Weak polyelectrolyte membranes with a wide ion-exchange capacity (IEC) range and limited water swelling

Abstract

The present disclosure provides a tunable polyelectrolyte membrane formed from crosslinking acrylic acid and poly(ethylene glycol) diacrylate. The membrane may be referred to as AA-PEGDA and it exhibits a wide ion-exchange capacity (IEC: 0 ~ 4 meq / g) range and limited water swelling ((f) w'. 0.07 - 0.69) and wherein by controlling the external pH, the charged group (COO-) concentration can be changed on the same chemical structure. Also provided are devices comprising the polyelectrolyte membrane and methods of making and using the device and / or polyelectrolyte membrane. A membrane may have the following structure:

Description

Attorney Docket No. 074339.00328WEAK POLYELECTROLYTE MEMBRANES WITH A WIDE ION-EXCHANGE CAPACITY (IEC) RANGE AND LIMITED WATER SWELLINGCROSS REFERENCE TO RELATED APPLICATIONS

[0001] The instant application claims the benefit of priority to U.S. Provisional Application No. 63 / 687,538, filed on August 27, 2024, the disclosure of which is incorporated herein by reference.BACKGROUND OF THE DISCLOSURE

[0002] As the world’s population grows rapidly, clean technologies related to environment, energy, food, and health have garnered significant interest for sustainability and decarbonization. Polymer membranes are one of the key elements in these clean technologies including gas, liquid and vapor separations, solid state electrolytes in batteries and fuel cells, environmental remediation, resource recovery, barrier and packaging application, and health care. The advancement of these technologies is highly dependent on the design of innovative polymer membranes.

[0003] Charged polymer membranes, where anionic or cationic groups are covalently bonded to polymer backbone, draw significant attention due to their versatile and tunable transport properties in the above applications. Altering charged group composition combined with polymer backbone architecture and topology lead to varied transport properties of small molecules (ions, water, gases, etc.) coupled with morphological changes in polymer membranes. In particular, fundamental understanding of the effect of charged group type and concentration on water and ion transport is essential for establishing the chemistry-structure- property relationship in charged polymer membranes.

[0004] Two representative challenges that hinder the mechanistic understanding of water and ion transport are different polymer chemistries used for comparisons and high- water swelling. First, different polymer chemistries used in different polymer membranes make proper comparisons challenging for mechanistic understanding. A benchmark, representative class of charged polymers in the literature is strong cation-exchange membranes such as sulfonated tetrafluoroethylene (Nafion®), sulfonated polysulfone, and sulfonated polystyrenic series. As sulfonate group’s concentration and counter ion type change, ion and water transport properties (diffusivity, solubility, permeability and conductivity) in polymers are greatly affected. However, when sulfonate group’s concentration is varied on the same polymer backbone, such chemical modification simultaneously changes the chemical structure of the polymer, and often alters processingmethods (e.g., solvents, membrane formation parameters) in order to accommodate these chemical changes, significantly affecting the polymer morphology. These unavoidable chemical and morphological changes upon varying the sulfonate group concentration (and other molecular parameters) make systematic comparisons between the polymers challenging. Thus, if a suitable polymer platform can be designed in which the effect of charge group content on water and ion transport can be investigated without changing the chemical structure of polymers, i.e., on the same chemical structures, such platform can be a significant milestone in the field.

[0005] Second, high water swelling in charged polymers complicates the physical, molecular-level picture of water and ion transport in these materials. Water and ion transport (sorption and diffusion) properties are greatly affected by the charged groups and sorbed water content in polymers. When exposed to water, charged polymers can sorb a significant amount of water, as charged groups like to be surrounded by water via dielectric effect. Equilibrium water swelling is established when the osmotic pressure of water reaches an equilibrium with the elastic force exerted by polymer chains. For a clear understanding, the effects of the charged group and sorbed water content on transport properties need to be decoupled and independently studied. However, changing the charged group simultaneously changes the sorbed water content in membranes. In highly swollen polymers, any changes originated from tuning the charged group can be screened by the changes in water content. Because of this difficulty, mechanistic and theoretical understanding regarding the influence of charged groups on water and ion transport remains incomplete: little literature exists that independently and systematically varies these parameters. Lack of basic property data (diffusivity, solubility, permeability and conductivity) limits the ability to elucidate a fundamental theoretical foundation and design principles, thus slowing the progress of designing innovative materials.SUMMARY OF THE DISCLOSURE AND RELATED INFORMATION

[0006] Described is a library of weak polyelectrolyte membranes: crosslinked acrylic acid - polyethylene glycol) diacrylate (AA-PEGDA) networks, with a wide ion-exchange capacity (IEC: 0 ~ 4 meq / g) range and limited water swelling ((pw= 0.07 - 0.69).

[0007] To overcome the current limitations, presented herein is a series of crosslinked acrylic acid - poly(ethylene glycol) diacrylate (AA-PEGDA) copolymer networks with a wide range of ion-exchange capacity (IEC: 0 ~ 4 meq / g) and limited water swelling (pw0.07 - 0.69). Described is the successful formation of the crosslinked AA-PEGDA copolymernetwork series with limited water swelling. Transparent, free standing polymer membranes with uniform thickness were successfully prepared. The effect of polymer composition, i.e., the concentrations of AA monomer and PEGDA crosslinker molecular weights, as well as the external pH on the lECs, charged group concentrations and water contents in the polymers were investigated. The amount of AA monomer was changed to achieve a wide range of lECs between 0 - 4 mmol equivalent H+ per gram of a dry polymer [meq / g]. The PEGDA crosslinker’s molecular weights were varied to change the distance between network junctions, and thus, control the water volume fraction in the polymers ranging between 0.07 - 0.69. The water swelling was successfully limited while achieving a wide range of lECs in the polymers, and systematically changed the charged group concentrations on the fixed, same chemical structures by changing the external pH.

[0008] By controlling the external pH, the charged group (COO-) concentration can be systematically changed on the same chemical structure: the same polymer behaves like uncharged, neutral polymer at low pH whereas at pH = pKa, the same polymer is one half charged, and at high pH (»pKa), is fully charged. Their water content ((pw) is varied simultaneously but limited to a lower range due to network architecture. This library provides an extra freedom to tune lECs and a platform to investigate water and ion transport using the same chemical structure, for the first time. This platform can help advance mechanistic understanding of ion transport in charged polymers and can be used for clean technologies including gas, liquid and vapor separations, solid state electrolytes in batteries and fuel cells, environmental remediation, resource recovery, barrier and packaging application, and health care.BRIEF DESCRIPTION OF THE FIGURES

[0009] For a fuller understanding of the nature and objects of the disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying figures.

[0010] FIG. 1 A displays the chemical structure of crosslinked acrylic acid - poly(ethylene glycol) diacrylate (AA-PEGDA) random copolymer networks via UV-induced free radical polymerization.

[0011] FIG. IB displays pictures of transparent, free standing AA-PEGDA (10 - 2) films with a uniform thickness. The 10 - 2 formulation shows the maximum ion-exchange capacity (mlEC) = 2 meq / g with the PEGDA crosslinker length, n = 10.

[0012] FIG. 1C displays a molecular picture of dissociation process at varied external pH.

[0013] FIG. 2 displays the maximum ion-exchange capacity (mlEC) of crosslinked AA-PEGDA series as a function of acrylic acid (AA) monomer content [wt%] via conversion test. The dashed line is the theoretical mlEC in the polymers. Symbols are: •: n = 4 series, ■: n = 10 series, ▲ : n = 13 series. Error bars were included.

[0014] FIGS. 3A and 3B display ATR-FTIR spectra of dry (FIG. 3 A) and wet (FIG. 3B) states of crosslinked AA-PEDGA series with mlEC = 0 ~ 4 meq / g and PEGDA crosslinker length, n = 10. The films were soaked in DI water (pH = 5 ~ 6) for 2 days before ATR-FTIR analysis. Spectra of AA monomer and PEGDA crosslinker (n = 10) are shown for comparison. The spectra were vertically moved for easier viewing.

[0015] FIGS. 4A-4D display the effect of mlEC and PEGDA crosslinker length (n) on water volume fraction (W) (FIG. 4A), theoretical crosslinking density (vt) (FIG. 4B), ethylene oxide (EO) group content (FIG. 4C), and polymer density(FIG. 4D) in AA- PEGDA series. The films were soaked in DI water (pH = 5 ~ 6) for 2 days for water uptake measurement. Then the films were dried under vacuum for polymer density measurement. Symbols are: •: n = 4 series, ■: n = 10 series, ▲ : n = 13 series. Error bars are included in FIGS. 4A, 4B, and 4D.

[0016] FIG. 5A displays ATR-FTIR spectra of control, dry crosslinked PEGDA network (n = 10), i.e., 10 - 0 formulation vs. pH.

[0017] FIG. 5B displays ATR-FTIR spectra of dry crosslinked AA-PEGDA network with 10 - 2 formulation vs. pH. The 10 - 2 formulation has mlEC = 2 meq / g, and PEGDA crosslinker length, n = 10. Spectra were vertically moved for easier comparison.

[0018] FIG. 5C displays the degree of ionization (a) via POT titration and absorbance of COO- groups (at 1575 cm-1) vs. pH of 10 - 2 formulation. The solid line (a vs. pH) is the fitting by the modified Henderson-Hasselbalch equation. pKa value was determined at the halfway point (a = 0.5) of a vs. pH curve via POT titration. Error bars are included. The dashed lines (absorbance) are used to guide the eyes.

[0019] FIGS. 5D and 5E display absorbance of COO- groups (at 1575 cm-1) vs. pH summarized for n = 10 (FIG. 5D), and n = 13 (FIG. 5E) series. Error bars are included. The dashed lines (absorbance) are used to guide the eyes.

[0020] FIG. 6A displays the degree of ionization (a) and water volume fraction (W) vs. pH of 10 - 2 formulation. The solid line (a vs. pH) is the fitting by the modified Henderson-Hasselbalch equation. The dashed lines ((pwvs. pH) were included to guide the eyes. Error bars were included.

[0021] FIGS. 6B-6D display the water volume fraction ((pw) vs. pH in AA-PEGDA series with n = 10 (FIG. 6B), and n = 13 series (FIG. 6C). FIG. 6D includes both n = 10 and 13 series for easier comparison. Error bars were included.

[0022] FIGS. 7A and 7B display water and salt permeabilities (Pwand Ps) vs. l / (pw(FIG. 7 A) and permeability selectivity (ctu ) vs. water permeability (Pw) of 10 - 2 AA- PEGDA formulation (FIG. 7B) (symbols: •, o) along with hydrogels, acrylate and sulfonated polymers (grey symbols) in literature. Filled and empty symbols are Pwand Ps, respectively. A blue arrow shows the direction of both pH and degree of ionization (a) increase in the fixed 10 - 2 formulation. Error bars were included, and blue dashed lines were included to guide the eyes. Grey dashed lines through the data are the fits to Yasuda’s free volume model. Symbols are: (1) (•, o) : 10 - 2 AA-PEGDA membrane in this study, (2) (★, ☆): water and NaCl diffusivities in pure water (at l / (pw=1) at 25 °C, (3) (♦, A) : crosslinked PEGDA and PEGDA / PEGA networks, (4) (■, □) : acrylate polymers, (5) (A, A) : sulfonated polymers.

[0023] FIG. 8 displays wet and dry masses of AA-PEGDA series measured for water uptake experiment. Formulations of 4 - 0, 4 - 4, and 10 - 0 are shown. Error bars were included, and the dashed lines are used to guide the eyes.

[0024] FIG. 9 displays potentiometric pH titration procedure in this study.

[0025] FIG. 10 displays maximum ion-exchange capacity (mlEC) vs. acrylic acid (AA) monomer content [mol%] of AA-PEGDA series via conversion test. The dashed lines are the theoretical mlEC in the polymers. Symbols are: •: n = 4 series, ■: n = 10 series, ▲ : n = 13 series. Error bars were included.

[0026] FIG. 11 A displays dry and wet thickness of AA-PEDGA series (mlEC: 0 ~ 4 meq / g and PEGDA crosslinker length, n = 4, 10, and 13). The films were soaked in DI water (pH = 5 ~ 6) for 2 days before measuring wet thicknesses. Dry thicknesses were measured after drying the films under vacuum. Filled symbols are dry thicknesses and empty symbols are wet thicknesses. Error bars were included.

[0027] FIGS. 1 IB and 11C display dry thicknesses (FIG. 1 IB) and wet thicknesses (FIG. 11C) shown separately for easier viewing.

[0028] FIGS. 12A and 12B display ATR-FTIR spectra of dry (FIG. 12 A) and wet (FIG. 12B) states of AA-PEDGA series with mlEC = 0 ~ 4 meq / g and PEGDA crosslinker length, n = 4. The films were soaked in DI water (pH = 5 ~ 6) for 2 days before ATR-FTIRanalysis. Spectra of AA monomer and PEGDA crosslinker (n = 4) are shown for comparison. The spectra were vertically moved for easier viewing.

[0029] FIGS. 13A and 13B display ATR-FTIR spectra of dry (FIG. 13A) and wet (FIG. 13B) states of AA-PEDGA series with mlEC = 0 ~ 4 meq / g and PEGDA crosslinker length, n = 13. The films were soaked in DI water (pH = 5 ~ 6) for 2 days before ATR-FTIR analysis. Spectra of AA monomer and PEGDA crosslinker (n = 13) are shown for comparison. The spectra were vertically moved for easier viewing.

[0030] FIG. 14A displays the pH in the DI water after soaking AA-PEGDA films for 2 days at ambient temperature. Symbols are: •: n = 4 series, ■: n = 10 series, ▲ : n = 13 series. Error bars were included.

[0031] FIG. 14B displays the change of the pH in the DI water, i.e., the pH of the DI water before contacting the films (pH = 6.0 ± 0.2) - the pH of the DI water after soaking the films for 2 days. Symbols are: •: n = 4 series, ■: n = 10 series, ▲ : n = 13 series. Error bars were included.

[0032] FIG. 15 displays the effect of the maximum ion-exchange capacity (mlEC) (i.e., AA content) on water uptake (wu) in AA-PEGDA series. The films were soaked in DI water (pH = 5 ~ 6) for 2 days for water uptake measurement. Symbols are: •: n = 4 series, ■: n = 10 series, ▲ : n = 13 series. Error bars were included.

[0033] FIGS. 16A-16C displays ATR-FTIR spectra of dry AA-PEGDA series (n = 10) with mlEC = 1 meq / g (FIG. 16 A), mlEC = 3 meq / g (FIG. 16B), and mlEC = 4 meq / g (FIG. 16C) vs. pH. The spectra were vertically moved for easier viewing and the dashed lines are included for comparison.

[0034] FIG. 17A displays ATR-FTIR spectra of control, dry crosslinked PEGDA networks (n = 13), i.e., 13 - 0 formulation vs. pH.

[0035] FIGS. 17B-17E display ATR-FTIR spectra of dry crosslinked AA-PEGDA series n = 13) with mlEC = 1 meq / g (FIG. 17B), mlEC = 2 meq / g (FIG. 17C), mlEC = 3 meq / g (17D), and mlEC = 4 meq / g (FIG. 17E) vs. pH. The spectra were vertically moved for easier viewing and the dashed lines are included for comparison.

[0036] FIG. 18A displays ATR-FTIR spectra of control, wet crosslinked PEGDA networks (n = 10), i.e., 10 - 0 formulation vs. pH.

[0037] FIG. 18B displays ATR-FTIR spectra of the wet crosslinked AA-PEGDA networks with 10 - 2 formulation vs. pH. The 10 - 2 formulation has mlEC = 2 meq / g, and PEGDA crosslinker length n = 10. The spectra were vertically moved for easier comparison.

[0038] FIGS. 18C and 18D display the absorbance at 1575 cm’1of AA-PEGDA series vs. pH are summarized for n = 10 series (FIG. 18C), and n = 13 series (FIG. 18D). Error bars were included. The dashed lines are used to guide the eyes.

[0039] FIGS. 19A-19C display ATR-FTIR spectra of wet AA-PEGDA series (n = 10) with mlEC = 1 meq / g (FIG. 19 A), mlEC = 3 meq / g (FIG. 19B), and mlEC = 4 meq / g (FIG. 19C) vs. pH. The spectra were vertically moved for easier comparison and the dashed lines are used to guide the eyes.

[0040] FIG. 20A displays ATR-FTIR spectra of wet control crosslinked PEGDA networks (n = 13), i.e., 13 - 0 formulation vs. pH.

[0041] FIGS. 20B-20E displays ATR-FTIR spectra of the wet crosslinked AA- PEGDA copolymer networks (n = 13) with mlEC = 1 meq / g (FIG. 20B), mlEC = 2 meq / g (FIG. 20C), mlEC = 3 meq / g (FIG. 20D), and mlEC = 4 meq / g (FIG. 20E) vs. pH. The spectra were vertically moved for easier comparison and the dashed lines are used to guide the eyes.

[0042] FIGS. 21A-31C display the degree of ionization (a) via POT titration and absorbance at 1575 cm’1vs. pH of 10 - 1 (FIG. 21 A), 10 - 3 (FIG. 2 IB), and 10 - 4 (FIG. 21C) formulations. The solid line (a vs. pH) is the fitting by the modified Henderson- Hasselbalch equation. pKa value was determined at the halfway point (a = 0.5) of a vs. pH curve via POT titration. The dashed line (absorbance vs. pH) is used to guide the eyes. Error bars were included.

[0043] FIGS. 22A-22D display the degree of ionization (a) via POT titration and absorbance at 1575 cm’1vs. pH of 13 - 1 (FIG. 22 A), 13 - 2 (FIG. 22B), 13 - 3 (FIG. 22C), and 13 - 4 (FIG. 22D) formulations. The solid line (a vs. pH) is the fitting by the modified Henderson-Hasselbalch equation. pKa value was determined at the halfway point (a = 0.5) of a vs. pH curve via POT titration. The dashed line (absorbance vs. pH) is used to guide the eyes. Error bars are included.

[0044] FIGS. 23A-23C display the degree of ionization (a) via POT titration and water volume fraction (W) vs. pH of 10 - 1 (FIG. 23 A), 10 - 3 (FIG. 23B), and 10 - 4 (FIG. 23C) formulations. The solid line (a vs. pH) is the fitting by the modified Henderson- Hasselbalch equation. The dashed line (pwvs. pH) is used to guide the eyes. Error bars are included.

[0045] FIGS. 24A-24D display the degree of ionization (a) via POT titration and water volume fraction (W) vs. pH of 13 - 1 (FIG. 24 A), 13 - 2 (FIG. 24B), 13 - 3 (FIG.24C), and 13 - 4 (FIG. 24D) formulations. The solid line (a vs. pH) is the fitting by the modified Henderson-Hasselbalch equation. The dashed line (pwvs. pH) is used to guide the eyes. Error bars are included.

[0046] FIG. 25 displays an embodiment of the present disclosure.

[0047] FIG. 26 displays effect of ion-exchange capacity [mequiv / g] on Na+ion (filled dots) and CF ion (empty dots) concentration in sorbed water in a swollen membrane [mol / L] for AA-PEGDA series (colored dots) and uncharged polymers (grey empty square dots) and sulfonated polymers (grey diamond dots) in a IM NaCl solution via sorption-desorption experiment. Error bars were included. The dashed lines are used to guide the eyes.

[0048] FIG. 27 displays effect of volume fraction of water (< >w) on Na+ion (filled dots) and CF ion (empty dots) concentrations in sorbed water in a swollen membrane [mol / L] in AA-PEGDA series in a IM NaCl solution via sorption-desorption experiment. Error bars were included. The colored dashed lines are used to guide the eyes and the black dashed lines represent the condition where Kwand Kt are equal.

[0049] FIG. 28 displays effect of volume fraction of water (< >w) on Na+ion (filled dots) and CF ion (empty dots) solubility selectivity (Kw / Ki) for AA-PEGDA series (colored dots) and uncharged polymers (grey empty square dots) and sulfonated polymers (grey diamond dots) in a IM NaCl solution via sorption-desorption experiment in a log-log scale. Error bars were included. The solid line is the upper bound between ion solubility selectivity (Kw / Ki) and volume fraction of water ((pw).

[0050] FIG. 29 displays effect of water permeability Pw) [cm2 / s] on permeability selectivity (P / Ps') in AA-PEGDA series with n = 10 (filled dots) and n = 13 (empty dots) and hydrogels (grey diamond dots), polyamide films (grey circle dots), acrylate polymers (grey square dots), and sulfonated polymers (grey triangle dots) from other literature in a IM NaCl solution via direct permeation and osmotic permeation experiment. All data are plotted on a logarithmic scale. Error bars were included. The colored dashed lines are used to guide the eyes and the black dashed line is the upper bound between water permeability (w) and permeability selectivity Pw / Ps).

[0051] FIG. 30 displays effect of water diffusivity DP) [cm2 / s] on diffusivity selectivity Dw / Dsfrom free Na+ions) in AA-PEGDA series with n = 10 (filled dots) and n = 13 (empty dots) and hydrogels (grey diamond dots), polyamide films (grey circle dots), acrylate polymers (grey square dots), and sulfonated polymers (grey triangle dots) from other literature in a IM NaCl solution via direct permeation and osmotic permeation experiment.All data are plotted on a logarithmic scale. Error bars were included. The colored dashed lines are used to guide the eyes and the black dashed line is the upper bound between water diffusivity (Z>w) and diffusivity selectivity (DWIDSfrom free Na+ions).

[0052] FIG. 31 displays effect of external pH on salt permeability (Ps) of 10 - 2 AA- PEGDA series using different ions: NaCl (black circle symbols), LiCl (red square symbols), and KC1 (blue triangle symbols), and MgC12 (green circle symbols) via direct permeation. All data are plotted on a logarithmic scale. Error bars were included. The colored dashed lines are used to guide the eyes.

[0053] FIG. 32 displays effect of degree of ionization (<z) on salt permeability (Ps) of 10 - 2 AA-PEGDA series using different ions: NaCl (black circle symbols), LiCl (red square symbols), and KC1 (blue triangle symbols) via direct permeation. All data are plotted on a logarithmic scale. Error bars were included. The colored dashed lines are used to guide the eyes.

[0054] FIG. 33 displays effect of 1 / volume fraction of water (< >w) on salt permeability Ps) of 10 - 2 AA-PEGDA series using different ions: NaCl (black circle symbols), LiCl (red square symbols, KC1 (blue triangle symbols), and MgC12 (green circle symbols) via direct permeation. All data are plotted on a logarithmic scale. Error bars were included. The colored dashed lines are used to guide the eyes.DETAILED DESCRIPTION OF THE DISCLOSURE

[0055] Although claimed subject matter will be described in terms of certain examples, other examples, including examples that do not provide all of the benefits and features set forth herein, are also within the scope of this disclosure. Various structural, logical, process step, and electronic changes may be made without departing from the scope of the disclosure.

[0056] As used herein, unless otherwise indicated, “about”, “substantially”, or “the like”, when used in connection with a measurable variable (such as, for example, a parameter, an amount, a temporal duration, or the like) or a list of alternatives, is meant to encompass variations of and from the specified value including, but not limited to, those within experimental error (which can be determined by, e.g., a given data set, an art accepted standard, etc. and / or with, e.g., a given confidence interval (e.g. 90%, 95%, or more confidence interval from the mean), such as, for example, variations of + / - 10% or less, + / -5% or less, + / -1% or less, and + / -0.1% or less of and from the specified value), insofar such variations in a variable and / or variations in the alternatives are appropriate to perform in theinstant disclosure. As used herein, the term “about” may mean that the amount or value in question is the exact value or a value that provides equivalent results or effects as recited in the claims or taught herein. That is, it is understood that amounts, sizes, compositions, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and / or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error, or the like, or other factors known to those of skill in the art such that equivalent results or effects are obtained. In general, an amount, size, composition, parameter, or other quantity or characteristic, or alternative is “about” or “the like,” whether or not expressly stated to be such. It is understood that where “about,” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.

[0057] Ranges of values are disclosed herein. The ranges set out a lower limit value and an upper limit value. Unless otherwise stated, the ranges include the lower limit value, the upper limit value, and all values between the lower limit value and the upper limit value, including, but not limited to, all values to the magnitude of the smallest value (either the lower limit value or the upper limit value) of a range. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a numerical range of “0.1% to 5%” should be interpreted to include not only the explicitly recited values of 0.1% to 5%, but also, unless otherwise stated, include individual values (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5% to 1.1%; 0.5% to 2.4%; 0.5% to 3.2%, and 0.5% to 4.4%, and other possible sub-ranges) within the indicated range. It is also understood (as presented above) that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. Ranges can be expressed herein as from “about” one particular value, and / or to “about” another particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about, it will be understood that the particular value forms a further disclosure. For example, if the value “about 10” is disclosed, then “10” is also disclosed.

[0058] The articles “a” and “an” are used in this disclosure to refer to one or more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element.

[0059] As used herein, unless otherwise stated or indicated, “s” refers to second(s), “min” refers to minute(s), and “h” refers to hour(s).

[0060] As used herein, unless otherwise stated, the term “group” refers to a chemical entity that is monovalent (i.e., has one terminus that can be covalently bonded to other chemical species), divalent, or polyvalent (i.e., has two or more termini that can be covalently bonded to other chemical species). The term “group” also includes radicals (e.g., monovalent and multivalent, such as, for example, divalent radicals, trivalent radicals, and the like).Illustrative examples of groups include:

[0061] The present disclosure provides a tunable polyelectrolyte membrane comprising crosslinked acrylic acid - poly(ethylene glycol) diacrylate (AA-PEGDA) network that exhibits a wide ion-exchange capacity (IEC: 0 ~ 4 meq / g) range and limited water swelling (pw0.07 - 0.69) and wherein by controlling the external pH, the charged group (COO') concentration can be changed on the same chemical structure. Also provided are devices comprising the polyelectrolyte membrane and methods of making and using the device and / or poly electrolyte membrane.

[0062] In an aspect, the present disclosure provides membranes. The membranes are polymer membranes made from polymerization of acrylic acid and poly(ethylene glycol) di acrylate units (PEGDA).

[0063] A membrane of the present disclosure may be made by forming a reaction mixture comprising acrylic acid monomer, poly(ethylene glycol) diacrylate, water, and a photoinitiator; mixing the reaction mixture; casting the mixed reaction mixture on a substrate; irradiating the cast reaction mixture such that the membrane is formed; and optionally, washing the membrane. Various amounts of acrylic acid may be used. For example, the reaction mixture may comprise 0.01 to 30 weight percent acrylic acid relative to the total weight of the acrylic acid and PEGDA. Various amounts of PEGDA may be used. For example, the reaction mixture may comprise 70 to 99.99 weight percent PEGDA relative to the total weight of the acrylic acid and PEGDA. Without intending to be bound by any particular theory, it is considered that in a pre-polymer mixture (e.g., the reaction mixture) leads to higher ion-exchange capacity (IEC). Without intending to be bound by any particular theory, it is considered that longer PEGDA crosslinkers, increased amount of PEGDA crosslinker, and / or increased amount of water (solvent) in a pre-polymer mixture to provide alooser network with lower cross-linking density. The membrane may be removed from the substrate and optionally disposed on a different substrate. Alternatively, the membrane may be kept on the substrate for use. Alternatively, the membrane may be used without a substrate (i.e., a free standing membrane).

[0064] A membrane of the present disclosure is a polymer comprising a plurality of acrylic acid and poly(ethylene glycol) diacrylate units (PEGDA) units.polyethylene glycol) diacrylateThe PEGDA units may have various numbers (n) of ethylene glycol repeats. For example, the PEGDA may have 4 to 13 ethylene glycol repeats (e.g., 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13). In various examples, PEGDA has 4, 10, or 13 ethylene glycol repeats. In various examples, PEGDA has 10 ethylene glycol repeats. Each PEGDA may have the same or a different number of ethylene glycol units. In various examples, the repeats of ethylene glycol may have a molecular weight of 2 kg / mol to 10 kg / mol or greater.

[0065] In various examples, a membrane of the present disclosure comprises the following structure:or a partially or completely deprotonated form thereof, where n is 4 to 13 (e.g., 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13). The amount of protonation / deprotonation can be tuned by adjusting the pH. Without intending to be bound by any particular theory, it is considered that changing the protonation state (e.g., amount of protonation) can change the ion permeability. For example, increasing the pH increases the charge of the membrane, which leads to higher ion permeability and diffusivity. Thus, using Na+and Cl’ as examples, as pH increases and the membrane becomes more negatively charged (higher a), Na+solubility increases — oftenexceeding water solubility, whereas Cl solubility decreases below that of water. In various examples, the membrane has a polymer density of about 1 to about 1.5 g / cm3, including all 0.01 values and ranges therebetween (e.g., 1.16-1.36 or 1.2-1.3) and a theoretical crosslinking density of about 2.5 to about 10.5 mol / cm3, including all 0.01 values and ranges therebetween. As used throughout, the polymer density is a dry density. It is expected that swollen densities may change. A membrane may have a desirable mesh size. For example, the mesh size (e.g., pore diameter or longest linear dimension) may be about 5 to about 15 nm, including all 0.1 nm values and ranges therebetween (e.g., 10-12 nm). When dry, the membrane may have a longest linear dimension (e.g., thickness) of about 225 pm to about 375 pm, including all integer nanometer values and ranges therebetween (e.g., 250 pm to 350 pm). It is expected the thickness will increase when the membrane is wet. See Table 1.

[0066] A membrane of the present disclosure may have various desirable properties. For example, a membrane may exhibit a wide ion-exchange capacity and limited water swelling. For example, the ion-exchange capacity may be from about 0 to about 4 meq / g, including every 0.001 meq / g value and range therebetween. For example, the water swelling (solubility) may be about 0.05 to 0.8, including every 0.001 value and range therebetween (e.g., 0.07 to 0.69). For example, a membrane may exhibit a charged group concentration in sorbed water in a swollen polymer of 0 to 3.5 mol / L, including all 0.01 mol / L values and ranges therebetween (e.g., 0-3.14 mol / L). For example, a membrane may have a water solubility (Kw) of 0.04 to 0.85, including all 0.001 values and ranges therebetween (e.g., 0.07-0.69). For example, a membrane may have a water uptake of 0.2 to 1.8 g / g, including all 0.001 g / g values and ranges therebetween (e.g., 0.34-1.65 g / g). For example, a membrane may have a desirable ionic sodium and / or ionic chloride concentration in sorbed water in a swollen polymer. For example, a membrane may retain a Na+concentration of 0 to 4.5 mol / L, including all 0.01 values and ranges therebetween (e.g., 0.2-4.2 mol / L). For example, a membrane may retain a CF concentration of 0.0 to 0.4 mol / L, including all 0.01 mol / L values and ranges therebetween (e.g., 0-0.35 mol / L). For example, the membrane may have a salt solubility of 0.1 to 0.4, including all 0.01 values and ranges therebetween (e.g., 0.17- 0.33).

[0067] As it relates to permeability and diffusivity, a membrane of the present disclosure may display various desirable features. For example, a membrane may have a water permeability of 1 x 10'6to 6 x 10'6cm2 / s, including all 0.01 x 10'6cm2 / s values and ranges therebetween (e.g., 1 x 10'6to 5.5 x 10'6cm2 / s). For example, a membrane may have a water permeability of 3 x 10'6to 9 x 10'6cm2 / s, including all 0.01 x 10'6cm2 / s values andranges therebetween (e.g., 3.6 x 10'6to 8.4 x 10'6cm2 / s). For example, a membrane may have a salt permeability of 1.75 x 10'8to 5 x 10'7cm2 / s, including all 0.01 x 10'8values and ranges therebetween (e.g., 2.1 x 10'8to 4.6 x 10'7cm2 / s). For example, a membrane may have a salt diffusivity of 8 x 10'8to 2.25 x 10'6cm2 / s, including all 0.01 x 10'8cm2 / s values and ranges therebetween (e.g., 8.6 x 10'8to 1.9 x 10'6cm2 / s). For example, the permeability selectivity may have 10 to 60, including all integer values and ranges therebetween (e.g., 12-51), and a diffusivity selectivity of 2 to 50, including all integer values and ranges therebetween (e.g., 4-44). In various examples, a membrane has an ion selectivity of about 2 to about 3 or about 2 to about 5 depending on feed conditions (e.g., Li+ / Mg2+).

[0068] In an aspect, the present disclosure provides devices. A device of the present disclosure may comprise a membrane of the present disclosure.

[0069] Examples of devices include, but are not limited to, a filter or sensor, or a device used in power and energy generation (e.g., fuel cells, battery, flow cells, electrochemical systems chemical and biochemical manufacturing and recycling, bio- and pharmaceutical processing, environmental element extraction, rare earth element recovery, remediation, resource recovery (e.g., critical recycling), health-related devices (e.g., drug delivery, sensor, drug capture, hemodialysis), water purification (e.g., water pump, ion- selective separations, reverse osmosis desalination, nanofiltration, ultrafiltration), vapor, liquid and gas separations, barrier and packaging materials and electrochemical separations. For example, a device comprising a membrane of the present disclosure may be used as a polymer electrolyte in a battery, fuel cell, or power cell.

[0070] In various examples, a membrane of the present disclosure may be disposed on a substrate. The substrate upon which the membrane is disposed may be porous. In various examples, the porosity of the substrate may be the same as the membrane (e.g., the pores are about the same size as the pores membrane). In various examples, the pores of the substrate may be larger than the pores of the membrane. In various examples, the pores of the substrate may be smaller than the pores of the membrane. In various examples, the pores of the substrate vary in the substrate. For example, some of the pores of the substrate may be smaller than the pores of the membrane, some may be the same size, and others may be larger, or any permutation. Examples of substrates include, but are not limited to, porous polysulfane polymers or a polymer made from acrylic acid and polyethylene glycol) diacrylate units (PEGDA) units. If substrate may be the same polymer as the membrane, or a different polymer than the membrane. When the substrate is made from acrylic acid and poly(ethylene glycol) diacrylate units (PEGDA) units (like the membrane), the ratios ofacrylic acid and PEGDA may be the same or different or the PEGDA may have a different number of ethylene glycol repeats than the polymer of the membrane. In various examples, the substrate and the membrane are different thicknesses. For example, the membrane may be thinner than the substrate and the substrate has the function of providing mechanical support to the membrane.

[0071] In an aspect, the present disclosure provides methods of using devices and membranes of the present disclosure. The membrane may be used for various ion-involving applications in energy, environment and health. pH-responsive tunability makes it suitable for adaptive ion control applications, including energy devices, separation processes, and sensors.

[0072] In various examples, a method of the present disclosure is desalination of water. Water comprising a salt may be contacted with a membrane of the present disclosure. The membrane may be affixed to a substrate or present in a desalination device, such as, for example, a filter.

[0073] In various examples, membranes of the present disclosure may be used for separating water, ions, small molecules, such as neutral, charged, and polar species dissolved in water for various water purification and liquid-based separations. Size exclusion, interaction differences, charge exclusion and dielectric differences and / or any combination of thereof can be used to tune selectivity (a measure of purity of permeate or reject) toward target molecules and reject others. Mesh size (which may be controlled, for example, via PEGDA crosslinker length and composition) can be used to tune water (liquid) flux across a membrane to provide suitable productivity and high throughput. For example, a sample (e.g., aqueous mixture) that comprises or is suspected of comprising a target (e.g., a material that may be sorbed into or by the membrane) is passed through the membrane and at least a portion of the target is captured by the membrane. The target may then be selectively removed from the membrane.

[0074] The steps of the method described in the various embodiments and examples disclosed herein are sufficient to carry out the methods of the present invention. Thus, in an embodiment, the method consists essentially of a combination of the steps of the methods disclosed herein. In another embodiment, the method consists of such steps.

[0075] The following Statements provide various examples of the present disclosure. They are not intended to be limiting in any way.Statement 1. A membrane comprising a crosslinked polymer comprising acrylic acid units and poly(ethylene glycol) diacrylate units (PEGDA), wherein the ethylene glycol repeats of the PEGDA have 4 or more repeat units and the membrane is porous.Statement 2. A membrane according to Statement 1, wherein the pores of the membrane have a longest linear dimension of about 5 to about 15 nm in diameter.Statement 3. A membrane according to Statement 1 or Statement 2, wherein the ethylene glycol repeats of the PEGDA have 4, 10, or 13 repeat units.Statement 4. A membrane according to Statement 1 or Statement 2, wherein the membrane comprises the following structure:or a deprotonated or partially deprotonated variant thereof, wherein n is 4 to 13 (e.g., 4, 5, 6,7, 8, 9, 10, 11, 12, or 13.Statement 5. A membrane according to any one of the preceding Statements, wherein the membrane exhibits an ion-exchange capacity of about 0 to about 4 meq / g, including all values and ranges therebetween.Statement 6. A membrane according to any one of the preceding Statements, wherein the membrane exhibits limited water swelling.Statement 7. A membrane according to Statement 6, wherein the water swelling capacity is 0.05 to 0.8.Statement 8. A membrane according to Statement 7, wherein the water swelling capacity is 0.07 to 0.69.Statement 9. A membrane according to any one of the preceding Statements, wherein polymer has a polymer density of about 1 to about 1.5 g / cm3, including all 0.01 values and ranges therebetween.Statement 10. A membrane according to Statement 9, wherein the polymer density is 1.2 to 1.3 g / cm3, including all 0.01 values and ranges therebetween.Statement 11. A membrane according to any one of the preceding Statements, wherein the polymer has a theoretical crosslinking density of about 2.5 to about 10.5 mol / cm3, including every 0.01 mol / cm3value and range therebetween.Statement 12. A membrane according to any one of the preceding Statements, wherein the weight percent of acrylic acid units is 0.01 to 30 weight percent relative to the total weight percent of the membrane, including all 0.001 weight percent values and ranges therebetween.Statement 13. A membrane according to any one of the preceding Statements, wherein the weight percent of PEGDA is 70 to 99.99 weight percent relative to the total weight percent of the membrane, including all 0.001 weight percent values and ranges therebetween.Statement 14. A membrane according to any one of the preceding Statements, wherein the ethylene oxide content is 150 to 1300 mol% relative to the total amount of acrylic acid monomer and PEGDA monomer.Statement 15. A membrane formed by forming a reaction mixture comprising acrylic acid monomer, poly(ethylene glycol) diacrylate (PEGDA), water, and a photoinitiator; mixing the reaction mixture; casting the mixed reaction mixture on a substrate; irradiating the cast reaction mixture such that the membrane is formed; and optionally, washing the membrane, optionally, removing the membrane from the substrate.Statement 16. A membrane according to Statement 15, wherein the reaction mixture comprises 70 to 99.99 weight percent PEGDA monomer relative to the sum of the weight of acrylic acid and poly(ethylene glycol) diacrylate, including all 0.001 weight percent values and ranges therebetween.Statement 17. A membrane according to Statement 15 or Statement 16, wherein the reaction mixture comprises 0.01 to 30 weight percent acrylic acid relative to the sum of the weight of acrylic acid monomer and polyethylene glycol) diacrylate monomer, including all 0.001 weight percent values and ranges therebetween.Statement 18. A membrane according to any one of Statements 15 to 17, wherein the polymer density is about 1 to about 1.5 g / cm3.Statement 19. A membrane according to Statement 18, wherein the polymer density is about 1.2 to about 1.3 g / cm3.Statement 20. A membrane according to any one of Statements 15 to 19, wherein the theoretical crosslinking density is 2.5 to 10.5 mol / cm3.Statement 21. A membrane according to any one of the preceding Statements, wherein water permeability is 3 x 10'6to 9 x 10'6cm2 / s .Statement 22. A membrane according to any one of the preceding Statements, wherein the water / salt selectivity is 30 to 15.Statement 23. A device comprising the membrane according to any one of the preceding Statements.Statement 24. A device according to Statement 23, wherein the device is a filter, sensor, fuel cell, battery, flow cell, electrochemical system, water pump, barrier material, or packaging material.Statement 25. A method for isolating or separating a target from an aqueous mixture comprising passing the aqueous mixture through a membrane according to any one of Statements 1 to 22 or a device according to any one of Statements 23 or 24, wherein at least a portion of the target is retained in and / or on the membrane.

[0076] The following examples are presented to illustrate the present disclosure. They are not intended to be limiting in any matter.EXAMPLE 1

[0077] This example provides a description of a polymer membrane of the present disclosure.

[0078] Charged polymer membranes are of great interest in clean technologies for sustainability due to their tunable transport properties. Designing new innovative charged polymers for clean technologies is highly dependent on the mechanistic understanding of water and ion transport in these materials. In this context, described herein is a systematic library of weak polyelectrolyte membranes: crosslinked acrylic acid - poly(ethylene glycol) diacrylate (AA-PEGDA) networks, with a wide range of ion-exchange capacity (IEC = 0 ~ 4 meq / g) and limited water swelling ((pw= 0.07 - 0.69). An acrylic acid (AA) monomer was chosen as a weakly charged group to control the charged group concentrations in the polymers, i.e., the maximum ion-exchange capacity (mlEC) at the varied external pH.Polyethylene glycol) diacrylates (PEGDAs) with different molecular weights were used as crosslinkers to control crosslinking densities in the networks. Specifically, in one fixed polymer composition, by controlling the external pH, the charged (COO') group concentration can be systematically changed on the same chemical structure: the same polymer behaves like an uncharged neutral polymer (the degree of ionization, a = 0) at low pH, whereas at pH = pKa, the same polymer is one half charged (a = 0.5), and, at high pH (»pKa), is fully charged (a = 1), providing extra freedom to tune lECs and an opportunity to investigate water and ion transport using the same chemical structure, for the first time. The differences in polymer transport properties versus pH in the fixed chemical structure in this study can be achieved by substantially varying the chemical structure of the other polymers in literature. In addition to changing the chemical structure of polymers, this AA-PEGDA series can provide extra freedom to modify transport properties via simply changing pH and enable us to develop a mechanistic understanding of water and ion transport in charged polymer membranes. FIG. 25 displays an embodiment of the present disclosure.

[0079] To overcome the current limitations, described herein is a series of crosslinked acrylic acid - poly(ethylene glycol) diacrylate (AA-PEGDA) random copolymer networks with a wide range of ion-exchange capacity (IEC = 0 ~ 4 meq / g) and limited water swelling ((pw= 0.07 - 0.69). First, an acrylic acid (AA) monomer was selected as a weakly charged group to control the charged group concentrations in the polymers by varying the external pH. The pKa of AA monomer is around 4.5, and, upon dissociation, carboxylic acid forms negatively charged carboxylate group as:The degree of ionization, a, is defined as the ratio of concentrations [M] between dissociated and total dissociable groups as:

[0080] In one fixed composition of the AA-PEGDA series, as the external pH in a solution equilibrated with a polymer membrane changes, the amount of charged groups (COO' concentration in this study) or the degree of ionization (a) in the polymer is systematically varied on the same chemical structure as shown in FIG. 1C. If the external pH is lower than the pKa of the polymer (pH « pKa), acrylic acid groups in the polymer do not dissociate, and the polymer behaves like an uncharged neutral polymer (a = 0). If the external pH is equal to the pKa (pH = pKa), one half of the acrylic acid groups in the polymer dissociates whereas the remaining half does not (a = 0.5). As the external pH increases abovethe pKa (pH » pKa), the amount of dissociated groups in the polymer increases until all acrylic acid groups dissociate (a = 1). By controlling the external pH in solution, the charged group concentration in one polymer can be systematically changed on the same chemical structure. Second, to limit water swelling, poly(ethylene glycol) diacrylates (PEGDAs) with varied molecular weights (250 - 700 g / mol) were used as crosslinkers to systematically control water content in the polymers via altering the distance between network junctions. The proposed crosslinked AA-PEGDA network series enables us to control the charged group and sorbed water content systematically and independently. Thus, the effect of charged groups on water and ion transport using the same polymer chemical structure can be studied while limiting sorbed water content. This library of materials provides a platform to elucidate the mechanistic understanding of water and ion transport in charged polymers.

[0081] Described herein is the successful formation of the crosslinked AA-PEGDA copolymer network series with a wide IEC range (IEC = 0 ~ 4 meq / g) and limited water swelling and show the water and salt transport properties of one fixed chemical formulation at varied external pH to demonstrate the proof of concept. Transparent, free standing polymer membranes with uniform thicknesses were successfully prepared. The effect of polymer compositions, i.e., the concentrations of AA monomer and PEGDA crosslinker molecular weights, were investigated, as well as the external pH on the lECs, charged group concentrations and water contents in the polymers. The amount of AA monomer was changed to achieve a wide range of IEC from 0-4 mmol equivalent H+per gram of a dry polymer [meq / g], PEGDA crosslinker’s molecular weights were varied to change the distance between network junctions, and thus, control the water volume fraction (W) in the polymers ranging between 0.07-0.69. Compared to other charged polymers in literature, the water swelling was limited while achieving a much wider range of lECs (0 ~ 4 meq / g) in the polymers, and systematically changed the charged group concentrations on the same chemical structures by changing the external pH.

[0082] In addition, using one fixed AA-PEGDA formulation, it was shown that water and salt transport properties can be systematically tuned at varied external pH. As the external pH increases between pH = 5 ~ 12, the dissociated charged (COO') groups increase (as the degree of ionization, a increases between 0 ~ 1), and thus, water volume fraction ((pw) increases in the same chemical structure. This leads to the exponentially increased water and salt permeabilities (Pwand Ps), following Yasuda’s free volume model. The differences in polymer transport properties of the fixed chemical formulation in this study canbe achieved by substantially varying the chemical structure of other polymers in literature. This demonstrates that, in addition to changing the chemical structure of polymers, this AA- PEGDA series can provide extra freedom to modify polymer transport properties via simply changing pH and to enable development of a mechanistic understanding of water and ion transport in charged polymer membranes.

[0083] Materials and Experimental

[0084] Materials. A series of crosslinked acrylic acid - poly(ethylene glycol) diacrylate (AA-PEGDA) copolymer network film is prepared via UV-induced free radical polymerization as shown in FIG. 1. The monomer is acrylic acid (AA, 8.00181, Millipore Sigma, Burlington, MA). Crosslinkers are poly(ethylene glycol) diacrylates (PEGDA, 475629, 437441, and 455008, Millipore Sigma, Burlington, MA) with different molecular weights (Mn= 250, 575, and 700 g / mol). Different PEGDA crosslinkers represent the varying numbers of ethylene oxide (EO) repeating units (n = 4, 10, and 13) between network junctions. The photoinitiator is 2,2-dimethoxy-2-phenylacetophenone (DMPA, 196118, Millipore Sigma, Burlington, MA), and the solvent is ultrapure deionized (DI) water (18.2 MQ cm, Millipore Direct-Q 5 UV system, Merck, Germany). Polymerization reactants were used as received.

[0085] Membrane preparation. Free standing membranes of crosslinked AA-PEGDA copolymer networks were prepared via UV-induced free radical polymerization (see FIG. 1). The desired amounts of AA monomer, PEGDA crosslinker, 5 wt% DI water and 0.1 wt% DMPA photoinitiator (with respect to the total weight of AA and PEGDA) as shown in Table 1 were well-stirred to form transparent, homogeneous prepolymer mixtures in glass jars covered by aluminum foil. The foil was used to prevent ambient light exposure before film casting. The prepolymer mixtures were rigorously stirred for 30 min followed by gentle mixing to eliminate bubbles. A fixed volume (3 ml) of the prepolymer mixture was poured onto a leveled quartz plate (CGQ-0620-20, Chemglass Life Sciences, Vineland, NJ). Spacers with a thickness of 305 pm (19470, Precision Brand, Downers Grove, IL) were placed between two quartz plates to control film thickness. The prepolymer mixture between the two quartz plates was placed under UV lamp (254 nm) (Spectrolinker XL- 1000 UV Crosslinker, Spectronics Corporation, Melville, NY) and was radiated for 90 seconds to form a transparent, uniform thickness, free standing film as shown in FIG. IB. The film was then immersed in DI water for 2-3 days while DI water was frequently changed to remove any unreacted reactants from the film. Circular film coupons with a diameter of 2.2 cm (7 / 8 inch)were prepared using a punch die (66002, Mayhew Steel Products, Turners Falls, MA) for further characterization.

[0086] The nomenclature of the AA-PEGDA series in this disclosure is, the number of repeating units in a PEGDA crosslinker ( ) - the maximum ion-exchange capacity (mlEC), i.e., n - mlEC, for easier comparison. For example, 10 - 2 formulation denotes the crosslinked AA-PEGDA network with the number of EO repeating units in PEGDA 575 g / mol, i.e., n = 10, and the maximum ion-exchange capacity, mlEC = 2 meq / g.

[0087] Polymer characterization

[0088] Water uptake (wM) and volume fraction of waterEquilibrium water swelling in the polymers was measured by gravimetric water sorption (water uptake) experiment. A circular film coupon (diameter is 2.2 cm = 7 / 8 inch) was immersed in DI water at ambient temperature (21-22 °C) until it reached equilibrium water swelling. Excess water on the coupon surface was gently dabbed using dust-free tissue papers to measure wet mass [mg], mw, using an analytical balance (MS304TS / 00, Mettler Toledo, Columbus, OH). The wet mass of the coupon was measured frequently to confirm if equilibrium water swelling was reached. The coupon was then dried at 50 °C in a vacuum oven (281 A, Thermo Fisher Scientific, Waltham, MA) and its dry mass [mg], mdwas measured frequently until the drymass reached equilibrium (see FIG. 8). Equilibrium water swelling or water uptake [g / g], wu, is calculated as:Equilibrium volume fraction of water in a swollen polymer [cm3 / cm3], (pw, is the ratio of the volume of sorbed water in a swollen polymer to the volume of a swollen polymer as:where pwand ppare the densities of water and polymer, respectively. It was assumed that the ideal mixing and volume additivity of water in polymer. The water uptake and volume fraction of water in the polymers are summarized in Table 1.

[0089] Note that the soaking time of a polymer coupon in DI water was estimated using the characteristic time scale of water diffusion in the polymer, tc~ l2 / Dw, where I [ m] is the wet thickness of the polymer film and Dw[cm2 / s] is water diffusivity in the polymer, and was ensured to be much longer than the tcin order to reach equilibrium water swelling. The 4 - 0 formulation (crosslinked PEGDA network with n = 4) showing the slowest water diffusivity (£ ) among the AA-PEGDA series reaches equilibrium water swelling within a day as shown in FIG. 8.

[0090] Polymer density (pp) and crosslinking density (vt). Polymer density [g / cm3], ppwas determined using the Archimedes’ principle. A density measurement kit (ML-DNY-43, Mettler Toledo, Columbus, OH) in an analytical balance was used at ambient temperature to measure ppas:where mdand m(are the masses of a dry polymer coupon in air and in an auxiliary liquid, respectively, and pi is the density of the auxiliary liquid. The auxiliary liquid used in this study was n-heptane (34873, Millipore Sigma, Burlington, MA), as the AA-PEGDA series shows negligible uptake of n-heptane.

[0091] Theoretical crosslinking density [mol / cm3], vt, was estimated from the concentration of vinyl (C = C) groups in a PEGDA crosslinker in each polymer coupon as:where mcis the mass of a PEGDA crosslinker [g], mdis the mass of a dry polymer coupon [g], and Mnis the number-average molecular weight of a PEGDA crosslinker [g / mol]. The prefactor of 2 notes each PEGDA crosslinker has two vinyl groups.

[0092] ATR-FTIR. The chemical structures of the crosslinked AA-PEGDA series and reactants were analyzed using an attenuated total reflection mode Fourier transform infrared spectroscopy (ATR-FTIR, NICOLET i S50 FT-IR, Thermo Fisher Scientific, Waltham, MA). Prior to measurement, hydrated polymer coupons were soaked in DI water overnight, whereas, dry polymer coupons were dried at 50 °C overnight in a vacuum oven to remove residual water. Background and sample spectra were collected using 64 scans at a resolution of 4 cm’1between 500 and 4000 cm’1for each measurement. The background spectrum was subtracted from the sample spectrum using a software (OMNIC, Thermo Fisher Scientific, Waltham, MA) to obtain the data.

[0093] Potentiometric pH Titration. Potentiometric (POT) pH titration was conducted to systematically change the amount of dissociated charged (COO') groups in the AA-PEGDA series as described in FIG. 9. A circular polymer coupon (diameter = 2.2 cm) was dried at 50 °C for 24 hrs in a vacuum oven and its dry mass (md) was measured. The polymer coupon was then immersed in 100 ml DI water for 2 days to reach equilibrium water swelling. DI water used in pH titration was exposed in air at ambient temperature for 24 hrs before use to reach an equilibrium amount of dissolved carbon dioxide (CO2) in water. The pH of the CO2 equilibrated DI water before soaking polymer coupons was measured using a pH meter (SevenDirect SD50, Mettler Toledo, Columbus, OH) and was in the range of pH = 6.0 ± 0.2. The measured pH was in a similar range (pH = 5.65) as reported previously. After soaking the polymer coupon in the DI water, the wet mass (mw) of the coupon was measured frequently to confirm equilibrium water swelling. The pH of the DI water at equilibrium (with the soaked polymer coupon) was measured again before starting the pH titration.

[0094] Next, the varied amount of 0.1 M sodium hydroxide (NaOH, S5881, Millipore Sigma, Burlington, MA) solution was added to the DI water to reach desired pH in the external solution. The polymer coupon soaked in the NaOH solution was placed on an orbital shaker (Labnique, Hunt Valley, MD) for 24 hrs to complete the titration. The final pH of the NaOH solution was measured using a pH meter, and the equilibrium wet mass (jnW)NaOH^aq) of the polymer coupon was recorded. When the pH titration was completed, the polymer coupon was dried at 50 °C overnight in a vacuum oven. The ATR-FTIR analysis was performed on the wet and dry polymer coupons in each step to confirm no chemical degradation occurred during the pH titration (see FIGS. 3, 5, 12, 13, and 16-20).

[0095] In addition, the added mmol equivalent NaOH per grams of a dry polymer [meq / g], xNa0H, was systematically varied (0.1 - 5 meq / g) with respect to the maximumamount of charged groups (COOH in this study) in a polymer coupon [meq / g], i.e., mlEC as shown in Table 2. For example, the polymer coupon of 10 - 2 formulation shows mlEC = 2.0 meq / g, and when this coupon is soaked in the NaOH solution of xNa0H= 2.0 meq / g, then the moles of Na+in the system equal the moles of the COOH groups in the polymer coupon. If the same polymer coupon (10 - 2) is soaked in the NaOH solution of xNa0H= 1.0 or 3.0 meq / g, then the moles of Na+in the system is 50 % lower or 50% higher than the moles of the COOH groups in the coupon. An added volume of 0.1 M NaOH solution [ml], VNa0H^aqis calculated as:is the concentration of NaOH solution (0.1 M).

[0096] The soaking time of a polymer coupon in NaOH solution was estimated using the characteristic time scale of salt diffusion in the polymer, tc~ l2 / Ds, where Dsis salt diffusivity (salt is sodium chloride, NaCl, S9888, Millipore Sigma, Burlington, MA) as described herein and was ensured to reach equilibrium. Because of the slower salt diffusion rate in the AA-PEGDA series with n = 4, only AA-PEGDA series with n = 10 and 13 was studied for the pH titration (n = 4 series were excluded).Table 2. fa] Added mmoi equivalent NaOH per grams of a dry polymer [meq'gj. with respect to the maximum ioa-exehange capacity (mlEC) [meq g] in a polymer coupon (hiring pH titration. NaOH concentration (G) [M] or molar ionic strength (I) [M] of NaOH solution used during pH titration for [b] « ~ 10 and [c] n « 13 series are shown.(a] NaOH amount (xWMr) (t»«Wl[h] NaOH concentration (G) [M] or Moiar ionic strength (Ip [M] (w IQ series)|c] NaOH concentration (Cv) [Ml or Molar ionic strength (I)* [Ml (n ~ 13 series)

[0097] Degree of ionization (a) via POT titration. Degree of ionization (<z) of AA- PEGDA series at varied external pH was determined by potentiometric (POT) titration. As a strong base (0.1 M NaOH solution in this study) is added, H+originating from dissociable COOH groups can react with anion (OH ) from the strong base (NaOH). If the added amount of NaOH solution (xNa0H) is less than the total amount of dissociable COOH groups in a polymer coupon (xNa0H< mlEC), only a fraction of dissociable COOH groups can dissociate with respect to xNa0H. In this case, we assume a = xNa0H / mIEC, indicating the added moles of OH' match the moles of dissociated COO' groups. If the added amount of NaOH (xNa0H) equals the total amount of dissociable COOH groups (xNa0H= mlEC), almost all COOH groups dissociate and present as COO' groups, leading to a = 1. If the added NaOH amount is larger than the total amount of dissociable COOH groups (xNa0H> mlEC), all COOH groups dissociate and present as COO' groups. In this case, a stays at 1. As a result, a can be expressed as:

[0098] Modified Henderson-Hasselbalch equation. In AA-PEGDA series in this study, weakly acidic COOH groups in a polymer coupon dissociate in an aqueous solution to form:pKais defined as the negative logarithm of apparent acid dissociation constant in the polymer coupon as:pH is defined as the negative logarithm of H3O+concentration in the solution as: pH = - log [H3O+] (11)To estimate the degree of ionization (a) in the polymer coupon at a given pH condition, the Henderson-Hasselbalch equation is used to correlate the degree of ionization (a) with pKaand pH in the system as: pH = pKa+ log(a / (l - a)) (12)To best fit the data, the modified Henderson-Hasselbalch equation can be used as: pH = pKa+ B ■ log(a / (l - a)) (13) where B is the empirical fitting parameter. In this study, the modified Henderson-Hasselbalch equation was used to estimate the degree of ionization (a) and pKain the polymers.

[0099] Transport property characterization

[0100] Water permeability (Pw) and water solubility (Kw). Water permeability coefficient (Pw) was estimated from water flux measurement using a diffusion osmosis apparatus (ME-6940, PASCO, Roseville, CA). Water flux was measured during salt permeability test where water flux is driven by an osmotic pressure difference (An) across a membrane, as described previously. A polymer membrane coupon (D = 30.16 mm) was titrated following the procedure described herein using a 1.0 M NaCl solution and then soaked in DI water for 24 hrs. The polymer membrane was clamped between two chambers of the diffusion cell where the upstream and downstream chambers contained 80 mL of 1.0 M NaCl solution and 80 mL of DI water. Each chamber had a stir bar to ensure rigorous and homogeneous mixing during the measurement. Two capillary tubes were fastened to the top of each chamber and contained the same solution as in their respective chambers. In an early stage (at pseudo-steady state), water flux, driven by the osmotic pressure difference (ATT) across the membrane, leads to the increase of the solution level in the upstream capillary tubeand the decrease of the solution level in the downstream capillary tube. The increased liquid volume (AV) of the downstream tube was recorded as a function of time (AV / At) and hydraulic water permeability coefficient, Pw [f ■ pm / (m2■ h ■ bar)] can be calculated as:where I is the wet membrane thickness during the test, A is the active membrane area (3.14 cm2), pwis the water density (1 g / cm3), Ap is the hydrostatic pressure difference applied on the membrane (in our study, Ap = 0) and ATT is the osmotic pressure difference across the membrane. The osmotic pressure in the downstream chamber which initially contained DI water (at t = 0) is assumed to be 0, because of its relatively low salt concentration range during the entire duration of the experiment. The osmotic pressure of the upstream chamber which initially contained 1.0 M NaCl solution was calculated using the Pitzer model and is 46.37 bar.

[0101] Based on the solution-diffusion model, water diffusion is driven by the water concentration gradient in a dense polymer membrane. Thus, diffusive water permeability, Pw [cm2 / s] can be expressed in terms of hydraulic water permeability (P ) as:where R is the ideal gas constant, T is the absolute temperature, Vwis the partial molar volume of water in the polymer membrane which is assumed to be identical to the molar volume of water in solution (18 cm3 / mol), Kwis the water solubility coefficient of the polymer, and / is the Flory-Huggins interaction parameter. Based on the Flory-Huggins theory, / can be estimated by the water activity (aw) in the swollen polymer to the water concentration (Kw) in the polymer as:where Kwcan be experimentally measured (i.e., water volume fraction, (pw) and the pure water has an activity value, aw= 1. Using this information, Pw can be calculated from Pw and x values using the eqn. (15). Thus, diffusive water permeability, Pw values were used in the analysis.

[0102] Water solubility coefficient (Kw) or water partition coefficient is the ratio of water concentration in a polymer membrane Cw) to the water concentration of an external solution as:The Cw value is related to the volume fraction of water in a swollen polymer ((pw) herein as:where Mwis the molecular weight of water (18 g / mol). Thus, the eqn. (17) can be rewritten as:The value can be approximated as the density of pure water (w) in dilute solutions. The contiguous water contacting the polymer membrane is assumed to have pure water density (w). With these reasonable assumptions, the eqn. (19) can be rewritten as:Kw= <Pw (20)Therefore, Kwequal the volume fraction of water in the swollen polymer membrane ((pw) and can be estimated from water uptake measurement.

[0103] Salt permeability (Ps). Salt permeability coefficient (Ps) was measured using direct permeation cells with dual chambers (Diffusion cells, Adams & Chittenden Scientific Glass, Berkeley, CA) at 25 °C and atmospheric pressure. A polymer membrane coupon (D = 30.16 mm) was titrated following the procedure described herein using a 1.0 M NaCl solution and then was soaked in DI water for 1 day. The polymer membrane was clamped between two chambers where the donor and receiver chambers were filled with 35 ml of 1.0 M NaCl solution and 35 ml of DI water. A stir bar in each chamber was used for rigorous and homogeneous mixing during the experiment. The temperature was maintained at 25 °C using an isotemp water circulator (Isotemp Immersion Circulator, 4100C, Thermo Fisher Scientific, Waltham, MA). As salt (NaCl) diffuses across the polymer membrane from the donor chamber to the receiver chamber (initially containing DI water), the diffused salt gradually changes the conductivity in the receiver chamber. The conductivity in the receiver chamber was recorded as a function of time using a conductivity probe (LR325 / 01, WTW, Oberbayem, Germany) and meter (InoLab Cond 730, STW, Oberbayem, Germany). Using the calibration curve correlating conductivity to salt concentration, the salt concentration in the receiver chamber was calculated from the recorded conductivity. By measuring the salt concentration change as a function of time in the receiver chamber, the salt permeability coefficient, Ps, can be calculated as:where VRis the volume of donor and receiver chambers (35 ml), A is the active membrane area (1.77 cm2), I is the wet membrane thickness during the measurement, CR[t] and CD[0]are the salt concentration in the receiver chamber at time t and the initial salt concentration in the donor chamber (1.0 M NaCl) at time t.

[0104] Results and Discussion

[0105] Chemical structure of crosslinked AA-PEGDA network films

[0106] A series of the crosslinked AA-PEGDA copolymer networks was successfully synthesized via UV-induced free radical polymerization as shown in the FIG. 1A.Transparent, free standing films with uniform thicknesses (with a variability < 3-5 %) were prepared as shown in FIG. IB and Table 1. After soaking a polymer film in DI water (pH = 5 ~ 6) for 2 days, the thickness of the wet polymer film was measured using a micrometer (H- 2780, Mitutoyo, Japan) when equilibrium water swelling was reached. The thickness of the dry polymer film was measured after drying the film at 50 °C for 2 days in a vacuum oven. As AA content (wt%) increases (mlEC increases), the dry and wet film thicknesses decrease because of increased interaction by the added AA monomers as shown in FIG. 11. As the number of EO repeating units in a PEGDA crosslinker increases (n = 4, 10, and 13), the dry and wet film thicknesses increase due to decreased crosslinking density (vt). Note that as a PEGDA crosslinker’s molecular weight increases from 250 g / mol to 700 g / mol, the number of EO repeating unit in the PEGDA, n increases from n = 4 to n = 13, leading to a looser crosslinked network.

[0107] The conversion rate [%] between the mass of a prepolymer mixture and the mass of a formed polymer network was recorded as: . > _ 100 (22)where the mass of a prepolymer mixture is the sum of the masses of AA monomer, PEGDA crosslinker, and DMPA photoinitiator. The average conversion rate of the AA-PEGDA series is 98.4 ± 1.2 %, indicating the successful formation of the networks (see Table 1). FIG. 2 shows that as the amount of AA monomer (wt%) in prepolymer mixtures increases, the total amount of dissociable charged groups (i.e., mlEC) in the resultant network films linearly increases. Two IEC indices were introduced, the maximum ion-exchange capacity, mlEC [meq / g] and the effective ion-exchange capacity, elEC [meq / g] to conveniently quantify the amount of dissociable and dissociated charged groups in the polymers. The total amount of dissociable charged groups (COOH in this study) in polymers is quantified using the maximum ion-exchange capacity, mlEC, the maximum mmol equivalent H+per gram of a dry polymer [meq / g]. On the other hand, the effective ion-exchange capacity, elEC, represents the amount of dissociated charged groups (COO' in this study) in a dry polymer[meq / g]. In this study, mlEC is solely dependent on AA content (wt%), whereas elEC is affected both by AA content (wt%) and the external pH in the solutions. In a fixed, same chemical structure (i.e., mlEC and PEGDA crosslinked length n are fixed), elEC is proportional to the degree of ionization (<z) as: elEC = mlEC - a (0 < a < 1) (23)

[0108] In contrast, when the number of EO repeating units (n = 4, 10, and 13) in a PEGDA crosslinker changes, mlEC is not affected, since only acrylic acid (AA) groups can dissociate and contribute to mlEC. The dashed line in FIG. 2 is the theoretical mlEC of the polymers which corresponds to the conversion data, again confirming the successful synthesis of the AA-PEGDA series with a wide range of mlEC and varied crosslinking densities (vt) (also see Table 3). Additional analysis in the polymer composition can be found in FIG. 10.

[0109] To further assist the quantification of ion-exchange capacity (IEC) in the polymers, charged group concentrations, C™ of AA-PEGDA series were calculated at varied external pH. In Table 3, the charged group concentrations (C"1) of both dissociable COOH groups and dissociated COO' groups in the AA-PEGDA series (in both dry and hydrated states) at the lowest pH (pH = 5 ~ 6) and the highest pH (pH = 11 - 12) was reported to show the ranges in charged group contents. The experimental mlEC via conversion test, the degree of ionization (<z) and elEC values were included for comparison. In each AA-PEGDA composition, the total amount of dissociable COOH groups (i.e., the mmol of dissociable COOH groups per cm3of a dry polymer) at the lowest pH = 5 - 6 is in a similar range with the total amount of dissociated COO' groups (i.e., the mmol of dissociated COO' groups per cm3of a dry polymer) at the highest pH = 11 - 12, as expected. Note that because of the slower salt diffusion rate in the n = 4 series, only n = 10 and 13 series were studied for the pH titration.

[0110] The chemical structures of the AA-PEGDA series were confirmed by the ATR-FTIR using dry and wet films as shown in FIG. 3. The films were soaked in DI water (pH = 5 ~ 6) for 2 days, and then dried at 50 °C overnight in a vacuum oven before ATR- FTIR analysis (AA monomer and PEGDA crosslinker were measured without drying). The spectra of the dry AA-PEGDA series (mlEC = 0 ~ 4 meq / g) using the same PEGDA crosslinker (Mn= 575 g / mol or n = 10) are shown in FIG. 3A. The control spectra of AA monomer and PEGDA crosslinker are also shown for comparison. The spectra of the AA- PEGDA series and the control PEGDA crosslinker show distinct peaks at 1726 cm’1(ester C = O stretching) and 1110 cm’1(ether C - O - C stretching), indicating the successful incorporation of PEGDA crosslinker in the polymers. Also, the spectra of the AA-PEGDA series and the control AA monomer exhibit a clear peak at 1700 cm’1(acrylate C = O stretching), confirming the presence of AA monomers (C = O from COOH groups) in thepolymers. The disappearance of the bands at 809 cm’1(CH2 = CH twisting / wagging) and 1636 cm’1(CH2 = CH stretching) in the AA-PEGDA series suggests the successful free radical polymerization.

[0111] FIG. 3B shows the spectra of the wet AA-PEGDA series (n = 10). The films were equilibrated in DI water (pH = 5 ~ 6) to reach equilibrium water swelling. The blue areas located at 2800 - 3600 cm’1and 1640 cm’1indicate H - O - H bending vibration from water in hydrated polymers. In a fixed PEGDA crosslinker length (n), as mlEC increases between 0 ~ 4 meq / g, the polymers sorb more water with increasing AA content, and thus, the intensities in the related water peaks increase. Also, in a fixed mlEC, as PEGDA crosslinker length increases (n = 4, 10, and 13) (see FIGS. 12 and 13), the related water peak intensities increase similarly as the polymers sorb more water with decreasing crosslinking density (vt). The absorbance spectra of the other AA-PEGDA series show similar trends as shown in the FIGS. 12 and 13.

[0112] When the AA-PEGDA films were soaked in DI water (pH = 5 ~ 6) for 2 days, the peak originating from dissociated COO' groups at 1575 cm’1is not significant with increasing mlEC and increasing PEGDA crosslinker length (see FIGS. 3B, 12B, and 13B). The peak at 1575 cm’1is related to the antisymmetric stretching bonds of the COO' groups. The amount of dissociated charged (COO') groups (at 1575 cm'1) is negligible (degree of ionization, a = 0.05 ± 0.02 % as shown in FIG. 14 and Tables 3 and 4) in the polymers soaked in DI water (pH = 5 ~ 6), as also confirmed by potentiometric (POT) titration. Therefore, the external pH ranges higher than pH = 5 were focused on in this study. Detailed information on the degree of ionization (a) vs. pH and dissociation process are discussed below.Table 4. Degree of iomzation [%]. a iu AA-PEGDA series calculated from the pH changes recorded la FIG. 14.mlEC [meq / g]0.04 ± 0.03

[0113] Effect of polymer composition on water content (<pw) and polymer density(pp). Controlling water swelling in the AA-PEGDA series is required for fundamental understanding of water and ion transport in these materials. In this section, the effect of polymer composition, i.e., the amount of AA content (i.e., mlEC = 0 ~ 4 meq / g) and PEGDA crosslinker length (n = 4, 10, and 13) on water content (< >w) and polymer density (p) in the AA-PEGDA series in DI water (i.e., the lowest pH = 5 ~ 6 in this study) is described. FIG. 4A shows the volume fraction of water,in a swollen polymer [cm3sorbed water / cm3of a swollen polymer] as a function of mlEC and PEGDA crosslinker length ri) in DI water (pH = 5 ~ 6). The wet masses and dry masses of three representative AA-PEGDA films are shown in FIG. 8, and similar data were obtained for all other compositions. Gravimetric water uptake data can also be found in FIG. 15.

[0114] First, at a fixed mlEC, as PEGDA crosslinker length (ri) increases, <pwincreases because of increased free volume in loosely crosslinked networks. As PEGDA crosslinker length (ri) increases, the distance between network junctions increases and crosslinking density (vt) decreases, leading to increased free volume in the polymers. Moreover, as PEGDA crosslinker length (ri) increases, hydrophilic EO group content increases, leading to increased (pwas shown in FIGS. 4B and 4C.

[0115] Second, at a fixed PEGDA crosslinker length (n), the AA-PEGDA series shows different (pwtrends with increasing mlEC. In the AA-PEGDA series with the fixed PEGDA crosslinker length, n = 4, as mlEC increases, <pwincreases from 0.069 to 0.181. In contrast, the AA-PEGDA series with n = 10 and n = 13 shows the almost constant <pwwith increasing mlEC. The reason for these different (pwtrends comes from the competing contributions of vtand hydrophilic EO group content in the polymers. As described in the previous section, the AA-PEGDA series in DI water (pH = 5 ~ 6) behaves like an uncharged polymer, as their degree of ionization (a) is very low (a = 0.05 ± 0.02 %) as reported elsewhere28. As AA content (wt%) increases, mlEC increases, whereas, the amount of PEGDA crosslinker decreases in the polymers. The decreased PEGDA crosslinker content corresponds to decreased vtand decreased EO group content (mol%) in the polymers, offering competing effects on (pw. Decreased vtleads to increased (pw, whereas, decreased EO group content decreases (pw. In the AA-PEGDA series with n = 4, as mlEC increases, the effect of decreased vton (f)wis a dominant factor rather than the effect of decreased EO content on (pw. As a result, as mlEC increases in the n = 4 series, <pwincreases. On the other hand, in the AA-PEGDA series where n = 10 and n = 13, as mlEC increases, the effects ofdecreased vtand EO content on (pwoffset each other, leading to the almost constant (pw.(see FIGS. 4B and 4C)

[0116] FIG. 4D shows the polymer densities, pp[g / cm3] of the AA-PEGDA series with varied mlEC and PEGDA crosslinker length (n). The films were soaked in DI water (pH = 5 ~ 6) for 2 days and then dried at 50 °C for 2 days in a vacuum oven before measurement. At a fixed mlEC, as PEGDA crosslinker length (n) increases from n = 4 to 13, ppdecreases because of decreased vt. At a fixed PEGDA crosslinker length, as mlEC increases, ppincreases due to increased interaction induced by the increased AA content in the polymers, as reported previously. This pptrend is consistent with dry and wet thicknesses versus polymer compositions as shown in FIG. 11.

[0117] The advantages of the AA-PEGDA series are in their tunability of charged group concentration on fixed, same chemical structures by changing the external pH in solutions (see FIG. 1C). In this section, described is the systematic changes of dissociated charged (COO') groups in the AA-PEGDA series as a function of the external pH via potentiometric (POT) titration and ATR-FTIR analysis and their water contents (< >w) in the resultant membranes. FIG. 5A exhibits the spectra of control, dry crosslinked PEGDA network with mlEC = 0 meq / g and PEGDA crosslinker length n = 10 (nomenclature is 10 - 0) at varying external pH in solutions. This crosslinked PEGDA network does not contain AA monomer, i.e., dissociable COOH group (i.e., mlEC = 0 meq / g) and serves as a control. The control crosslinked PEGDA network shows absorbance peak at 1726 cm'1originating from C = O stretching bonds from PEGDA crosslinkers’ O - C = O moieties and no absorbance peak related to AA monomers’ COO' groups (at 1575 cm'1), as expected. As the external pH increases, no change in chemical structure is observed in the spectra, as expected. Note that experiments were performed within the time window that no chemical degradation occurs in the pH ranges (pH = 5 ~ 12). The control crosslinked PEGDA network with mlEC = 0 meq / g and PEGDA crosslinker length n = 13 (nomenclature is 13 - 0) shows the similar absorbance spectra as shown in FIG. 17A.

[0118] In contrast, the AA-PEGDA series with dissociable COOH groups shows distinctly different trends. FIG. 5B shows the spectra of the dry AA-PEGDA network with mlEC = 2 meq / g, and PEGDA crosslinker length n = 10 (nomenclature is 10 - 2) at the varied external pH in solutions. In AA-PEGDA series, the absorbance peak at 1575 cm'1represents the antisymmetric stretching bonds of dissociated COO' groups, whereas, theabsorbance peak at 1700 cm’1is related to C = O stretching bonds originating from both (1) AA monomers’ COOH groups and (2) PEGDA crosslinkers’ O - C = O moieties. As the external pH increases, the amount of dissociated COO' groups increases as confirmed by the increasing absorbance peaks at 1575 cm'1(COO' groups). Simultaneously, the amount of undissociated COOH groups decreases as shown in the decreasing absorbance peaks at 1700 cm'1(C = O from COOH groups). However, because the absorbance peak at 1700 cm'1also includes the C = O stretching bonds from PEGDA crosslinkers’ O - C = O moieties (at 1726 cm'1), as the external pH increases to pH = 11 ~ 12, the decreasing peaks at 1700 cm'1do not disappear. This is due to the presence of PEGDA crosslinkers, as consistent with previous reports.

[0119] To further quantify the amount of dissociated charged (COO') groups in AA- PEGDA series, the degree of ionization (a) at varied external pH in the polymers was measured via potentiometric (POT) titration and correlated the degree of ionization (a) with ATR-FTIR analysis. FIG. 5C shows a versus pH of the 10 - 2 AA-PEGDA network determined via POT titration, and the absorbance intensities of dissociated COO' groups (at 1575 cm'1) via ATR-FTIR analysis. The solid line of a vs. pH represents the fitting by the modified Henderson-Hasselbalch equation. A molecular schematic at different pH ranges is shown to describe the dissociation process in the AA-PEGDA series. As the external pH increases, the amount of dissociated charged (COO') groups increases, and a increases between 0 ~ 1, following the modified Henderson-Hasselbalch equation. The a vs. pH trend is well aligned with the absorbance intensities of dissociated COO' groups (at 1575 cm'1) via ATR-FTIR analysis. If pH < 7, most COOH groups do not dissociate (a = 0) and the AA- PEGDA series behaves like an uncharged neutral polymer, corresponding to the negligible absorbance intensities of COO' groups. As the external pH increases between pH = 7 and pH = 10, the amount of dissociated charged (COO') groups increases in a steeper manner. Thus, a increases similarly between 0 ~ 1, also correlating with the increasing absorbance intensities of COO' groups. At pH > 10, almost all COOH groups dissociate and present as COO' groups, and thus, a reaches 1, as confirmed by the maximum absorbance intensities of COO' groups. Therefore, our a vs. pH analyses via both POT titration and ATR-FTIR analysis show the successful systematic control of dissociated charged (COO') groups versus pH. Also, the absorbance intensities of COO' groups (at 1575 cm'1) via ATR-FTIR analysis are reasonably well correlated with a in the polymers. The ATR-FTIR spectra of all other AA-PEGDA series (dry and wet states) vs. pH are shown in FIGS. 16-20. Analyses of allother AA-PEGDA series show the similar a vs. pH trends as well as the strong correlation between a vs. the absorbance intensities of COO' groups as shown in FIGS. 21 and 22.

[0120] The abrupt increase in the dissociated COO' groups (both in a and absorbance intensities) vs. pH is correlated with pKa values in the polymers. Note that pKa value was determined at the halfway point (a = 0.5) of a vs. pH curve as shown in FIG. 5C. The pKa of AA monomer is around 4.5 in dilute condition. The pKa values in the AA-PEGDA series are in the range of 7.85 ~ 9.10 depending on polymer composition via POT titration as shown in FIGS. 21 and 22. The increased pKa in the AA-PEGDA series compared with the pKa of AA monomer is likely due to the suppressed ionization in crosslinked networks as reported previously. Higher crosslinking density in AA-PEGDA series decreases the proximity of COOH groups, and thus, shifts the pH titration curve to higher pH ranges (i.e., increased pKa) because of increased electrostatic interaction between COOH groups.

[0121] FIGS. 5D and 5E summarize the increased absorbance intensities of dissociated COO' groups (at 1575 cm'1) versus pH in all dry AA-PEGDA series (n = 10 and 13) with mlEC = 1 ~ 4 meq / g. The motivation of plotting the absorbances of COO' groups vs. pH comes from the fact that the absorbances of COO' groups via ATR-FTIR analysis well represent the degree of ionization (a) in the AA-PEGDA series as shown in FIGS. 5C, 21, and 22. The absorbances (at 1575 cm'1) of the control PEGDA networks (10 - 0 and 13 - 0) are also shown for comparison and exhibit negligible changes as a function of pH, as expected. The trend is similar among all AA-PEGDA series with different mlEC and PEGDA crosslinker length (n). At a fixed PEGDA crosslinker length (n), as mlEC increases, the absorbance intensities of dissociated COO' groups (at 1575 cm'1) significantly increases, as expected.

[0122] The wet AA-PEGDA series shows similar trends in the ATR-FTIR analysis (see the FIGS. 18-20), but their absorbance intensities are lower than those in the dry samples. This is attributed to diluted concentrations of COO' groups in the wet samples due to increased water content in the polymers.

[0123] FIG. 6 shows the sorbed water content ((pw) at varied external pH in the AA- PEGDA series. The <pwvalues of the control, crosslinked PEGDA networks with n = 10 and 13 (10 - 0 and 13 - 0 formulations) are shown for comparison. Without AA monomer in the networks (mlEC = 0 meq / g), the control, crosslinked PEGDA networks do not contain dissociable charged (COO') groups (see FIGS. 5D-5E), showing no <pwchange versus the external pH, as shown in FIGS. 6B-6D. In contrast, in the AA-PEGDA series, as the externalpH increases, (pwincreases because of increased amount of dissociated COO' groups (i.e., the increased degree of ionization, a) in the polymers as shown in FIG. 6A. FIG. 6A shows the strong correlation between the degree of ionization (a) and <pwas a function of pH in the 10 - 2 formulation, and the similar trends can be found in all other AA-PEGDA series as shown in FIGS. 23 and 24. As the external pH increases, the dissociated COO' groups like to be surrounded by water, and thus, <pwincreases until the osmotic pressure of water reaches equilibrium with the elastic resistance of the polymer network. As a result, increasing trends in (f)wclosely correlate with the increased amount of dissociated COO' groups in the polymers.

[0124] In a fixed PEGDA crosslinker length (n), as mlEC increases, the changes in <pwversus the pH increase due to increased amount of dissociated COO' groups as shown in FIGS. 6B and 6C. In a fixed mlEC, as PEGDA crosslinker length (n) increases, the changes in (f)wversus the pH increase due to decreased crosslinking density (vt) in the polymers as shown in FIG. 6D. A looser network with lower crosslinking density can sorb more water than does a tighter network. In the n = 10 series (see FIG. 6B), the changes in (f)ware between 0.32 ~ 0.65 as the degree of ionization (a) changes between 0 and 1. In the n = 13 series (see FIG. 6C), the changes in (f)ware in the range of 0.40 ~ 0.69 as 0 < a < 1. Thus, while covering a wide mlEC range (0 ~ 4 meq / g), equilibrium water swelling is successfully controlled and limited to a lower range in the AA-PEGDA series.

[0125] For comparison, other charged polymers in literature show a narrower, limited range of lECs but higher water swelling. For instance, a benchmark proton-exchange membrane (PEM), i.e., commercially available sulfonated tetrafluoroethylene (Nafion®) shows lECs between 0.90 ~ 1.01 meq / g and their (f)wis 0.34. Sulfonated stryrenic pentablock copolymers (Nexar®) show lECs between 0.4 ~ 2.1 meq / g and their (f)win the range of 0.16 ~ 1.44, respectively. Sulfonated crosslinked networks (2-acrylamide-2-m ethyl- 1- propanesulfonic acid (AMPS) - poly(ethylene glycol) diacrylate (PEGDA) copolymers) exhibit lECs between 0.44 ~ 1.93 meq / g with (f>wbetween 0.35 ~ 0.67. Disulfonated poly(arylene ether sulfone)’ s showed lECs between 0.92 ~ 1.78 meq / g and <pwbetween 0.1 ~ 0.48. Compared to the reported charged polymers, the AA-PEGDA series provides lower water swelling (0.07 - 0.69) while achieving a much wider IEC range between 0 ~ 4 meq / g. Furthermore, by controlling the external pH in solutions, the charged group concentration can be systematically changed on a fixed chemical structure, providing extra freedom to tuneIECS and an opportunity to investigate water and ion transport on the same chemical structure, for the first time.

[0126] Effect of charged group concentration on transport properties. In this disclosure, in the fixed chemical structure, the amount of dissociated charged (COO') groups, i.e., charged group concentration in a polymer, was systematically changed at varied external pH. In this section, described is the effect of charged group concentration at varied external pH on water and salt transport properties in the fixed 10 - 2 AA-PEGDA network membrane (mlEC = 2 meq / g, and PEGDA crosslinker length n = 10) to demonstrate the proof of concept. The changes in charged group concentrations in the fixed chemical formulation significantly influence water and salt transport properties as shown in FIG. 7. It was also of interest to note whether the water and salt transport properties could be further correlated using free volume theory.

[0127] Transport of small molecules (e.g., water, ions, and gases) across polymer membranes occurs through free volume elements (i.e., cavities or pores) which are unoccupied spaces between polymer chains assisting in molecular transport. Using the solution-diffusion model for dense polymer membranes, permeability coefficient of penetrant i, Pt can be written as the product of diffusivity coefficient,and solubility coefficient, K of penetrant i as:

[0128] The Cohen and Turnbull’s free volume model predicts that diffusivity of penetrant i, can be related to the free volume of a polymer (y ) as:where v* is the characteristic volume needed for a small molecule’s diffusion across the polymer membrane. Since permeability Ptis related to diffusivity Dtby Pt= Dt■ K permeability Ptcan also correlate well with the polymer’s free volume (ty) as reported previously. This is the case for most polymers because diffusivity in most polymers spans about 10 orders of magnitude while solubility varies within two orders of magnitude. Therefore, in a first order approximation, permeability Ptshows strong correlation with the polymer’s free volume (ty) as:

[0129] If the free volume in the polymer (y ) scales linearly with the volume fraction of penetrant in the polymer, then permeability Pt(and diffusivityscales exponentiallywith the changes in the penetrant volume fraction in the polymer. In hydrated polymers such as AA-PEGDA series in this study, the water (penetrant) volume fraction in the swollen polymer (< >w) can be expressed as water solubility or water uptake, Kw.

[0130] Based on free volume theory, Yasuda and coworkers suggested that the free volume of a hydrated polymer (ry) can be expressed as the summation of the free volume of the polymer (Vfpoiymer) and the free volume of water (V;H2O)AS:

[0131] Since salt (NaCl) permeation through a dry, dehydrated polymer membrane is likely to be negligible, most salt is expected to permeate through the hydrated areas in the polymer. As a result, the available free volume for salt permeation is assumed to be the free volume of added water in the polymer, and the eqn. (27) can be rewritten as: ty = Kw■ VfH20(28)

[0132] Consequently, the salt diffusivity (s) in the hydrated polymer membrane can be reformulated as:where Dois the salt (NaCl) diffusivity in pure water at 25 °C (1.47 X 10'5cm2 / s), B* is the proportionality constant with respect to v* and VfH20. Thus, the salt permeability (Ps) in the hydrated polymer membrane can be rewritten using Ps= Ds■ Ksas:where Ksis the salt solubility in the polymer. Therefore, if the salt permeability (Ps) is plotted against 1 / KW(i.e.,alinear relationship with a slope (B‘) is expected, starting at the intercept of 1 / KW= 1 (i.e., the salt diffusivity in pure water).

[0133] FIG. 7A shows the water and salt (NaCl) permeabilities (Pwand Ps) as a function of 1 / KW(i.e., \ / '(pw) from this study (10 - 2 AA-PEGDA membrane) along with other hydrated polymers such as hydrogels, acrylate and sulfonated polymers in literature for comparison. Other hydrated polymers in literature include (1) PEGDA based hydrogels such as crosslinked PEGDA networks (Mn= 575 and 700 g / mol) and PEGDA / poly(ethylene glycol) acrylate network (PEGDA Mn= 700 g / mol, PEGA Mw= 380 g / mol), (2) acrylate polymers such as hydroxypropyl methacrylate (HPMA) polymer, glycerol methacrylate (GMA) polymer, HPMA / methyl methacrylate (HPMA / MMA) copolymers, HPMA / glycidyl methacrylate (HPMA / GdMA) copolymers, HPMA / GMA copolymers, hydroxyethyl methacrylate (HEMA) polymer, HEMA / MMA copolymers, GMA / tetraethylene glycoldimethacrylate (GMA / TEGDMA) copolymers, MMA / GMA copolymers, and cellulose acetate, and (3) sulfonated polymers such as disulfonated poly(arylene ether sulfone) (BPS) copolymers and 2-acrylamido-2-methyl-l -propanesulfonic acid (AMPS)-PEGDA copolymers. The 10 - 2 AA-PEGDA membrane as well as these other polymers in literature show both water and salt permeabilities (Pwand Ps) scale exponentially with l / (pw, indicating that a reasonable analysis can be done using Yasuda’s free volume model. The dashed lines through the data are the fitting using Yasuda’s free volume model. As the membrane hydrophilicity increases (pwincreases), the plots of logand log Ps- vs. l / (pware linear, as consistent with previous reports.

[0134] In one fixed chemical structure of the 10 - 2 AA-PEGDA membrane, as the external pH increases between pH = 5 ~ 6 to pH = 11 ~ 12, the dissociated charged (COO') groups increase, and the degree of ionization (a) increases between a = 0 and a = 1. Subsequently, water volume fraction (0^) increases in the same chemical structure, leading to exponentially increased water and salt permeabilities Pwand Ps). Specifically, in the fixed 10 - 2 formulation, as the external pH changes between pH = 5 ~ 6 and pH = 11 ~ 12, the charged group concentration (C™) increases between C™ = 0.000 ± 0.000 mmol / cm3and 2.154 ± 0.097 mmol / cm3(as a increases between 0 ~ 1), and the water volume fraction (W) increases between <pw= 0.330 ± 0.004 and <pw= 0.542 ± 0.015 (see Tables 1, 3 and 5). Simultaneously, the water permeability (Pw) increases exponentially between Pw= 1.27 x 10-6cm2 / s and Pw= 3.53 x 10-6cm2 / s, whereas, the salt permeability (Ps) also increases exponentially between Ps= 3.15 x 10-8cm2 / s and Ps= 1.23 x 10-7cm2 / s. Interestingly, the changes in Pwand Psversus pH in the fixed 10 - 2 formulation can be brought about by substantially changing the chemical structure of other polymers in literature. For instance, the differences in Pwand Psversus pH in the fixed 10 - 2 formulation can be achieved by varying the sulfonation level (between 20 ~ 40 mol%) and ionic form (K or H forms) in sulfonated polysulfones (BPS), or altering the sulfonated monomer content (between 0 ~ 40 mol%) in AMPS-PEGDA polymers, or varying the acrylate monomer content (between 15 - 100 mol%) in acrylate polymers, or changing water content (between 0 - 80 wt%) in the crosslinked PEGDA networks. This implied that, in addition to varying the chemical structure of polymers via lengthy and cost-intensive synthetic routes, the AA-PEGDA series provides extra freedom to tune polymer transport properties via simply varying the external pH in the fixed chemical structure.

[0135] In addition, the slope of the salt permeability (Ps) versus l / (pwis steeper than that of the water permeability (Pw) versus l / (pw,asconsistent with previous reports. Larger penetrants (e.g., hydrated salts) show a stronger dependence on free volume than do smaller penetrants (e.g., water). In this disclosure, hydrated Na+and Cl’ ions are larger than water molecules, exhibiting lower Psthan Pw, as well as a stronger dependence on free volume changes in polymers than do smaller water molecules.

[0136] In order to characterize polymer membrane’s intrinsic capability to separate water and salt for water purification and desalination applications, water / salt permeability selectivity ( w / ) is defined as the ratio of water permeability (Pw) to salt permeability (Ps) as:

[0137] According to the permeability-selectivity tradeoff relationship developed for gas separation membranes, a polymer membrane showing high permeability tends to sacrifice selectivity, as shown in FIG. 7B. FIG. 7B shows water / salt permeability selectivityplotted against water permeability (Pw) of the 10 - 2 AA- PEGDA membrane in this study along with the other polymers in literature. In the fixed 10 - 2 AA-PEGDA membrane, as pH increases between pH = 5 ~ 12, the charged COO’ group concentration increases with increasing a = 0 ~ 1 (see Table 3), leading to the increased water permeability (Pw) between Pw= 1.27 x 10-6cm2 / s and Pw= 3.53 x 10-6cm2 / s, and the decreased water / salt selectivity (ctu ) between aw / = 28 and aw / = 20. This is consistent with the permeabilityselectivity tradeoff relationship. This again demonstrates that the transport properties of the AA-PEGDA series can be successfully tuned via changing the external pH using one fixed chemical structure. Also, the differences in selectivity-permeability ( aw / vs. Pw) of the fixed 10 - 2 formulation in this study can be achieved by significantly varying the chemical structure of the other polymers in literature as mentioned above. This reiterates that in addition to changing the chemical structure of polymers, this AA-PEGDA series can provide additional opportunity to modify polymer transport properties and enable us to develop a mechanistic understanding of water and ion transport in charged polymer membranes. This new library of AA-PEGDA series can offer a much broader IEC range (0 ~ 4 meq / g) with limited water swelling for a wider range of membrane-based clean technologies spanning environment, energy and health.Table S. Polymer density theoretical crosslinking density water uptake (wu) and water volume fraction ($w) of AA-PEGDA series at the highest pH (pH ~ 11 - 12). An average value with a standard deviation was reported for each measurement with at least three samples to report” Theoretical crcmhaking density (ef) was detetnthsed using the eqa (d). c Water uptake (w\;) was calculated using the eqa. (3),;iWater volume traction) was calculated using the e<pt (4).

[0138] Conclusions

[0139] Charged polymer membranes are of great interest due to their versatile and tunable transport properties for clean technologies in sustainability and decarbonization. Designing new innovative charged polymers for these clean technologies is dependent on the mechanistic understanding of water and ion transport in these materials. Two representative challenges that previously hindered fundamental understanding of water and ion transport in charged polymers are (1) different polymer chemistries used for comparison and (2) high water swelling. To overcome these limitations, described herein is a systematic library of weak polyelectrolyte membranes, i.e., crosslinked acrylic acid - poly(ethylene glycol) diacrylate (AA-PEGDA) random copolymer networks with a wide ion-exchange capacity (TEC = 0 ~ 4 meq / g) range and limited water swelling ((pw= 0.07 - 0.69). An acrylic acid (AA) monomer was chosen as a weakly charged group to control the charged group concentrations in the polymers, i.e., maximum ion-exchange capacity (mlEC) at the varied external pH. Poly(ethylene glycol) diacrylates (PEGDAs) with different crosslinker lengths (n = 4, 10 and 13) were used as crosslinkers to control crosslinking density (vt) in the networks.

[0140] In DI water (pH = 5 ~ 6), as mlEC increases and PEGDA crosslinker length increases, water contentchanges due to the competing effects of crosslinking density (yt) and ethylene oxide (EO) content in the polymers. As the external pH increases, theamount of dissociated COO' groups increases, leading to higher (pw, but is limited to a lower range due to network architecture. Compared to other charged polymers in literature, our AA- PEGDA series provides a much wider IEC range (0 ~ 4 meq / g) with lower water swelling (0.07 - 0.69). Specifically, in a fixed polymer composition, by controlling the external pH, the charged group (COO') concentration can be systematically changed on the same chemical structure: the same polymer behaves like an uncharged neutral polymer (a = 0) at low pH, whereas at pH = pKa, the same polymer is one half charged (a = 0.5), and, at high pH (»pKa), is fully charged (a = 1). Thus, as the external pH increases between pH = 5 ~ 12 , the dissociated charged (COO') groups and water volume fraction ((pw) increase (as a increases between 0 ~ 1) in the same chemical structure, leading to the exponentially increased water and salt permeabilities (Pwand Ps), following Yasuda’s free volume model. The differences in polymer transport properties of the fixed 10 - 2 formulation in this study can be achieved by substantially varying the chemical structure of other polymers in literature. This implies that, in addition to changing the chemical structure of polymers, this AA-PEGDA series can provide extra freedom to modify polymer transport properties via simply changing pH, enabling us to develop a mechanistic understanding of water and ion transport in charged polymer membranes. The present disclosure is expected to catalyze the design of new innovative charged polymer membranes for a wide range of applications in energy, environment, and health.EXAMPLE 2

[0141] This example provides a description of a polymer membrane of the present disclosure.

[0142] Polymer membranes of the present disclosure achieved a wide (tunable) ionexchange capacity (0~ 4 mequiv / g) — (1) significantly higher than other conventional ionexchange membranes — (2) via adjusting the external pH using the same chemical structure. This feature enables the precise control of target ion (e.g., Na+) concentration in membranes for various ion-involving applications in energy, environment and health. pH-responsive tunability makes it suitable for adaptive ion control applications, including energy devices, separation processes, and sensors. See FIG. 26.

[0143] Tunable Ion Solubility Selectivity in one polymer membrane: By adjusting the external pH, we can modulate ion solubility selectivity Kw / K in the same AA-PEGDA membrane. This offers a useful toolbox to control ion partition between the membrane andsurrounding external solution without changing membrane composition. See FIGs. 27 and 28.

[0144] Opposite Behavior of Counter-ion (Na+) vs Co-ion (Cl’): For Na+(counterion): As pH increases and the membrane becomes more negatively charged (higher a), Na+solubility increases — often exceeding water solubility — due to Donnan attraction. See FIGs. 27 and 28.

[0145] For Cl’ (co-ion): The opposite occurs. As pH increases and the membrane becomes more charged, Cl" solubility decreases below that of water, due to Donnan exclusion. See FIGs. 27 and 28.

[0146] Using one Polymer, a broad range of functionality achieved. Unlike other membranes, this system enables a wide range of ion transport properties on the same polymer chemical structures by varying the external pH, allowing multi-functional use without changing chemical structures. See FIGs. 27 and 28.

[0147] Energy-related devices: pH-controlled enhancement of cation (e.g., Li+, Na+) solubility improves ion conductivity, making the membrane suitable for power generation.

[0148] Water Treatment & Desalination: Reduced co-ion (e.g., Cl ) solubility at high pH enables effective ion rejection, which is useful for desalination and water purification systems

[0149] Smart Separation & Sensing: Tunable ion solubility via pH allows selective ion uptake or exclusion using the same polymer membrane, enabling applications in sensors, selective ion recovery, and responsive separation membranes.

[0150] Single system tunability: Unlike conventional membranes that require different chemistries to adjust selectivity, our AA-PEGDA membranes allow permeability and diffusivity selectivity (P PS, D Ds) to be tuned in the same polymer chemical structure by changing pH.

[0151] pH-dependent behavior: As pH increases, membrane charge increases, leading to higher ion permeability and diffusivity.

[0152] Potential applications: This feature is advantageous for systems where enhancing both water and ion transport is critical, such as: High-flux energy membranes (e.g., fuel cells, flow batteries), Ion-driven water pumps or osmotically active membranes, Controlled nutrient or drug delivery platforms

[0153] Tunable salt permeability via pH: Salt permeability (P^ can be adjusted over more than one order of magnitude by simply changing pH within the same membrane, enabling dynamic membrane functionality adaptable to varying environments. (FIG. 31).

[0154] Cation-specific transport behavior: Observable differences in Psamong NaCl, LiCl, and KC1 imply the possibility of ion-specific selectivity, which is crucial for selective ion removal or separation technologies.

[0155] Ion Selectivity tuning without changing chemistry: Unlike many conventional membranes that require chemical modification, this system allows ion transport properties to be modulated by external stimuli (e.g., pH) while keeping the same material composition — ideal for multi-functional and reusable membrane systems.

[0156] Although the present disclosure has been described with respect to one or more particular embodiments and / or examples, it will be understood that other embodiments and / or examples of the present disclosure may be made without departing from the scope of the present disclosure.

Claims

CLAIMS:

1. A membrane comprising a crosslinked polymer comprising acrylic acid units and poly(ethylene glycol) diacrylate units (PEGDA), wherein the ethylene glycol repeats of the PEGDA have 4 or more repeat units and the membrane is porous.

2. The membrane according to claim 1, wherein the pores of the membrane have a longest linear dimension of about 5 to about 15 nm in diameter.

3. The membrane according to claim 1, wherein the ethylene glycol repeats of the PEGDA have 4, 10, or 13 repeat units.

4. The membrane according to claim 1, wherein the membrane comprises the following structure:or a deprotonated or partially deprotonated variant thereof, wherein n is 4 to 13.

5. The membrane according to claim 1, wherein the membrane exhibits an ion-exchange capacity of about 0 to about 4 meq / g.

6. The membrane according to claim 1, wherein the membrane exhibits limited water swelling.

7. The membrane according to claim 6, wherein the water swelling capacity is 0.05 to 0.8.

8. The membrane according to claim 7, wherein the water swelling capacity is 0.07 to 0.69.

9. The membrane according to claim 1, wherein polymer has a polymer density of about 1 to about 1.5 g / cm3.

10. The membrane according to claim 1, wherein the polymer density is 1.2 to 1.3 g / cm3.

11. The membrane according to claim 1, wherein the polymer has a theoretical crosslinking density of about 2.5 to about 10.5 mol / cm3.

12. The membrane according to claim 1, wherein the weight percent of acrylic acid units is 0.01 to 30 weight percent relative to the total weight percent of the membrane.

13. The membrane according to claim 12, wherein the weight percent of PEGDA is 70 to 99.99% weight percent relative to the total weight percent of the membrane.

14. The membrane according to claim 1, wherein the ethylene oxide content is 150 to 1300 mol% relative to the total amount of acrylic acid monomer and PEGDA monomer.

15. A membrane formed by forming a reaction mixture comprising acrylic acid monomer, poly(ethylene glycol) diacrylate, water, and a photoinitiator; mixing the reaction mixture; casting the mixed reaction mixture on a substrate; irradiating the cast reaction mixture such that the membrane is formed; and optionally, washing the membrane optionally, removing the membrane from the substrate.

16. The membrane according to claim 15, wherein the reaction mixture comprises 70 to 99.99 weight percent PEGDA monomer relative to the sum of the weight of acrylic acid and poly(ethylene glycol) diacrylate.

17. The membrane according to claim 15, wherein the reaction mixture comprises 0.01 to 30 weight percent acrylic acid relative to the sum of the weight of acrylic acid monomer and poly(ethylene glycol) diacrylate monomer.

18. The membrane according to claim 15, wherein the polymer density is about 1 to about 1.5 g / cm3.

19. The membrane according to claim 18, wherein the polymer density is about 1.2 to about 1.3 g / cm3.

20. The membrane according to claim 15, wherein the theoretical crosslinking density is 2.5 to 10.5 mol / cm3.

21. The membrane according to claim 1 or claim 15, wherein water permeability is 3 x 10'6to 9 x 10'6cm2 / s .

22. The membrane according to claim 1 or claim 15, wherein the water / salt selectivity is 30 to 15.

23. A device comprising the membrane according to claim 1 or claim 15.

24. The device according to claim 23, wherein the device is a filter, sensor, fuel cell, battery, flow cell, electrochemical system, water pump, barrier material, or packaging material.

25. A method for isolating or separating a target from an aqueous mixture comprising passing the aqueous mixture through a membrane according to claim 1 or claim 15 or a device according to claim 23, wherein at least a portion of the target is retained in and / or on the membrane.

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