A high-strength ionic liquid gel and a method for preparing the same

Abstract

The present application relates to a kind of high-strength ionic liquid gel and its preparation method, compared with the low strength (generally less than 1MPa) of the ionic liquid gel existing at present, small modulus, its high strength, high transparency and multifunctionality make it more practically applicable value. The raw material of gel is composed of vinyl monomer, imidazole-based ionic liquid and photoinitiator, and the primary ionic liquid gel is obtained by in-situ photoinitiated polymerization, then it is treated by "warming-quenching" and finally the ionic liquid gel of the present application is obtained. The preparation method of the present application is simple and fast, which can be completed within 1h. The ionic liquid gel prepared by the present application has high strength (8-40MPa), high transparency (92%-98%), and also has the functions of conductivity, recyclability, sensing and shape memory, etc., and has broad application prospects in the fields of flexible electronics, intelligent medical treatment and soft robot, etc.

Description

Technical Field

[0001] This invention pertains to methods for preparing ionic liquid gels, specifically a high-strength ionic liquid gel and its preparation method. It provides a rapid and simple method for preparing ionic liquid gels, resulting in a high-strength, transparent, and multifunctional material that can be applied in fields such as flexible electronics, smart healthcare, and green new energy. Background Technology

[0002] Ionic liquid gels are gel-like materials obtained by dispersing polymers or small organic / inorganic molecules in an ionic liquid medium. Due to the excellent properties of ionic liquids, such as ionic conductivity at room temperature, wide liquid range, and thermoelectric stability, ionic liquid gels exhibit excellent transparency, conductivity, high / low temperature resistance, stretchability, and stimulus responsiveness. Ionic liquid gels have broad application prospects and market value in fields such as solid electrolytes, energy storage, photothermal conversion, sensors, soft robotics, and smart materials. However, at present, ionic liquid gels still suffer from drawbacks such as low mechanical strength and complex and time-consuming preparation methods, which not only increase manufacturing costs but also limit their practical application. Currently, the main methods for preparing ionic liquid gels are as follows: (1) Small molecule self-assembly method, the ionic gel prepared by this method is usually semi-transparent and has a tensile strength in the kPa range; (2) Solvent replacement method, the method uses ionic liquid to replace the water / alcohol in the pre-prepared water / alcohol gel to prepare ionic liquid gel, the method is complicated, time-consuming and has the problem of poor compatibility between ionic liquid and polymer network; (3) Direct polymerization method, the method refers to polymerizing polymer monomers directly in ionic liquid to obtain ionic liquid gel, there are two initiation methods: thermal initiation and photoinitiation, but only monomers and ionic liquids with similar properties can be compatible. In the currently reported ionic liquid gels, the tensile strength of the gel is usually less than 1 MPa and the elastic modulus is usually less than 10 MPa. Therefore, in view of the shortcomings of ionic liquid gels, the development of new high-strength ionic liquid gel preparation methods has important practical significance and application value. Chinese invention patent CN 106632775 A discloses a method for preparing ionic liquid gel, in which vinyl monomers are polymerized in ionic liquid by photoinitiation, and ionic liquid gel is finally obtained by adjusting and optimizing the formula. The gel exhibits a maximum tensile strength of 0.67 MPa and an elongation at break of 1400%. Chinese invention patent CN 111533847 A discloses a method for preparing high-strength ionic liquid gels using a one-pot method, co-polymerizing physically crosslinking monomers, ionic liquid monomers, and dispersing monomers in solution to obtain the ionic liquid gel. The ionic liquid gel prepared by this method has a maximum strength of 6.29 MPa and an elongation at break of 680.3%. Although invention patents have disclosed methods for preparing high-strength ionic gels, these methods still suffer from complex preparation processes and insufficient gel strength. To address these issues, this patent proposes an in-situ photopolymerization method combined with a "heating-quenching" post-treatment. By adjusting the phase separation structure of the ionic liquid gel, it successfully prepares an ionic liquid gel with strength far exceeding that of most existing gels. Summary of the Invention

[0003] Technical problems to be solved

[0004] To overcome the shortcomings of existing technologies, this invention proposes a high-strength ionic liquid gel and its preparation method. Based on photoinitiated free radical polymerization of organic polymers, one or more monomers are polymerized to prepare the ionic liquid gel. Taking advantage of the high critical phase transition temperature of the ionic liquid gel, a "heating-quenching" post-treatment method is used to improve its mechanical strength, elongation at break, and light transmittance. The resulting ionic liquid gel possesses high strength (8–40 MPa), high elongation (30%–650%), high transmittance (92%–98%), 3D printing capability, shape memory, recyclability, and sensing functionality, showing broad application prospects in flexible electronics, intelligent medical devices, and soft robotics.

[0005] Technical solution

[0006] A method for preparing a high-strength ionic liquid gel, characterized by the following steps:

[0007] Step 1: In-situ polymerization of vinyl monomers and photoinitiators in imidazole ionic liquids yields primary ionic liquid gels;

[0008] Step 2: The primary ionic liquid gel is treated by "heating-quenching" to improve its light transmittance and mechanical properties.

[0009] The imidazole-based ionic liquid comprises 50% to 90% of the total gel mass; the photoinitiator comprises 0.03% to 0.5% of the vinyl monomer mass.

[0010] The in-situ polymerization in step 1 uses ultraviolet light with a wavelength of 365nm and a light source intensity of 6W / m. 2 ~300W / m 2 The ultraviolet light irradiation time is 1 to 10 minutes, with the next best option being 10 minutes to 3 hours.

[0011] The post-treatment of "heating-quenching" in step 2 involves heating at a temperature range of 80-120℃, holding at that temperature for 2-30 minutes, and quenching at a cooling rate of 50℃ / min-120℃ / min, with a cooling temperature range of -40℃-25℃.

[0012] The vinyl monomer is one or more of acrylamide AM, N,N-dimethylacrylamide DMAAm, acrylic acid AA, dimethylaminoethyl methacrylate DMAEMA, polyethylene glycol methacrylate PEGMA, and hydroxyethyl methacrylate HEMA, wherein at least AM monomer is included.

[0013] The imidazole-based ionic liquid is a hydrophilic ionic liquid, its cation is a 1,3-disubstituted imidazole cation, the substituent is a straight-chain saturated alkyl group, and the number of carbon atoms in the substituent is preferably 2 to 4, and less preferably 2 to 12.

[0014] The imidazole-based ionic liquid has bromide ions (Br₂) as its anion. - ), tetrafluoroborate ion (BF4) - One or more of the trifluoroacetic acid (TFA) ions.

[0015] The photoinitiator is one or more of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone (I2959), 2,4,6-(trimethylbenzoyl)diphenylphosphine oxide (TPO), 2-hydroxy-2-methyl-1-phenylpropanone (1173), or 1-hydroxycyclohexylphenyl ketone (184).

[0016] A high-strength ionic liquid gel obtained by the preparation method is characterized in that a primary ionic liquid gel is obtained by in-situ photoinitiated polymerization of vinyl monomer, imidazole ionic liquid and photoinitiator, and then subjected to "heating-quenching" to obtain a high-strength ionic liquid gel with a strength of 8-40 MPa, an elongation at break of 30%-650%, and a high transmittance of 92%-98%.

[0017] A method for using the high-strength ionic liquid gel, characterized in that: the ionic liquid gel has multifunctional properties such as shape memory, recyclability, and conductivity; its shape memory capability is achieved by heating the ionic liquid gel to 80-120°C to change the shape of the gel, fixing the shape by cooling to -40-25°C, and restoring the gel to its initial shape during reheating; its recyclability is achieved by dissolving the ionic liquid gel in a solvent to obtain a transparent solution, and then reshaping it by evaporating the solvent.

[0018] Beneficial effects

[0019] This invention proposes a high-strength ionic liquid gel and its preparation method. Compared with existing ionic liquid gels that have low strength (generally less than 1 MPa) and low modulus, its high strength, high transparency, and multifunctionality make it more valuable for practical applications. The gel's raw materials consist of vinyl monomers, imidazole ionic liquids, and photoinitiators. A primary ionic liquid gel is obtained through in-situ photoinitiated polymerization, followed by a "heating-quenching" post-treatment to finally obtain the ionic liquid gel of this invention. The preparation method of this invention is simple and rapid, and can be completed within 1 hour. The ionic liquid gel prepared by this invention exhibits high strength (8–40 MPa), high transparency (92%–98%), and also possesses electrical conductivity, recyclability, sensing, and shape memory functions, showing broad application prospects in flexible electronics, intelligent medical devices, and soft robotics.

[0020] The advantages of this invention compared to the prior art are:

[0021] Compared to existing ionic liquid gel materials (whose tensile strength is generally below 1 MPa and modulus is generally below 10 MPa), the ionic liquid gel of this invention is obtained by in-situ photoinitiated polymerization of vinyl monomers and imidazole-based hydrophilic ionic liquids. The ionic liquid gel of this invention has… Ultra-high mechanical properties Its strength is between 8 and 40 MPa, and it also has a breaking elongation of 30% to 650% and a high transmittance of 92% to 98%. It has the functions of 3D printing, shape memory, recyclability and sensing.

[0022] Compared to existing methods for preparing ionic liquid gel materials, this invention, based on photoinitiated polymerization, innovatively proposes a "heating-quenching" post-treatment of the primary ionic liquid gel to further improve its various properties. In this invention... In-situ photopolymerization + "heating-quenching" post-treatment It not only enables the rapid and simple preparation of ionic liquid gels (with a total preparation time of less than 1 hour), but also effectively improves the light transmittance and mechanical properties of ionic liquid gels. Attached Figure Description

[0023] Figure 1 The diagram shows the preparation method of the present invention and the chemical structure of the ion gel.

[0024] Figure 2 These are optical images of embodiments 1, 2, and 3 of the present invention.

[0025] Figure 3 The transmittance test curves are for embodiments 1, 2, and 3 of this invention.

[0026] Figure 4 The tensile stress-strain curves are shown in Embodiments 1, 2, and 3 of the present invention.

[0027] Figure 5 The image shows a 3D printed test piece from Embodiment 1 of the present invention.

[0028] Figure 6 This is a photograph of the recycling experiment process in Embodiment 1 of the present invention. Detailed Implementation

[0029] The present invention will now be further described in conjunction with the embodiments and accompanying drawings:

[0030] This invention prepares a primary ionic liquid gel by direct polymerization in an ionic liquid, and then obtains the ionic liquid gel of this invention through a subsequent "heating-quenching" post-treatment. First, the ionic liquid, monomer, and initiator are mixed to obtain a colorless and transparent precursor solution. Second, the solution is irradiated with ultraviolet light to obtain the primary ionic liquid gel. Subsequently, the ionic liquid gel is heated and then quenched to improve its transmittance, mechanical strength, and elongation, ultimately yielding a high-strength, transparent, and multifunctional ionic liquid gel. The phase separation structure within the ionic liquid gel of this invention can be controlled through the "heating-quenching" process, thus resulting in mechanical properties far exceeding those of most other existing ionic liquid gels.

[0031] The ionic liquid selected in this invention is a disubstituted imidazolyl ionic liquid that is in a liquid state at room temperature. Preferably, it is a 1,3-disubstituted imidazolyl ionic liquid, wherein the substituent is a straight-chain saturated alkyl group, and the number of carbon atoms in the substituent is preferably 2 to 4, and less preferably 2 to 12.

[0032] The imidazole-based ionic liquid selected in this invention is a hydrophilic ionic liquid. Preferably, the anion of the imidazole-based ionic liquid is a bromide ion (Br₂). - ), tetrafluoroborate ion (BF4) - One or more of the trifluoroacetic acid (TFA) ions.

[0033] In this invention, the ionic liquid content is 50% to 90% of the total gel mass.

[0034] The monomers used in this invention are hydrophilic vinyl monomers, which may be one or more of acrylamide (AM), N,N-dimethylacrylamide (DMAAm), acrylic acid (AA), dimethylaminoethyl methacrylate (DMAEMA), polyethylene glycol methacrylate (PEGMA), and hydroxyethyl methacrylate (HEMA), wherein at least AM monomer is included. The homopolymers or copolymers obtained by polymerizing these hydrophilic monomers are hydrophilic polymers, which have a certain compatibility with the hydrophilic ionic liquid used in this invention.

[0035] In this invention, the content of the hydrophilic polymer is 10% to 50% of the total mass of the gel.

[0036] The initiator used in this invention is a photoinitiator, preferably 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone (I2959) or 2,4,6-(trimethylbenzoyl)diphenylphosphine oxide (TPO) or 2-hydroxy-2-methyl-1-phenylpropanone (1173) or 1-hydroxycyclohexylphenyl ketone (184).

[0037] In this invention, the initiator content is 0.03% to 0.5% of the total polymer mass.

[0038] The ultraviolet light used in this invention has a wavelength of 365 nm and a light source intensity of 6 W / m². 2 ~300W / m 2 The preferred duration of ultraviolet irradiation is 1 to 10 minutes, and the next preferred duration is 10 minutes to 3 hours.

[0039] In this invention, the initially obtained ionic liquid gel undergoes a "heating-quenching" post-treatment to further improve the gel's light transmittance and mechanical properties. The preferred heating temperature range is 80–120°C, with a holding time of 2–30 min. The preferred quenching cooling rate is 50°C / min–120°C / min, and the preferred cooling temperature range is -40°C to 25°C.

[0040] The ionic liquid gel prepared by this invention has multifunctionality and shape memory properties. Heating the gel to 80–120°C can change its shape, cooling it to -40–25°C can fix its shape, and the gel can return to its initial shape during reheating.

[0041] The ionic liquid gel prepared by this invention is easy to recycle and reprocess. After dissolving the ionic liquid gel with a solvent, a transparent solution can be obtained, and it can be reshaped by evaporating the solvent.

[0042] The ionic liquid gel prepared by this invention has ionic conductivity.

[0043] The preparation method of the present invention (using 1-ethyl-3-butyl-imidazolium bromide as the ionic liquid, AM as the monomer, and I2959 as the initiator, for example):

[0044] Add 10-50 parts by mass of AM monomer and 0.03-0.5 parts by mass of I2959 to 50-90 parts by mass of 1-ethyl-3-butyl-imidazolium bromide ionic liquid, and sonicate at 25-50°C for 5-30 min until the mixture becomes a homogeneous and transparent precursor solution. Pour the solution into a glass mold and use 6W / m 2 Irradiation with ultraviolet light for 10 minutes yields a preliminary ionic liquid gel. The primary ionic liquid gel is then subjected to a "heating-quenching" post-treatment, where it is heated at 80-120°C for 10-20 minutes, then removed and rapidly cooled (60°C / min) to room temperature to obtain the ionic liquid gel of this invention. The post-treatment temperature should be high enough to ensure sufficient mobility of the gel polymer molecular chains, but not so high that the gel cannot maintain its shape.

[0045] Implementation Example 1:

[0046] 1-Ethyl-3-butyl-imidazolium bromide (1 g), AM (0.5 g), and I2959 (0.005 g) were added to a brown bottle, shaken thoroughly, and sonicated for 20 min to obtain a colorless, transparent, homogeneous solution. This solution was poured into a glass mold and heated using 6W / m² water. 2 Irradiation with ultraviolet light for 10 minutes resulted in the untreated ionic liquid gel after demolding. The gel was then placed in an oven at 120°C for 20 minutes, followed by rapid cooling to obtain a colorless, transparent, and homogeneous ionic liquid gel. This gel exhibits the self-healing polyurethane's tensile strength of 10.4 MPa, elongation at break of 386.7%, and light transmittance of 98%, along with excellent electrical conductivity, shape memory properties, and recyclability.

[0047] Implementation Example 2:

[0048] 0.95 g of 1-ethyl-3-butyl-imidazolium bromide, 0.55 g of AM, and 0.005 g of I2959 were added to a brown bottle, shaken thoroughly, and sonicated for 20 min to obtain a colorless, transparent, homogeneous solution. The solution was poured into a glass mold and heated using 6 W / m² water. 2 Irradiation with ultraviolet light for 10 minutes yielded an untreated ionic liquid gel after demolding. The gel was then placed in an oven at 120°C for 20 minutes, followed by rapid cooling to obtain a colorless, transparent, and homogeneous ionic liquid gel. This gel exhibited a tensile strength of 19.1 MPa, an elongation at break of 229%, and a light transmittance of 91.8%, as well as excellent electrical conductivity, shape memory properties, and recyclability.

[0049] Implementation Example 3:

[0050] 0.9 g of 1-ethyl-3-butyl-imidazolium bromide, 0.6 g of AM, and 0.005 g of I2959 were added to a brown bottle, shaken thoroughly, and sonicated for 20 min to obtain a colorless, transparent, homogeneous solution. The solution was poured into a glass mold and heated using 6 W / m² water. 2 Irradiation with ultraviolet light for 10 minutes resulted in the untreated ionic liquid gel after demolding. The gel was then placed in an oven at 120°C for 20 minutes, followed by rapid cooling to obtain a colorless, transparent, and homogeneous ionic liquid gel. This gel exhibited a tensile strength of 31.1 MPa, an elongation at break of 30.2%, and a light transmittance of 92.2%. It also demonstrated excellent electrical conductivity, shape memory properties, and recyclability.

[0051] Implementation Example 4:

[0052] 0.95 g of 1-ethyl-3-butyl-imidazolium bromide, 0.55 g of AM, and 0.005 g of TPO were added to a brown bottle, shaken thoroughly, and sonicated for 20 min to obtain a colorless, transparent, homogeneous solution. The solution was poured into a glass mold and heated using 6 W / m² water. 2Irradiation with ultraviolet light for 10 minutes yielded an untreated ionic liquid gel after demolding. The gel was then placed in an oven at 120°C for 20 minutes, followed by rapid cooling to obtain a colorless, transparent, and homogeneous ionic liquid gel. This gel exhibited a tensile strength of 16.8 MPa, an elongation at break of 255%, and a light transmittance of 92.5%. It also demonstrated excellent electrical conductivity, shape memory properties, and recyclability.

[0053] Implementation Example 5:

[0054] 0.9 g of 1-butyl-3-butyl-imidazolium bromide, 0.5 g of AM, and 0.005 g of I2959 were added to a brown bottle, shaken thoroughly, and sonicated for 20 min to obtain a colorless, transparent, homogeneous solution. The solution was poured into a glass mold and heated using 6 W / m² water. 2 Irradiation with ultraviolet light for 10 minutes yielded an untreated ionic liquid gel after demolding. The gel was then placed in an oven at 120°C for 20 minutes, followed by rapid cooling to obtain a colorless, transparent, and homogeneous ionic liquid gel. This gel exhibited a tensile strength of 25.3 MPa, an elongation at break of 42.1%, electrical conductivity, excellent electrical conductivity, shape memory properties, and recyclability.

[0055] Implementation Example 6:

[0056] 1-Ethyl-3-butyl-imidazolium bromide (1 g), AM (0.3 g), DMAAm (0.2 g), and I2959 (0.005 g) were added to a brown bottle, shaken thoroughly, and sonicated for 20 min to obtain a colorless, transparent, homogeneous solution. This solution was poured into a glass mold and heated using 6W / m² water. 2 Irradiation with ultraviolet light for 10 minutes resulted in the untreated ionic liquid gel after demolding. The gel was then placed in an oven at 80°C for 10 minutes, followed by rapid cooling to obtain a colorless, transparent, and homogeneous ionic liquid gel. This gel exhibits the self-healing polyurethane's tensile strength of 6.3 MPa, elongation at break of 650%, and light transmittance of 94.0%, along with excellent electrical conductivity, shape memory properties, and recyclability.

[0057] Implementation Example 7:

[0058] 1-Ethyl-3-butyl-imidazolium bromide (1 g), AM (0.3 g), PEGMA (0.2 g), and I2959 (0.005 g) were added to a brown bottle, shaken thoroughly, and sonicated for 20 min to obtain a colorless, transparent, homogeneous solution. This solution was poured into a glass mold and heated using 6W / m² water. 2Irradiation with ultraviolet light for 10 minutes yielded an untreated ionic liquid gel after demolding. The gel was then placed in a 90°C oven for 10 minutes, followed by rapid cooling to obtain a colorless, transparent, and homogeneous ionic liquid gel. This gel exhibited a tensile strength of 10.8 MPa, an elongation at break of 430%, and a light transmittance of 95.2%. It also demonstrated excellent electrical conductivity, shape memory properties, and recyclability.

Claims

1. A method for preparing a high-strength ionic liquid gel, characterized in that... The steps are as follows: Step 1: In-situ polymerization of vinyl monomers and photoinitiators in imidazole ionic liquids yields primary ionic liquid gels; Step 2: The primary ionic liquid gel is treated with "heating-quenching" to improve its light transmittance and mechanical properties; The imidazole-based ionic liquid comprises 50% to 90% of the total gel mass; the photoinitiator comprises 0.03% to 0.5% of the vinyl monomer mass. The "heating-quenching" post-treatment in step 2 involves heating at a temperature range of 80~120 ℃, holding at that temperature for 2~30 min, and quenching at a cooling rate of 50 ℃ / min~120 ℃ / min, with a cooling temperature range of -40℃~25℃. The high-strength ionic liquid gel has a strength of 8~40 MPa, an elongation at break of 30%~650%, and a transmittance of 92%~98%. The vinyl monomer is one or more of acrylamide AM, N,N-dimethylacrylamide DMAAm, acrylic acid AA, dimethylaminoethyl methacrylate DMAEMA, polyethylene glycol methacrylate PEGMA, and hydroxyethyl methacrylate HEMA, wherein at least AM monomer is included. The anion of the imidazole-based ionic liquid is one or more of bromide ions, tetrafluoroborate ions, and trifluoroacetic acid ions.

2. The method for preparing the high-strength ionic liquid gel according to claim 1, characterized in that: The in-situ polymerization in step 1 uses ultraviolet light with a wavelength of 365 nm and a light source intensity of 6 W / m². 2 ~300 W / m 2 The ultraviolet light exposure time is 1~10 min.

3. The method for preparing the high-strength ionic liquid gel according to claim 1, characterized in that: The imidazole-based ionic liquid is a hydrophilic ionic liquid, with a 1,3-disubstituted imidazole cation and a straight-chain saturated alkyl substituent having 2 to 4 carbon atoms.

4. The method for preparing the high-strength ionic liquid gel according to claim 1, characterized in that: The photoinitiator is one or more of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone, 2,4,6-(trimethylbenzoyl)diphenylphosphine oxide, 2-hydroxy-2-methyl-1-phenylpropanone, or 1-hydroxycyclohexylphenyl ketone.

5. A high-strength ionic liquid gel obtained by the preparation method according to any one of claims 1 to 4.

6. The high-strength ionic liquid gel according to claim 5, characterized in that: The ionic liquid gel described above has the multifunctionality of shape memory, recyclability, and conductivity. Its shape memory capability is that the ionic liquid gel changes shape after being heated to 80~120 ℃, and the shape is fixed by cooling to -40~25 ℃. During the reheating process, the gel returns to its initial shape. Its recyclability is that the ionic liquid gel can be dissolved in a solvent to obtain a transparent solution, and then reshaped by evaporating the solvent.

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