CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. Provisional Application No. 62/892,440 filed August 27, 2019, which is hereby incorporated herein by reference in its entirety.

STATEMENT OF GOVERNMENT SUPPORT

This invention was made with government support under Grant no. DE-SC0019272 awarded by the Department of Energy. The government has certain rights in the invention.

FIELD

The present disclosure relates to polymer film fabrication methods for making coatings, components and membranes for resource recovery and processing, separation processes, and other uses. In particular, the methods of fabrication relate to mixed-matrix polymer films and membranes formed via aspects of nonsolvent induced phase separation.

BACKGROUND

Well-controlled methods of fabricating polymer films tailored to specific end use applications, such as transport or separation of resources, minerals, ions or other chemical species from gases and liquids, is of great interest. Polymer films are capable of high selectivity towards certain compounds or ions and, therefore, are advantageously useful in resource recovery, materials processing, and separation industries. Polymer films can be formed from a combination of an organic polymer with an inorganic crystal structure. In general, the crystal structure permits the desired selectivity, while the organic polymer functions as a nonporous membrane. Historically, a wide variety of inorganic and organic porous materials, such as zeolites, silica, carbon molecular sieves, and carbon nanotubes have been used as fillers in polymer films.

Metal organic frameworks (MOFs) are a class of crystalline inorganic materials. UiO-66, for example, has proven to be a desirable MOF due in part to its outstanding chemical and thermal stability. UiO-66 has the formula Zr604(0H)4(BDC)6 (BDC = 1,4-benzene- dicarboxylate). This compound has strong coordination bonds between the hard-acid — hard-base interactions of the zirconium atoms and carboxylate oxygens, thus resulting in the exceptional chemical and thermal stabilities. Polymer membranes have been formed through the process of phase inversion. In phase inversion, a solution of polymer and solvent are cast in a uniformly thick layer on a flat surface. The coated substrate is then immersed into a nonsolvent, which is miscible with the solvent but immiscible with the polymer. Through the immersion process, the solvent exits the coating layer and the polymer solidifies forming the membrane. Conventional phase inversion processes generate thermodynamic instability and liquid-liquid demixing of the polymer and solvent, leading to the formation of porous voids in the membrane. Such processes have been used to produce porous membranes and integrally skinned asymmetric membranes characterized by a porous layer of polymer with a dense skin layer on top of the porous structure.

Methods of producing a dense nonporous polymer film are needed, in particular, films without any associated and automatically formed porous layer. Also needed are methods of forming a dense film layer that can quickly form to capture nanoparticles before settling or aggregation, and whereby the transport properties of chemical species across the film are determined by the nanoparticles distributed therein. Such films also could be laminated upon other films or supports, to successfully decouple tailoring of the film and the support or other layers, rather than forming them in situ, as with conventional phase inversion.

Using previous methods, it is not possible to scale up and efficiently mass manufacture mixed-matrix polymer films in a timely, defect-free, manner, or to prepare stable and robust films and membranes fine-tuned for their desired end uses, and which do not include the negative side effects of prior methods.

Improved methods of manufacturing polymer films and mixed matrix membranes (MMMs) incorporating such polymer films and other components, such as nanoparticles, MOFs, and additional layers, laminations, and support materials are needed.

SUMMARY

The present disclosure relates to methods of fabricating nonporous polymer films and mixed-matrix polymer films through aspects of nonsolvent phase separation combined with other process steps and conditions to efficiently provide robust and defect-free films. In one aspect, the disclosure provides a method for making a nonporous polymer film by mixing a polymer with a solvent to form a dope solution; mixing nanoparticles with the dope solution to form a nanoparticle dope solution; depositing the nanoparticle dope solution on a substrate to a first thickness; and contacting at least a portion of the deposited dope solution with a nonsolvent to form the nonporous polymer film having a second thickness; wherein the first thickness is from 400% to 1600% greater than the second thickness (e.g., from 400% to 1000% from 1000% to 1600%, from 400% to 600%, from 600% to 800%, from 800% to 1000%, from 1000% to 1200%, from 1200% to 1400%, from 1400% to 1600%, from 500% to 1600%, from 400% to 1500%, or from 500% to 1500%). The polymer comprises, for example, a material selected from the class of polymers listed in Table 1, or a material selected from the examples of polymers listed in the second column of Table 1. In one embodiment, the polymer comprises a material selected from the group consisting of polysulfone, polybenzimidazole, Torlon poly(amideimide), and cellulose acetate. The solvent may comprise, for example, a material selected from the solvents listed in Table 1. A mass ratio of the polymer to the solvent may be from 5% to 40% (e.g., from 5% to 20%, from 20% to 40%, from 5% to 15%, from 15% to 25%, from 25% to

40%, from 5% to 30%, from 10% to 40%, or from 10% to 30%).

Table 1. Polymer classes, polymer examples, and Typical Solvents.

In a preferred embodiment, the nanoparticles comprise metal organic framework (MOF) particles. In one aspect, the nonporous polymer film is in the form of a layer having a first and second surface and comprises a continuous pathway of nanoparticles across the film. The nanoparticles may be selected for example from materials such as UiO-66, UiO-66-(COOH)2, UiO-66-NH2, and derivatives or mixtures of any of the above and other suitable MOFs. A mass ratio of the nanoparticles to the polymer may be, for example, from 1% to 60% (e.g., from 1% to 30%, from 30% to 60%, from 1% to 20%, from 20% to 40%, from 40% to 60%, from 1% to 50%, from 10% to 60%, or from 10% to 50%). In another aspect, the nonsolvent is chilled prior to the immersing step. In one aspect, the nonsolvent comprises a material selected from the group consisting of isopropyl alcohol, n- propyl alcohol, glycerol, hexane, a solution of lithium chloride in water, and a solution of calcium chloride in water.

In one aspect, the nonporous polymer film has a thickness from 0.1 to 10 microns (e.g., from 0.1 micron to 5 microns, from 5 microns to 10 microns, from 0.1 micron to 1 micron, from 1 micron to 10 microns, from 1 micron to 5 microns, from 0.5 microns to 10 microns, from 0.1 microns to 9 microns, or from 0.5 microns to 9 microns). In another aspect the contacting step comprises immersing the deposited dope solution in a bath of the nonsolvent and the nonporous polymer film forms within 30 seconds after the immersing step (e.g., 30 seconds or less, 20 seconds or less, 10 seconds or less, 5 seconds or less, or 1 second or less).

The disclosure also provides in another example laminating the nonporous polymer film to another polymer film of the same or different composition, or applying the nonporous polymer film to a substrate. The substrate may comprise, for example, a material selected from the group consisting of a nonwoven paper; a nonporous polymer film; a metal foil; silica; indium tin oxide; a porous ultra- or microfiltration membrane; or a sacrificial support.

The depositing step may comprise any of spin-coating, doctor blade casting, slot-die coating, dip-coating or gravure coating.

In another aspect, additional compounds may be added to the nonsolvent bath to modify and tune the bath’s interactions with the polymer solution. These additional compounds may be salts, including salts having high osmotic pressure, such as lithium chloride or magnesium chloride.

In another embodiment, the present disclosure provides a method of making a dense nonporous polymer film, comprising mixing a polymer with a solvent to form a dope solution, wherein the polymer is dissolved in the solvent, the polymer is selected from the group consisting of cellulose acetate, polysulfone, polybenzimidazole, Torlon poly(amideimide), PEBAX 2533 poly(ether-block-amide), and poly[l-trimethylsilyl)-l-propyne], the solvent is selected from the group consisting of anhydrous tetrahydrofuran, N,N-dimethylacetamide, N- methyl-2-pyrrolidone, dichloromethane, and mixtures thereof, wherein a mass ratio of the polymer to the solvent is from 10-20% (e.g., from 10% to 15%, from 15% to 20%, from 10% to 12%, from 12% to 14%, from 14% to 16%, from 16% to 18%, from 18% to 20%, from 10% to 18%, from 12% to 20%, or from 12% to 18%); depositing the dope solution on a substrate to form a dope solution layer having a first thickness of from 1 to 100 microns on the substrate (e.g., from 1 micron to 50 microns, from 50 microns to 100 microns, from 1 micron to 20 microns, from 20 microns to 40 microns, from 40 microns to 60 microns, from 60 microns to 80 microns, from 80 microns to 100 microns, from 1 micron to 90 microns, from 10 microns to 100 microns, or from 10 microns to 90 microns); and immersing the dope solution layer in a nonsolvent to form a dense nonporous polymer film having a second thickness, wherein the nonsolvent is miscible with the solvent, the polymer is insoluble in the nonsolvent, the nonsolvent is selected from the group consisting of isopropyl alcohol, n-propyl alcohol, glycerol, lithium chloride dissolved in water, calcium chloride dissolved in water, and mixtures thereof, and upon initiation of the immersing step the polymer film is formed within a range of from greater than 0 to 8 seconds (from greater than 0 seconds to 4 seconds, from 4 seconds to 8 seconds, from greater than 0 seconds to 7 seconds, from greater than 0 seconds to 5 seconds, from 1 second to 8 seconds, or from 1 second to 7 seconds); wherein the polymer film is dense, non-porous, and has a thickness from 400% to 800% less than the first thickness (e.g., from 400% to 600%, from 600% to 800%, from 400% to 500%, from 500% to 600%, from 600% to 700%, from 700%, to 800%, from 400% to 700%, from 500% to 800%, or from 500% to 700%).

The present disclosure also provides, among other aspects, a method of making a mixed- matrix polymer film, comprising: mixing a polymer with a solvent and nanoparticles to form a nanoparticle dope solution, wherein the polymer is dissolved in the solvent, the polymer is selected from the group consisting of cellulose acetate, polysulfone, polybenzimidazole, Torlon poly(amideimide), PEBAX 2533 poly(ether-block-amide), and poly[l-trimethylsilyl)-l- propyne], the solvent is selected from the group consisting of anhydrous tetrahydrofuran, N,N- dimethylacetamide, N-methyl-2-pyrrolidone, dichloromethane, and mixtures thereof, and the nanoparticles are selected from the group consisting of UiO-66, UiO-66-(COOH)2, UiO-66-NH2, and mixtures thereof, wherein a mass ratio of the polymer to the solvent is from 10-20% (e.g., from 10% to 15%, from 15% to 20%, from 10% to 12%, from 12% to 14%, from 14% to 16%, from 16% to 18%, from 18% to 20%, from 10% to 18%, from 12% to 20%, or from 12% to 18%), and wherein a mass ratio of the nanoparticles to the polymer is from 20-40% (e.g., from 20% to 30%, from 30% to 40%, from 20% to 25%, from 25% to 30%, from 30% to 35%, from 35% to 40%, from 20% to 35%, from 25% to 40%, or from 25% to 35%); depositing the nanoparticle dope solution on a substrate to form a uniform nanoparticle dope solution layer having a first thickness on the substrate; and immersing the nanoparticle dope solution layer in a bath of nonsolvent to form the mixed-matrix polymer film having a second thickness, wherein the nonsolvent is miscible with the solvent, the polymer is insoluble in the nonsolvent, the nonsolvent is selected from the group consisting of isopropyl alcohol, n-propyl alcohol, glycerol, lithium chloride dissolved in water, calcium chloride dissolved in water, and mixtures thereof, and upon initiation of the immersing step the mixed matrix polymer film is formed within a range of 0 to 8 seconds; wherein the mixed-matrix polymer film is isotropic and the polymer phase is nonporous, has a second thickness from 0.1 to 10 microns, and the first thickness is 400% to 800% greater than the second thickness.

In another aspect, the present disclosure provides a method of making a dense isotropic nonporous polymer film by mixing a polymer with a solvent to form a dope solution; depositing the dope solution on a substrate to form a dope solution layer having a first thickness of from 1 to 100 microns on the substrate; and immersing the dope solution layer in a nonsolvent to form a dense nonporous polymer film having a second thickness, wherein the nonsolvent is miscible with the solvent, the polymer is insoluble in the nonsolvent; wherein the dense isotropic nonporous polymer film is formed within a range of 0.1 to 30 seconds after initiation of the immersing step (e.g., from 0.1 seconds to 15 seconds, from 15 seconds to 30 seconds, from 0.1 seconds to 10 seconds, from 10 seconds to 20 seconds, from 20 seconds to 30 seconds, from 0.1 seconds to 25 seconds, from 1 second to 30 seconds, or from 1 second to 25 seconds); and wherein the second thickness is from 400% to 1600% less than the first thickness.

In yet another aspect the present disclosure provides a method of nonsolvent induced film deposition for making a nonporous polymer film from a deposited dope solution, by selecting a polymer, solvent, and nonsolvent; depositing a dope solution formed from the polymer and solvent to form a thin film; and immersing the thin film is a bath of the nonsolvent; wherein the deposited dope solution has a transition thickness in the range of 1 to 100 microns and the nonporous polymer film exhibits a contraction ratio in the range of 400% to 1600%. The nonporous polymer film is formed within, for example, less than 30 seconds after immersing the thin film in the nonsolvent and the thin film has a thickness in the range of 1 to 100 microns.

In another aspect, the method of nonsolvent induced film deposition further includes mixing the polymer and solvent with metal organic framework particles before depositing the dope solution wherein the particles are dispersed in the dope solution to form a mixed matrix membrane after immersing the dope solution in the nonsolvent. The mixed matrix membrane may comprise a percolating network of metal organic framework particles. The method can include applying the mixed matrix membrane to a substrate, including for example a substrate that is at least partially miscible with the mixed matrix membrane. In a particular aspect, the nonsolvent comprises a salt, the polymer comprises a material selected from the group consisting of cellulose polymers (e.g., cellulose acetate, cellulose triacetate, cellulose nitrate, and cellulose acetate butyrate), polysulfone, polybenzimidazole, and Torlon poly(amideimide), and the particles comprise a material selected from the group consisting of UiO-66, UiO-66-(COOH)2, and U1O-66-NH2.

The resulting polymer films and MMMs are useful in a variety of products and processes as, for example, coatings and membrane components. The MMMs are particularly useful in separating desired ions from aqueous liquids, including salty liquids, produced water from mining, fracking and oil recovery, and brine, when the dispersed nanoparticles comprise selected MOFs, as taught herein. The MMMs are also useful in separating desired gases from gas mixtures, and the separation of ions from water. These and other embodiments are illustrated herein below and described in the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A - FIG. IF depicts SEM images of (FIG. 1A) a polyester nonwoven substrate material, (FIG. IB) a film of pure polysulfone laminated onto the substrate material depicted, (FIG. 1C) a film of polysulfone containing 40 wt% UiO-66-COOH MOF laminated onto the substrate material depicted, (FIG. ID) an additional film of polysulfone containing 40 wt% UiO- 66-COOH MOF laminated onto the substrate material depicted, (FIG. IE) a film of polysulfone containing 40 wt% UiO-66-NH2 MOF laminated onto the substrate material depicted, (FIG. IF) an additional film of polysulfone containing 40 wt% UiO-66-NH2 MOF laminated onto the substrate material depicted.

FIG. 2. depicts a generic ternary phase diagram for a ternary polymer-solvent-nonsolvent system for a glassy polymer. Relevant features include the binodal curve which constitutes the boundary between thermodynamically stable and unstable regimes and the vitrified regime, in which no demixing, and consequently no pore formation, can occur. Also depicted is the position of a hypothetical binary polymer-solvent solution, and the relative effects of the processes of solvent extraction and nonsolvent absorption into the liquid polymer solution film.

FIG. 3. depicts an idealized path through the polymer phase space followed during contact with the nonsolvent bath which produces a dense isotropic film. Since the paths do not intersect the binodal curve, the solution does not undergo thermodynamic demixing and does not form porous voids.

FIG. 4. depicts an idealized path through the polymer phase space followed during contact with the nonsolvent bath which produces an integrally skinned membrane. Paths through phase space associated with the top surface of the liquid polymer film intersect the vitrification line, while paths through phase space associated with the bottom layers of the liquid polymer solution film intersect the binodal curve, generating pores. The resulting structure will be an integrally skinned membrane comprising an isotropic nonporous top surface layer and a porous polymer subsurface layer.

FIG. 5. depicts an idealized path through the polymer phase space followed during contact with the nonsolvent bath which produces a porous membrane or film. Since all paths intersect the binodal curve, all portions of the liquid polymer solution film undergo thermodynamic demixing and the resulting membrane or film will be porous. FIG. 6. depicts a procedure for the formation of a nonporous isotropic film via nonsolvent-induced film deposition (NIFD), according to aspects of the present disclosure.

When the liquid polymer film is cast or deposited at a thickness less than the transitional thickness, t*, an isotropic nonporous polymer film is formed.

FIG. 7. depicts a procedure via which an integrally skinned membrane may be produced. When the liquid polymer film is cast or deposited at a thickness greater than the transitional thickness, t*, an isotropic nonporous polymer film will form atop a porous polymer layer.

FIG. 8. depicts a procedure via which a porous polymer film may be produced. In such a case, when the solvent and/or the nonsolvent have not been chosen according to the nonporous teachings herein, a porous film results.

FIG. 9. depicts the contraction of the liquid polymer film, having a first thickness tinitiai, to an isotropic nonporous polymer film having a second thickness tfmai, the ratio of which is referred to herein as the “contraction ratio”.

FIG. 10A - FIG. 10B. depicts the lamination of a polymer film produced via nonsolvent induced film deposition onto a porous substrate material in which (FIG. 10A) the substrate material is not miscible with the polymer dope solution and (FIG. 10B) the substrate material is at least partially miscible with the polymer dope solution.

FIG. 11. depicts a nonporous film of polysulfone produced via nonsolvent induced film deposition. A transition from porous to nonporous can be seen where the casting thickness is changed from t<t* to t>t*.

FIG. 12. depicts a nonporous film of polybenzimidazole produced via nonsolvent induced film deposition displaying structural color due to its thinness.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In one preferred embodiment, the present disclosure relates to methods of fabricating nonporous polymer films via aspects of nonsolvent induced film deposition (NIFD). Such films can advantageously include uniformly dispersed particles, nanoparticles, and/or MOFs.

The present disclosure provides techniques for the rapid condensation of dissolved polymer-solvent solutions containing well-dispersed nanoparticles into a dense uniform film, in which the transport of chemical species across the resulting film is modified through the incorporation of the nanoparticles. The resulting films comprise a polymer matrix in which the nanoparticles are dispersed. This mixed matrix membrane (MMM) can be deposited onto, and removed from, a non-interacting substrate, resulting in a freestanding polymer film, or the resulting film can be deposited onto, and incorporated with, a porous support material, which provides mechanical stability to the resulting composite membrane.

In one aspect of this technique, high molecular weight polysulfone polymer (Udel P-3500 MCB7 LCD, Solvay Specialty Polymers) is dissolved in anhydrous tetrahydrofuran solvent (THF), while simultaneously being combined with well-dispersed metal-organic framework (MOF) particles (UiO-66- (COOH)2 and UiO-66-NH2) in THF, such that the mass ratio of polymer to solvent, and the mass ratio of MOF to polymer (for example, 15% and 20-40%) are sufficient to yield a defect free film.

The polymer/MOF solution is deposited at a controlled thickness onto a substrate material. This may be accomplished by spin-coating, doctor blade casting, gravure coating, slot- die coating, dip coating, spray coating or any number of similar techniques. The resulting thin coating of polymer/MOF solution is then immersed in a bath of non-solvent for the polymer of choice. Among others, isopropyl alcohol (IP A), n-propyl alcohol, glycerol, lithium chloride in water (such as 6 molal), and calcium chloride in water (such as 6 molal) are suitable non solvents. Other casting conditions, such as depositing polymer solution coatings which are too thick, results in hybrid structures, in which a nonporous polymer film is formed atop a porous polymer film.

The polymer solution coating typically contracts by 400-800%, resulting in films having a thickness, for example, between 0.1 and 10 microns, and the phase inversion process is generally completed quite rapidly, for example, in 1-10 seconds. The process may be conducted batchwise or continuously and is readily scalable to industrial size continuous production.

Generally, according to an aspect of this disclosure, the polymer can be dissolved into a solvent with or without additional components, for example, nanoparticle MOFs. Once the polymer is dissolved in the solvent, and optionally any additional components, all or a portion of the resulting polymer mixture, suspension, or solution is cast, e.g., deposited on a substrate or carrier. The conditions, such as the thickness of the as-cast mixture or solution of the selected polymer, solvent, and nonsolvent components, as discussed herein, produce a dense nonporous film optionally containing uniformly dispersed particles, after contacting the solution or mixture with a suitable nonsolvent for the respective polymer. The methods disclosed herein also are applicable to formation of nonporous coatings without any particulate materials, but the rapidity of the phase inversion producing a dense film make this process highly advantages when a uniform dispersion of nanoparticles is desired, including processes using relatively high loadings of nanoparticles, so as to form interconnected pathways for ions through the nanoparticle pores or windows across the full thickness of the MMM.

By “nonporous” herein, we mean that the polymer component of the resulting film or mixed matrix is essentially free of permanent holes that span the film or mixed matrix from one surface to the opposite surface; in a preferred embodiment the polymer component of the film or mixed matrix manufactured by aspects of NIFD has no permanent holes that span a sample of the film or mixed matrix; accordingly, for example, in a lithium ion separation system, transport of lithium ions across the MMM will be solely or virtually solely a function of the nanoparticles or, preferably, MOFs, dispersed in the polymer. The nonporous nature of the polymer film can be determined by, such as, scanning electron microscopy or other suitable imaging techniques. It should be apparent that the fabrication methods result in films that are significantly different that those resulting from prior nonsolvent induced phase separations, which result in porous membranes. It is surprising that films formed by aspects of nonsolvent induced film deposition according to the present disclosure would provide nonporous polymers. Generally, nonsolvent phase separation forms combinations of integrally skinned membranes with thick porous layers and thin skins, essentially, an asymmetric porous structure.

The as-deposited solution or mixture film, typically along with the selected substrate or carrier, is then contacted with or immersed in a chosen nonsolvent. Preferably, the solvent and nonsolvent are readily miscible. Suitable examples are provided herein, but other suitable combinations may be used provided that the polymer is insoluble in the nonsolvent. By “insoluble” herein, we mean that only a very small portion, such as <10% by weight, <5% by weight, or preferably, <1% of the polymer dissolves in the nonsolvent. By “miscible” herein, we mean that a very large portion, such that all or essentially all proportions of the solvent present in the as-deposited solution film dissolves in the nonsolvent. As described in more detail below, upon contact or immersion of the polymer solution or mixture in the nonsolvent, a phase inversion occurs wherein the solvent exits the deposited or cast layer, and the polymer rapidly solidifies into a uniform, dense film bathed in a solution of nonsolvent and solvent.

The rapidity of the solidification can be controlled, as discussed herein, and can be remarkable quick, which advantageously permits formation of mixed matrix films via quenching before particles can otherwise aggregate or settle, and without any convection currents, voids, or associated porous layers, which are characteristics of the prior processes of using nonsolvent phase separation to prepare membranes. As discussed herein, we have found that the thicknesses of the cast solution or mixture and of the resulting nonporous film can be tailored to specific end uses and, at least in part, can be manipulated to control the formation of films without associated porous layers, voids, or microcracks. The dense film or mixed-matrix polymer film can then be removed from the substrate or carrier, or the substrate or carrier can comprise or be part of the resulting mixed-matrix polymer film membrane.

The polymer films or mixed-matrix polymer films produced by the present disclosure can be subsequently deposited on a substrate (such as a different substrate than the substrate or carrier used during manufacturing the film) to form a composite membrane. For instance, two or more films made by the present disclosure may be laminated together to achieve chemical species separation properties in gas or liquid separations. Use of aspects of the disclosed methods also advantageously allows fabrication in which the film fabrication and the properties of the desired support, if any, are decoupled. This allows for fine tuning of film support combinations because a porous polymer support is not an automatic component of the as- fabricated film, as in conventional phase inversion processes. In addition, the polymer solidification is rapid, allowing lamination of like or otherwise miscible or soluble polymer components on one another. The present disclosure also provides for deposition of polymer films that are not suitable to dip-coating, e.g., polysulfone, and polybenzimidazole, because the solvents used with such materials are either not compatible with substrates or supports or are relatively slow for evaporative processes. For instance, aspects of the present disclosure allow deposition or lamination of a thin layer of polybenzimidazole on a porous support to form a composite membrane. Thus, film properties and support mechanical properties can be independently tailored for desired applications and end uses.

Mixed-matrix polymer films can be used as membranes in gas and liquid separation due to their high selectivity for certain gases and ions. As noted above, these films have been made to combine the inorganic MOF with the organic polymer. As disclosed herein, NIFD provides methods of producing MMMs that can be used at a commercial scale to produce films in a shorter duration than the prior art and produce defect-free MMMs. The disclosed methods achieve forming nonporous matrix polymer films that can be very thin or relatively thick. These films can be made in a thickness from the submicron regime to tens of microns. Preferably, the films can be from 0.5 microns to 30 microns thick (e.g., from 0.5 microns to 15 microns, from 15 microns to 30 microns, from 0.5 microns to 10 microns, from 10 microns to 20 microns, from 20 microns to 30 microns, from 1 micron to 30 microns, from 0.5 microns to 25 microns, or from 1 micron to 25 microns). An additional benefit of NIFD according to aspects of the present disclosure is that films produced by this method can be essentially isotropic and can have uniformly dispersed nanoparticles, including MOFs at relatively high loadings (e.g., 30% to 50%, 60%, 70% or more) capable of forming continuous MOF pathways for travel of ions across the MMM, which can be highly advantageous for separating lithium and other ions from liquid mixtures.

Metal-organic frameworks (MOFs) are a class of crystalline inorganic materials that have recently become of great interest as components in MMMs for liquid and gas separation processes, such as separation of ions from aqueous fluids. Due in part to their chemical flexibility, MOFs also can provide opportunities to tune and optimize interfacial interactions between the MOF and the organic polymer, thus reducing chances for instability and mechanical failure. In addition, it is possible to select a MOF with optimal functional groups that can significantly enhance the surface area, porosity, and acceptable thermal stability, thereby improving selectivity and adsorption uptake in the resulting mixed matrix film.

The metal organic framework can comprise any suitable metal organic framework. Examples of metal organic frameworks include, but are not limited to, UiO-66, ZIF, HKUST-1, derivatives thereof, and combinations thereof. In some examples, the metal organic framework comprises ZIF-8, ZIF-7, derivatives thereof, or combinations thereof. In some examples, the metal organic framework comprises UiO-66, derivatives thereof, or combinations thereof. The metal organic-framework can, for example, be selected from the group consisting of UiO-66, UiO-66-(COOH)2, U1O-66-NH2, U1O-66-SO3H, UiO-66-Br, and combinations thereof. In some examples, the plurality of metal organic framework particles comprises UiO-66, UiO-66- (COOH)2, U1O-66-SO3H, UiO-66-Br, or combinations thereof. In certain examples, the metal organic framework can comprise UiO-66-(COOH)2, U1O-66-NH2, or combinations thereof. Alternative MOFs and MMM compositions and related methods of use are disclosed in our co pending applications, titled “Mixed Membranes and Methods of Making and Use Thereof,” filed as U.S. Application Serial No. 62/892,439 on August 27, 2019, and its corresponding PCT application, which is filed the same day as this disclosure. The MOFs, MMM compositions, and methods of making and using them as disclosed in these co-pending applications are hereby incorporated by reference herein.

The methods of manufacturing films and mixed-matrix polymer films of the present disclosure can be operated in continuous, semi-continuous, or batch-wise processes. The disclosure in one aspect provides for large commercial scale production but is not limited thereto; the production of polymer films and mixed membrane components according to the present disclosure can occur at lab scale to a commercial scale by adapting the process to achieve desired throughputs given the teachings herein. Because the processes can be operated rapidly without evaporation or heat, and can operate with relatively concentrated solutions of polymer and nanoparticle loadings, detrimental thermal convection currents and other non uniformities within the deposited solution or mixture do not occur in any appreciable degree so as to interfere with the beneficial properties of the polymer film or MMM. In a preferred aspect, the resulting polymer film or mixed matrix membrane material is isotropic and uniform throughout, and/or is characterized by a uniform dispersion of any MOFs or optional particles therein.

In order to appropriately mix the polymer and the solvent, the polymer should be soluble in the solvent, as defined herein. Thus, the polymer can readily dissolve in the solvent to form a solution of the polymer in the solvent. Prior to mixing, the polymer can be a liquid or a solid. For instance, the polymer can be initially provided as a powder or granule of the desired polymer. Alternatively, the polymer can be in a liquid form, already dissolved or suspended into a solution or carrier liquid. Prior to mixing, the solvent should be in a liquid form. Mixing together the polymer and solvent results in a “dope solution,” which is a solution, suspension or mixture containing solvent and polymer.

Generally, any polymer that can be mixed into a solvent, including but not limited to known “solution-processable” polymers, can be used in the methods of the present disclosure; suitable solvents and nonsolvents are selected according to the teachings herein. Preferably, a polymer is selected that can form a nonporous isotropic and stable film and is compatible with any desired nanoparticles or MOFs. The polymer can consist of or include, for example, cellulose acetate, polysulfone, poly(amideimide), polybenzimidazole, polyethersulfone, polyphenylsulfone, polyimide, polyacrylonitile, poly (ethylene oxide), poly(ether ether ketone), poly(vinylidene fluoride), poly(ethylene chlorotrifluoroethylene), polycarbonate, polystyrene, poly(ether-block-amide), acrylonitrile butadiene styrene, and derivatives and combinations of the aforementioned. The polymer can similarly comprise bisphonenolsulfone (BPS) polymers and derivatives thereof. The polymer can also include sulfonated polymer derivates, for example, sulfonated poly(ether ether ketone), sulfonated polysulfone, and sulfonated poly (ether sulfone). A nonexhaustive list of suitable solution-processable polymers includes those listed in the Table 1. The polymer can include mixtures or combinations of any of the aforementioned polymers and other suitable polymers. In one aspect of the present disclosure, a preferred polymer is polysulfone or cellulose acetate.

The solvent can further be selected depending on the ability of the solvent to successfully coat a film layer on a substrate or carrier at a desired uniform thickness. Upon mixing, such as sonication or other methods, the polymer molecules disperse throughout the solvent thereby resulting in a homogeneous system. Suitable solvents for use with respective polymers depend on the solubility of the polymer in the solvent. Suitable solvents can consist of or include any of tetrahydrofuran, N-methyl-2-pyrrolidone, tetrahydrofuran/N-methyl-2-pyrrolidone blends, and N,N-dimethylacetamide. The solvent similarly may also comprise acetamide derivatives, for example, diethylacetamide and methylethyleacetamide. The solvent may also include, for example, additional or alternative amide solvent derivatives, such as, dimethylformamide and methylethylformamide. The solvent also can be or include methyl-tetrahydrofuran, gamma- valerolactone, dihydrolevoglucosenone, and methanesulfonic acid. The solvent can be formed of any of these or other suitable solvents as a single component or may be formed from a combination of such solvents.

The process of mixing the polymer and the solvent includes mixing a suitable concentration of polymer in the solvent given to the teachings herein. The polymer is mixed at a concentration below its solubility limit (e.g. 60-95%, in some cases, but as low as 10-20% in others). However, at very low concentrations, the solution will not form a film via methods other than evaporation. Without wishing to be bound by theoretical mechanisms of film formation, the “critical entanglement concentration”, i.e., the concentration of solution above which polymer molecules may broadly be described as entangled with other polymer molecules, may typically be between 2 wt% to 10 wt% polymer depending on both the solvent and the polymer molecular weight and may be regarded as a lower practical concentration limit. For example, the mass ratio of the polymer to solvent can be from 5 - 40% by mass, or preferably 10 - 30% by mass, or more preferably 10 - 20% by mass. In particular, the polymer must be soluble in the solvent at the desired concentration. Generally higher molecular weight polymers form films at lower concentrations of polymer. The concentration of polymer to be included may be determined by desired characteristics for depositing the dope solution on the substrate or carrier, and the nature of the substrate or carrier. For example, depending on the thickness of the deposition, the desired nonporous film thickness, a desired viscosity for deposition, either a greater or lesser concentration of polymer can be included in the solvent. The concentration of polymer reflects the thickness for deposition of the material on the substrate or carrier, and also the thickness of the resulting nonporous polymer film or mixed-matrix polymer film. The “transitional thickness”, t*, is the thickness at which the polymer liquid film may be coated in the nonsolvent induced film deposition (NIFD) process to form a dense nonporous isotropic film and can be determined for a given polymer dope solution and nonsolvent composition given the teachings herein. At thicknesses above this value, comparatively thick polymer films with discrete porous voids will be formed. In this case, an integrally skinned membrane may be formed, however the ratio of porous volume to non-porous film volume with be much higher than in the known nonsolvent-induced phase separation process. For example, in casting a film slightly above the transitional thickness t*, a polymer film with 10%, 5%, or as low as 1%, porous volume may be formed. Casting a film below the transitional thickness t* will result in a film with no visible porous voids. In contrast, integrally skinned membranes produced via conventional nonsolvent- induced phase separation may have porous volume of 50%, 80%, or often in excess of 90%. The present disclosure includes teachings that allow an individual of ordinary skill in the art to produce polymer dope solution and nonsolvent compositions which result in surprisingly large transitional thicknesses in the range of 1 to 100 microns, and surprisingly large contraction ratios in the range of 100% to as large as 1600% or more.

Generally, dope solution formulations which produce dense skin layers will produce a certain thickness skin layer dependent on the properties of the polymer dope solution and the nonsolvent bath. The self-limiting thickness of the nonporous layer may be regarded as the maximum film thickness that can be achieved via the nonsolvent-induced film deposition (NIFD) method. Consequently, the maximum thickness at which the dope solution may be deposited on a substrate will be the dope solution film that contains the same amount of polymer as the dense film at its self-limiting thickness. While not wishing to be bound by theory, if the maximum self-limiting film thickness, t _sL . for a given weight percent polymer dope solution in a given nonsolvent is 10 microns, then the transitional thickness, t ^* , is related to this by the density of the pure polymer film and the mass concentration of the polymer in the dope solution, defined as p _poiym er = P solution polymer- where p solution is the density of the polymer dope solution (e.g. in g /cm ³ ), w _polymer is the mass fraction of polymer in the solution (e.g. 20 percent by mass), and p _po iymer is the mass concentration of polymer in the dope solution (e.g. in g/cm ³ ). The relation between the self-limiting film thickness and the transitional casting thickness is thus

The contraction ratio, r, can be expressed as the ratio of the thickness of the cast liquid film, t _cast , and the thickness of the resulting nonporous polymer film, tf _iLm . At the transition pure thickness, this ratio then becomes r = - ^p v°iymer - _º t_ p _{Qr a} gj _ven nonsolvent and dope

Psolution ^w polymer ^sl solution composition, r is thus typically inversely proportional to the weight fraction of polymer, Wpoiymer- subject to the effects of dope solution density. On the other hand, t _sL is proportional to the polymer concentration. For two dope solutions, labelled 1 and 2, in which solution 1 is a solution of polymer and solvent, and solution 2 is a solution of the same polymer and solvent, but with a higher mass percentage of polymer, solution 1 will have a transitional thickness of tj and solution 2 will have a transitional thickness of t ₂ . From the above discussion, t < tj. Assuming that p _so iution does not change inversely in proportion to w _poiymer . then r _t < r ₂ . As a result, if solution 1 and solution 2 are both cast at a thickness t < t{, solution 1 will form a thinner film than solution 2.

Suitable supports and carriers include any material having a uniformly flat surface for casting or depositing a dope solution. A support or carrier material may also be modified to be uniformly flat for casting or depositing the dope solution by one or o more of heat pressing, calendaring, or coating with a compatibilizing layer. Preferably, the surface also is compatible with nonsolvent, and can be readily manipulated to facilitate immersion of the cast or deposited film therein in a continuous or industrial scale process. In some aspects, the substrate or carrier is a component of a desire separation membrane including the solidified polymer. In other aspects, the carrier is merely a temporary backing, such as a nonwoven paper or fiber material from which the polymer film can be readily removed and the applied as a coating on another material. If desired, the substrate or carrier can be impregnated with additional components to facilitate desired functions, such as release of the nonporous film. Suitable substrates or carriers may include, for example, nonwoven papers made from materials such as polyester, cellulosic materials, nylon, and similar compounds with desired compatibility with the solvent ; nonporous polymer films such as polyethylene, polypropylene, nylon, poly(vinylchloride), and other such materials ; metal foils such as aluminum, copper, and tin; a suitable substrate coated with nanoparticles such as silica, or other such materials; conductive films such as indium tin oxide; a prepared substrate designed to act as a component in a final product, such as a film of battery electrode material, or a conductive contact material; finely porous materials such as ultra- and microfiltration membranes; sacrificial supports such as those made from dissolvable, or etchable materials like copper or polyvinylalcohol; and more generally any film-like material which has desired properties and suitable and desired compatibility with the solvents and nonsolvents used.

In a particularly preferred aspect of this disclosure, additional components, for example, nanoparticles, are added to the dope solution to obtain desired selectivity and permeability properties in the mixed-matrix polymer film. The addition of nanoparticles results in a “nanoparticle dope solution” wherein such nanoparticles are preferably uniformly disbursed throughout the dope solution. Such uniform dispersion can be achieved via mechanical mixing, sonication, or other means. The nanoparticles can be added after the polymer and the solvent have been mixed to form the dope solution, or the nanoparticles can be mixed in simultaneously with the polymer and solvent as the polymer and solvent are being mixed. The MOFs or other nanoparticles can be “primed” by any suitable method to enhance interaction between the nanoparticle and the polymer to improve stability. For example, the nanoparticle may be dispersed in solvent and added slowly to a polymer dope solution containing sufficient polymer that the final concentration of polymer and nanoparticles is the desired amount. The nanoparticle may be dispersed in solvent and a small amount, for example 10%, 5%, or less than 1% of the total polymer may be added to the nanoparticle to promote nanoparticle-polymer interaction, and the remaining polymer may be added after the nanoparticles are well-dispersed. The nanoparticle may be dispersed via a number of means with the simultaneous aid of surfactant molecules, including compounds such as dodecylamine, sodium dodecylsulfate, sodium deoxycholate, or similar compounds known to art, which help to promote the mixing and compatibility of the nanoparticle with the polymer phase. The nanoparticle dope may comprise a mixture of two or more different nanoparticles, or mixtures of the same nanoparticle having different size ranges, to prevent nanoparticle aggregation and promote mixing. The mixing of the polymer, solvent, and nanoparticles can also occur in a single mixing step or the nanoparticles can be subsequently added to the polymer dope solution. In an alternative mixing procedure, metal organic framework particles are mixed in a solvent, such as anhydrous tetrahydrofuran, sealed in a vial and mixed via sonication bath to break up and exfoliate the MOF particles. In several, for example, four or more additions, 1/8, 1/8, 1/4, and 1/2, respectively, of dry polymer powder are added to the vial, with the vial being sealed and mixed until the solution appears homogeneous between each addition. Approximately three hours of stirring are provided between each addition. Once the nanoparticles are combined with the polymer and the solvent into a nanoparticle dope solution, the solution can be deposited on the substrate or carrier. In one embodiment, the solvent is split into two parts. The nanoparticles are added to one of the portions of solvent and sonicated to combine the two materials. The polymer is then added to and dissolved in the other portion of the solvent and sonicated. Then all or parts of the solutions can be combined to achieve the desired concentration of polymer and nanoparticle in the nanoparticle dope solution, and, if desired, the combined solution can be further sonicated and the cast or deposited using the teachings herein.

The additional components, for example, nanoparticles, are preferably MOFs in various aspects of the present disclosure. Generally, the additional components in the form of nanoparticles can comprise any MOF that results in the mixed-matrix polymer film having the desirable selectivity, permeability, and stability for its particular end use applications. For example, UiO-66 has particularly desirable properties in a mixed-matrix polymer films prepared herein for ion separation processes, particularly lithium ion separations from salty aqueous liquids or brine. These nanoparticles preferably comprise UiO-66, UiO-66-(COOH)2, UiO-66- NFh, and/or mixtures thereof. UiO-66 is a metal organic framework made up of Zn.OTOHh clusters with 1,4-benzodicarboxylic acid struts. UiO-66-(COOH)2 and U1O-66-NH2 are MOFs that include the UiO-66 backbone, but have different functionalized groups, which result in different properties in the mixed-matrix polymer film. In some examples, the plurality of metal organic framework particles can comprise a functionalized metal organic framework, for example, UiO-66 MOF particles functionalized with crown ether moieties in or on the MOF channel to restrict the pore size opening or enhance the binding capacity of the MOF. Preferably, the nanoparticles comprise at least one of UiO-66-(COOH)2 and U1O-66-NH2 or derivatives thereof. Nanoparticles such as these are commercially available. Alternatively, these nanoparticles can be made by processes known in the art and can be chosen for their selectivity of certain ionic species from aqueous fluids or other environments where they are found either for natural resource recovery such as lithium ion separation and collection for such as construction of batteries and the like, for fluoride ion separation from contaminated groundwater and environmental clean-up processes, or any of a multitude of other end-use chemical separation systems or coating needs. The nanoparticles can have any suitable average particle size to achieve desired properties in the resulting mixed-matrix polymer films. For instance, the nanoparticles, for example, can have an average particle size of from, 100 - 1000 nm, from 8 - 300 nm, or preferably, from 50 - 100 nm. Importantly, the particle size must be less than the final film thickness desired and designed by the choice of polymer concentration and coating thickness, or the particles may penetrate through the polymer film. Moreover, depending on the desired properties of the mixed-matrix polymer film, differing concentrations of nanoparticles can be included in the solution. The mass ratio of nanoparticles to polymer can be any suitable ratio, preferably from 40 - 60%, 1 - 20%, or 20 -40% by mass, with different nanoparticles, having different mechanisms of augmenting the properties of the final film, performing best at different mass loadings relative to polymer. The mass ratio of the nanoparticles to nanoparticle dope solution can be any suitable ratio, for example, from 6 - 24%, 0.1% - 20% or 10 - 30% by mass.

Depending on the concentration of polymer and nanoparticle in the solvent, the solvent can easily be cast or spread across a substrate or carrier at a uniform consistency and thickness. The nanoparticle dope solution can be deposited in generally any desired thickness with the understanding that the resulting solidified polymer film or mixed-matrix polymer film will have a thickness substantially less than the as- deposited thickness. The nanoparticle dope solution can be deposited at a thickness of from 0.1 to 100 microns, preferably 0.5 to 40 microns, and more preferably 1 to 30 microns, including just a few microns to tens of microns. In one aspect, the nanoparticle dope solution is deposited on the substrate or carrier at a thickness of 0.5 microns to 40 microns.

In one aspect of the present disclosure, the nanoparticle dope solution can be deposited very quickly onto the substrate or carrier and solidified. Without wishing to be limited by any particular theory or underlying mechanism, the present inventors believe that a highly beneficial feature of the present disclosure is the ability to quickly form the solidified film before the dope solution or its additives can change by, for example, settling, aggregation, convection, evaporation, etc. Essentially, because the present disclosure describes a method that in one aspect rapidly forms a polymer film, minimal time is allowed for particles (or other additives) to unduly aggregate or settle, or voids to form, or associated microcrack anomalies to jeopardize the robust nature of the resulting films for use and handling. Aggregates generally refers to the formation of clusters of large particles whose large size can potentially lead to increased rates of settling, rather than the formation of uniformly dispersed percolating networks of nanoparticles which, in some systems, can be relatively buoyant and preferred in some applications, such as ion separation in liquids wherein MOFs or other nanoparticles in such networks are selective for desired ions.

Thus, the present disclosure permits formation of the polymer film before the solution can change to have localized undesired properties. Indeed, the solidification of the nonporous layer can be so rapid, on the order of a few seconds, that in one embodiment the nonsolvent is first chilled to a temperature in the range of 0 - 10 °C (e.g. refrigeration), -20 - 0 °C (e.g. freezing), or broadly -50 - 0 °C, before immersing the cast or deposited film; in this way, a somewhat thicker polymer film or mixed matrix membrane can be achieved, such as a one having a thickness in the range of 1-5 microns, or 1-2 microns. Thus, such control of demixing can provide a relatively thick and uniform dense skin without formation of any underlying porous polymer as in conventional phase inversion.

The maximum thickness of polymer film or mixed matrix film that can be formed by the present disclosure is dependent, in part, on the deposition thickness of the cast dope solution. For example, if less polymer is available in the deposited dope solution than is required to produce a desired film thickness, then a thinner film is produced than desired. Through the present disclosure, films of a range of thicknesses are possible for each combination of selected polymer, solvent, non-solvent and optional nanoparticle system. The dope solution can be optimized to produce either thicker or thinner films through adjusting, for example, polymer concentration, MOF concentration, viscosity, casting technique, and type of solvent. If the as-cast dope solution is deposited in a thickness that is greater than is appropriate (the transitional thickness), an asymmetric or porous polymer film will result. Using the thicknesses, components, optional evaporation or exposure to a second nonsolvent, and related teachings explained herein, a nonporous film or mixed matrix membrane is consistently achieved.

The nanoparticle dope solution can be deposited on the substrate or carrier in any manner that can deposit a solution at a desired thickness across an acceptable substrate or carrier. The method can include, for example, casting a film across the substrate or carrier, spin-coating a film across the substrate or carrier, doctor blade casting a film across the substrate, slot-die casting a film across the substrate, dip-coating the substrate film in the dope solution, or gravure coating the film across the substrate or carrier. The dope solution should have appropriate viscosity for the desired deposition method. Any appropriate dope solution viscosity may be deposited given the teachings herein, so long as the as-cast or deposited film has the desired thickness and is relatively uniformly applied to avoid pockets and asymmetries.

After the solution is deposited on the substrate or carrier, the substrate or carrier along with the deposited dope solution or nanoparticle dope solution is contacted with, or immersed in, a nonsolvent to effect a phase change of the dope solution or nanoparticle dope solution into a nonporous polymer film or a mixed-matrix polymer film, as the case may be. The nonsolvent effects the phase change of the dope solution by removing the solvent and allowing the polymer to rapidly solidify, thereby creating a nonporous polymer of a desired thickness on the substrate or carrier. Suitable nonsolvents are selected that are miscible with the solvent but not the polymer and nanoparticle. Thus, by immersing the nanoparticle dope solution in the nonsolvent, the solvent rapidly exits the polymer and a polymer film or mixed-matrix polymer film is formed. During solidification of the polymer, the thickness of the as- cast or deposited dope solution is reduced to the polymer film or mixed matrix film thickness by a factor typically in the range of 400% to 800% reduction in thickness, but has been demonstrated to be as high as 1600% in some cases herein. The reduction in thickness can also be smaller, depending on the amount of solvent in the nanoparticle dope solution, the chilled temperature of the nonsolvent, and other factors.

Suitable nonsolvents depend on both the polymer and the solvent. The following nonsolvents are particularly suitable for use with certain polymers referred to in the present disclosure: isopropyl alcohol, glycerol, hexane, solution of lithium chloride in water at a concentration of, for example, 6 molal, and solutions of calcium chloride in water at a concentration of, for example, 6 molal. The nonsolvent can also be liquid alkanes at room temperature, for example, heptane, cyclohexane, and isocetane. The nonsolvent can also be liquid polyethylene glycol and its derivatives, for example, polyethylene glycol having an average molecular weight of 200, 400, or 600. The nonsolvent can be an alcohol, for example, 1- propanol, butanol (and its derivatives), and pentanol (and its derivatives). The nonsolvent can be glycerol, ethylene glycol, propylene glycol (and its derivatives), liquid sugars, and sugar alcohols. The nonsolvent can be acetates, for example ethyl acetate and butyl acetate. The nonsolvent can include aromatic compounds, for example, toluene and xylene. The nonsolvent can include water and saturated systems, for example, salt brine in water, concentrated sugar solution, and water-organic mixtures. The nonsolvent can be a single compound or can be a combination of these compounds. The most important aspect of the nonsolvent is that it is selected because it is miscible with the selected solvent and immiscible with the polymer. The nonsolvent should be selected to work with the polymer and the solvent in a manner that achieves rapid removal of the solvent from the deposited dope solution. The nonsolvent is chosen such that it interacts with the solvent at a rate that permits deposition of a single nonporous polymer film without a porous layer, voids, or microcracks.

The nanoparticle dope solution and the substrate are contacted with or immersed in the nonsolvent for a sufficient amount of time to effect the phase change. The phase change process can typically occur, depending on the polymer, solvent, nonsolvent, and film thickness in less than 30 seconds, from 0.1 to 15 seconds, or from 5 to 10 seconds. Due to the rapid phase change, an isotropic polymer layer may be formed. The nonsolvent enters the deposited solution and removes the solvent thereby depositing a film on the substrate or carrier. The nonsolvent can be contained in a bath that the substrate and nanoparticle dope solution film pass through at a desired speed. Thus, the disclosure herein contemplates a continuous process in which the nanoparticle polymer solution is deposited on the substrate or carrier, by, for example, doctor blade casting, and then is passed through a bath of nonsolvent whereby the process takes between, for example 5 to 10 seconds to pass the substrate and nanoparticle dope solution through the bath of nonsolvent, and then the substrate and mixed-matrix polymer film is removed from the nonsolvent bath. In a continuous application of this system, additional associated processes, such as solvent exchange, lamination of additional materials such as sealants and coatings to provide particular properties such as fouling resistance, may be applied after the film is formed. In addition, prior to the casting procedure, the substrate may be prepared by any suitable technique including via continuous solvent impregnation, or the application of additional layers to provide chemical or mechanical support, or to otherwise support the desired end-use of the film. The nonsolvent bath may be kept chilled or heated depending on process conditions. Since solvent and potentially polymer and additives to the polymer solution are continuously released into the nonsolvent, the nonsolvent may be continuously regenerated by the use of one or more of adsorption columns, membranes, filters, distillation, gas absorption or stripping, electro- or photo-chemical oxidation of the solvents, and liquid extraction.

The dope solution or nanoparticle dope solution can be wet processed, dry-wet processed, or wet-wet processed. In wet processing, the solution is deposited on the substrate or carrier and then immersed directly in the nonsolvent to effect the desired phase change. In dry- wet processing, the solution is deposited on the substrate or carrier and prior to immersion in the nonsolvent, is contacted with air. In wet-wet processing, the is deposited on the substrate, contacted with a first nonsolvent, and then contacted with a second nonsolvent. Any of the described nonsolvents can function as either the first or second nonsolvent in a wet-wet process.

Having described certain embodiments of methods for manufacturing dense isotropic polymer films and mixed-matrix polymer films, and having shown illustrative details of particular embodiments, it will be understood that the specific examples given below are employed in a descriptive sense only and are not for the purpose of limitation. Various modifications to the embodiments may be made without departing from the spirit and scope of the present invention which is limited only by the appended claims. For example, for fabricating mixed matric materials incorporating nanoparticles, such nanoparticles can be the aforementioned MOFs, but may also contain other functionalized groups or comprise any other MOFs or nanoparticles depending on the desired properties of the mixed-matrix polymer film. In addition, the resulting polymer film may be a nonporous film containing no nanoparticles, which may be used as a coating for any end use product or process where a polymer coating is desired. The nonporous polymer film may also be utilized as an intermediate in making composite membranes, laminates, and porous films given the teachings herein.

EXAMPLES

Example 1: Fabrication of Uniform Dense Polysulfone Film

Polysulfone (Udel P-3500 LCD MB7, Solvay Specialty Polymers) was dissolved in anhydrous tetrahydrofuran to form a dope solution. The Udel P-3500 LCD MB7 is dried overnight at a temperature of at least 135 °C to 150 °C, under vacuum. Under anhydrous conditions, the dope solution will be clear with no observable color and no obvious turbidity.

The dope solution contained 20% by weight polysulfone. The dope solution was then cast onto a glass substrate at a thickness of 80 microns under ambient conditions. The ambient condition of the laboratory was between 20 and 25 °C and between 40% and 60% relative humidity. The cast liquid film was immersed in an anhydrous isopropyl alcohol at ambient conditions and a solid polymer film was deposited on the glass substrate. Prior to immersing the film into the nonsolvent bath, the nonsolvent bath was kept covered to minimize water intrusion into the nonsolvent bath. The presence of trace amounts of water will cause the formation of porous voids. The resulting film of polysulfone was ten microns thick and was nonporous and optically transparent. An example of a film produced via this procedure is shown in FIG. 11. Similar to the procedure described above, additional dope solutions comprising 15 wt% polysulfone Udel P-3500 LCD MB7 dissolved in anhydrous tetrahydrofuran, and 10 wt% polysulfone Udel P-3500 LCD MB7 dissolved in anhydrous tetrahydrofuran, were formed according the experimental conditions discussed above. Under the ambient conditions discussed above, portions of the solution were cast sequentially onto glass substrates at varying thicknesses and immersed into anhydrous isopropyl alcohol. The first casting thickness was 80 microns, and the casting thickness was subsequently reduced by 10 microns until a nonporous film of polysulfone resulted. In the case of 15 wt% polysulfone, a nonporous film of polysulfone was observed to form at an initial casting thickness of 60 microns, and the resulting film was 5 microns thick. In the case of 10 wt% polysulfone, a nonporous film of polysulfone was observed to form at an initial casting thickness of 40 microns, and the resulting film was 2.5 microns thick. These results, summarized in Table 2, demonstrate that the transitional casting thickness for polysulfone is linearly proportional to the concentration of polysulfone in the dope solution, and that the contraction ratio of the film may reach as high as 1600%.

Table 2: Results from polysulfone casting from tetrahydrofuran dope solution into anhydrous isopropyl alcohol.

Example 2: Fabrication of Uniform Dense Polybenzimidazole Film

Polybenzimidazole (Celazole) was dissolved in N,N-dimethylacetamide to form a dope solution. Celazole is hygroscopic and will absorb greater than 15% water by mass. The Celazole and N,N-dimethylacetamide must be anhydrous to form the nonporous polymer film. The dope solution contained 10% by weight of poly benzimidazole. The dope solution was then case onto a glass substrate at a thickness of 10 microns. The cast liquid film was immersed in heptane thereby depositing a solid polymer film on the substrate. No care was taken to prevent water absorption into the heptane, as water is sparingly soluble in heptane. The resulting film of polybenzimidazole was 800 nanometers thick and was nonporous. An example of a film produced via this procedure is shown in FIG. 12.

Example 3: Fabrication of MMM of Polysulfone/MOF

Polysulfone (Udel P-3500 LCD MB7, Solvay Specialty Polymers) was dissolved in tetrahydrofuran with a nanoparticle (UiO-66, 50-100 nm average particle size) to form a dope solution. Care was taken to ensure the polysulfone and solvent were anhydrous as discussed in Example 1. The nanoparticles were received dry and were not further dried. The dope solution contained 20% by weight of polysulfone and 13% by weight of UiO-66. The dope solution containing the polymer and MOF was cast onto a glass substrate at a thickness of 40 microns under the ambient conditions discussed in Example 1. The cast liquid film was immersed in anhydrous isopropyl alcohol thereby depositing a solid polymer film. Care was taken to prevent water contamination in the nonsolvent bath as discussed in Example 1. The resulting film of polysulfone/UiO-66 was five microns thick and nonporous. The resulting film was 40% by weight UiO-66.

Example 4: Fabrication Using Cold Nonsolvent Bath for Poly(amideimide) Film

To determine the effect of a cold nonsolvent on the formation of polymer film, Poly(amideimide) (Torlon 4000T-MV, Solvay Specialty Polymers) was dissolved inN-methyl- 2-pyrrolidone and tetrahydrofuran to form a dope solution. The dope solution contained 20% by weight poly(amideimide), 40% by weigh N-methyl-2-pyrrolidone, and 40% by weight tetrahydrofuran. Care was taken to ensure that polysulfone and solvents were anhydrous as discussed in Example 1. The dope solution was case onto a glass substrate at a thickness of 20 microns under ambient conditions as discussed in Example 1. The cast liquid film was immersed in anhydrous isopropyl alcohol at a temperature of -17 °C to deposit a solid polymer on the substrate. The isopropyl alcohol was chilled in a sealed vessel and exposed to the ambient laboratory conditions only immediately before the immersion of the cast liquid film to minimize moisture absorption from the air. The resulting poly(amideimide) film was three microns thick and nonporous. The cold temperature of the nonsolvent bath retards the rate of nonsolvent intrusion into the cast liquid film, thereby delaying the formation of a porous layer and enabling thicker polymer films to be deposited on the substrate. Example 5: Fabrication of Composite Membrane on Support

Polysulfone (Udel P-3500 LCD MB7, Solvay Specialty Polymers) was dissolved in tetrahydrofuran to form a dope solution. The dope solution contained 20% by weight polysulfone. Care was taken to ensure that polysulfone and solvents were anhydrous as discussed in Example 1. A porous support that is compatible (i.e. immiscible) with tetrahydrofuran was prepared. The substrate comprised a non-woven paper material that was impregnated by a solvent. The non-woven paper could also be impregnated by air, a solvent, a nonsolvent, or a blend of a solvent and nonsolvent. To impregnate the non-woven paper material, the paper was saturated with an impregnation solvent consisting of 50:50 by volume N- methyl-2-pyrrolidone and isopropyl alcohol and excess solvent was removed with a rubber roller. Care was taken to ensure that the impregnation solvent blend was anhydrous. The dope solution was cast onto the prepared support at a thickness of 20 microns under ambient conditions as discussed in Example 1. The cast liquid film was immersed in an isopropyl alcohol nonsolvent thereby depositing a polymer film. Care was taken to prevent water contamination in the nonsolvent bath as discussed in example 1. The composite membrane consisted of 2.5 microns polysulfone film laminated to a paper mechanical support.

Example 6: Preparation of Polysulfone/MOF Casting Solution

In a different embodiment, a sample of tetrahydrofuran was split into two equal parts forming solution 1 and solution 2. To solution 1, MOFs UiO-66-NH2 and UiO-66-(COOH)2 are added in and then solution 1 is sonicated. Polysulfone was dissolved in solution 2 and then solution 2 was sonicated. Care was taken to ensure that the components were free of water contamination as discussed in Example 3. Twenty percent of solution 2 was added to solution 1 and then the resulting solution 1 was sonicated. The remainder of solution 2 was added to solution 1 and then the resulting solution 1 was sonicated. The resulting solution was 10 % by weight polysulfone. The resulting solution was further mixed and then sonicated. This solution can then be cast onto a substrate or carrier at a desired thickness, as discussed in Example 3.

Example 7: Fabrication of Uniform Dense Polysulfone Film in a Modified Water Bath Polysulfone (Udel P-3500 LCD MB7, Solvay Specialty Polymers) was dissolved in tetrahydrofuran to form a dope solution. The dope solution contained 20% by weight polysulfone. Care was taken to ensure the polymer and solvent were anhydrous as discussed in Example 1. The dope solution was then cast onto a glass substrate at a thickness of 40 microns under ambient conditions as discussed in Example 1. The cast liquid film was immersed in a solution of 6 mol/kg lithium chloride in deionized water and a solid polymer film was deposited onto the glass substrate. The resulting film of polysulfone was 5 microns thick and was nonporous.

Example 8: Fabrication of Uniform Dense Polysulfone Film in a Second Modified Water Bath

Polysulfone (Udel P-3500 LCD MB7, Solvay Specialty Polymers) was dissolved in dichloromethane to form a dope solution. The dope solution contained 20% by weight polysulfone. Care was taken to ensure the polymer and solvent were anhydrous as discussed in Example 1. The dope solution was then cast onto a glass substrate at a thickness of 40 microns under ambient conditions as discussed in Example 1. The cast liquid film was immersed in a solution of 6 mol/kg calcium chloride in deionized water and a solid polymer film was deposited onto the glass substrate. The resulting film of polysulfone was 5 microns thick and was nonporous.

Example 9: Fabrication of Uniform Dense Poly[l-(trimethylsilyl)-l-propyne] Film in a Modified Water Bath

Poly[l-(trimethylsilyl)-l-propyne] (PTMSP) was dissolved in tetrahydrofuran for form a dope solution. Care was taken to ensure the polymer and solvent were anhydrous as discussed in Example 1. The dope solution contained 10% by weight PTMSP. The dope solution was then cast onto a glass substrate at a thickness of 80 microns under ambient conditions as discussed in Example 1. The cast liquid film was immersed in a solution of 6 mol/kg lithium chloride in deionized water and a solid polymer film was deposited onto the glass substrate. The resulting film of PTMSP was 10 microns thick and was nonporous.

Example 10: Fabrication of Uniform Dense PEBAX 2533 Film

PEBAX 2533, a poly(ether-block-amide) block copolymer consisting of a Nylon 12 (amide) block and a poly(tetramethylene oxide) (ether) block, the ratio of ether to amide being 3 : 2, was dissolved in anhydrous N-methyl-2-pyrrolidone to form a dope solution. The PEBAX 2533 was stored in a vacuum desiccator prior to use, but was not heated to dry, as it has a low melting temperature. Care was taken to ensure the solvent as anhydrous as discussed in Example 1. The dope solution contained 10% by weight PEBAX 2533. The dope solution was then cast onto a glass substrate at a thickness of 100 microns under ambient conditions as discussed in Example 1. The cast liquid film was immersed in heptane and a solid polymer film was deposited on the glass substrate. No particular care was taken to avoid water absorption in the heptane bath for reasons discussed in Example 2. The resulting film was 10 microns thick and translucent.

Example 11: Comparative Example Use of Inappropriate Solvent-Nonsolvent Combinations Improper Solvent

Following the general experimental conditions discussed in Example 1, a dope solution comprising 20% polysulfone Udel P-3500 LCD MB7 can be formed by dissolving the polysulfone in anhydrous tetrahydrofuran. A similar solution comprising 20% polysulfone Udel P-3500 LCD MB7 can be formed by dissolving the polysulfone in anhydrous N-methyl-2- pyrrolidone. Both dope solutions may be cast onto glass substrates at a thickness of 80 microns and both cast liquid films may be immersed into an anhydrous isopropanol bath under the conditions discussed in Example 1. The film formed from the dope solution containing anhydrous tetrahydrofuran will be dense, uniform, and optically transparent, with a thickness of 10 microns. The film formed from the dope solution containing anhydrous N-methyl-2- pyrrolidone will comprise a nonporous skin layer of 1 micron thickness, and porous layer 50 microns in thickness. The film formed from anhydrous tetrahydrofuran may be removed from the glass substrate and deposited on a different material or may be formed on an alternate substrate material. The membrane formed from anhydrous N-methyl-2-pyrrolidone consists of an integrated layer of nonporous polymer film and porous polymer foam, which cannot easily be separated.

Example 12: Comparative Example Use of Inappropriate Solvent-Nonsolvent Combinations Improper Nonsolvent

Following the general experimental conditions discussed in Example 1, two identical dope solutions comprising 20% polysulfone Udel P-3500 LCD MB7 can be formed by dissolving the polysulfone in anhydrous tetrahydrofuran. Both dope solutions may be cast onto glass substrates at a thickness of 80 microns. One cast liquid film may be immersed in a water bath, and the other cast liquid film may be immersed into an anhydrous isopropanol bath under the conditions discussed in Example 1. The film formed from the dope solution immersed in anhydrous isopropanol will be dense, uniform, and optically transparent, with a thickness of 10 microns. The film formed from the dope solution immersed in water will comprise a dense, but porous film with large pores. Example 13: Comparative Example Use of Inappropriate Solvent-Nonsolvent Combinations I m miscible Solvent-Nonsolvent Pair

Following the general experimental conditions discussed in Example 1, a dope solution comprising 10% poly[l-(trimethylsilyl)-l-propyne] (PTMSP) can be formed by dissolving the PTMSP in cyclohexane. The dope solution may be cast onto a glass substrate at a thickness of 100 microns. The cast liquid film may be immersed into a water bath. Since cyclohexane is insufficiently soluble in water to be extracted, no solvent extraction or phase separation will occur, and neither a dense or porous film will result.

Example 14: Comparative Example Use of Inappropriate Casting Thickness - Casting Above the Transitional Thickness

Following the general experimental procedures discussed in Example 1, a dope solution comprising 20% polysulfone Udel P-3500 LCD MB7 can be formed by dissolving the polysulfone in anhydrous tetrahydrofuran. A similar dope solution can be formed comprising 10% polysulfone in anhydrous tetrahydrofuran. The dope solution comprising 20 wt% polysulfone may be cast onto two glass substrates at thicknesses of 80 microns and 40 microns. These liquid films may then be immersed in anhydrous isopropanol as discussed in Example 1. The film cast at 80 microns will result in a dense polymer film 10 microns in thickness, while the film cast at 40 microns will result in a dense polymer film 5 microns in thickness. These results demonstrate a contraction ratio of 8 : 1. Similarly, the dope solution comprising 10 wt% polysulfone may be cast onto two glass substrates at thicknesses of 80 microns and 40 microns. These liquid films may then be immersed in anhydrous isopropanol as discussed in Example 1. The film cast at 80 microns will result in an integrally skinned membrane with a skin layer 2.5 microns thick atop a porous layer. The film cast at 40 microns will result in a dense polymer film 2.5 microns thick. This result demonstrates a contraction ratio of 16 : 1. The transitional thickness for a the 20% polysulfone solution in anhydrous tetrahydrofuran has been found to be 80 microns, while the transitional thickness for a 10% polysulfone solution in anhydrous tetrahydrofuran has been found to be 40 microns. Since both films formed from the 20% polysulfone solution are cast below the transitional thickness, no porous layers are formed. Since the 10 wt% polysulfone film cast at 80 microns was cast at a thickness greater than the transitional thickness, a porous layer was formed. It is thus demonstrated that the transitional thickness is positively related to polymer concentration. It is similarly thus demonstrated that the contraction ratio is negatively related to polymer concentration. Example 15: Comparative Example Inappropriate Nonsolvent Composition

Following the general experimental procedures discussed in Example 1, a dope solution comprising 20% polysulfone Udel P-3500 LCB MB7 can be formed by dissolving the polysulfone in anhydrous tetrahydrofuran. The dope solution may be cast onto two glass substrates at 80 microns thickness. One cast liquid film may be immersed into an anhydrous isopropanol bath under the conditions discussed in Example 1. In this case, a nonporous polysulfone film with a thickness of 10 microns will form. The second cast liquid film may be immersed into an isopropanol bath which is contaminated with 1 wt% water. In the second case, a film which contains porous structure, and may or may not be integrally skinned, will form. The presence of water in the systems optimized for anhydrous nonsolvents will result in porous membranes.

Example 16: Determination of Suitable Salt Compositions

Following Examples 6, 7, and 8, dense isotropic polymer films may be formed from concentrated saltwater nonsolvent baths in lieu of anhydrous nonsolvent baths. As these solutions are no longer sensitive to water contamination and are easily handled and stored, they are of particular industrial relevance. Following the experimental conditions discussed in Example 1, a solution of 20 wt% Polysulfone Udel P-3500 LCD MB7 may be dissolved in anhydrous tetrahydrofuran. This dope solution may be cast on a glass substrate at a thickness of 80 microns and immersed into a nonsolvent bath comprising a solution of lithium chloride in water at a concentration of 6 molal. The resulting film will be 10 microns thick and nonporous. The dope solution may similarly be cast in an identical manner and immersed in a water bath. The resulting film will be porous. Thus, on the continuum between 0 and 6 molal lithium chloride in water, there exists a preferred concentration of lithium chloride, below which a porous film will result. Without wishing to be bound by theory, it is hypothesized that this composition is related to the osmotic pressure of the water, lithium chloride being sparingly soluble in polysulfone and tetrahydrofuran. It is similarly hypothesized that the preferred composition and the polymer solution concentration will be positively related. It is reasonable to expect that compositions near the preferred composition will yield control over the formation of integrally skinned membranes as well.

Example 17: Determination of Osmotic Pressure Control over Film Formation

Following the above example, a wide range of osmotic agents (equivalently, solutes) may be utilized to modulate the behavior of the polymer film formed via nonsolvent induced film deposition (NFID). In particular, solutes which exert high osmotic pressure, such as, but not limited to, dimethylsulfoxide, glycerol, propylene glycol, ethylene glycol, sucrose, or poly(ethylene glycol), may be combined with water to form blended nonsolvents which act similarly to the inorganic salt additive discussed in Examples 6, 7, and 8. Blends of such solvents with water, or blends of such solvents with each other, will comprise systems with preferred compositions, as discussed in Example 16, and form systems in which the composition is similar to or between two demonstrated compositions, to likewise result in dense isotropic polymer films.

Example 18: Lamination of Polymer Films and Membranes

Following the general experimental conditions discussed in Example 1, if the contact time between a dope solution, e.g., one comprising 20 wt% polysulfone Udel P-3500 LCD MB7 dissolved in anhydrous tetrahydrofuran, and a support material, is low (e.g., on the order of 5 seconds or less), the properties of the underlying support material will not be appreciably affected by the contact with the polymer dope solution in the time between when contact is initiated and the time at which the film has been fully set via contact with the nonsolvent. In such a case, if the contact time between the dope solution and the support material is low (e.g., on the order of 5 seconds or less), the properties of the resulting nonporous isotropic film will not be substantially altered. Thus, for example, such a dope solution may be cast onto a polysulfone ultrafiltration membrane having a fully porous structure, at a thickness of 10 microns, and immersed without delay into a bath of anhydrous isopropanol or a bath of water containing 6 molal lithium chloride. The result would be a laminated polysulfone membrane comprising a nonporous skin layer resulting from the nonsolvent induced film deposition process, but likely less than, 1.25 microns, and a porous support layer the same thickness and same porosity as the ultrafiltration membrane support. It is hypothesized that an intermediate area, 0.1-1 microns in thickness, may comprise a transition layer having intermediate porosity.

Example 19: Lamination of Dissimilar Polymer Films

Following the general experimental conditions discussed in Example 1, if the contact time between a dope solution and a dense polymer film, is low (e.g., on the order of 5 seconds or less), the properties of the underlying polymer film will not be appreciable affected by the contact with the polymer dope solution in the time between when contact is initiated and the time at which the film has been fully set via contact with the nonsolvent. Thus one dope solution, e.g., one comprising 20 wt% polysulfone Udel P-3500 LCD MB7 dissolved in anhydrous tetrahydrofuran, may be formed, and a second dope solution, e.g., one comprising 10 wt% poly[l- (trimethylsilyl)-l-propyne] (PTMSP) dissolved in anhydrous tetrahydrofuran, may be formed. The first dope solution may be cast onto a glass substrate at a thickness of 80 microns under the general experimental procedures discussed in Example 1 and immersed into a solution of lithium chloride in water at a concentration of 6 molal. A dense film 10 microns in thickness will result. The surface of this film may be then rinsed and dried to remove excess lithium chloride in water. Next, the second dope solution comprising 10 wt% PTMSP in anhydrous tetrahydrofuran may be cast atop the dense polysulfone film at a thickness of 80 microns and immersed into a solution of lithium chloride in water at a concentration of 6 molal, without delay. The result of such a procedure would be a PTMSP film of 10 microns thickness laminated directly to a polysulfone film of 10 microns thickness. It is hypothesized that an intermediate area, 0.1-1 microns in thickness, may comprise a transition layer having intermediate composition. It is envisioned that such a process is readily repeatable, allowing one to construct a plurality of polymer layers laminated together. One application of such a structure would be the integration of a smooth compatibilizing layer, known as a gutter layer, to fabricate a composite membrane as discussed in the above example. Another application of such a structure would be to construct a polymer layer to seal or protect a polymer layer formed underneath it, to provide anti-fouling, anti-abrasion, or similar protective qualities. Another application of such a structure would be to laminate materials having different optical refractive indices. An alternating stack of films with different refractive indices, known as a distributed Bragg reflector, can be used for form mirrors with tunable wavelengths of reflections. Distributed Bragg refractors have been fabricated from laminated polymer films for applications to sensors.

Example 20: Control over Phase Separation

Many polymer material combinations and polymer composite combinations are known to result in insoluble combinations. For example, polybenzimidazole (Celazole) is insoluble with the polyimide HAB-6FDA-CI. Blends of Celazole and HAB-6FDA-CI have been shown to provide superior permeability to pure Celazole membrane films when the HAB-6FDA-CI is thermally-rearranged and the HAB-6FDA-CI is well-dispersed in the Celazole. However pure blends of Celazole and HAB-6FDA-CI are known to undergo macroscopically visible phase separation when formed into membranes via evaporation from N,N-dimethylacetamide solvent. A blend of Celazole and HAB-6FDA-CI may be dissolved in N,N-dimethylacetamide at 10-20 wt% total polymer, and induced to mix, if necessary, via mechanical agitation, for example by one or more of shaking, blending, sonicating, stirring, and shear mixing, forming a temporary emulsion. This mechanically agitated solution may then be cast without delay onto a substrate material and immersed in a bath of heptane following the general experimental cautions discussed in Example 2. In this case, the rapid setting of the material via the nonsolvent induced film deposition (NIFD) process would result in polymer domains of the dispersed HAB-6FDA- CI phase, with polymer domains on the order of 5 microns or less. Considering a hypothetical blend of two polymers, A and B, it is thus hypothesized that a continuum of polymer phase separation, from pure A, to A with dispersed B, to A and B percolating throughout, to B with dispersed A, to pure B, can be achieved. Considering a hypothetical blend of a polymer A with an additive B, it is thus hypothesized that a continuum of phase separation, from pure A, to A with dispersed B, to B percolating through A, can be achieved.

Example 21: Control over Self-Assembled Phase Separation

It is known to literature that certain block copolymers self-assemble into well-ordered mesoscale phase domains. Considering a polymer comprising two mutually insoluble blocks of A and B, a continuum of phases is known to exist for different ratios of the length of the A block to the B block. In an idealized case, a continuum of structures from pure A, uniformly distributed spheres of B in A, aligned cylinders of B distributed in A, percolating gyroids of B formed in A, lamellar stacks of alternating A and B, percolating gyroids of A formed in B, aligned cylinder of A distributed in B, uniformly distributed spheres of A in B, and pure B, can be achieved. The aligned cylinder morphology is particularly desired for membrane applications. For example, polystyrene-block-poly(4-vinylpyridine) (138000-b-41000 g/mol) can be formed into a dope solution comprising 20 wt% polymer, 56 wt% N,N-dimethylformamide, and 24 wt% tetrahydrofuran. This solution may be cast onto a glass substrate at a thickness of, e.g., 200 microns, then allowed to evaporate freely in air for 20 seconds before being immersed in a water bath. The resulting film would comprise a skin layer with the desirable aligned cylindrical pore morphology and a porous subsurface layer. Other combinations of evaporation time and polymer composition would lead to different skin layer morphologies. The teachings herein may be adapted to such systems to yield dense, nonporous, phase-separated films of polymer comprising the desired phase-separated morphologies discussed above, spanning the entire thickness of the resulting film without the associated formation of porous voids, nor the formation of disordered regions. These films may be laminated to other materials as discussed in Examples 5, 18, and 19. These films may be applicable to their desired applications as-is or may be treated to remove one of the two blocks to yield regularly-sized pores templated by the removable material.

Example 22: Preparation of Uniform Dense Cellulose Acetate Films and the Effect of Polymer Content

Similar to Example 1, cellulose acetate (Eastman, CA-398-30, ds 2.45) was dissolved in anhydrous tetrahydrofuran to form dope solutions. The cellulose acetate was dried at 80 ^° C overnight under vacuum prior to use. A resulting solution containing 10 wt% cellulose acetate was slightly hazy, but free-flowing. A resulting solution containing 5 wt% cellulose acetate was transparent and free-flowing. Under the ambient conditions discussed in Example 1, cellulose acetate films were cast at 40 microns onto a glass plate and immersed into a solution of 7.5 mol/kg lithium chloride in deionized water. Films cast from a 10 wt% solution formed dense optically transparent films of approximately 10 microns thickness. Films cast from a 5 wt% solution formed a slightly cloudy film, indicating the presence of pores. Films are preferably formed with sufficient polymer content to avoid the formation of porous voids.

Example 23: Fabrication of MM Ms of Cellulose Acetate/MOF

A dope solution containing a 6:4 mass ratio of cellulose acetate to UiO-66-(COOH)2 MOF and a 9: 1 mass ratio of anhydrous tetrahydrofuran to cellulose acetate was formed according to the general conditions discussed in Example 22. To ensure that the MOF and polymer were well mixed, the MOF was initially dispersed in the requisite amount of solvent and sonicated in a bath sonicator for at least 30 minutes to mix. Subsequently, cellulose acetate was added in four additions comprising 1/8, 1/8, 1/4, and 1/2 of the total requisite polymer amount. Between each addition, the dope solution was sealed and stirred until the solution appeared homogenous without any evidence of unmixed polymer. The homogenization steps were performed for approximately 3 hours between each addition.

The resulting polymer solution was free-flowing and opaque white. The solution was cast onto a glass plate at a casting thickness of 20 microns and immersed into a nonsolvent bath containing 7.5 mol/kg lithium chloride in deionized water, similar to Example 22. The resulting film was dense and approximately 5 microns thick, but translucent rather than transparent due to the incorporation of MOF nanoparticles.

The resulting films were analyzed via salt permeation measurements and found to exhibit high permeability of lithium chloride with respect to magnesium chloride, with a Li/Mg selectivity in excess of 100. The selectivity was assayed by monitoring the diffusion of lithium chloride or magnesium chloride across a sample of the membrane film between two reservoirs, one (donor cell) containing 34 mL of 1.0 M solution of the desired salt, and the other (receptor cell) containing deionized water. The movement of ions across the membrane into the receptor cell was monitored via the conductivity of the receptor cell solution.

Example 24: Fabrication and Testing of Cellulose Acetate-MOF Composite Membranes Produced via Evaporation or Nonsolvent-Induced Film Deposition (NIFD).

A polymer solution dope to contain 6:4 cellulose acetate (Eastman Kodak, ds 2.45) to UiO-66-(COOH)2 MOF and 9: 1 tetrahydrofuran to cellulose acetate, by mass, is mixed in the following manner. MOF and anhydrous tetrahydrofuran are mixed in a sealed vial and mixed via sonication bath to break up and exfoliate the MOF particles. In four additions, 1/8, 1/8, 1/4, and 1/2, respectively, of the dry polymer powder are added to the vial, with the vial being sealed and mixed until the solution appears homogeneous between each addition. Approximately three hours of stirring is provided between each addition. The resulting solution has a color and consistency reminiscent of PVA glue.

A film of approximately 5 microns thickness was fabricated via a nonsolvent-induced film deposition process by casting the aforementioned cellulose acetate-MOF dope solution onto a glass plate at a casting thickness of 30 microns, then immersing the polymer film in a nonsolvent solution of 7.5 molal lithium chloride in water. The resulting film was non-porous. A similar film was manufactured utilizing a 50:50 mixture of glycerol and water (by mass) as the nonsolvent in lieu of 7.5 molal lithium chloride solution. The resulting film was non-porous, and approximately 5 microns thick, but had less transparency than the film produced in 7.5 molal lithium chloride. A similar film was produced by instead evaporating the solvent in air for 10 minutes. The resulting film was non-porous and approximately 5 microns thick. The resulting films were immersed in DI water for storage overnight before testing.

A sample of each of the resulting films was tested in an ion permeation apparatus.

Testing using 1.0 M solutions of LiCl and MgCh. sequentially, and repeating the test sequence twice, the Li/Mg selectivity of the mixed-matrix membrane film produced in 7.5 molal LiCl solution was found to be on the order of 124. The Li/Mg selectivity of the evaporated film was found to be on the order of 62. The selectivity of the film produced in a 50:50 mixture of glycerol and water had lower selectivity, on the order of 24.6, and developed a defect after the first test. Table 3: Single-salt permeability/selectivity characterization for membranes produced via evaporation and nonsolvent-induced film deposition (NIFD). Example 25: Testing of Cellulose Acetate-MOF Composite Membranes on Natural Lithium- containing Brine.

A sample of natural lithium-containing brine containing -80,000 ppm Mg ²⁺ ; -19,000 ppm Li+; -5400 ppm potassium, sodium, and calcium combined; with the anion balance consisting predominately of chloride (>99.5%); and with trace amounts of sulfate and boron, was used as a challenge solute for a cellulose acetate-MOF MMM fabricated by the above procedure. The brine was free of silt and foulants and had a pH of approximately 4.5 and a specific gravity of -1.5. The concentration of samples of the brine and the result of the permeation test were analyzed via optical emission spectroscopy (OES) using a Varian ICP-OES with the 2-3 strongest characteristic wavelengths investigated for each element. A standard addition method was used to assay each compound, utilizing 0, 1, 2, and 3 ppm spikes of each analyte. The permeation test was conducted in the standard manner over the course of 22.48 hours. At the end of the test, the components of the receptor cell were assayed via OES, and the resulting Li:Mg selectivity (a_(Li:Mg)) was calculated. The resulting selectivity was found to be -127.9, which is comparable to that measured via the single salt permeation tests using 1.0 M feed LiCl and MgCh (-6000 ppm Li and -19000 ppm Mg, respectively).

Table 4: Results of lithium/ magnesium selective permeation from a natural lithium-containing brine for a membrane produced via nonsolvent-induced film deposition.

The compositions, systems, and methods of the appended claims are not limited in scope by the specific compositions and methods described herein, which are intended as illustrations of a few aspects of the claims and any compositions, systems and methods that are functionally equivalent are within the scope of this disclosure. Various modifications of the compositions, systems, and methods in addition to those shown and described herein are intended to fall within the scope of the appended claims. Further, while only certain representative compositions, systems, and methods, and aspects of are specifically described, other compositions, devices, systems and methods and combinations of various features of the compositions, devices, systems and methods are intended to fall within the scope of the appended claims, even if not specifically recited. Thus a combination of steps, elements, components, or constituents can be explicitly mentioned herein; however, all other combinations of steps, elements, components, and constituents are included, even though not explicitly stated.