JP7570634B2 - Polymer composite thin film and method for producing the same - Google Patents

Description

The present invention relates to a polymer composite thin film that mainly contains a polymer material, and in particular to a polymer composite thin film that has high functionality and significantly improved film strength.

Recently, interest in organic and inorganic nano-membranes has been growing. In the inorganic field, the unique properties of graphene, an inorganic carbon compound, have attracted worldwide attention, and the international development race has suddenly intensified. This trend has also spread to other inorganic materials with nano-thickness, such as _MoS2 , and has now created a new research field as a two-dimensional material.

On the other hand, in the case of organic systems, there has been a huge amount of research from biochemical and biophysical standpoints on biomembranes with nano-order thicknesses. In addition, organic nanomembranes as industrial materials are expected to have unique properties as two-dimensional materials, but in order to promote practical use, it is necessary to realize large areas, no defects, self-supporting properties, structural stability, etc.

As an example of organic nanomembranes as industrial materials, there are high hopes for the development of excellent separation membranes that take advantage of nano-order thicknesses. In order to maximize the separation function of a separation membrane, it is desirable to make the membrane as thin as possible from the perspective of ensuring high permeability. However, in that case, there is a high possibility that the mechanical strength will decrease and the membrane will become fragile and unsuitable for practical use. In other words, there is a trade-off between making the separation membrane thin from a functional perspective and its mechanical strength. To solve this problem, it is thought to be effective to combine a functional membrane that is as thin as possible with a strong support and skeletal structure that does not interfere with its function.

A technology relating to such a polymer composite thin film is a gas separation membrane having a gas separation layer containing a crosslinked cellulose resin and cellulose nanofibers, in which the crosslinked cellulose resin has, in its crosslinked structure, the following groups: ^* -O-M-O- ^* , ^* -S-M-S- ^* , ^* -NR ^a C(=O)- ^* , ^* -NR ^b C(=O)NR ^{b- *} , ^* -O-CH ₂ -O- ^* , ^* -S-(CH ₂ ) ₂ -S- ^* , ^* -OC(=O)O- ^* , ^* -SO ₃ ^- N ⁺ (R ^c ) ₃ - ^* and ^* -P(=O)(OH)O ^- N ⁺ (R ^d ) ₃ - A gas separation membrane (wherein M represents a divalent to tetravalent metal atom, and R ^a , R ^b , R ^c and R ^d each independently represent a hydrogen atom or an alkyl group; ^* represents a linking site ⁾ is known, which has at least one linking structure selected from the group consisting of the following:

According to Patent Document 1, by forming a gas separation membrane with a gas separation layer using a cross-linked cellulose resin having a specific linking structure in the cross-linked structure, it is possible to provide a gas separation membrane that has excellent gas permeability as well as excellent gas separation selectivity, is resistant to plasticization even when used under high temperature, high pressure and high humidity conditions, exhibits excellent gas separation performance, is less susceptible to the effects of toluene and other impurities present in natural gas, has excellent folding resistance, can be processed into various module shapes, can be manufactured with a high yield, and further exhibits stable gas separation performance from the beginning of use.

Patent No. 6349026

However, according to the technology described in Patent Document 1, cellulose nanofibers may be added to the gas separation layer constituting the gas separation membrane, and the thickness of the gas separation layer is preferably 50 nm to 1 μm, but it is assumed that the gas separation layer containing crosslinked cellulose resin is formed on the upper side of a gas-permeable support layer (porous layer). More specifically, a composite membrane having both a gas separation layer and a porous layer is formed by applying a coating liquid (dope) containing the components constituting the gas separation layer (cellulose resin and crosslinking agent) to at least the surface of a porous support. With this configuration, the resulting gas separation membrane has a thickness of 10 μm to 200 μm.

In other words, the gas separation layer described in Patent Document 1 functions as a gas separation membrane by being formed on a porous layer, and there is no suggestion that the gas separation layer having a nano-order thickness can independently constitute a gas separation membrane, or that this gas separation membrane can exhibit a gas separation function.

In addition, the porous layer is composed of, for example, a porous membrane of an organic polymer, but there is no mention of the gas permeability of the parts of this porous layer other than the voids, and the presence of the porous layer may reduce the overall gas permeability of the gas separation membrane.

Furthermore, in the gas separation membrane described in Patent Document 1, in order to construct the gas separation layer from a cross-linked cellulose resin having a specific linking structure in the cross-linked structure, a specific metal complex is used as a cross-linking agent, and a metal bridge is formed by a ligand exchange reaction with the cellulose resin. In this case, the concentration of the cellulose resin and the metal complex as a cross-linking agent in the coating solution is set to a certain level or less to suppress the ligand exchange reaction in the coating solution, and further, by coating this coating solution as a thin film on a porous support layer, the ligand exchange reaction is quickly promoted with the rapid evaporation of the solvent, forming a metal bridge structure in the cellulose resin. This results in a complex microstructure of the gas separation layer, and as a result, the manufacturing process is also complex.

The present invention was devised to solve these problems with the conventional technology, and aims to provide a polymer composite thin film that is highly functional and has practical structural stability (self-supporting properties) due to its extremely thin structure, using a simpler configuration that combines (combines) a nanomembrane with flexible functionality and a nanosupport with excellent mechanical strength.

The present invention, which has been made to solve the above problems, is a polymer composite thin film that is characterized by being self-supporting due to the fact that a polymer thin film having a thickness of 100 nm or less is composited with a fibrous structure having a diameter smaller than the thickness of the polymer thin film.

This makes it possible to obtain a polymer composite thin film that combines high functionality and high mechanical strength, even if the polymer thin film is not self-supporting.

The present invention also relates to a polymer composite thin film in which a self-supporting polymer thin film having a thickness of 100 nm or less is composited with a fibrous structure having a diameter smaller than the thickness of the polymer thin film.

This makes it possible to obtain a polymer composite thin film that combines high functionality with even higher mechanical strength, provided that the polymer thin film itself is self-supporting.

In addition, the present invention relates to a fibrous structure that is composed of an organic polymer.

This makes it possible to produce polymer composite thin films at lower cost.

The present invention also provides a fibrous structure in the form of cellulose nanofiber.

As a result, since the material cost of cellulose nanofibers is extremely low, it becomes possible to produce polymer composite thin films at lower cost.

In addition, the present invention is such that the polymer thin film is mainly composed of polysiloxane.

As a result, since thin films made of polysiloxane generally have self-supporting properties, it is possible to obtain polymer composite thin films with superior mechanical strength.

In addition, the present invention is such that the polymer thin film is mainly composed of a crosslinkable polymer.

This makes it possible to obtain a polymer composite thin film with high functionality and high mechanical strength even by using cross-linkable polymers such as epoxy resins, which are more common polymer materials.

In addition, the present invention provides that the polymer thin film has gas separation properties.

This makes it possible to remove specific gases from a gas stream using a polymer composite thin film.

In addition, the present invention provides a polymer thin film that selectively allows carbon dioxide to pass through.

This makes it possible to remove (separate) carbon dioxide from a gas using a polymer composite thin film.

In addition, the present invention has a polymer thin film that separates oxygen and nitrogen in the air.

This allows the polymer composite thin film to function as an air separation membrane, making it possible to increase or decrease the oxygen or nitrogen concentration in the air.

In this way, the present invention makes it possible to obtain a polymer composite thin film that has high functionality and high mechanical strength.

1(a) to 1(d) are explanatory diagrams showing the structure of a polymer composite thin film 1 according to the present invention. Photographs (a) to (d) show the deflection of the films obtained in Comparative Example 1 and Example 1 when the same load was applied to the films. Graph showing the relationship between stress (σ) and deflection (ε) in the films obtained in Comparative Example 1 and Example 1 Photograph showing the appearance of a CNF/PDMS film with circular damage.

Figures 1(a) to (d) are explanatory diagrams showing the structure of a polymer composite thin film 1 according to the present invention. Hereinafter, an embodiment of the present invention will be described with reference to Figure 1. The polymer composite thin film 1 is composed of a polymer thin film 2 and cellulose nanofibers 3 as fibrous structures.

As shown in Figures 1(a) to (d), the polymer composite thin film 1 has a structure in which cellulose nanofibers 3 are contained within the polymer thin film 2. Specifically, as shown in Figures 1(a) and 1(b), the cellulose nanofibers 3 may all be contained within the polymer thin film 2 and be unevenly distributed on one side of the surface of the polymer thin film 2, as shown in Figure 1(a) and 1(b), or part of the cellulose nanofibers 3 may be exposed to the outside of the polymer thin film 2 as shown in Figure 1(c), or the cellulose nanofibers 3 may all be contained within the polymer thin film 2 and be uniformly dispersed within the polymer thin film 2 as shown in Figure 1(d).

In this way, the polymer composite thin film 1 of this embodiment has a configuration in which the polymer thin film 2 and the cellulose nanofibers 3 are composited. The cellulose nanofibers 3, which are organic polymers, form fibrils as small fibers (fibrous structures). Fibrils have high mechanical strength as a material, and by being composited with the polymer thin film 2, the polymer composite thin film 1 exhibits extremely high mechanical strength. Furthermore, the cellulose nanofibers 3 are manufactured at low cost by mechanical defibration from abundant resources such as wood, and are also environmentally friendly materials as they are plant fibers.

As materials for the polymer thin film 2, for example, vinyl polymers, polysiloxanes, and cross-linked polymers can be suitably used. Here, it is said that vinyl polymers and polysiloxanes alone cannot ensure the mechanical strength (self-supporting) at a film thickness (for example, 100 nm or less) at which functionality such as gas separation can be effectively exhibited. In this case, by combining the polymer thin film 2, which is mainly composed of vinyl polymers or polysiloxanes, with cellulose nanofibers 3, it is possible to achieve both functionality and self-supporting properties of the polymer composite thin film 1, which is composed of these components.

On the other hand, cross-linked polymers are considered to be self-supporting materials even at film thicknesses where their functionality can be effectively demonstrated (for example, 100 nm or less, similar to vinyl polymers and polysiloxanes). Here, a cross-linked polymer refers to a polymer that has a three-dimensional network structure (cross-linked structure) formed by bonding multiple linear polymer chains through a chemical reaction, and includes, for example, epoxy resins in which epoxy and amino groups as functional groups are cross-linked through a chemical reaction.

As for epoxy resin, an example of a self-supporting polymer thin film having a thickness of 20 nm is described in "A Large, Freestanding, 20 nm Thick Nanomembrane Based on an Epoxy Resin, H. Watanabe, T. Kunitake, Volume 19, Issue 7, Pages 909-912, 2007."
(https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.200601630)
It is published in.

By combining a polymer thin film 2, whose main component is a cross-linkable polymer, with cellulose nanofibers 3, the polymer composite thin film 1, which contains these components, can ensure functionality as well as even greater mechanical strength.

In this embodiment, the thickness D2 of the polymer thin film 2 is set to 100 nm or less. By setting the thickness D2 of the polymer thin film 2 to 100 nm or less, it is possible to significantly improve the functionality (here, gas separation properties) of the polymer composite thin film 1. Furthermore, in this embodiment, the thickness D1 of the polymer composite thin film 1 is also set to 100 nm or less.

In other words, in the configurations of Figures 1(a), (b), and (d), the polymer thin film 2 that completely encapsulates the cellulose nanofibers 3 within the film is the polymer composite thin film 1 itself, so the thickness D1 of the polymer composite thin film 1 = the thickness D2 of the polymer thin film 2, and in the configuration in which part of the cellulose nanofibers 3 is exposed from the polymer thin film 2 as in Figure 1(c), the thickness D1 of the polymer composite thin film 1 > the thickness D2 of the polymer thin film 2.

The cellulose nanofibers 3 have a diameter (e.g., 4 nm to 90 nm) smaller than the thickness of the polymer thin film 2. By making the diameter of the cellulose nanofibers 3 smaller than the thickness of the polymer thin film 2, the functionality of the polymer thin film 2 is fully exhibited. Conversely, if the diameter of the cellulose nanofibers 3 is made larger than the thickness of the polymer thin film 2, the effective surface area of the film is reduced, making it difficult to exhibit its functionality.

In Figure 1, the cellulose nanofibers 3 of the same fiber length are shown aligned in a specific direction, but this is merely a schematic representation. In reality, the fiber lengths of the cellulose nanofibers 3 vary (5 μm or more), and the cellulose nanofibers 3 are oriented in all directions and are contained in the polymer thin film 2 in a complex entangled state.

In this embodiment, cellulose nanofibers, which are organic polymers, such as oxidized cellulose nanofibers (oxidized CNF) and a mixture of cellulose nanofibers 3 and oxidized cellulose nanofibers can be preferably used as the fibrous structure, but other organic polymers may also be used as the fibrous structure. Examples of other organic polymers that can be used include polymers produced by manufacturing methods such as electrospinning, fibrin, which is a protein formed by bundling fine fibers and is involved in blood clotting, peptides, collagen, etc., and further, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) may also be used.

Here, for example, if DNA is used as the fibrous structure, since DNA is a fiber with a diameter of 2 nm, if the thickness of the polymer composite thin film 1 is greater than 2 nm, functionality and mechanical strength can be achieved at the same time. In other words, the thickness of the polymer composite thin film 1 according to the present invention can be in the range of 2 nm to 100 nm by selecting the fibrous structure. Even if the fibrous structure is limited to cellulose nanofibers 3, the thickness can be in the range of 4 nm to 100 nm.

Below, we will explain Example 1 of the present invention. First, a CNF dispersion containing 0.11 weight percent cellulose nanofiber 3 (hereinafter sometimes referred to as "CNF") (manufactured by Chuetsu Pulp Industries, Nanoforest-S (Nanoforest is a registered trademark)) was prepared, and ion-exchanged water was added to this to prepare a CNF aqueous solution with a specified CNF concentration, which was used in the subsequent operations.

Separately, a base material of polydimethylsilicone (PDMS) resin (a type of polysiloxane, SYLGARD184 (SYLGARD is a registered trademark) manufactured by Dow Corning Toray) and a curing agent were mixed in a ratio of 10:1, and hexane was added to this to prepare a 10 weight percent PDMS/hexane solution. A specified amount of hexane was added to this to prepare PDMS/hexane solutions of different concentrations, which were used in the subsequent operations.

Prior to the preparation of polymer composite thin film 1, a polyhydroxystyrene (PHS)/ethanol solution (15 weight percent) was first spin-coated (3,000 rpm/1 min) onto a glass substrate to form a PHS layer, which was then dried. The substrate was then treated with oxygen plasma to make the surface hydrophilic.

The CNF aqueous solution prepared by the above procedure was spin-coated onto this substrate, then the PDMS/hexane solution was spin-coated, and the substrate was then heated at 100°C for 30 minutes.

After cooling to room temperature, the substrate was immersed in ethanol (a stripping solution), and the film was peeled off from the substrate in the stripping solution. The film thus obtained (polymer composite thin film 1) is hereafter referred to as the CNF/PDMS film. This CNF/PDMS film was fixed to a concentric circular frame made of Kapton film, and the film was removed from the stripping solution. It was visually confirmed that the CNF/PDMS film fixed to the concentric circular frame had no defects and was self-supporting.

In addition, in order to use in the bulge test described below, several samples were obtained by varying the number of times the spin coating operation of the CNF aqueous solution (hereinafter sometimes referred to as the "CNF spin coating operation") was performed in the above process.

As a comparative example 1, a film was produced in which a PDMS layer was formed directly on a glass substrate coated with PHS without performing the CNF spin coating operation. Hereafter, this film will be referred to as the PDMS film.

The mechanical strength of the film prepared as Example 1 and Comparative Example 1 was evaluated by a bulge test. The films used in the test were four types: (i) PDMS film as Comparative Example 1, (ii) a film obtained by performing a single CNF spin coating operation and then spin coating PDMS on top of that (CNF/PDMS film), (iii) a film obtained by performing five CNF spin coating operations and then spin coating PDMS on top of that (CNF-5/PDMS film), and (iv) a film obtained by performing ten CNF spin coating operations (CNF-10/PDMS film).

The film thicknesses of the polymer composite thin films 1 (ii) to (iv) created in Example 1 were all 100 nm or less, specifically in the range of 50 nm to 75 nm. The PDMS film (i) used as Comparative Example 1 was exceptionally formed to a film thickness of 150 nm. This is because if the film thickness of the PDMS film (i) was set to 50 nm to 75 nm, the same as the other samples obtained in Example 1, it would break immediately when taken out into air (it would not be self-supporting), and a comparison with Example 1 would not be possible.

The samples prepared in Comparative Example 1 and Example 1 were attached to the bottom surface of a cylindrical glass tube, and ion-exchanged water was dripped from the top of the glass tube to apply a weight to the film. The stress (σ) and strain (ε) were calculated from the shape of the film that expanded (warped) due to the weight load.

Figures 2(a) to (d) are photographs showing the deflection of the films obtained in Comparative Example 1 and Example 1 when the same load was applied. Specifically, the film deflection was observed when the same load (water: 3.5 mL introduced, liquid pressure: approximately 437 Pa) was applied to Comparative Example 1 and Example 1. Here, Figure 2(a) shows the state of the PDMS film, (b) the state of the CNF/PDMS film, (c) the state of the CNF-5/PDMS film, and (d) the state of the CNF-10/PDMS film.

Figure 3 is a graph showing the relationship between stress (σ) and deflection (ε) in the films obtained in Comparative Example 1 and Example 1. Specifically, Figure 3 shows the relationship between stress (σ) and deflection (ε) calculated from the load pressure for each film, film radius, film thickness, deflection length, and film arc length when deflected.

Figures 2 and 3 show that the film obtained in Example 1, in which CNF and PDMS are layered (having the configuration shown in either Figure 1 (a) to (c) depending on the manufacturing conditions), clearly shows a difference in the film's deflection when subjected to water pressure load, with the amount of deflection decreasing as the amount of CNF introduced increases. In addition, as the number of CNF layers increases, the stress also increases (and conversely, the deflection decreases), confirming that the introduction of CNF improves the mechanical strength of the entire film.

Figure 4 is a photograph showing the appearance of a CNF/PDMS film on which circular damage had occurred. The circular damage was created by piercing the CNF/PDMS film with a needle with a sharp tip. As shown in Figure 4, even when some kind of external damage was inflicted on this CNF/PDMS film, the damage was limited to a part of the film and did not spread over the entire film. Furthermore, the same was true when circular damage was created on the CNF-5/PDMS film and the CNF-10/PDMS film.

On the other hand, in the case of a PDMS film, if such damage is formed, the entire film shrinks and breaks in an instant, and the film structure cannot be maintained. Considering this together with the other evaluation results of Example 1, it can be determined that CNF is present in the obtained polymer composite thin film 1. In addition, the selectivity for CO ₂ and N ₂ was maintained at about 10. In the case of a PDMS film alone, the CO ₂ /N ₂ selectivity is about 10 to 11 (References: Shigenori Fujikawa, Miho Ariyoshi, Roman Selyanchyn, Toyoki Kunitake, Chemistry Letters, 2019, Vol. 48, No. 11, 1351-1354), so it can be said that none of the films produced have defects that cause gas leakage.

Below, Example 2 of the present invention will be described. Ion-exchanged water was further added to the CNF dispersion liquid with 0.11 weight percent CNF prepared in Example 1 to prepare diluted solutions with different CNF concentrations. CNF/PDMS films were produced using the prepared diluted solutions. The film thickness of the CNF/PDMS film as the polymer composite thin film 1 obtained in Example 2 was all approximately 50 nm to 75 nm.

The CNF/PDMS film and the PDMS film were placed on a porous polyacrylonitrile film and a gas permeability test was performed. The permeability of the CNF/PDMS film to carbon dioxide ( _CO2 ) and nitrogen ( _N2 ) and the _CO2 / _N2 selectivity are shown in Table 1. The results of the gas permeability test of the PDMS film are shown in the leftmost column of Table 2, which will be described later.

The same selectivity was observed in all the CNF/PDMS films prepared in Example 2, and it can be seen that all the films obtained had no defects that would cause gas leakage. The _CO2 and _N2 permeabilities were lower than those of a PDMS film of the same thickness (about 50 nm, as described later). In general, films made of CNF have low gas permeability, which supports the idea that CNF is also introduced into this film.

Below, we will explain Example 3 of the present invention. A CNF/ethanol dispersion was prepared so that the content of cellulose nanofiber 3 (CNF) (Nanoforest-S, manufactured by Chuetsu Pulp Industry Co., Ltd.) was 0.072 weight percent.

Separately, the base and hardener of commercially available polydimethylsilicone (PDMS) resin (Toray Dow Corning, SYLGARD 184) were mixed in a volume ratio of 10:1, and the previously prepared CNF/ethanol dispersion and hexane were added to this to prepare a 0.5 volume percent CNF/PDMS/hexane solution, which was used in the subsequent operations.

Next, a polyhydroxystyrene (PHS)/ethanol solution (15 weight percent) was spin-coated (3000 rpm/1 min) onto a glass substrate, and after forming a PHS layer, the substrate was treated with oxygen plasma to make the surface hydrophilic. The CNF/PDMS/hexane solution prepared in the above-mentioned procedure was dropped onto the substrate, and the substrate was rotated at 4000 rpm for 1 min, after which the substrate was heated at 100°C for 30 min.

After cooling to room temperature, the substrate was immersed in ethanol and the film was peeled off from the substrate. The film obtained in this manner is hereafter referred to as a CNF-PDMS film. This CNF-PDMS film is composed of polydimethylsilicone resin with CNF evenly dispersed, and has a different structure from the CNF/PDMS film (in which CNF and PDMS form a layer) described in Example 1 etc. In other words, the CNF-PDMS film obtained in Example 2 has the structure shown in Figure 1 (d).

This CNF-PDMS film was placed on a porous polyacrylonitrile film and a gas permeation test was performed. As Comparative Example 2, a film (PDMS film) was also produced using only SYLGARD184 as the raw material without mixing cellulose nanofiber 3.

The _CO2 and _N2 permeabilities and _CO2 / _N2 permeation selectivity ratios of the films prepared by changing the concentration of each film solution are shown in Table 2. That is, Table 2 shows the relationship between the amount of CNF dispersion mixed and the properties of the obtained CNF-PDMS films (No. 1 to No. 5).

Here, the presence or absence of self-supporting ability is judged based on the criterion of whether or not the thin film (film) can maintain its flat membrane shape without breaking when it is peeled off from the substrate in the stripping solution and then lifted up into the air while floating in the liquid. In other words, if the membrane structure is maintained without breaking even in the air, it is judged to be "self-supporting," whereas if the membrane structure is maintained while floating in the stripping solution after the substrate is peeled off, but it easily breaks when taken out into the air, it is judged to be "not self-supporting" (listed as "easily breaks in air" in [Table 2]).

Note that the limit for a PDMS film to be self-supporting is a film thickness of about 150 nm, and any thinner film has an extremely high rate of film rupture. Therefore, for the PDMS films in [Table 2], the thin film was not lifted into the air, but instead was scooped up onto a porous polyacrylonitrile film in a stripping solution and used for gas permeation testing.

All of the films produced in Example 3, including the PDMS film, had a thickness of about 50 nm. As described above, the PDMS film without CNF mixed in was unable to maintain a flat membrane shape on its own and broke due to shrinkage, so no flat membrane with sufficient self-supporting properties for use in gas permeation tests was obtained, but all of the films with CNF mixed in were self-supporting.

Below, we will explain Example 4 of the present invention. In Example 4, the polymer material constituting the polymer thin film 2 is a crosslinkable polymer. First, an aqueous dispersion of cellulose nanofiber 3 (CNF) (Nanoforest-S, Chuetsu Pulp Industry) was prepared so that it was 0.11 weight percent, and this was used in the subsequent operations.

A PCGF-PEI/chloroform solution was also prepared containing 4 weight percent of crosslinkable polymers (epoxy resins) Poly[(o-cresyl glycidyl ter)-co-formaldehyde] (hereinafter sometimes referred to as "PCGF") (ALDRICH, Mn 870) and Polyethylenenimine, branched (hereinafter sometimes referred to as "PEI") (ALDRICH, Mn ~ 10,000). After stirring this solution for 4 hours at 40°C, further chloroform was added to prepare a 1 weight percent PCGF-PEI/chloroform solution, which was used in the subsequent operations.

A polyhydroxystyrene (PHS)/ethanol solution (15 weight percent) was spin-coated (3000 rpm/1 min) onto a glass substrate, and after forming a PHS layer, the substrate was treated with oxygen plasma to make the surface hydrophilic. The CNF aqueous dispersion prepared in the above-mentioned procedure was spin-coated (1500 rpm, 2 min) onto the substrate, and the substrate was heated at 100°C for 1 min.

Then, the substrate was spin-coated (3000 rpm, 1 minute) with the 1 weight percent PCGF-PEI/chloroform solution described above. The substrate was then heated at 100°C for 5 minutes. After cooling to room temperature, the substrate was immersed in ethanol, and the film (polymer composite thin film 1) was peeled off from the substrate. The thickness of the film obtained in Example 4 was 75 nm.

The polymer composite thin film 1 obtained in Example 4 was visually confirmed to have no defects and to be self-supporting. In addition, a test was conducted to apply a water pressure load in the same manner as described in Example 1. As a result, the amount of deflection decreased as the amount of CNF introduced increased.

Example 5 of the present invention will be described below. In Example 5, instead of the above-mentioned CNF aqueous solution, a 0.05 wt% CNF+oxidized CNF aqueous solution was used, which was a mixture of equal amounts of CNF and oxidized CNF (oxidized cellulose nanofiber), and the PDMS concentration of the PDMS/hexane solution was set to 0.5 v/v%. Furthermore, the spin coating operation of the CNF+oxidized CNF aqueous solution was performed only once, and a film (CNF+oxidized CNF/PDMS film) was produced using the same process as in Example 1. When the cross section of the produced film was observed with a scanning electron microscope, the film thickness of the CNF+oxidized CNF/PDMS film was 30 nm.

The CNF+oxidized CNF/PDMS film was placed on a porous polyacrylonitrile film and a gas permeation test was performed. The permeabilities of carbon dioxide ( _CO2 ), nitrogen ( _N2 ) and oxygen ( _O2 ), as well as the selectivity ratios of _CO2 / _N2 , _CO2 / _O2 and _O2 / _N2 are shown in Table 3.

As shown in Table 3, the CNF+oxidized CNF/PDMS film of Example 5 also exhibits a very high _CO2 permeability, and high _O2 and _N2 permeability values. Focusing on _O2 and _N2 , the _O2 / _N2 selectivity is 2.3, clearly indicating that the CNF+oxidized CNF/PDMS film has an air separation function that separates oxygen and nitrogen in the air. In other words, the polymer composite thin film 1 according to the present invention functions as an air separation membrane, and can increase or decrease the oxygen concentration or nitrogen concentration in the air.

Now, the air separation function of the CNF + CNF oxidized/PDMS film is exerted by a layer made of PDMS (polymer thin film, hereafter sometimes referred to as the "PDMS layer"), but as the thickness of the PDMS layer increases, the permeability decreases, which becomes a practical barrier. However, by combining the PDMS layer with a layer made of CNF (or CNF + CNF oxidized), the mechanical strength is improved, and it is possible to thin the PDMS layer in the polymer composite thin film 1 to the utmost limit.

In Example 5, as described above, the thickness of the CNF + oxidized CNF/PDMS film is 30 nm, and the thickness of the PDMS layer excluding the thickness of the layer composed of CNF + oxidized CNF is thought to be about 10 nm to 20 nm. By making the PDMS layer extremely thin in this way, it is possible to achieve high _O2 and _N2 permeability exceeding 1000 GPU (3000 GPU).

In addition, since the polymer composite thin films 1 shown in Examples 1 to 3 also contain a thinned PDMS layer, it is clear that these polymer composite thin films 1 have an air separation function.

The polymer composite thin film 1 according to the present invention has high functionality and high mechanical strength, and therefore can be suitably applied to, for example, gas separation membranes used in CCS (Carbon dioxide Capture and Storage) for separating and recovering _CO2, a greenhouse gas generated by the combustion of fossil fuels, from sources such as power plants and factories. The polymer composite thin film 1 according to the present invention can also be suitably applied to oxygen enrichment devices that utilize air with high oxygen concentration (air with low nitrogen concentration), high-concentration oxygen masks, plant factories, oxygen combustion power plants, oxygen combustion boilers, and the like, as well as inert gas fire extinguishing equipment that utilizes air with high nitrogen concentration (air with low oxygen concentration).

1 Polymer composite thin film 2 Polymer thin film 3 Cellulose nanofiber 10 Circular damage

Claims (15)

a non-self-supporting polymer thin film made of polysiloxane and having a thickness of 100 nm or less;
A fibrous structure having a diameter smaller than the thickness of the polymer thin film and contained in the polymer thin film ;
Equipped with
The polymer composite thin film is characterized in that the fibrous structure and the polymer thin film are combined to have self-supporting properties, and the film thickness is 2 nm to 100 nm . The polymer composite thin film according to claim 1, characterized in that the fibrous structures are composed of organic polymers. The polymer composite thin film according to claim 2, characterized in that the fibrous structure is a cellulose nanofiber or a mixture of cellulose nanofiber and oxidized cellulose nanofiber. The polymer composite thin film according to any one of claims 1 to 3, characterized in that the polymer thin film has gas separation properties. The polymer composite thin film according to any one of claims 1 to 4, characterized in that the polymer thin film is selectively permeable to carbon dioxide. The polymer composite thin film according to any one of claims 1 to 5, characterized in that the combined thickness of the polymer thin film and the fibrous structure is 30 nm to 75 nm. The polymer composite thin film according to claim 3 , comprising: a layer composed of the polysiloxane; and a layer composed of the polysiloxane and the cellulose nanofibers. The polymer composite thin film according to claim 7 , wherein the layer composed of the polysiloxane and the cellulose nanofibers is formed by superposing a plurality of layers of the cellulose nanofibers. A method for producing a polymer composite thin film according to any one of claims 3 to 8, comprising the steps of:
The fibrous structure is a cellulose nanofiber,
A first step of preparing a cellulose nanofiber solution containing the cellulose nanofibers and a polymer material-containing solution containing the polysiloxane;
A second step of forming a first layer by applying the cellulose nanofiber solution onto a substrate on which a polymer layer that dissolves in a stripping solution has been formed, so as to cover the polymer layer;
a third step of applying and heating the polymer material-containing solution so as to cover the first layer to form a second layer;
a fourth step of immersing the substrate in the stripping solution to strip a polymer composite thin film composed of the first layer and the second layer from the substrate;
A method for producing a polymer composite thin film, comprising: The method for producing a polymer composite thin film according to claim 9, characterized in that the solvent of the cellulose nanofiber solution is water, and the solvent of the polymer material-containing solution is hexane. The method for producing a polymer composite thin film according to claim 9 or 10, characterized in that the first layer is formed by repeating the process of applying the cellulose nanofiber solution multiple times. A method for producing a polymer composite thin film according to any one of claims 3 to 8, comprising the steps of:
The fibrous structure is a cellulose nanofiber,
A first step of preparing a cellulose nanofiber dispersion by dispersing the cellulose nanofibers in a first solvent;
A second step of mixing the cellulose nanofiber dispersion and a second solvent with the polysiloxane to obtain a mixed solution;
a third step of applying the mixed solution to a substrate on which a polymer layer that dissolves in a stripping solution has been formed, and heating the mixed solution so as to cover the polymer layer, thereby forming a polymer composite thin film;
a fourth step of immersing the substrate in the stripping solution to strip the polymer composite thin film from the substrate;
A method for producing a polymer composite thin film, comprising: The method for producing a polymer composite thin film according to claim 12, characterized in that the first solvent is ethanol and the second solvent is hexane. The polymer layer is formed by applying an ethanol solution containing polyhydroxystyrene,
The method for producing a polymer composite thin film according to any one of claims 9 to 13, characterized in that the stripping solution is ethanol. The method for producing a polymer composite thin film according to any one of claims 9 to 14, characterized in that the surface of the polymer layer is subjected to a hydrophilic treatment.

Images