 1 to 27. 44. The method of embodiment 42 or 43, wherein the charge switchable filtration membrane is as defined in any one of embodiments 1 to 27.45. The method of any one of embodiments 42 to 44, wherein the solvent is N-methyl-2-pyrrolidone (NMP), DMAC, DMF, CHCI3, or a mixture thereof.46. The method of any one of embodiments 42 to 45, wherein the non-solvent is water, an alcohol (such as ethanol, methanol, isopropanol), or a mixture thereof.47. The method of any one of embodiments 42 to 46, wherein the non-solvent is water and wherein the water is at a basic or acidic pH, preferably at a basic pH.48. The method of any one of embodiments 42 to 47, wherein the non-solvent is water and wherein the water is at a temperature between about 8°C and about 12°C.49. The method of any one of embodiments 42 to 48, wherein the pore-forming agent is polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), an inorganic additive such as LiCI and TiC>2, or a surfactant such as Tween®-80.50. The method of any one of embodiments 42 to 49, wherein the pore-forming agent is present at a concentration between about 0.5 and about 15 wt.%, preferably between about 2 and about 8 wt.%, based on the weight of the hydrophobic host polymer.51. The method of any one of embodiments 42 to 50, further comprising the step to tuning the isoelectric point of the membrane by modifying the ratio of repeat units bearing positively ionizable weak base functional groups and repeat units bearing negatively ionizable weak acid functional groups in the charge switchable polymeric additive.52. The method of any one of embodiments 42 to 51, further comprising the step to tuning porosity of the membrane by modifying the viscosity of the casting solution.53. The method of embodiment 52, wherein the viscosity of the casting solution is modified by varying the concentration of components thereof, preferably of the hydrophobic host polymer.54. The method of any one of embodiments 42 to 53, wherein the hydrophobic host polymer is present in the casting solution at a concentration ranging from about 5% to about 30% by weight, based on the total weight the polymer solution.55. The method of any one of embodiments 42 to 54, wherein the charge switchable polymeric additive is present in the casting solution at a concentration ranging from about 2% to about 12% by weight, based on the total weight the polymer solution.56. A method of tuning the isoelectric point of the charge switchable filtration membrane of any one of embodiments 1 to 27, the method comprising the step of adjusting the ratio of repeat units bearing positively ionizable weak base functional groups and repeat units bearing negatively ionizable weak acid functional groups in the charge switchable polymeric additive.57. A method of filtering a feed using the charge switchable filtration membrane of any one of embodiments 1 to 27, the method comprising the step of contacting the feed with one side of the membrane and allowing materials to be separated from the feed to pass through the membrane as a permeate58. Use of the charge switchable filtration membrane of any one of embodiments 1 to 27 for filtering a feed. 59. The method of embodiment 57 or the use of embodiment 58, being for use is in a water purification application, in a gas separation application, or in a biomedical filtration application, or being for the separation of proteins or other biomolecules from the feed.60. The method of embodiment 57 or 59 or the use of embodiment 58 or 59, further comprising selecting, as the charge switchable filtration membrane, a membrane that has an isoelectric point that is about the isoelectric point of a contaminant and / or foulant to be removed from the feed.61. The method of any one of embodiments 57 and 59 to 60 or the use of any one of embodiments 58 or 59 to 60, further comprising the step of tuning the surface charge of the membrane by modifying the pH of the feed.62. The method of any one of embodiments 57 and 59 to 61 or the use of any one of embodiments 58 or 59 to 61 , further comprising the step of tuning the hydrophilicity of the membrane by modifying the pH of the feed.63. The method or the use of embodiment 62, wherein the pH is modified by introducing an acid, a base, or C02or N2gas into the feed.The method of any one of embodiments 57 and 59 to 63 or the use of any one of embodiments 58 or 59 to 63, further comprising using a control mechanism to adjust the pH and thereby tuning the surface charge of the membrane in real-time.The method of any one of embodiments 57 and 59 to 64 or the use of any one of embodiments 58 or 59 to 64, wherein the filtering is in continuous operation with real-time monitoring of the surface charge of the membrane.The method of any one of embodiments 57 and 59 to 65 or the use of any one of embodiments 58 or 59 to 65, further comprising the step of cleaning the membrane.The method or use of embodiment 66, wherein the cleaning is carried out after the membrane has been used for filtrating the feed.The method or use of embodiment 66 or 67, further comprising, after said cleaning, the step of reusing the membrane to filter a feed.The method or use of any one of embodiments 66 to 68, wherein the cleaning comprises the step of i) creating or increasing a negative surface charge on the membrane by contacting the membrane liquid with a pH higher than the isoelectric point of the membrane.The method or use of any one of embodiments 66 to 69, wherein the cleaning comprises the step of ii) creating or increasing a positive surface charge on the membrane by contacting the membrane liquid with a pH lower than the isoelectric point of the membrane.The method or use of any one of embodiments 66 to 70, wherein the cleaning comprises the step of Hi) increasing the hydrophilicity of the membrane by contacting the membrane liquid with a pH at least one pH point higher than the isoelectric point of the membrane.The method or use of any one of embodiments 66 to 71, wherein the cleaning comprises the step of iv) decreasing the hydrophilicity of the membrane by contacting the membrane liquid with a pH approximately corresponding to the isoelectric point of the membrane.The method or use of any one of embodiments 69 to 72, wherein two or more (preferably all of) steps i) to iv are carried out consecutively (in any order).The method or use of any one of embodiments 66 to 73, wherein the cleaning further comprises the step of reversing liquid flow across the membrane.The method or use of any one of embodiments 66 to 74, wherein the cleaning is carried out in situ at the location where the membrane has been used or will be used to filter the feed.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In the appended drawings:Figure 1 shows the preparation of membrane using the phase inversion methodFigure 2 shows a stirred filtration cell.Figure 3 shows a filtration systemFigure 4 shows a membrane holder.Figure 5 shows the IR spectra of PS, PS-b-PDMAEMA0.3-ran-PtBMA0.7, PS-b-PDMAEMA0.3-ran-PMAAc0.7. Figure 6 shows the 1 H NMR spectra of PS, PS-b-PDMAEMA0.3-ran-PtBuMA0.7, PS-b-PDMAEMA0.3-ran-PMAAc0.7. Figure 7 shows the zeta potential plotted against pH of PS-b-PDMAEMA0.5-ran-PMAAc0.5, PS-b-PDMAEMA0.3-ran-PMAAc0.7 and PS-b-PDMAEMA0.2-ran-PMAAc0.8.Figure 8 shows SEM images of PES and PES23%-CoP-PVP5% membranes (Figure 8A: cross-section, Figure 8B: top surface)Figure 9 shows the impact of CoP and PVP addition in the PES membrane on the adsorption density of TBO and OA II dyes.Figure 10 shows the recyclability and Repeatability of dye adsorption and desorption of the neat PES and PES23%-CoP-PVP5% membranes (A and D represent adsorption and desorption, respectively.)Figure 11 shows the contact angles of water and diiodomethane on the membrane surface of PES23%-CoP-PVP5% at different pH (2, 4.5, and 11) and neat PES.Figure 12 shows the pH dependence of the zeta potential for all membrane samples determined in 0.001 mol / l KCI. Figure 13 shows the protein flux, raw protein, and whey protein rejection of neat PES, PES23%-CoP, PES23%-CoP-PVP5% and, PES23%-CoP-PVP5%-50.Figure 14 shows a) Daily water filtration productivity (mL / day) and, b) Daily productivity difference (in %) between PES23%-CoP-PVP5% and neat PES membranes.Figure 15 shows the molecular weight cutoff (MWCO) analysis of the Neat PES and pH-responsive membranes Figure 16 shows the durability of PES23%-CoP-PVP5% and PES23%-CoP-PVP5%-50 over 2, 5, and 12 hours.DETAILED DESCRIPTION OF THE INVENTION

[0013] Turning now to the invention in more details, there is provided a charge switchable filtration membrane. There is also provided a charge switchable polymeric additive as well as a polymer blend comprising this additive and a kit that can be used for manufacturing such a membrane. Methods of manufacturing and using such membranes are also provided.

[0014] The polymeric additive of the invention is a charge switchable polymeric additive. This means that the polymeric additive can undergo reversible transitions of its charge from positive to neutral to negative and from negative to neutral to positive. In other words, the polymeric additive of the invention is a reversible positive-to-neutral-to-negative charge switchable filtration membrane. The charge switch is induced by pH, at low pH levels, the polymer becomes positively charged, while at high pH levels, it shifts to a negative charge, and at the isoelectric point, it remains neutral. Thus, it can be said that the polymeric additive of the invention is a positive-to-neutral-to-negative pH-responsive charge switchable polymeric additive.

[0015] Similarly, the filtration membrane of the invention is a charge switchable filtration membrane. This means that the membrane can undergo reversible transitions of its surface charge from positive to neutral to negative. In other words, the membrane of the invention is a positive-to-neutral-to-negative charge switchable filtration membrane. Notably, the surface charge includes the charge of all the surface meeting the filtration feed. In other words, it includes the internal surface of the pores in the membrane as well as external surface of the membrane.

[0016] Of note, this is significantly different from having the capacity of switching change from neutral to positive or from neutral to negative. To the best of the inventors’ knowledge, published reports have only discussed pH-responsive membranes that shift from positive to neutral or negative to neutral, without addressing the switch from positive to negative. Unlike any other reported technology, the membrane of the invention offers charge switchability from positive to negative for membrane applications.

[0017] In the membrane of the invention, the surface charge switch is induced by pH. By incorporating the positive-to-neutral-to-negative pH-responsive charge switchable polymeric additive of the invention, the membrane of the invention gains the ability to dynamically switch surface charge in response to pH variations. At low pH levels, the membrane surface becomes positively charged, while at high pH levels, it shifts to a negatively charged state and in between, at its isoelectric point, it remains neutral. Thus, it can be said that the membrane of the invention is a positive-to-neutral-to-negative pH-responsive surface charge switchable filtration membrane.

[0018] The charge change can be easily obtained by exposing the polymeric additive or the membrane of the invention to a solution of a correct pH. For the membrane, this can easily be achieved on-site via the filtration feed. This technology creates a unique capability on membrane surface for specific applications which requires charge switching properties.

[0019] The ability to switch surface charge on demand via pH adjustment confers several significant technical advantages to the membrane of the invention. One of these pertains to the filtration of proteins and other peptides including oligopeptides, polypeptides, etc. Protein molecules are zwitterionic and pH / ion-responsive due to the presence of both carboxyl and amino groups, being negatively charged above their isoelectric point and positively charged below it. Hence, the membrane of the invention that can switch between positively and negatively charged surfaces is particularly interesting for applications involving proteins.

[0020] Also, the charge-switching capability revolutionizes membrane performance. The charge-switching capability lets the membrane of the invention release contaminants and / or foulants during acid or basic cleaning cycles,which constituted another advantage of the invention. The membrane can repel contaminants and / or foulants through electrostatic repulsion and facilitate easy cleaning and water passage. This dynamic behavior reduces fouling, enhances cleaning efficiency, extends the membrane's operational life, limits membrane cost, and offers efficient solutions for various applications, including water treatment, industrial filtration, and biomedicine.

[0021] Indeed, membrane fouling can significantly reduce the efficiency and lifespan of conventional membranes used in separation processes. Fouling occurs when contaminants and / or foulants accumulate on the membrane surface, leading to decreased performance and increased maintenance requirements. By incorporating the pH-responsive charge switchable polymeric additive of the invention, membranes that can actively repel contaminants and / or foulants and facilitate easier cleaning are provided. This solution is particularly valuable in applications such as water treatment, industrial filtration, and biomedicine, where maintaining high membrane performance and reducing downtime for maintenance are critical.

[0022] The membranes of the invention are also advantageous because of a significant saving in harsh and toxic chemicals in cleaning, water consumption saving, GHG emission, cost saving in chemical usage, higher efficiency in filtration and shorter time of cleaning. Conventional approaches to address fouling include the use of chemical cleaning agents, and backwashing. Chemical cleaning agents can effectively remove accumulated contaminants and / or foulants but often lead to membrane degradation over time and environmental concerns due to the disposal of harsh and toxic cleaning chemicals. A constant charge membrane is able to solve the issue of fouling in some extend but it is still challenging for all types of fouling species. Zwitterionic polymers have been also integrated in membranes for creating anti-fouling performance for fatty and hydrophobic compounds. However, most fouling species remains challenging in the industry because of the complexity arising from their properties in changing charge and complex integration with the surface of membranes. Thus, the end-users have to use tremendous amounts of cleaning agnents, water and time for recovering their membranes in close cleaning cycles. Overall, while these methods provide temporary or partial solutions to fouling, they are often limited by cost, environmental impact, and the need for frequent maintenance.

[0023] The clever use of the charge switchable polymeric additive results in advanced membranes with superior functional properties. They provide a solution to the persistent challenges of fouling and maintenance in conventional membrane technologies. A user can select a different charge designed membrane for their specific applications. This innovative approach results in membranes that are more effective and durable for applications in water treatment and protein separation, providing a balance between high permeability and superior separation performance.

[0024] Other advantages of the invention will be described further below.Charge Switchable Filtration Membrane, Polymeric Additive, Polymer Blend, and Kit

[0025] The charge switchable filtration membrane comprises a porous layer comprising a hydrophobic host polymer and a charge switchable polymeric additive, wherein the charge switchable polymeric additive is dispersed within the host polymer, and wherein the charge switchable polymeric additive is an amphiphilic block copolymer comprising a hydrophobic block and a hydrophilic block, wherein the hydrophilic block comprises repeat units bearing a positively ionizable weak base functional group and repeat units bearing a negatively ionizable weak acid functional group.

[0026] Herein, “dispersed” means that the molecules of the polymeric additive are distributed, or spread out, throughout a matrix of the hydrophobic host polymer, which forms a continuous phase.

[0027] As noted above, the present invention also relates to a polymer blend. Notably, this polymer blend can be used for manufacturing the membrane of the invention. The polymer blend comprises the hydrophobic host polymer and the charge switchable polymeric additive as defined above as well as optionally a pore-forming agent.

[0028] As noted above, the present invention also relates to a kit for manufacturing the membrane of the invention. The kit comprises the hydrophobic host polymer and the charge switchable polymeric additive as defined above as well as optionally a pore-forming agent. In embodiments, the kit further comprises instructions to manufacture and / or to use the membrane of the invention.

[0029] The pore-forming agent is used for manufacturing the membrane of the invention. It will be more defined in the next section. Some of the pore-forming agent may or may not remain in the membrane of the invention after manufacture. Thus, in embodiments, the charge switchable filtration membrane further comprises the pore-forming agent. In alternative embodiments, the charge switchable filtration membrane is free of the pore-forming agent.

[0030] Furthermore, the present invention also relates to a charge switchable polymeric additive for manufacturing the membrane of the invention. The charge switchable polymeric additive is as defined above i.e., it is an amphiphilic block copolymer comprising a hydrophobic block and a hydrophilic block, wherein the hydrophilic block comprises repeat units comprising a positively ionizable weak base functional group and repeat units comprising a negatively ionizable weak acid functional group.

[0031] All embodiments hereinbelow regarding the host polymer and the charge switchable polymeric additive relate to all the above aspects of the invention.

[0032] In embodiments, the membrane exhibits a finger-like structure. In the context of filtration membrane microstructure, such a finger-like structure is well-known and refers to a specific type of porous architecture often found in asymmetric membranes. These asymmetric membranes have a thin, dense top layer (skin, surface layer) supported by a more porous sublayer (foundation layer). The finger-like structures are part of this sublayer. These finger-like structures are elongated, finger-shaped voids or pores that extend from the dense top layer into the porous sublayer. They are formed during the phase separation process when the polymer solution used for manufacturing the membrane undergoes liquid-liquid de-mixing. The formation of finger-like structures involves two main steps. First, pore initiation, in which initial pores form at the interface between the polymer solution and the nonsolvent. The second step is pore growth during which the initial pores grow into elongated, finger-like shapes as the polymer solution continues to phaseseparate. Overall, the surface layer sets faster and creates a thin layer with smaller pores while the bottom layer has more time to form, which gives enough time to the polymer chain to self-assemble and create the finger-like structure. The finger-like structure helps in providing mechanical support to the membrane while maintaining high permeability.

[0033] More specifically, the membrane can exhibit a finger-like structure comprising a surface layer on top of a foundation layer, wherein the surface layer is thinner than the foundation layer, wherein the surface layer and the foundation layer each comprises pores, and wherein the pores of the surface layer are smaller than the pores of thefoundation layer. In embodiments, the surface layer represents about 1% to 20%, preferably about 2% to 10%, and more preferably about 3% to about 7%, of the total thickness of the membrane. In embodiments, the surface layer has an average thickness of about 2 pm to about 10 pm, preferably about 3 pm to about 7 pm. In embodiments, the foundation layer has an average thickness of about 50 pm to about 150 pm, preferably about 70 pm to about 100 pm. In embodiments, the pores of the foundation layer are elongated and arranged approximately perpendicularly to the surface of the membrane. In embodiments, the pores of the foundation layer have an average length of at least 20 pm. An example of such microstructure is shown in Figure 10a, right column. In embodiments, the surface layer is enriched in amphiphilic block copolymer. This means that there is a greater concentration of the amphiphilic block copolymer in the surface layer than in the foundation layer. As noted above, this asymmetric microstructure results naturally from the casting method used to create the membrane, which will be described below.

[0034] Typically, the membrane of the invention is supported on a porous support to increase the mechanical strength of the membrane. The porous support can be any porous support typically used for filtration membrane in the art. In embodiments, the porous support is a non-woven mat, for example of polyethylene, polypropylene, or polyethylene terephthalate. The porous support in not particularly limited in terms of its thickness. A person of skill in the art would not to select a proper thickness based on the limitation of their given application. The porous support can have an average thickness of about 0.06 mm to about 1 mm, preferably about 0.2mm, such as about 0.18 mm.

[0035] Herein, hydrophobic mean a material repels water. For example, it can be characterized by a high contact angle when a water droplet is placed on its surface. Conversely, Herein, hydrophilic mean a material attracts water. For example, it can be characterized by a low contact angle when a water droplet is placed on its surface. Notably these contact angles can be measured using the well-known sessile drop technique in which a drop of deionized water is placed on a surface and photographed immediately. The contact angle is measured between the tangent to the droplet's surface and the surface of the material and is determined using the photograph. Using this technique, a hydrophobic material exhibits a contact angle greater than 90 degrees while a hydrophilic material exhibits a contact angle smaller than 90 degrees. It should be understood that in the context of the invention, when discussing e.g. a hydrophobic block of an amphiphilic block polymer, the contact angle for the hydrophobic block should be made using a polymer comprising only the hydrophobic block.

[0036] In embodiments, the hydrophobic host polymer is any such polymer conventionally used for filtration membranes. Non-limiting examples of hydrophobic host polymers include polyether sulfone (PES), polystyrene (PS), polyvinylidene difluoride (PVDF), or polyacrylonitrile (PAN). In preferred embodiments, the hydrophobic host polymer is PES.

[0037] As noted above, the amphiphilic block copolymer comprises a hydrophobic block and a hydrophilic block. Thus, it can be illustrated as — [A]-b-[B]-, wherein [A] represents the hydrophobic block made of hydrophobic repeat units, [B] represents the hydrophilic block made of repeat units bearing negatively ionizable weak acid functional groups and positively ionizable weak base functional groups, and b indicates that this is a block copolymer. Furthermore, as noted above, the hydrophilic block comprises repeat units bearing a positively ionizable weak base functional group and repeat units bearing a negatively ionizable weak acid functional group. In embodiments, the repeat units bearinga positively ionizable weak base functional group and the repeat units bearing a negatively ionizable weak acid functional group are the same, that is the hydrophilic block comprises repeat units bearing both a positively ionizable weak base functional group and a negatively ionizable weak acid functional group. In alternative preferred embodiments, the hydrophilic block comprises a copolymer comprising repeat units bearing a positively ionizable weak base functional group and repeat units bearing a negatively ionizable weak acid functional group, wherein the repeat units bearing a positively ionizable weak base functional group and the repeat units bearing a negatively ionizable weak acid functional group are different from one another. Thus, the amphiphilic block copolymer can be illustrated -[A]-b-[(C)-(D)]— , preferably -[A]-b-[(C)-ran-(D)]-, wherein [A] represents the hydrophobic block, (C) represents the repeat unit bearing positively ionizable weak base functional group, (D) represents repeat units bearing a negatively ionizable weak acid functional group, b indicates that this is a block copolymer, ran indicates that this is block is made of a random copolymer. Herein, “statistically arranged” or “random” means that the repeat units are arranged in a sequence dictated by the reaction kinetics of the monomers. Both terms are commonly used interchangeably in the literature.

[0038] In embodiments, the hydrophobic block of the amphiphilic block copolymer has a molecular weight (Mw) between about 5000 Da and about 20000 Da.

[0039] In embodiments, the hydrophilic block of the amphiphilic block copolymer has a molecular weight (Mw) between about 5000 Da and about 20000 Da.

[0040] The hydrophobic block of the amphiphilic block copolymer acts as an anchor to link with the hydrophobic host polymer. As such, a variety of hydrophobic block are envisioned. Of course, the exact nature of the hydrophobic block will be selected in view of the exact nature of the host polymer. In embodiments, the hydrophobic block comprises polyacrylonitrile (PAN), polyether sulfone (PES), polypropylene (PP), polysulfide (PS), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or cellulose acetate, preferably PES or PVDF, and more preferably PES.

[0041] The hydrophobic block of the amphiphilic block copolymer acts confers the charge switching ability.

[0042] Herein, a “weak acid” is any acid with 3 < pKa< 9. Herein, a negatively ionizable weak acid functional group is a functional group that can donate a hydrogen atom at high pH to become ionized, i.e. negatively charged in that case. In embodiments, the negatively ionizable weak acid functional groups are carboxylic acids, sulfonic acids, and / or phosphoric acids. In embodiments, the repeat unit bearing negatively ionizable weak acid functional group are repeat unit of poly (acrylic acid), poly(ethyl acrylic acid), a polymethacrylic acid, poly(vinyl sulfate) PVS, poly (styrene sulfonate), polyphosphoric acid, or poly(vinylphosphonic acid), preferably polymethacrylic acid.

[0043] polymethacrylic acid.

[0044] Herein, a “weak base” is any base with a 3 < pKa< 11. Herein, a positively ionizable weak base functional group is a functional group that can accept a hydrogen atom at low pH to become ionized, i.e. positively charged in that case. Of note, a quaternary ammonium is permanently charged (cationic) regardless of pH and is thus not encompassed in “positively ionizable weak base functional groups”. In embodiments, the positively ionizable weak base functional groups are amidines, guanidines, amines (primary, secondary and / or ternary), imidazoles, and / orpyridines. In embodiments, the repeat units bearing positively ionizable weak base functional groups are repeat units of• poly(N-methyltetrahydropyrimidine) (PMTHP),• poly(p-azidomethylstyrene-co-styrene),• poly[2-methyl-1-(4-vinylbenzyl)-1 ,4,5,6-tetrahydropyrimidine],• poly(dimethyl acrylamide-co-(N-amidino)ethyl acrylamide) (P(DMA-co-NAEAA)), and• polyethylene oxide)-b-poly((N-amidino)dodecyl acrylamide).• poly[(2-dimethylamino) ethyl methacrylate] (PDMAEMA),• poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA), and• poly(3-N',N'-dimethylaminopropyl acrylamide) (PDMAPMA), or• poly(L-arginine methyl ester acrylamide-co-N-cyclopropyl acrylamide) (poly(AME-co-CPAM).

[0045] In preferred embodiments, the repeat units bearing positively ionizable weak base functional groups are repeat units of PDMAEMA, PDMAPMA or PMTHP.

[0046] In embodiments, the charge switchable polymeric additive is of formula:ranHOwherein R represents -NH(CH2)3N(CH3)2or 0(C H2)2N(C H3)2, preferably -NH(CH2)3N(CH3)2.

[0047] In embodiments, the charge switchable polymeric additive is present at a concentration between about 1 and about 15 wt.%, preferably between about 4 and about 8 wt.%, based on the weight of the hydrophobic host polymer.

[0048] It is an important advantage of the invention that the isoelectric point of the membrane / polymeric additive can be tailored simply by modifying the ratio of repeat units bearing positively ionizable weak base functional groups and repeat units bearing negatively ionizable weak acid functional groups. The isoelectric point is the pH at which the membrane / polymeric additive has an overall neutral charge; their negative charges being equal to their positive charges. This behavior can be attributed to the differing pKavalues of the negatively ionizable weak acid and positively ionizable weak base functional groups. The positively ionizable weak base will remain protonated and positively charged at pH < pKaof the positively ionizable weak base, and gradually deprotonate as the pH increases. In contrast, the negatively ionizable weak acid has lower pKaresulting in it being mostly protonated and neutral at low pH, anddeprotonating to become negatively charged at pH > pKaof the negatively ionizable weak acid.

[0049] In embodiments, the isoelectric point of the membrane is between about 3 and about 10.

[0050] This switchable charge characteristic allows the membrane to effectively repel and release adsorbed foulants during the cleaning cycles. When the membrane is exposed to acidic solutions, the positively charged positively ionizable weak base repels cationic foulants, while in basic conditions, the negatively charged negatively ionizable weak acid repels anionic contaminants and / or foulants. This alternating charge mechanism enhances the membrane's self-cleaning capabilities and extends its operational lifespan, ensuring sustained performance and reduced maintenance requirements.

[0051] It should also be noted that, in condition in which the membrane / polymeric additive exhibit a greater change (either positive or negative), the hydrophilicity of the membrane / polymeric additive is increased. Indeed, the membrane exhibits smaller contact angles at pH that are below or above its isoelectric point, while it exhibits higher contact angles at a pH corresponding to its isoelectric point. This highlight the reversible, pH-triggered hydrophilic-hydrophobic transition of the membranes, with low and high pH enhancing hydrophilicity, which is beneficial for high water permeability and reduced fouling.

[0052] By modifying the ratio of repeat units bearing positively ionizable weak base functional groups and repeat units bearing negatively ionizable weak acid functional groups, the isoelectric point can be tailored for a specific application. For example, in the dairy industry, proteins such as casein have an isoelectric point around pH 4.5 and operational conditions are typically around pH 6. In such conditions, using a membrane with an isoelectric point around pH 4.5, leads to the deprotonation of the negatively ionizable weak acid functional groups, increasing surface energy, decreasing protein adsorption due to electrostatic repulsion and enhanced hydrophilicity. Furthermore, the membrane's hydrophilic nature at high pH helps minimize protein adsorption, reducing fouling and maintaining higher membrane performance and longevity. Thus, in embodiments, a membrane with an isolectric point that is about the isoelectric point of a contaminant and / or foulant to be removed from a feed using the membrane, is used.

[0053] In embodiments, the isoelectric point of the membrane / polymeric additive is between about 3 and about 10.

[0054] In embodiments, the membrane of the invention is a microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), or reverse osmosis (RO) membrane.

[0055] In embodiments, the membrane of the invention is in the form of a flat sheet or a hollow fiber.

[0056] The present invention also relates to a method of tuning the isoelectric point of the membrane of the invention by adjusting the ratio of repeat units bearing positively ionizable weak base functional groups and repeat units bearing negatively ionizable weak acid functional groups in the charge switchable polymeric additive.Method of manufacturing

[0057] There is also provided a method of manufacturing a filtration membrane, preferably a filtration membrane as described above. The method comprises:a) providing a casting solution by dissolving a hydrophobic host polymer, a charge switchable polymeric additive, and a pore-forming agent in a solvent,b) casting the casting solution onto a substrate,c) submerging the substrate bearing the casting solution in a coagulation bath containing a non-solvent, thereby causing precipitation of the hydrophobic host polymer, the charge switchable polymeric additive, and the poreforming agent to form the membrane.

[0058] The method of the invention relies on phase inversion via immersion precipitation. It is a widely used membrane preparation method. The casting solution is cast on a substrate and then the substrate bearing the casting solution is submerged in the coagulation bath. Due to the solvent and non-solvent exchange, precipitation takes place.

[0059] It is an advantage of the invention that the membrane can be manufactured simply by adding the charge switchable polymeric additive into a solution for casting a membrane such as that already in industrial use. This is compatibility makes it easy and cheap to manufacture the membrane of the invention.

[0060] In the method of the invention, the surface layer of the membrane gets enriched in charge switchable polymeric additive. Indeed, when the substrate bearing the casting solution is submerged in the coagulation bath, the hydrophilic blocks of the charge switchable polymeric additive spontaneously migrate to the polymer / water interface, where they form a hydrophilic, fouling-resistant layer on the membrane surface and internal pores. This happens because of interfacial energy and without the copolymers leaching out of the membrane matrix. Compared to surface modification techniques, this surface segregation method is simpler and more convenient for large-scale membrane production, as it allows for the adjustment of membrane structures and performance in a single step. This is thus a simple and effective method to enhance the hydrophilicity of membrane surfaces and is easily integrated with industrial processes.

[0061] Herein, a “non-solvent” is a liquid in which the hydrophobic host polymer, the charge switchable polymeric additive, and the pore-forming agent are not soluble. Conversely, a “solvent” is a liquid in which the hydrophobic host polymer, the charge switchable polymeric additive, and the pore-forming agent are soluble.

[0062] In embodiments, the solvent is N-methyl-2-pyrrolidone (NMP), DMAC, DMF, CHCI3, or a mixture thereof.

[0063] In embodiments, the non-solvent is water, an alcohol (such as ethanol, methanol, isopropanol), or a mixture thereof.

[0064] When using water as the non-solvent, the pH has an impact of the level of charge switchable polymeric additive enrichment in the surface layer. There tends to be more polymeric additive in the surface layer at more basic pHs, such as a pH of 11.5, than at basic or neutral pHs. There also tends to be more polymeric additive in the surface layer at more acidic pHs, such as a pH of 2.5, than at neutral pHs, such as at a pH of 7. Thus, in embodiments, the water is at a basic or acidic pH, preferably at a basic pH. Furthermore, the temperature of the water has an impact on pore size. Decreasing the temperature of coagulation bath leads to smaller pore sizes. In embodiments, the coagulation bath contains water as the non-solvent, and the water is at a temperature between about 8°C and about 12°C.

[0065] In embodiments, the pore-forming agent is any such agent conventionally used for filtration membranes. Non-limiting examples of pore-forming agent include polyethylene glycol (PEG), and polyvinylpyrrolidone (PVP), both of which can be used in various molecular weights, as well as inorganic additives such as LiCI and TiC>2, and surfactants such as Tween®-80.

[0066] In embodiments, the pore-forming agent is present at a concentration between about 0.5 and about 15 wt.%, preferably between about 2 and about 8 wt.%, based on the weight of the hydrophobic host polymer.

[0067] In embodiments, the method further comprises the step to tuning the isoelectric point of the membrane. This can be done by modifying the ratio of repeat units bearing positively ionizable weak base functional groups and repeat units bearing negatively ionizable weak acid functional groups in the charge switchable polymeric additive. As noted above, this allows tailoring the membrane for a specific application. In embodiments, a membrane with an isolectric point that is about the isoelectric point of a contaminant and / or foulant to be removed from a feed using the membrane, is manufactured.

[0068] In embodiments, the method further comprises the step to tuning porosity of the membrane. This can be done by modifying the viscosity of the casting solution. The viscosity of the casting solution can be modified by varying the concentration of its various components, preferably the hydrophobic host polymer. Casting solutions with higher hydrophobic host polymer concentrations exhibit increased viscosity. This higher viscosity results in delayed demixing within the coagulation bath, thereby promoting the favored formation of a porous substructure with a relatively small pore size and thick top layer.

[0069] In embodiments, the hydrophobic host polymer is present in the casting solution at a concentration ranging from about 5% to about 30% by weight, based on the total weight the polymer solution.

[0070] In embodiments, the charge switchable polymeric additive is present in the casting solution at a concentration ranging from about 2% to about 12% by weight, based on the total weight the polymer solution.Method of use

[0071] There is also provided a method of filtering a feed using the membrane of the invention. This method comprises the step of contacting the feed with one side of the membrane and allowing materials to be separated from the feed to pass through the membrane as a permeate.

[0072] There is also provided the use of the membrane of the invention for filtration, i.e. for filtering a feed.

[0073] In embodiments, said use and method are in a water purification application. In embodiments, said use and method are in gas separation application. In embodiments, said use and method are in a biomedical filtration application. In embodiments, said use and method are for the separation of proteins or other biomolecules from a feed.

[0074] As noted above, a membrane with a specific isoelectric point are advantageously used for a specific application. In embodiments, a membrane with an isolectric point that is about the isoelectric point of a contaminant and / or foulant to be removed from a feed using the membrane, is used / selected for use. Thus, in embodiments, themethod / use further comprises selecting, as the charge switchable filtration membrane, a membrane that has an isoelectric point that is about the isoelectric point of a contaminant and / or foulant to be removed from the feed.

[0075] In embodiments, the method / use further comprises tuning the surface charge of the membrane by modifying the pH of the feed.

[0076] In embodiments, the method / use further comprises tuning the hydrophilicity of the membrane by modifying the pH of the feed.

[0077] In embodiments, the pH is modified by introducing an acid, a base, or C02or N2gas into the feed.

[0078] In embodiments, the method / use further comprises using a control mechanism to adjust the pH and thereby tune the surface charge of the membrane in real-time.

[0079] In embodiments, wherein the filtration is in continuous operation with real-time monitoring of the surface charge of the membrane.

[0080] In embodiments, the method / use further comprises cleaning the membrane. This cleaning is typically carried out after the membrane has been used for filtrating a feed. Indeed, in use, membranes may become clogged, which undesirable reduce flow through the membrane. The cleaning allows unclogging the membrane and restoring the membrane performances. Thus, in embodiments, the method / use further comprises, after said cleaning, reusing the clean membrane to filter a feed.

[0081] In embodiments, the cleaning comprises i) creating or increasing a negative surface charge on the membrane by contacting the membrane liquid with a pH higher than the isoelectric point of the membrane. In embodiments, the cleaning comprises ii) creating or increasing a positive surface charge on the membrane by contacting the membrane liquid with a pH lower than the isoelectric point of the membrane.

[0082] In embodiments, the cleaning comprises Hi) increasing the hydrophilicity of the membrane by contacting the membrane liquid with a pH at least one pH point higher than the isoelectric point of the membrane. In embodiments, the cleaning comprises iv) decreasing the hydrophilicity of the membrane by contacting the membrane liquid with a pH approximately corresponding to the isoelectric point of the membrane.

[0083] In embodiments, the cleaning further comprises reversing liquid flow across the membrane. This allows matter clogging the membrane to flow back out of the membrane, thus cleaning the membrane.

[0084] In embodiments, the cleaning is carried out in situ at the location where the membrane has been used or will be used to filter the feed.

[0085] In embodiments, two or more - or preferably all - i) to iv are carried out consecutively (in any order).Definitions

[0086] The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unlessotherwise indicated herein or clearly contradicted by context.

[0087] The terms "comprising", "having", "including", and "containing" are to be construed as open-ended terms (i.e., meaning "including, but not limited to") unless otherwise noted. In contrast, the phrase “consisting of” excludes any unspecified element, step, ingredient, or the like. The phrase “consisting essentially of” limits the scope to the specified materials or steps and those that do not materially affect the basic and novel characteristic(s) of the invention.

[0088] Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All subsets of values within the ranges are also incorporated into the specification as if they were individually recited herein.

[0089] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.

[0090] The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed.

[0091] No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0092] Herein, the term "about" has its ordinary meaning. In embodiments, it may mean plus or minus 10% or plus or minus 5% of the numerical value qualified.

[0093] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0094] Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of specific embodiments thereof, given by way of example only with reference to the accompanying drawings.DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0095] The present invention is illustrated in further details by the following non-limiting examples.Example 1

[0096] An on-demand surface charge switchable poly (ether sulfone) (PES) composite membrane blended with an amphiphilic block copolymer (CoP) additive was fabricated using the non-solvent induced phase separation (NIPS) method. The pH-responsive amphiphilic copolymer features a hydrophobic polystyrene (PS) block for anchoring and a hydrophilic poly (N, N-dimethylamino-2-ethylmethacrylate-ran-polymethacrylic acid) (PDMAEMA-ran-PMAAc) block for charge modulation. Among a series of copolymers, PS-b-PDMAEMAoa-ran-PMAAco? was found to have an isoelectric point around pH 4.5, which makes it particularly suitable for use with dairy proteins. Several PES / PS-b-PDMAEMA-ran-PMAAc ultrafiltration (UF) membranes were prepared by incorporating various concentrations of PES and polyvinylpyrrolidone (PVP, 40K) as pore-forming agents. The effects of composition on membrane structure, permeability, and performance were systematically investigated to determine the optimum composition for dairy applications. The membranes with 23wt% PES, 5wt% CoP, and 5wt% PVP (PES23%-CoP-PVP5%) cast at two speeds of 25 and 50 mm / s, being highly performant in terms of pure water permeability and pore size, were further characterized to determine the contact angle, surface zeta potential, membrane morphology, PEG separation, and protein rejection. The results indicate that the PDMAEMA-ran-PMAAc chains were segregated towards the surface and the membranes were endowed with a negative and positive charge with pH variation. It was also found that the PES23%-CoP-PVP5% membrane cast at a speed of 50 mm / s maintains high protein rejection rates (94.6% for raw protein and 98.6% for whey protein) but shows a reduced protein flux (24.5 L m2bar“1h“1) compared to PES23%-CoP-PVP5% cast at a speed of 25 mm / s speed, while the DI water flux remains high (88.3 L m2bar“1h“1). The results demonstrate that these charge-switchable ultrafiltration membranes have significant potential for antifouling and separation applications.Experimental MethodMaterials

[0097] PES (6020 P, Mw: 72000, BASF, Germany) was dried thoroughly before use. Polyvinylpyrrolidone (PVP, Mw: 40000, Aldrich) was used as a pore-forming agent in the casting solution. Styrene (99%, Fisher Scientific, Canada), tert-butyl methacrylate (tBuMA, 98%, Fisher Scientific, Canada), and 2-(dimethylamino) ethyl methacrylate (DMAEMA, 98%, Aldrich) were passed through a column of basic aluminum oxide before use. Azobis(isobutyronitrile) (Al BN, Aldrich) was recrystallized from methanol. Trifluoroacetic acid (TFA, 99%, Aldrich) was employed without further purification. S-(Thiobenzoyl) thioglycolic acid, a chain transfer agent (CTA, 99%, Aldrich), was used as received. Toluene (Fisher Scientific, Canada) was distilled before use. All other solvents were obtained at the highest purity available and used as received.Synthesis of PS-b-PDMAEMA-ran-PtBMA Diblock Copolymer (CoP) through Two-Step Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization

[0098] The two-step synthetic approach for the preparation of PS-b-PDMAEMA-ran-PtBMA diblock copolymer is presented in Scheme 1. Initially, styrene monomer (700 g, 6.721 mol), CTA (10.3 g, 0.0485 mol), and AIBN (1.57 g, 0.0096 mol) as an initiator were dissolved in toluene (100 mL) in a reaction vessel. The mixture was degassed through three freeze-evacuate-thaw cycles and then placed in a thermostat oil bath at 100 °C to initiate the reaction. The reaction was carried out under nitrogen for 24 hours. Purification was achieved by precipitating the resultant polystyrene into methanol, filtering it, and then vacuum drying it at 60 °C for one day to obtain the PS macro-CTA (product: 262 g).

[0099] In the second step in Scheme 1, as an example, PS macro-CTA (156 g) was redispersed in 100 mL of toluene along with AIBN (0.36 g, 0.0022 mol), tBuMA (205 g, 1.44 mol) and DMAEMA (83.82 g, 0.533 mol). This newmixture was treated with three freeze-evacuate-thaw cycles and then heated to 100°C for 24 hours. Following this, the resultant copolymer PS-b-PDMAEMA-ran-PtBMA was purified using n-hexane, precipitated, collected, and vacuum-dried at 60 °C for one day (product: 265 g). 1H NMR analysis of the copolymer composition revealed the degrees of polymerization for the obtained block copolymer.Preparation of PS-b-PDMAEMA-ran-PMAAc Diblock Copolymer through Hydrolysis of PS-b- PDMAEMA-ran-PtBMA

[0100] Subsequently, as shown in Scheme 1, the tertbutyl groups of the PtBMA in the block copolymers were hydrolyzed with TFA to yield PS-b-PDMAEMA-ran-PMAAc diblock copolymers. The hydrolysis of the PS-b-PDMAEMA-ran-PtBMA (265 g) was conducted in the presence of TFA (300 mL) in dichloromethane (DCM) (1600 mL) overnight, then the final product was collected by precipitating the reaction mixture in n-hexane, followed by vacuum drying at 60 °C for one day.Scheme 1. Synthesis of the amphiphilic diblock copolymer additiveMembrane Preparation through Phase Inversion Method

[0101] As schematically illustrated in Figure 1, to use the phase inversion method, a membrane casting solution is first prepared, comprising N-methyl-2-pyrrolidone (NMP) as the solvent, PES as the membrane polymer, PVP as the poreforming agent, and PS-b-PDMAEMA-ran-PMAAc as the pH-responsive polymer additive. Their relative amounts can be changed to vary the total concentration of the polymers and the composition of the membrane. After completely dissolving all components, the transparent solution is cast on a glass plate to achieve a uniform thickness of 200 micrometers. The membrane solution is then immediately submerged in a coagulation bath. The bath contains deionized (DI) water, adjusted to a pH of 11. The temperature of the bath is meticulously maintained at 12°C to optimize the phase inversion process. This environment induces the transformation of the casting solution from a liquid to a solid state, forming a porous membrane structure. The membranes were characterized using various techniques outlined below.Study of Adsorption and Desorption Behavior of the pH-Responsive Membrane

[0102] To investigate the reversible adsorption and desorption of dyes, two rectangular samples were excised from each pH-responsive membrane, measuring 10 mm in width and 10.5 mm in length. One membrane was immersed in 1 mL of Toluidine Blue O (TBO) dye solution, with a dye concentration of 1 mM at a pH of 10, while the other membrane was placed in 1 mL of Acid Orange II (AO II) solution, maintaining the same concentration but at a pH of 2. Both solutions were kept at a constant temperature of 25°C and were vortexed to facilitate adsorption using a multi-platform shaker (NA Cat. No. 88861021) set to 250 rpm for a duration of 6 hours. After that, the absorbance of the dye solutions was measured. The dye concentrations were quantified based on a pre-established standard curve. Following adsorption, the membrane samples were carefully removed from the dye solutions and rinsed with 0.1 mM NaOH and HCI solutions for TBO and OA II tests, respectively, to remove the non-complexed dyes. Desorption of the TBO dye from the membrane was performed using a 1 :1 solution by volume of deionized water and acetic acid. In contrast, the AO Il-stained samples were desorbed using deionized water adjusted to a pH of 10. Both desorption processes were conducted at 25°C for 15 minutes of vortexing. The absorbance of the dye solutions post-desorption was recorded, and the concentration data were recalibrated using the same calibration curve. The dye adsorption density (pimol cm-2) was calculated based on the surface concentration of grafted MAAc and DMAEMA polymers (represented by the COOH and (-N(CH3)2) groups, respectively, on the PES surface). This was determined from the optical density of the desorbed dye at 633 nm. The calculation assumed a 1:1 complexation between TBO and the carboxyl groups of the grafted MAAc polymer or between OA II and the tertiary amine groups of the grafted PDMAEMA polymer. To ensure accuracy, the above steps were repeated multiple times, allowing for a robust data set.Measurement of Membrane Porosity

[0103] The porosity of the prepared membranes was determined following the method described by Zhang et al38. A circular membrane sample with an area of 15 cm2was immersed in isopropanol for 24 hours under continuous stirring. After the immersion period, any excess isopropanol on the membrane surface was carefully removed. The wet membrane was then weighed and subsequently dried in a vacuum oven at 40°C until a constant weight was achieved. The porosity of the membrane was calculated using Equation (1):Ww- Wd£ = - A x I x pWhere Wwand Wd are the weight of the wet membrane and the dry membrane, respectively; A and I denote the area (cm2) and thickness (cm) of the wet membrane, respectively; and p is the density of isopropanol (g / cm3).Contact Angie Measurement

[0104] The sessile drop technique was used to measure the water contact angle of the membrane. A drop of deionized (DI) water was carefully placed on a membrane and photographed immediately. All reported results represent the average of at least 10 measured angles. The membrane was sectioned into three samples, each sample was immersed for two hours in DI water with adjusted pH values, one in pH 2, one in 4.5, and one in pH 10 using NaOH and HNO3 Then, each sample was promptly removed from its solution, attached to a glass slide, with watergently removed from its surface, and finally received the droplet for the contact angle analysis.

[0105] In addition, to calculate the surface energy using the Fowkes model, contact angle measurements with diiodomethane were performed. A drop of diiodomethane was carefully placed on the membrane and photographed immediately. Similar to the water contact angle measurements, the reported results represent the average of at least 10 measured angles. These measurements were carried out for each sample previously immersed in DI water with adjusted pH values (pH 2, pH 4.5, and pH 10).Using both contact angle measurements for water and diiodomethane, the surface energy was calculated using the Fowkes model, represented by Equation (2):Cos 0 = -1 + Z^y!^, x + 2^yspvxWhere:• 0 is the contact angle.• y , is the dispersive component of the surface energy of the solid.• YH is the dispersive component of the surface tension of the liquid.• ypv'sthe polar component of the surface energy of the solid.• ypvis the polar component of the surface tension of the liquid.• yivis the total surface tension of the liquid.The results are shown in Table 1.

[0106] Table 1. Surface tension and energy components of water and diiodomethane39Liquid YZr(mJV / m) Y^(mN / m) Viv(mN / m)Diiodomethane 50.8 50.8 0Eau 72.8 21.8 51.0Zeta Potential Measurement

[0107] Zeta potential measurements of polymers were conducted using a Zetasizer-Nano Series zeta potential analyzer (Malvern Instruments Ltd., UK, ±0.01 mV). Initially, an aqueous polymer solution (1 mg / mL) was prepared, and the pH was meticulously adjusted using HNO3 and NaOH to achieve solutions with pH of 2, 4, 6, 8, 10, and 11. Each polymer solution's zeta potential was then measured. To enhance the accuracy of the data, each measurement was repeated three times. For the measurements, 1.5 mL of each polymer solution was transferred into a dip cell and inserted into the zeta potential analyzer. The measurements were conducted at 25°C, with each sample being preequilibrated at this temperature for 2 minutes to ensure thermal stability before analysis.

[0108] The surface zeta potential of the membranes was performed using a Zeta potential electrokinetic analyzer (Anton Paar GmbH SurPASS, Austria). Two membrane pieces with a size of 20 mm x 10 mm were mounted in an adjustable gap cell using double-sided adhesive tape and filled with 0.001 mol / L KCI solution at room temperature. Thegap height was set to 100±20 pm and the pH of the bulk solution was adjusted automatically using the dosing unit of SurPASS 3 and 0.05 mol / L HCI and 0.05 mol / L KOH, respectively. At each pH, the zeta potential was determined in triplicate. The zeta potentials ( ) were calculated using the Helmholtz-Smoluchowski Equation (3):where U is the streaming potential, p is the pressure across the membrane, q is the viscosity of the electrolyte solution, £ is the dielectric constant of the electrolyte, £o is the vacuum permittivity and KB is the electrolyte conductivity. Pure Water Flux and Determination of MWCO Using PEGs

[0109] Membrane pure water flux was determined using a Solvent-resistant Stirred Cell (Cat. No. XFUF04701) illustrated in Figure 2. Deionized water was passed through a circular membrane sample (area = 15cm2), and the sample was preconditioned by passing DI water for 20 minutes until reaching a stable flux. Then, by passing 100 mL of DI water through the membrane, the pure water flux (J), which is defined as the volume of water that passes through the unit area of the membrane per unit of time, was calculated using Equation (4):Where AV is the volume of permeate (100 mL), A is the membrane active area and At is the measured filtration time.

[0110] Molecular weight cutoff (MWCO) is a key parameter that characterizes the pore size and rejection capabilities of a membrane. It is defined as the molecular weight at which 90% of a given solute is retained by the membrane. In this study, polyethylene glycols (PEGs) with molecular weights of 10,000 Da and 20,000 Da were utilized to determine the MWCO of the membranes. PEG aqueous solutions were prepared at a concentration of 2000 ppm and permeated through a circular membrane sample (15 cm2filtration area) using the same solvent-resistant stirred cell. The cell was stirred at 250 rpm using a magnetic stirrer and the applied pressure was 20 psi nitrogen gas. All membranes were preconditioned by passing deionized water at the applied pressure for 20 minutes until a steady state flux was guaranteed. After reaching a steady state, the PEG solution was put into the feed container and 15 mL of permeate was collected. The concentration of permeate was analyzed using a differential refractometer (Brookhaven BI-DNDC differential refractometer, sensitivity 2.5x109, double flow microcell, variable temperature from 20 to 80°C, and wavelength of 532 nm).Protein Filtration and Water Flux Recovery

[0111] We employed a custom-built filtration system to evaluate the protein filtration performance of our pH-responsive membranes, comparing them against neat PES membranes. The setup, depicted in the Process Flow Diagram (PFD) in Figure 3, features a SAER electro pump, a custom-made cooling tower, and a feed tank capable of holding up to 20 kg of solution. It includes pressure and temperature regulators, along with 10 membrane holders, each measuring 16.5 cm x 20 cm (shown in Figure 4). To ensure consistent results, three samples from each type of membrane were tested simultaneously, using nine of the ten membrane holders.

[0112] A 2000 ppm milk protein solution circulated within the system, with the temperature maintained at50°C viathe cooling tower, and the pressure set at 50 psi. The permeate was collected in graduated cylinders. The filtration experiment was conducted over a total duration of 100 hours. Every 8 hours, the system was drained (drain pH was 5.4 ± 0.2) and subjected to two wash cycles with deionized (DI) water: once under acidic conditions (pH 2) for 15 minutes, and once under basic conditions (pH 10, including DI water, bleach, etc.). This was followed by two additional rinses with DI water.

[0113] During the 8-hour filtration intervals, a camera captured images of the permeate in the graduated cylinders every 3 minutes to monitor water flux behavior. These images were then analyzed to determine the time intervals between each 100 mL of permeate, correlating these intervals to a pre-established flux rate.Analyse Using Scanning Electron Microscopy (SEM)

[0114] Scanning Electron Microscopy (SEM) was utilized to capture high-resolution images of membrane samples. The SEM imaging was performed using a Thermo Scientific Apreo 2 SEM. The samples were prepared by sputtercoating with a gold-palladium (Au-Pd) alloy to enhance electron conductivity and improve image quality.Result and DiscussionSynthesis of CoP: PS-b-PDMAEMA-ran-PMAAc

[0115] Figure 5 shows the IR spectra of PS, PS-b-PDMAEMAos-ran-PtBMAo?, and PS-b-PDMAEMAos-ran-PMAACO.7. Knowing that the peaks at 1365 and 1393 cm-1correspond to CH3 bending in theC-fCHsJs group of PtBuMA and that the peaks at 2770 and 2820 cm-1are assigned to CH3 stretching in the N-CH3 group of PDMAEMA, the spectra indicate the linking of the tBMA and DMAEMA random copolymer block onto PS, i.e., the successful synthesis of the PS-b-PDMAEMA-ran-PtBMAodiblock copolymer. After hydrolysis, the characteristic peak at 1720 cm1attributed to the stretching vibration of the carbonyl (C=O) group in tBMA, shifts towards the lower wavenumber at 1691 cm1representing C=O in a protonated carboxylic acid and the broad peak in the range of 2500-3800 cm1appears, which belongs to the characteristic adsorption of the hydroxyl group in carboxylic acid. These results indicate the transformation of PS-b-PDMAEMA03-ran-PtBMA07to PS-b-PDMAEMAos-ran-PMAAco ? after the hydrolysis reaction.

[0116] PS, PS-b-PDMAEMAo3-ran-PtBMAo7, and PS-b-PDMAEMAos-ran-PMAAco? were also confirmed by1H NMR and the spectra are shown in Figure 6. Compared to the PS-b-PDMAEMAos-ran-PtBMAovspectrum, the proton adsorption peak at 1.4 ppm that was assigned to the proton on tert-butyl group disappears in the PS-b-PDMAEMAo 3-ran-PMAAco.7 curve, which indicates that at least 95% of the tBuMA repeated units are hydrolyzed. The peak at 2.35 ppm is assigned to the CH3 of the tertiary amine in PDMAEMA. Furthermore, the chemical composition of the PS-b-PDMAEMA-ran-PtBuMAcan be calculated from the ratio between the area of the CH3 peak at 1.44 ppm for PtBuMA, and the CH3 peak at 2.35 ppm for PDMAEMA.

[0117] The average molecular weights (Mn, Mw) and polydispersity index (PDI) of PS, PS-b-PDMAEMAos-ran-PtBMAo ? were measured byGPC in Chloroform (Table 2). After hydrolysis, PS-b-PDMAEMAo 3-ran-PMAAco .7 presents challenges in obtaining accurate GPC measurements due to its amphiphilic structure consisting of one hydrophobic and one fully hydrophilic block. This structure can lead to non-ideal interactions with the GPC column and solventsystem, making separation difficult and resulting in inaccurate molecular weight distribution.

[0118] Table 2. Molecular Weights of PS and PS-b-PDMAEMAoa-ran-PtBMAco?.Polymer code M„^,pcaMw, GPC PDI PS 9031 10249 1.135PS-b-PDMAEMA0 rran-PtBMA0 731158 42017 1.349aNumber-averaged molecular weights from GPC measurements are calibrated on mono-disperse polystyrene standards.

[0119] All the above characterizations give strong evidence for the successful grafting of tBMA and DMAEMA onto Ps backbones with only a two-step process.Zeta potential of Ps-b-PDMAEMA-ran-PMAAc

[0120] The pH-dependent zeta potential of the synthesized PS-b-PDMAEMA-ran-PMAA was measured across a pH range from 2 to 11 for the copolymers with different molar ratios of PDMAEMA and PMAA. Figure 7 shows the results for three diblock copolymers: PS-b-PDMAEMAo.5-ran-PMAAco.5, PS-b-PDMAEMAo s-ran-PMAAco? and PS-b-PDMAEMAo.2-ran-PMAAco.8. They display different isoelectric points (lEPs), indicating the pH at which their negative charges are equal to their positive charges. This behavior can be attributed to the differing pKavalues of PDMAEMA and PMAA. PDMAEMA has a pKaof approximately 7.540, which causes it to remain protonated and positively charged at lower pH levels (pH < pKa) and gradually deprotonate as the pH increases. In contrast, PMAA has a lower pKaof around 441, resulting in it being mostly protonated and neutral at low pH, and deprotonating to become negatively charged at higher pH (pH > pKa). This switchable charge characteristic allows the membrane to effectively repel and release adsorbed foulants during the cleaning cycles. When the membrane is exposed to acidic solutions, the positively charged PDMAEMA repels cationic foulants, while in basic conditions, the negatively charged PMAA repels anionic contaminants and / or foulants. This alternating charge mechanism enhances the membrane's self-cleaning capabilities and extends its operational lifespan, ensuring sustained performance and reduced maintenance requirements.

[0121] The PS-b-PDMAEMAo.5-ran-PMAAco.5 polymer maintains a positive zeta potential until pH = 6.2, its isoelectric point, transitioning to negative values only at higher pH levels. This behavior suggests that this polymer composition is less suited for applications requiring a neutral charge at lower pH values, as the surface charge remains positive until higher pH levels are reached. The zeta potential curve of PS-b-PDMAEMAoa-ran-PMAAco? shows an isoelectric point at approximately pH 4.5, making it particularly suitable for applications involving dairy proteins, which have similar isoelectric points. Similarly, PS-b-PDMAEMAo 2-ran-PMAAco s has an isoelectric point slightly below pH 4, suggesting its potential application in systems with slightly lower pH values. The consistent transition in zeta potential reinforces its responsiveness to pH changes. By having the diblock copolymer additive in PES membranes, the varying zeta potentials can influence the hydrophilic and hydrophobic nature of the membrane surfaces. At lower pH levels, the protonation of DMAEMA increases hydrophilicity, and at higher pH, the deprotonation of PMAA also increases hydrophilicity.

[0122] The data demonstrate that the choice of monomer ratios significantly influences the zeta potential and, consequently, the suitability of these polymers for specific applications. For dairy protein-related applications, the PS-b-PDMAEMAo.3-ran-PMAAco.7 polymer is ideal due to its matching isoelectric point and responsive zeta potential behavior. This alignment with the isoelectric point of dairy proteins ensures optimal interaction and performance in membrane applications. Overall, the results indicate that the tuning of the DMAEMA and MAA ratio in the copolymer allows for the design of pH-responsive membranes tailored to specific needs. The ability to control the isoelectric point and zeta potential enhances the versatility and effectiveness of these polymers in various environmental and industrial applications.Effect of PES concentration and PVP as an additive on morphology and permeability of the prepared membranes

[0123] PES blend membranes were fabricated using the nonsolvent-induced phase separation (NIPS) method, incorporating CoP as an additive. From literature reports1819, it appears that casting solutions with higher PES concentrations exhibit increased viscosity. This higher viscosity results in delayed demixing within the coagulation bath, thereby promoting the favored formation of a porous substructure with a relatively small pore size and thick top layer. Therefore, in this study, the concentrations of PES were gradually increased— 21 wt.%, 22 wt.%, 22.5 wt.%, and 23 wt.%— while maintaining 5 wt.% of CoP with respect to PES, to determine the optimal concentration for achieving tight ultrafiltration (UF) membrane with smaller pore sizes. As shown in Table 5, the permeability dropped dramatically from 53.43 L / m2.h.bar to 28.18 L / m2.h.bar when the PES concentration increased from 21wt.% to 23wt.%, resulting from reduced pore size. Among the different formulations, the membrane with the smallest pore size (3.9-4.1 nm) was selected for the subsequent stages of membrane fabrication.

[0124] Table 3. Water flux and average pore size of the membranes fabricated at different PES concentrations in the casting solutionPES CoP CoP / PES NMP Flux Pore size em rane (wt.%) (wt.%) (wt.%) (wt.%) (L-m^.bar^h1) (nm) PES21%-CoP 20.78 1.04 5 78.18 55.97 8.06-8.59 PES22%-CoP 21.76 1.09 5 77.15 41.74 7.45-8.50 PES22.5%-CoP 2225 1 11 5 7664 3206 559-615 PES23%-CoP 22 74 1 14 5 76 12 25 80 55-57

[0125] In the next step, the effect of adding PVP to the membrane solution with 23wt.% PES and 5wt.% CoP was investigated. The effect of PVP concentration on the formation of membrane pores is well-documented45-48. The addition of PVP promotes the formation of microvoids in the membrane sublayer and more porous structures, enhancing membrane permeability through instantaneous demixing. However, beyond a certain point, further PVP addition increases the casting solution's viscosity and increases the kinetic hindrance to phase separation, slowing the diffusional exchange rate of solvent and nonsolvent during phase inversion. This delayed demixing results in a denser top layer and suppression of macrovoid formation in the membranes and a sponge-like structure, ultimately reducingpermeate flow. The same behavior was observed in this study, where three relatively high concentrations of PVP -5wt.%, 7wt.%, and 10wt.%- with respect to the PES were added to the membrane solution. As shown in Table 6, The water flux of the neat PES23% membrane was obtained at 66 L / m2.h.bar. When the CoP was added to neat PES the water flux was significantly reduced to 28.18 due to polymer segregation in the membrane pores. The addition of 5 wt.% PVP significantly increases the permeability compared to PES23%-CoP due to the formation of large microvoids. However, increasing the PVP concentration from 5 wt.% to 10 wt.% results in a decrease in permeability gradually from 114 to 46 L / m2. h.bar, indicating the suppression of microvoids. The membrane PES23%-CoP-PVP5% with the highest performance in terms of pure water permeability was further studied by measuring contact angle and zeta potentials and the membrane morphology was characterized using scanning electron microscopy (SEM).

[0126] Table 4. Water flux and average pore size of the membranes fabricated at different PVE concentrations in the casting solutionPES CoP PVP NMP PVP / PES CoP / PES Flux Pore size em rane (wt.%) (wt.%) (wt.%) (wt.%) (wt.%) (wt.%) (L.m2.bar'.h -1) (nm)Neat PES 23 - 77 - 66 9.5-99 PES23%-CoP 22 74 1 14 - 76 12 - 5 28 18 5.5-5.7 PES23%-CoP-PVP5% 22.48 1.124 1.124 75.27 5 5 114 11.59-11.7 PES23%-CoP-PVP5%-50 22.48 1.124 1.124 75.27 5 5 88 8.52-8.66 PES23%-CoP-PVP7% 22.38 1.120 1.57 74.93 7 5 82 9.43-9.46 PES23%-CoP-PVP10% 22 23 1 11 2 22 7443 10 5 76 8 91-8 94Membrane morphology

[0127] Membrane surface morphology as well as cross-section structure was visualized by using SEM. As shown in Figure 8, neat PES and PES23%-CoP-PVP5% had asymmetric structures with a thin, fine porous selective barrier and a much thicker, porous sub-structure. Many previous publications have explained the phenomena behind the formation of this typical structure4950. PES shows a finger-like structure with many microvoid forms, while adding PVP and CoP results in larger microvoids and wider pore size distribution. That is due to the high affinity of PVP to nonsolvent. Visualization of the surface morphology of the PES23%-CoP-PVP5% membrane revealed a fine pore structure with dimensions in the nanometer range (<12 nm). Note that a drying process was performed using a non-solvent exchange method to minimize the collapse of the pore structure.Determination of the Carboxy! and amino Group Concentration on the functionaiized membrane surface by Reaction with TBO and OA ii

[0128] The concentration of the carboxylic acid (-COOH) and amino (-NfCHs)?) groups on the membrane surface of PES23%-CoP-PVP with 5%, 7%, and 10% of PVP was evaluated by the dye adsorption method. In the alkaline solution, the negative carboxylic acid groups on the membrane surface adsorb the TBO molecules with a positive charge because of the attractive electrostatic interaction. The other samples were placed in an acidic solution, where the (SO3-) groups on acid orange II can be attracted by the protonated amino groups. After the saturated adsorption, the membranes were immersed in acid and base solution to elute TBO and OA II respectively. The concentrations ofTBO and OA II dyes in the solution were determined using a UV-Vis spectrophotometer at 485 nm and 633 nm, respectively, from which the surface COOH and amino group concentrations were calculated. Figure 9 displays the dye adsorption surface density from the added PS-b-PDMAEMA-ran-PMAAc on the modified PES surface. The carboxyl group (COOH) surface concentrations for neat PES and PES23%-CoP are 58.45 and 137.83 pimol / cm2, respectively. This result indicates that incorporating PS-PDMAEMA-PMAA into PES increases the COOH surface density, leading to improved dye adsorption. Likewise, the OA adsorption measurements resulted in amino surface concentrations of 45.98 and 121.69 pimol / cm2for neat PES and PES23%-CoP, respectively, indicating a lower amount of DMAEMA compared to COOH on the PES23%-CoP surface. For the membranes with different PVP concentrations, while keeping the amount of copolymer CoP additive, the dye adsorption remains largely unchanged because, and only the porosity changes.

[0129] To confirm the reversibility and repeatability of the pH-responsive charge-switching behavior in membranes, simultaneous TBO and OA II dye adsorption-desorption experiments were performed for up to six cycles. As shown in Figure 10(a,b), the adsorption capacity for both OA II and TBO remains above 90% across all cycles. This indicates that the charge-switching properties, when pH is altered from acidic to basic, are stable and can be reused multiple times. Conversely, the neat PES did not exhibit significant adsorption or desorption behavior, likely due to its lack of charge-switching capability.Contact Angle measurements

[0130] The contact angle measurements of PES membranes incorporated with pH-responsive polymers were carried out at different pH levels (2, 4.5, and 11). The results in Figure 11 and Table 7 provide insights into the surface wettability and the hydrophilic-hydrophobic transition of the membranes.

[0131] Table 5. calculated surface tensions of PES23%-CoP-PVP5%.Contact angle of the pH-responsive Calculated pH-responsive membrane (Degree) membrane surface energy (mN / m) Solvent Water Diiodomethane y , y yil7PH2 27 + 3.14 37+ 1.57 41.01 29.56 70.584.5 (IP) 67 + 4.18 29+ 1.12 44.58 7.06 51.6411 19 + 3.22 35+ 1.84 42.11 32.04 74.15

[0132] At pH 2, the water contact angle is 27.35°, indicating a highly hydrophilic surface due to the protonation of PDMAEMA (-NH(CH3)2+) and the presence of neutral PMAA (COOH) groups, which enhance water affinity4051. At pH 4.5, the contact angle increases to 67.88°, indicating a more hydrophobic surface as both PDMAEMA and PMAA are partially charged, balancing each other out and reducing the polymer’s affinity for water. At pH 11 , the contact angle is 19.46°, reflecting a hydrophilic surface due to the deprotonation of PMAA (COO ) and the neutral state of PDMAEMA (-NH(CH3)2). These results demonstrate the reversible, pH-triggered hydrophilic-hydrophobic transition of the membranes, with low and high pH enhancing hydrophilicity, beneficial for high water permeability and reduced fouling.

[0133] The calculated surface energy data further elucidates these changes (Table 7). At pH 2, the total surface energy (ysv) is 70.58 mN / m, with a dispersive component (ySy) of 41.01 mN / m and a polar component (ys^) of 29.56 mN / m. This high surface energy corresponds to the low contact angle, indicating strong interactions between the membrane surface and water molecules, enhancing hydrophilicity. At the isoelectric point (pH 4.5), the total surface energy decreases to 51.64 mN / m, with a dispersive component of 44.58 mN / m and a polar component of 7.06 mN / m. The reduced polar component and increased contact angle suggest decreased hydrophilicity and increased hydrophobicity due to the balanced charges on the membrane surface. At pH 11, the total surface energy increases to 74.15 mN / m, with a dispersive component of 42.11 mN / m and a polar component of 32.04 mN / m. The high surface energy at this pH, reflected by the low contact angle, indicates enhanced hydrophilicity due to the deprotonation of PMAA and the neutral state of PDMAEMA.

[0134] The contact angle measurements using diiodomethane further support these observations. Diiodomethane is a non-polar liquid, and its contact angle provides insights into the dispersive interactions on the membrane surface. At pH 2, the contact angle is 37°, at pH 4.5, the contact angle decreases to 29°, and at pH 11, the contact angle increases slightly to 35°. These values indicate that the dispersive interactions remain relatively constant across the pH range. The significant changes in surface energy are primarily due to variations in the polar component, driven by the protonation or deprotonation of the pH-responsive polymer on the membrane surface, rather than changes in dispersive interactions.

[0135] These results highlight the significant changes in surface energy and their implications for protein adsorption and cellular interactions. At high pH, the deprotonation of PMAA to COO' increases the surface energy, leading to decreased protein adsorption due to electrostatic repulsion and enhanced hydrophilicity. This property is particularly advantageous in the dairy industry, where proteins such as casein have an isoelectric point around pH 4.5 and operational conditions are typically around pH 6. Under these conditions, the membrane's hydrophilic nature at high pH helps minimize protein adsorption, reducing fouling and maintaining higher membrane performance and longevity52. This behavior is supported by studies showing that hydrophilic surfaces with high surface energy at higher pH levels exhibit reduced protein adsorption due to electrostatic repulsion between the negatively charged membrane surface and protein molecules5354. Furthermore, the reduction in protein adsorption at high pH contributes to antifouling, essential for long-term operational stability in industrial applications1455. This switchable charge characteristic also allows for effective cleaning using acidic and basic solutions alternately, releasing adsorbed foulants and regenerating the membrane surface. This reduces the need for harsh chemical cleaning agents and extends the operational lifespan of the membranes.Membrane surface charge

[0136] The apparent zeta potential versus pH was measured to obtain information about membrane surface charge. As shown in Figure 12, the neat PES exhibited a negative charge across the entire pH range, originating from the sulfone groups (O=S=O) present in the PES. However, the introduction of an amphiphilic copolymer and PVP additiveinto the polymer solution significantly changed the surface charge properties of the PES membrane. The PES23%-CoP-PVP5% and PES23%-CoP-PVP5%-50 membranes displayed charge switchability, shifting from positive to negative with increasing pH with the isoelectric point around 4, which is similar to the isoelectric point of the diblock copolymer dissolved in aqueous solution (Figure 7). The zeta potential of these membranes increased from 0 mV to 15 mV as the pH decreased from 4 to 2, due to the protonation of the tertiary amine groups in PDMAEMA. In contrast, as the pH was increased from 4 to 10, all carboxylic acid groups in the blend membranes converted to COO, leading to a negatively charged surface. At high pH levels, the charge becomes more negative primarily due to the higher content of MAAc in the copolymer compared to PDMAEMA. Additionally, the presence of the functional groups of PVP (O=C-N) contributes to this increased negative charge45. Although these two membranes have different pore sizes, due to the limitation of the Helmholtz-Smoluchowski Equation regarding the pore size of ultrafiltration membranes56’57, this difference is not well justified in the graph.Water flux recovery and productivity difference

[0137] The results from the study of various membranes: Neat PES-25, PES23%-CoP, PES23%-CoP-PVP5%, and PES23%-CoP-PVP5%-50 demonstrate significant differences in DI water flux, protein flux, and protein rejection, which can be attributed to the incorporation of the pH-responsive polymer and PVP as a pore-forming agent. The operating pH of around 6 is critical as it influences the surface charge of the membranes and the charge of the proteins being filtered. At pH 6, the membranes are negatively charged due to the deprotonation of the carboxylic acid groups of PMA, while the proteins, with isoelectric points around 4 for whey protein and 5 for raw protein, are also negatively charged5657. This negative charge on both the membrane surface and proteins results in electrostatic repulsion, reducing fouling and enhancing flux58.

[0138] As shown in Figure 13, the neat PES membrane shows high rejection rates for both raw protein (1 % whey protein) 90.5% and whey protein (8% whey protein) 98.8%. but suffers from low protein flux (12.7 L m2bar“1h“1) and pure water flux (66 L m2bar“1h“1), indicating limited permeability and higher susceptibility to fouling59. In contrast, the PES23%-CoP membrane, with the pH-responsive polymer, maintains high rejection rates (90.2% for raw protein and 98.7% for whey protein) while slightly improving protein flux (15.0 L m2bar“1h“1) but lowering pure water flux, this decrease of pure water flux could be explained by a decrease of pore size due to the presence of the pH-responsive polymer. To address this problem, a pore forming agent was added to the membrane casting solution.

[0139] The PES23%-CoP-PVP5% membrane, which includes PVP as a pore-forming agent, shows a significant increase in DI water flux (114 L m2bar“1h“1) and a higher protein flux (29.0 L m2bar“1h“1) compared to PES23%-CoP while maintaining high rejection rates (94.0% for raw protein and 98.5% for whey protein). This improvement indicates that the pH-responsive polymer enhances membrane permeability by inducing the electrostatic repulsion that repels protein contaminants and / or foulants more effectively, thereby reducing fouling60. Also, the addition of PVP increases the membrane's porosity, facilitating water passage without compromising separation performance61.

[0140] Finally, the PES23%-CoP-PVP5%-50 membrane, cast at a higher speed of 50, maintains high protein rejection rates (94.6% for raw protein and 98.6% for whey protein) but shows a reduced protein flux (24.5L m2bar“1h“1) compared to PES23%-CoP-PVP5%-25, while the DI water flux remains high (88.3 L m2bar“1h“1). The higher casting speed likely creates a denser membrane structure, which slightly decreases water flux but maintains excellent overall performance62.

[0141] Figure 14a presents the daily water filtration productivity (in mL / day) of (PES23%-CoP-PVP5%) compared to neat PES membranes over 16 days. Each day, the membranes filtered water from a raw protein feed for 8 hours, followed by an acid-base cleaning cycle before the next run. From the data, it is evident that the PES23%-CoP-PVP5% membrane consistently exhibits higher productivity compared to the neat PES membrane throughout the 16-day period. The productivity of the pH-responsive membrane remains around 1400 mL / day, while the neat PES membrane averages around 1000 mL / day. This 40% increase in productivity can be attributed to the pH-responsive properties and enhanced porosity of the PES23%-CoP-PVP5%, which allow for higher water flux and reduced fouling due to the reversible charge switching. Figure 14b illustrates the daily productivity difference (in %) between PES23%-CoP-PVP5% and neat PES membranes, showing a positive trend over the 16 days. The productivity difference starts at around 20% and gradually increases to over 30%. This increasing productivity difference indicates that the performance gap between the pH-responsive membrane and neat PES widens over time. Several factors contribute to this trend. Firstly, the dynamic charge switching of the PES23%-CoP-PVP5% continues to mitigate fouling more effectively than the static properties of the neat PES membrane, which suffers from progressive fouling and reduced permeability. Secondly, the acid-base cleaning cycles are more effective for PES23%-CoP-PVP5% due to their responsive nature, leading to better recovery of initial flux compared to the neat PES membrane.

[0142] This innovative approach results in membranes that are more effective and durable for applications in water treatment and protein separation, providing a balance between high permeability and superior separation performance. The dynamic charge-switching mechanism facilitates easier cleaning and longer operational life, reducing the need for harsh chemical cleaners and offering a sustainable and efficient solution for various industrial applications63.PEG rejection

[0143] To evaluate the effective pore sizes of membranes, MWCOs were obtained by analyzing the ultrafiltration of polyethylene glycol (PEG) with various molecular weights (Figure 15). The MWCO of the membrane was defined to be the equivalent PEG molecularweightatthe rejection value of 90%. (WKDa and 20KDa). The PEG concentrations in both the feed solution and the permeate were measured using a differential refractometer (Brookhaven BI-DNDC).

[0144] As shown in Figure 15, the rejection values of the neat PES membrane for PEG of WKDa and 20KDawere 80.3% and 98.4%, respectively. When CoP was added to the PES, there was a slight increase in PEG rejection, attributed to the reduction in pore size caused by the presence of the pH-responsive polymer. Conversely, the addition of PVP as a pore-forming agent to the PES-CoP-PVP membrane resulted in decreased PEG rejection rates, with values of 53.5% and 81.5% for 10KDa and 20KDa PEG, respectively. The reduced PEG rejection corresponds to the increased effective membrane pore sizes of membranes with the addition of PVP. Finally, the PES-CoP-PVP-50 membrane, cast at a higher speed of 50, shows higher PEG rejection and that the MWCO is almost 20KDa for this membrane. This is mainly because of the increased thickness of the top layer, supplying more sufficient barriers forthe permeation of organic PEGs and resulting in decreased effective pore size.Membrane Durability

[0145] To evaluate whether there is no more residue and unattached polymer on the surface of the membranes, a durability test was conducted by using the Toluidine blue (TBO) dye. The membranes were used directly after the casting step without doing an extra washing step. The membrane was immersed in a base solution with pH=11.2 and kept for different times 2h, 5h and, 12h in a sonication bath at 50 °C. In the next step, each membrane sample was subjected to an adsorption experiment using distinct dye solutions. The absorbance of the dye solutions after desorption was recorded and recalibrated using the calibration curve. To ensure accuracy, the above steps were repeated five times, allowing for a robust data set. In conclusion of this test, the membranes need to be preconditioned before conducting of operation with food materials like commercial membranes. As shown in Figure 16, After a slight reduction between 2 to 5 hours of sonication, there is no change in the level of COOH groups on the membrane, which implies stable functionalization and the absence of copolymer release.Conclusion

[0146] In this study, an on-demand surface charge switchable antifouling membrane was prepared by integrating the amphiphilic block copolymer PS-b-PDMAEMAos-ran-PMAAcoyinto a PES matrix using the phase inversion method. The hydrophilic block, PDMAEMA-ran-PMAAc, as a random copolyelectrolyte, enabled the membrane to dynamically switch surface charge in response to pH changes. At basic pH, the membrane repels negatively charged proteins, while at acidic pH, the positively charged DMAEMA enhances the rejection of positively charged molecules, reducing fouling and facilitating cleaning processes. The PES23%-CoP-PVP5% membrane, enhanced with PVP as a poreforming agent, exhibited significant performance improvements, with a pure water flux of 114 L m2bar“1h“1and a protein flux of 29.0 L m2bar“1h“1, while maintaining high protein rejection rates (94.0% for raw protein and 98.5% for whey protein). The PES23%-CoP-PVP5%-50 membrane, cast at a higher speed, also maintained excellent protein rejection with a slightly reduced water flux. Over 16 days, the pH-responsive PES23%-CoP-PVP5% membrane demonstrated a 40% increase in productivity compared to the neat PES membrane, attributed to its advanced porosity and reversible charge-switching properties that enhanced the water flux and minimized fouling. Moreover, the stability of the copolymer functionalization was confirmed by the consistent COOH group levels after sonication in the base bath for 12h. Overall, the integration of the charge-switchable diblock copolymer into PES membranes offers a versatile solution with tunable wettability, improved antifouling properties, and effective cleaning, making it highly suitable for various environmental and industrial applications.

[0147] The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.REFERENCES

[0148] The present description refers to a number of documents, the content of which is herein incorporated by reference in their entirety. These documents include, but are not limited to, the following:1. Liu, Z., Wang, W., Xie, R., Ju, X. J. & Chu, L. Y. Stimuli-responsive smart gating membranes. Chemical Society Reviews vol. 45460-475 Preprint at https: / / doi.Org / 10.1039 / c5cs00692a (2016).2. Koros, W. J. & Zhang, C. Materials for next-generation molecularly selective synthetic membranes. Nat Mater 16, 289-297 (2017).3. Nunes, S. P. et ai. Thinking the future of membranes: Perspectives for advanced and new membrane materials and manufacturing processes. Journal of Membrane Science vol. 598 Preprint at https: / / doi.Org / 10.1016 / j.memsci.2019.117761 (2020).4. Cheng, X. Q. et al. Towards sustainable ultrafast molecular-separation membranes: From conventional polymers to emerging materials. Progress in Materials Science vol. 92 258-283 Preprint at https: / / doi.Org / 10.1016 / j.pmatsci.2017.10.006 (2018).5. Robeson, L. M. The upper bound revisited. J Memb Sci 320, 390-400 (2008).6. Park, H. B., Kamcev, J., Robeson, L. M., Elimelech, M. & Freeman, B. D. Maximizing the right stuff: The tradeoff between membrane permeability and selectivity. Science vol. 356 1138-1148 Preprint at https: / / d0i.0rg / l 0.1126 / science.aab0530 (2017).7. She, Q., Wang, R., Fane, A. G. & Tang, C. Y. Membrane fouling in osmotically driven membrane processes:A review. Journal of Membrane Science vol. 499 201-233 Preprint at https: / / doi.Org / 10.1016 / j.memsci.2015.10.040 (2016).8. Chen, W., Qian, C., Zhou, K. G. & Yu, H. Q. Molecular Spectroscopic Characterization of Membrane Fouling:A Critical Review. Chem vol. 4 1492-1509 Preprint at https: / / doi.Org / 10.1016 / j.chempr.2018.03.011 (2018).9. Jones, K. L. &0’melia, C. R. Protein and Humic Acid Adsorption onto Hydrophilic Membrane Surfaces: Effects of PH and Ionic Strength. Journal of Membrane Science vol. 165 (2000).10. Hester, J. F., Banerjee, P. & Mayes, A. M. Preparation of Protein-Resistant Surfaces on Poly(vinylidene fluoride) Membranes via Surface Segregation. Macromolecules 32, 1643-1650 (1999).11. Zhu, L. J., Zhu, L. P., Zhang, P. Bin, Zhu, B. K. & Xu, Y. Y. Surface zwitterionicalization of poly(vinylidene fluoride) membranes from the entrapped reactive core-shell silica nanoparticles. J Colloid Interface Sci 468, 110-119 (2016).12. Hashino, M. et al. Effect of surface roughness of hollow fiber membranes with gear-shaped structure on membrane fouling by sodium alginate. J Memb Sci 366, 389-397 (2011).13. Vrijenhoek, E. M., Hong, S. & Elimelech, M. Influence of Membrane Surface Properties on Initial Rate of Colloidal Fouling of Reverse Osmosis and Nanofiltration Membranes. Journal of Membrane Science vol. 188 (2001).14. Rana, D. & Matsuura, T. Surface modifications for antifouling membranes. Chem Rev 110, 2448-2471 (2010).15. Li, R. et al. Inkjet printing of dopamine followed by UV light irradiation to modify mussel-inspired PVDF membrane for efficient oil-water separation. J Memb Sci 619, (2021).Okoro, H. K., Ndlwana, L, Ikhile, M. I., Barnard, T. G. & Ngila, J. C. Hyperbranched polyethylenimine-modified polyethersulfone (HPEI / PES) and nAg@HPEI / PES membranes with enhanced ultrafiltration, antibacterial, and antifouling properties. Heliyon 7, (2021).Kaner, P., Rubakh, E., Kim, D. H. & Asatekin, A. Zwitterion-containing polymer additives for fouling resistant ultrafiltration membranes. J Memb Sc / 533, 141-159 (2017).Chen, X., Zhai, Y., Han, X., Liu, H. & Hu, Y. Surface chemistry-dominated underwater superoleophobic mesh with mussel-inspired zwitterionic coatings for oil / water separation and self-cleaning. Appl Surf Sci 483, 399— 408 (2019).Ma, T. et al. Fabrication of electro-neutral nanofiltration membranes at neutral pH with antifouling surface via interfacial polymerization from a novel zwitterionic amine monomer. J Memb Sci 503, 101-109 (2016). Zhao, Y. F., Zhu, L. P., Yi, Z., Zhu, B. K. & Xu, Y. Y. Improving the hydrophilicity and fouling-resistance of polysulfone ultrafiltration membranes via surface zwitterionicalization mediated by polysulfone-based triblock copolymer additive. J Memb Sci 440, 40-47 (2013).Liang, B. et al. Substrate-independent polyzwitterionic coating for oil / water separation membranes. Chemical Engineering Journal 362, 126-135 (2019).Ofridam, F. et al. pH-sensitive polymers: Classification and some fine potential applications. Polymers for Advanced Technologies vol. 32 1455-1484 Preprint at https: / / doi.org / 10.1002 / pat.5230 (2021).Melia, M., Tagliabue, A., Mollica, L, Vaghi, S. & Izzo, L. Inducing pH control over the critical micelle concentration of zwitterionic surfactants via polyacids adsorption: Effect of chain length and structure. J Colloid Interface Sci 606, 1636-1651 (2022).Nielen, W. M., Willott, J. D. & de Vos, W. M. Solvent and ph stability of poly(Styrene-alt-maleic acid) (psama) membranes prepared by aqueous phase separation (aps). Membranes (Basel) 11, (2021).Slowikowska, M., Wojcik, A. J., Wolski, K., Hatalak, A. & Zapotoczny, S. Light-promoted synthesis of surface-grafted polymers bearing pyridine groups by metal-free ATRP in microliter volumes. Polymer (Guildf) 234, (2021).Tomicki, F., Krix, D., Nienhaus, H. & Ulbricht, M. Stimuli-responsive track-etched membranes via surface-initiated controlled radical polymerization: Influence of grafting density and pore size. J Memb Sci 377, 124— 133 (2011).Schepelina, O. & Zharov, I. Poly(2-(dimethylamino)ethyl methacrylate)-modified nanoporous colloidal films with pH and ion response. Langmuir 24, 14188-14194 (2008).Schacher, F., Ulbricht, M. & Muller, A. H. E. Self-supporting, double stimuli-responsive porous membranes from polystyrene-block-poly(N,N-dimethylaminoethyl methacrylate) diblock copolymers. Adv Fund Mater 19, 1040-1045 (2009).Singh, N., Wang, J., Ulbricht, M., Wickramasinghe, S. R. & Husson, S. M. Surface-initiated atom transfer radical polymerization: A new method for preparation of polymeric membrane adsorbers. J Memb Sci 309, 64-72 (2008).Hu, K. & Dickson, J. M. Development and characterization of poly(vinylidene fluoride)-poly(acrylic acid) pore-filled pH-sensitive membranes. J Memb Sci 301, 19-28 (2007).31. Karppi, J., Akerman, S., Akerman, K., Sundell, A. & Penttila, I. Adsorption of metal cations from aqueous solutions onto the pH responsive poly(vinylidene fluoride grafted poly(acrylic acid) (PVDF-PAA) membrane. Journal of Polymer Research 17, 71-76 (2010).32. Zhang, L. X., Cai, S. L, Zheng, Y. Bin, Cao, X. H. & Li, Y. Q. Smart homopolymer modification to single glass conical nanopore channels: Dual-stimuli-actuated highly efficient ion gating. Adv Fund Materia, 2103-2107 (2011).33. Ye, H. et al. Protein adsorption and desorption behavior of a pH-responsive membrane based on ethylene vinyl alcohol copolymer. RSC Adv7, 21398-21405 (2017).34. Ndlwana, L, Sikhwivhilu, K., Moutloali, R. & Ngila, J. C. Heterogeneous Functionalization of Polyethersulfone:A New Approach for pH-Responsive Microfiltration Membranes with Enhanced Antifouling Properties. Journal of Membrane Science and Research 6, 178-187 (2020).35. Zhu, X., Loo, H. E. & Bai, R. A novel membrane showing both hydrophilic and oleophobic surface properties and its non-fouling performances for potential water treatment applications. J Memb Sci 436, 47-56 (2013).36. Peng, J., Su, Y., Shi, Q., Chen, W. & Jiang, Z. Protein fouling resistant membrane prepared by amphiphilic pegylated polyethersulfone. Bioresour Technol 102, 2289-2295 (2011).37. Zhao, X., Su, Y., Chen, W., Peng, J. & Jiang, Z. PH-responsive and fouling-release properties of PES ultrafiltration membranes modified by multi-functional block-like copolymers. J Memb Sci 382, 222-230 (2011).38. Zhang, G. et al. Novel polysulfone hybrid ultrafiltration membrane prepared with TiO2-g-HEMA and its antifouling characteristics. J Memb Sci 436, 163-173 (2013).39. Kim, Y., Rana, D., Matsuura, T. & Chung, W. J. Influence of surface modifying macromolecules on the surface properties of poly(ether sulfone) ultra-filtration membranes. J Memb Sci 338, 84-91 (2009).40. Stawski, D. Poly(N,N-dimethylaminoethyl methacrylate) as a bioactive polyelectrolyte - production and properties. Royal Society Open Science vol. 10 Preprint at https: / / doi.org / 10.1098 / rsos.230188 (2023). 41. Parnell, A. J. et al. Synthesis, characterization and swelling behaviour of poly(methacrylic acid) brushes synthesized using atom transfer radical polymerization. Polymer (Guildf) 50, 1005-1014 (2009).42. Sun, Y., Wang, S., Wu, M., Song, X. & Xu, S. Synthesis, performance regulation and application of pH / temperature responsive polymer PMAA-b-PDMAEMA. Huagong Jinzhan / Chemical Industry and Engineering Progress 43, 480-489 (2024).43. Saroha, S., Jewrajka, S. K. & De, S. Theoretical quantification of pH-responsiveness of blend membrane.Polymer (Guildf) 290, (2024).44. Yu, S. et al. Preparation of PMMA-Based Temperature / pH Responsive Nanoparticles Encapsulating 5- Fluorouracil and Methotrexate In Situ by One-Pot Dispersion Photopolymerization. Macromol Biosci 24, (2024).45. Al Malek, S. A., Abu Seman, M. N., Johnson, D. & Hilal, N. Formation and characterization of polyethersulfone membranes using different concentrations of polyvinylpyrrolidone. Desalination 288, 31-39 (2012).46. Vatsha, B., Ngila, J. C. & Moutloali, R. M. Preparation of antifouling polyvinylpyrrolidone (PVP 40K) modified polyethersulfone (PES) ultrafiltration (UF) membrane for water purification. Physics and Chemistry of the Earth 67-69, 125-131 (2014).47. Saljoughi, E. & Mohammadi, T. Cellulose acetate (CA)Zpolyvinylpyrrolidone (PVP) blend asymmetric membranes: Preparation, morphology and performance. Desaiination 249, 850-854 (2009).48. Yoo, S. H., Kim, J. H., Jho, J. Y., Won, J. & Kang, Y. S. Influence of the addition of PVP on the morphology of asymmetric polyimide phase inversion membranes: Effect of PVP molecular weight. J Memb Sci 236, 203— 207 (2004).49. Wienk, I. M. et ai. Recent Advances in the Formation of Phase inversion Membranes Made from Amorphous or Semi-Crystaiiine Polymers. Journal of Membrane Science vol. 113 (1996).50. Boom, R. M., Wienk, I. M., Van Den Boomgaard, T. & Smolders, C. A. Microstructures in Phase Inversion Membranes. Part 2. The Role of a Polymeric Additive*. Journal of Membrane Scrence vol. 73 (1992). 51. Dos Santos De MacEdo, B. et al. Effect of pH on the Complex Coacervation and on the Formation of Layers of Sodium Alginate and PDADMAC. ACS Appl Mater Interfaces (2020) doi: 10.1021 / acs.langmuir.9b03216.52. Hina, M., Bashir, S., Kamran, K., Ramesh, S. & Ramesh, K. Synthesis and characterization of self-healable poly (acrylamide) hydrogel electrolytes and their application in fabrication of aqueous supercapacitors. Polymer (Guildf) 210, (2020).53. Gao, W. J. J., Lin, H. J., Leung, K. T. & Liao, B. Q. Influence of elevated pH shocks on the performance of a submerged anaerobic membrane bioreactor. Process Biochemistry 45, 1279-1287 (2010).54. Gao, S. L. et al. Comparative analysis of polyamide nanofiltration membranes resistance to different acids:Insights from experiments and density functional theory simulations. J Memb Sci 694, (2024).55. Botto, M. et al. Bacterial Biofilms: A Common Cause of Persistent Infections. Annu. Rev. Plant Physiol. Plant Mol. Biolvo\. 64 https: / / www.science.org (1998).56. Zhao, C., Xue, J., Ran, F. & Sun, S. Modification of polyethersulfone membranes - A review of methods.Progress in Materials Science vol. 58 76-150 Preprint at https: / / doi.Org / 10.1016 / j.pmatsci.2012.07.002 (2013).57. Huisman, I. H., Pradanos, P. & Hernandez, A. The Effect of Protein-Protein and Protein-Membrane Interactions on Membrane Fouling in Ultrafiltration. Journal of Membrane Science vol. 179 (2000).58. Tijing, L. D. et al. Fouling and its control in membrane distillation-A review. Journal of Membrane Science vol.475215-244 Preprint at https: / / doi.Org / 10.1016 / j.memsci.2014.09.042 (2015).59. Shi, X., Tai, G., Hankins, N. P. & Gitis, V. Fouling and cleaning of ultrafiltration membranes: A review. Journal of Water Process Engineering vol. 1 121-138 Preprint at https: / / doi.org / 10.1016 / jjwpe.2014.04.003 (2014).60. Almaie, S., Vatanpour, V., Rasoulifard, M. H. & Seyed Dorraji, M. S. Novel negatively-charged amphiphilic copolymers of PVDF-g-PAMPS and PVDF-g-PAA to improve permeability and fouling resistance of PVDF UF membrane. React Fund Polym 179, (2022).61. Liu, F., Hashim, N. A., Liu, Y., Abed, M. R. M. & Li, K. Progress in the production and modification of PVDF membranes. Journal of Membrane Science vol. 375 1-27 Preprint athttps: / / doi.Org / 10.1016 / j.memsci.2011.03.014 (2011).62. Park, H. B., Kamcev, J., Robeson, L. M., Elimelech, M. & Freeman, B. D. Maximizing the right stuff: The tradeoff between membrane permeability and selectivity. Science vol. 356 1138-1148 Preprint at https: / / doi.Org / 10.1126 / science.aab0530 (2017).63. Van Der Bruggen, B. & Vandecasteele, C. Removal of Pollutants from Surface Water and Groundwater by Nanofiltration: Overview of Possible Applications in the Drinking Water Industry. www.elsevier.com / locate / envpol.• CN 102641754 B• CN 116407962 B• CN 117181024 B• CN 117732262 A• EP 0405872 A1• EP 1 694724 A1• EP 4026808 A1• EP 4526023 A1• KR 20150025886 A• US 5,736,051• US 8,505,745 B2• US 8,940,333 B2• US 9,061,267 B2• US 9,183,972 B2• US 10,293,308 B2• US 10,710,026 B2• US 10,913,058 B2• US 10,919,032 B2• US 10,962,537 B2• US 10,987,639 B2• US 11,027,988 B2• US 11,046,826 B2• US 12,240,771 B2• US 2013 / 0085190 A1• US 2021 / 0009728 A1• US 2024 / 0043599 A1• US 2024 / 0367112 A1• US 2025 / 0186988 A1• WO 2011 / 057882 A1• Anuradha et al. ACS Appl. Mater. Interfaces 2024, 16, 44, 61344-61359• Bajpai et al. Designed Monomers and Polymers, 10(2), 181-192.• Bao et al. Separation and Purification Technology, Volume 287, 2022, 120479.• Bayramoglu et al. (2008), Polym. Int. , 57: 70-76.• Chatterjee et al. J. Mater. Chem. A, 2014,2, 8396-8406• Chen et al. Water 2025, 17(2), 254• Das et al. J. Appl. Polym. Sci., 108: 1273-1280.• Du et al. J. Appl. Polym. Sci., 131, 40685.• Estrada-Villegas et al. Iran Polym J 28, 639-647 (2019).• Farroq et al., Journal of Membrane Science, Volume 611, 1 October 2020, 118181• Frazar et al. Gels 2022, 8(10), 668.• Huang et al. J. Appl. Polym. Sci., 46374, doi: 10.1002 / app.46374• Jia et al. Journal of Chemical & Engineering Data 202065 (2), 725-736• Jiang et al. Water Research, Volume 268, Part B, 1 January 2025, 122749• Kaku et al. Mol. Syst. Des. Eng., 2024,9, 56-62• Khazdooz et al. RSC Appl. Polym., 2025,3, 885-896• Kumarasamy et al. ACS Cent Sci. 2020 Feb 27; 6(4): 487-492.• Li et al., Journal of Colloid and Interface Science, Volume 613, May 2022, Pages 234-243• Liu et al. ChemistrySelect, Volume 8, Issue 35, September 20, 2023, e202301391• Liu et al. Journal of Polymer Science, Volume 60, Issue 21 , Special Issue: Polymeric Membranes for Desalination, 1 November 2022, Pages 3009-3021• Liu et al. Journal of Water Process Engineering, Volume 47, June 2022, 102659• Liu et al. RSC Adv. 2020 Jan 27; 10(8):4232-4242.• Luo et al. Polymer Engineering and Science, Volume 63, Issue 10, October 2023, Pages 3343-3352 • Okten et al. European Polymer Journal, Volume 114, May 2019, Pages 176-188• Orakdogen, European Polymer Journal, Volume 96, November 2017, Pages 134-144• Orakdogen, J Polym Res 19, 9914 (2012).• Pafiti et al. Macromolecules 2011, 44, 13, 5352-5362.• Rando et al. ChemSusChem 2024, 17, e202301502.• Salek et al . RSC Adv. , 2021 , 11 , 33461 -33470• Sun et al. Chemical Industry and Engineering Progress 43.1: 480.• Unsal et al. Analytics Chimica Acta, Volume 570, Issue 2, 16 June 2006, Pages 240-248• Xia et al. Colloid Polym Sci 299, 663-674 (2021).• Xue et al. Polymers 2022, 14(9), 1695.• Yamada et al. (2006) J. Appl. Polym. Sci., 99: 381-391.• Yao et al. Desalination, Volume 355, 1 January 2015, Pages 91-98• Yao et al. Journal of Colloid and Interface Science, Volume 437, 1 January 2015, Pages 124-131 • Ye et al. Langmuir 202541 (1), 945-954.• Ye et al. Polymer Engineering and Science, Volume 62, Issue 4, April 2022, Pages 1041-1051 • Ye et al. RSC Adv., 2017,7, 21398-21405• Ye et al., Journal of Membrane Science, Volume 641, 1 January 2022, 119849• Yu et al. Frontiers in Chemistry, Volume 11 -2023, doi.org / 10.3389 / fchem.2023.1193553 • Zhao et al., Colloids and Surfaces B: Biointerfaces, Volume 243, November 2024, 114118

Claims

CLAIMS:

1. A charge switchable filtration membrane comprising a porous layer comprising a hydrophobic host polymer and a charge switchable polymeric additive, wherein the charge switchable polymeric additive is dispersed within the host polymer, and wherein the charge switchable polymeric additive is an amphiphilic block copolymer comprising a hydrophobic block and a hydrophilic block, wherein the hydrophilic block comprises repeat units bearing a positively ionizable weak base functional group and repeat units bearing a negatively ionizable weak acid functional group.

2. The membrane of claim 1 , exhibiting a finger-like structure.

3. The membrane of claim 1 or 2, comprising a surface layer on top of a foundation layer, wherein the surface layer is thinner than the foundation layer, wherein the surface layer and the foundation layer each comprises pores, and wherein the pores of the surface layer are smaller than the pores of the foundation layer.

4. The membrane of claim 3, wherein the surface layer represents about 1 % to 20%, preferably about 2% to 10%, and more preferably about 3% to about 7%, of the total thickness of the membrane.

5. The membrane of claim 3 or 4, wherein the surface layer has an average thickness of about 2 pm to about 10 pm, preferably about 3 pm to about 7 pm.

6. The membrane of any one of claims 3 to 5, wherein the foundation layer has an average thickness of about 50 pm to about 150 pm, preferably about 70 pm to about 100 pm.

7. The membrane of any one of claims 3 to 6, wherein the pores of the foundation layer are elongated and arranged approximately perpendicularly to the surface of the membrane.

8. The membrane of any one of claims 3 to 7, wherein the pores of the foundation layer have an average length of at least 20 pm.

9. The membrane of any one of claims 3 to 8, wherein the surface layer is enriched in amphiphilic block copolymer.

10. The membrane of any one of claims 1 to 9, being supported on a porous support to increase the mechanical strength of the membrane.

11. The membrane of claim 10, wherein the porous support is a non-woven mat, preferably of polyethylene, polypropylene, or polyethylene terephthalate.

12. The membrane of claim 10 or 11 , wherein the porous support has an average thickness of about 0.06 mm to about 1 mm, preferably about 0.2mm, such as about 0.18 mm.

13. The membrane of any one of claims 1 to 12, wherein the hydrophobic host polymer is polyether sulfone (PES), polystyrene (PS), polyvinylidene difluoride (PVDF), or polyacrylonitrile (PAN), preferably PES.

14. The membrane of any one of claims 1 to 13, wherein the hydrophobic block of the amphiphilic block copolymer has a molecular weight (Mw) between about 5000 Da and about 20000 Da.

15. The membrane of any one of claims 1 to 14, wherein the hydrophilic block of the amphiphilic block copolymer has a molecular weight (Mw) between about 5000 Da and about 20000 Da.

16. The membrane of any one of claims 1 to 15, wherein the hydrophobic block of the amphiphilic block copolymer comprises polyacrylonitrile (PAN), polyether sulfone (PES), polypropylene (PP), polysulfide (PS), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or cellulose acetate, preferably PES or PVDF, and more preferably PES.

17. The membrane of any one of claims 1 to 16, wherein the negatively ionizable weak acid functional groups are carboxylic acids, sulfonic acids, and / or phosphoric acids.

18. The membrane of any one of claims 1 to 17, wherein the positively ionizable weak base functional groups are amidines, guanidines, amines, imidazoles, and / or pyridines.

19. The membrane of any one of claims 1 to 18, wherein the hydrophilic block comprises repeat units bearing both the positively ionizable weak base functional group and the negatively ionizable weak acid functional group.

20. The membrane of any one of claims 1 to 18, wherein the repeat units bearing the positively ionizable weak base functional group and the repeat units bearing a negatively ionizable weak acid functional group are different from one another.

21. The membrane of any one of claims 1 to 18 and 20, wherein the repeat unit bearing negatively ionizable weak acid functional group are repeat unit of poly (acrylic acid), poly(ethyl acrylic acid), a polymethacrylic acid, poly(vinyl sulfate) PVS, poly (styrene sulfonate), polyphosphoric acid, or poly(vinylphosphonic acid), preferably polymethacrylic acid.

22. The membrane of any one of claims 1 to 18, 20 and 21, wherein the repeat units bearing positively ionizable weak base functional groups are repeat units of• poly(N-methyltetrahydropyrimidine) (PMTHP),poly(p-azidomethylstyrene-co-styrene),poly[2-methyl-1 -(4-vinylbenzyl)-1 ,4,5,6-tetrahydropyrimidine],poly(dimethyl acrylamide-co-(N-amidino)ethyl acrylamide) (P(DMA-co-NAEAA)), and• polyethylene oxide)-b-poly((N-amidino)dodecyl acrylamide).• poly[(2-dimethylamino) ethyl methacrylate] (PDMAEMA),• poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA), and• poly(3-N', N'-dimethylaminopropyl acrylamide) (PDMAPMA), or• poly(L-arginine methyl ester acrylamide-co-N-cyclopropyl acrylamide) (poly(AME-co-CPAM), preferably repeat units of PDMAEMA, PMTHP or PDMAPMA.

23. The membrane of any one of claims 1 to 18 and 20 to 22, wherein the charge switchable polymeric additive isranHOof formula:wherein R represents - NH(CH2)3N(CH3)2or O(CH2)2N(CH3)2, preferably -NH(CH2)3N(CH3)2.

24. The membrane of any one of claims 1 to 23, wherein the charge switchable polymeric additive is present at a concentration between about 1 and about 15 wt.%, preferably between about 4 and about 8 wt.%, based on the weight of the hydrophobic host polymer.

25. The membrane of any one of claims 1 to 24, wherein the isoelectric point of the membrane is between about 3 and about 10.

26. The membrane of any one of claims 1 to 25, being a microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), or reverse osmosis (RO) membrane.

27. The membrane of any one of claims 1 to 26, being in the form of a flat sheet or a hollow fiber.

28. A charge switchable polymeric additive, wherein the charge switchable polymeric additive is an amphiphilic block copolymer comprising a hydrophobic block and a hydrophilic block, wherein the hydrophilic block comprises repeat units bearing a positively ionizable weak base functional group and repeat units bearing a negatively ionizable weak acid functional group29. The polymeric additive of claim 28, being as defined in any one of claims 1 to 27.

30. The polymeric additive of claim 28 or 29, being for manufacturing a charge switchable filtration membrane, preferably wherein the charge switchable filtration membrane is as defined in any one of claims 1 to 27.

31. A polymer blend comprising a hydrophobic host polymer and a charge switchable polymeric additive, wherein the charge switchable polymeric additive is an amphiphilic block copolymer comprising a hydrophobic block and a hydrophilic block, wherein the hydrophilic block comprises repeat units bearing a positively ionizable weak base functional group and repeat units bearing a negatively ionizable weak acid functional group.

32. The polymer blend of claim 31 , wherein the hydrophobic host polymer is as defined in any one of claims 1 to 27 and / or wherein the charge switchable polymeric additive is as defined in any one of claims 1 to 27.

33. The polymer blend of claim 31 or 32, being for manufacturing a charge switchable filtration membrane, preferably wherein the charge switchable filtration membrane is as defined in any one of claims 1 to 27.

34. A kit for manufacturing a charge switchable filtration membrane, the kit comprising a hydrophobic host polymer and a charge switchable polymeric additive, wherein the charge switchable polymeric additive is an amphiphilic block copolymer comprising a hydrophobic block and a hydrophilic block, wherein the hydrophilic block comprises repeat units bearing a positively ionizable weak base functional group and repeat units bearing a negatively ionizable weak acid functional group.

35. The kit of claim 34, wherein the hydrophobic host polymer is as defined in any one of claims 1 to 27 and / or wherein the charge switchable polymeric additive is as defined in any one of claims 1 to 27 .

36. The kit of claim 34 or 35, wherein the charge switchable filtration membrane is as defined in any one of claims 1 to 27.

37. The kit of any one of claims 34 to 36, further comprising instructions for manufacturing and / or using the charge switchable filtration membrane.

38. The membrane of any one of claims 1 to 27, the polymer blend of any one of claims 31 to 33, or the kit of any one of claims 34 to 37, further comprising a pore-forming agent.

39. The membrane, the polymer blend, or the kit of claim 38, wherein the pore-forming agent is polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), an inorganic additive such as LiCI and TiC>2, or a surfactants such as Tween®-80.

40. The membrane, the polymer blend, or the kit of claim 38 or 39, wherein the pore-forming agent is present at a concentration between about 0.5 and about 15 wt.%, preferably between about 2 and about 8 wt.%, based on the weight of the hydrophobic host polymer.

41. The membrane of any one of claims 1 to 27, the polymer blend of any one of claims 31 to 33, or the kit of any one of claims 34 to 37, being free of a pore-forming agent.

42. A method of manufacturing a charge switchable filtration membrane, the method comprising• providing a casting solution by dissolving a hydrophobic host polymer, a charge switchable polymeric additive, and a pore-forming agent in a solvent,• casting the casting solution onto a substrate,• submerging the substrate bearing the casting solution in a coagulation bath containing a non-solvent, thereby causing precipitation of the hydrophobic host polymer, the charge switchable polymeric additive, and the pore-forming agent to form the membrane.

43. The method of claim 42, wherein the charge switchable filtration membrane is as defined in any one of claims 1 to 27, wherein the hydrophobic host polymer is as defined in any one of claims 1 to 27 and / or wherein the charge switchable polymeric additive is as defined in any one of claims 1 to 27.

44. The method of claim 42 or 43, wherein the charge switchable filtration membrane is as defined in any one of claims 1 to 27.

45. The method of any one of claims 42 to 44, wherein the solvent is N-methyl-2-pyrrolidone (NMP), DMAC, DMF, CHCI3, or a mixture thereof.

46. The method of any one of claims 42 to 45, wherein the non-solvent is water, an alcohol (such as ethanol, methanol, isopropanol), or a mixture thereof.

47. The method of any one of claims 42 to 46, wherein the non-solvent is water and wherein the water is at a basic or acidic pH, preferably at a basic pH.

48. The method of any one of claims 42 to 47, wherein the non-solvent is water and wherein the water is at a temperature between about 8°C and about 12°C.

49. The method of any one of claims 42 to 48, wherein the pore-forming agent is polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), an inorganic additive such as LiCI and TiC>2, or a surfactant such as Tween®-80.

50. The method of any one of claims 42 to 49, wherein the pore-forming agent is present at a concentration between about 0.5 and about 15 wt.%, preferably between about 2 and about 8 wt.%, based on the weight of the hydrophobic host polymer.

51. The method of any one of claims 42 to 50, further comprising the step to tuning the isoelectric point of the membrane by modifying the ratio of repeat units bearing positively ionizable weak base functional groups and repeat units bearing negatively ionizable weak acid functional groups in the charge switchable polymeric additive.

52. The method of any one of claims 42 to 51, further comprising the step to tuning porosity of the membrane by modifying the viscosity of the casting solution.

53. The method of claim 52, wherein the viscosity of the casting solution is modified by varying the concentration of components thereof, preferably of the hydrophobic host polymer.

54. The method of any one of claims 42 to 53, wherein the hydrophobic host polymer is present in the casting solution at a concentration ranging from about 5% to about 30% by weight, based on the total weight the polymer solution.

55. The method of any one of claims 42 to 54, wherein the charge switchable polymeric additive is present in the casting solution at a concentration ranging from about 2% to about 12% by weight, based on the total weight the polymer solution.

56. A method of tuning the isoelectric point of the charge switchable filtration membrane of any one of claims 1 to 27, the method comprising the step of adjusting the ratio of repeat units bearing positively ionizable weak base functional groups and repeat units bearing negatively ionizable weak acid functional groups in the charge switchable polymeric additive.

57. A method of filtering a feed using the charge switchable filtration membrane of any one of claims 1 to 27, the method comprising the step of contacting the feed with one side of the membrane and allowing materials to be separated from the feed to pass through the membrane as a permeate58. Use of the charge switchable filtration membrane of any one of claims 1 to 27 for filtering a feed.

59. The method of claim 57 or the use of claim 58, being for use is in a water purification application, in a gas separation application, or in a biomedical filtration application, or being for the separation of proteins or other biomolecules from the feed.

60. The method of claim 57 or 59 or the use of claim 58 or 59, further comprising selecting, as the charge switchable filtration membrane, a membrane that has an isoelectric point that is about the isoelectric point of a contaminant and / or foulant and / or foulant to be removed from the feed.

61. The method of any one of claims 57 and 59 to 60 or the use of any one of claims 58 or 59 to 60, further comprising the step of tuning the surface charge of the membrane by modifying the pH of the feed.

62. The method of any one of claims 57 and 59 to 61 or the use of any one of claims 58 or 59 to 61, further comprising the step of tuning the hydrophilicity of the membrane by modifying the pH of the feed.

63. The method or the use of claim 62, wherein the pH is modified by introducing an acid, a base, or C02or N2gas into the feed.

64. The method of any one of claims 57 and 59 to 63 or the use of any one of claims 58 or 59 to 63, further comprising using a control mechanism to adjust the pH and thereby tuning the surface charge of the membrane in real-time.

65. The method of any one of claims 57 and 59 to 64 or the use of any one of claims 58 or 59 to 64, wherein the filtering is in continuous operation with real-time monitoring of the surface charge of the membrane.

66. The method of any one of claims 57 and 59 to 65 or the use of any one of claims 58 or 59 to 65, further comprising the step of cleaning the membrane.

67. The method or use of claim 66, wherein the cleaning is carried out after the membrane has been used for filtrating the feed.

68. The method or use of claim 66 or 67, further comprising, after said cleaning, the step of reusing the membrane to filter a feed.

69. The method or use of any one of claims 66 to 68, wherein the cleaning comprises the step of i) creating or increasing a negative surface charge on the membrane by contacting the membrane liquid with a pH higher than the isoelectric point of the membrane.

70. The method or use of any one of claims 66 to 69, wherein the cleaning comprises the step of ii) creating or increasing a positive surface charge on the membrane by contacting the membrane liquid with a pH lower than the isoelectric point of the membrane.

71. The method or use of any one of claims 66 to 70, wherein the cleaning comprises the step of iii) increasing the hydrophilicity of the membrane by contacting the membrane liquid with a pH at least one pH point higher than the isoelectric point of the membrane.

72. The method or use of any one of claims 66 to 71 , wherein the cleaning comprises the step of iv) decreasing the hydrophilicity of the membrane by contacting the membrane liquid with a pH approximately corresponding to the isoelectric point of the membrane.

73. The method or use of any one of claims 69 to 72, wherein two or more (preferably all of) steps i) to iv are carried out consecutively (in any order).

74. The method or use of any one of claims 66 to 73, wherein the cleaning further comprises the step of reversing liquid flow across the membrane.

75. The method or use of any one of claims 66 to 74, wherein the cleaning is carried out in situ at the location where the membrane has been used or will be used to filter the feed.

Images