A dynamic eutectic solvent, an ionic gel and a preparation method thereof

Abstract

The present invention discloses a dynamic deep eutectic solvent, an ionic gel and a preparation method thereof. Using ChCl as a hydrogen bond acceptor and LA as a hydrogen bond donor, a special dynamic deep eutectic solvent that undergoes ring-opening polymerization at high temperature is designed. In order to obtain a polymer material stable at room temperature, TA, DIB and AlCl3·6H2O are added thereto to form multiple dynamic bonds (disulfide bonds, hydrogen bonds, coordination bonds) to introduce dual physical and chemical crosslinking effects, thereby successfully preparing a dynamic deep eutectic solvent-based ionic gel PDDES by a solvent-free one-pot method. This method has the characteristics of easily available raw materials, green and solvent-free, and convenient operation. The ionic gel prepared by the present invention exhibits good mechanical properties, self-healing properties, adhesion properties, recyclability, strain sensitivity, etc., broadens the monomer range of polymerizable deep eutectic solvents, and provides ideas for the research of designing more novel deep eutectic solvents.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and particularly relates to a preparation method of an ion gel based on a dynamic deep eutectic solvent. Background Art

[0002] Polymerizable deep eutectic solvents (PDES) are a new type of deep eutectic solvents. The hydrogen bond donor (HBD) part contains polymerizable units, while the hydrogen bond acceptor (HBA) part provides zwitterions. In addition to having the same advantages as deep eutectic solvents, such as simple preparation, 100% atom utilization rate, and low cost, PDES can also be polymerized by thermal or light stimulation and have appeared in organic synthesis and functional materials. The PDES thus composed can serve both as a solvent and a monomer, and after undergoing a free radical polymerization reaction, a multifunctional elastomer material with good properties can be prepared. Since it plays an "integrated" role during the polymerization process and does not require other inconvenient processes, it shows a fast, solvent-free, and green preparation method. However, most of the reported PDESs are polymerized through double bond functional groups, and it is necessary to expand the monomer range of such polymerizable deep eutectic solvents (such as cyclic monomers). Summary of the Invention

[0003] The purpose of the present invention is to provide an ion gel based on a dynamic deep eutectic solvent, its preparation method, and sensing application. In the dynamic deep eutectic solvent provided by the present invention, choline chloride is used as the hydrogen bond acceptor, and lipoic acid is used as the hydrogen bond donor. Dynamic covalent disulfide bonds and dynamic non-covalent hydrogen bonds are introduced, and a three-dimensional cross-linked structure is formed by cross-linking dynamic covalent bonds and non-covalent bonds. At the same time, metal coordination bonds are supplemented, so that the system has good mechanical properties, self-healing properties, adhesion properties, strain sensing properties, recyclability, etc. The present invention uses easily available green bio-based raw materials and prepares the ion gel material by a simple thermal-induced ring-opening polymerization method.

[0004] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] A dynamic deep eutectic solvent includes a hydrogen bond acceptor and a hydrogen bond donor. The hydrogen bond acceptor includes a zwitterionic quaternary ammonium salt monomer; the hydrogen bond donor includes a double bond carboxylic acid or a cyclic carboxylic acid. Preferably, the hydrogen bond acceptor is one or more of choline chloride, anhydrous betaine, betaine monohydrate, ammonium chloride, methyltriphenylphosphonium bromide, benzyltriphenylphosphonium chloride, N,N-diethylethanolammonium chloride; the hydrogen bond donor is one or more of lipoic acid, sorbic acid, oleic acid, or linoleic acid.

[0006] In the present invention, the mass of the hydrogen bond acceptor is more than 20% of the mass of the hydrogen bond donor, preferably 20% - 50%.

[0007] The present invention discloses a preparation method of the above-mentioned dynamic deep eutectic solvent, which is obtained by mixing a hydrogen bond acceptor and a hydrogen bond donor; preferably, the hydrogen bond acceptor and the hydrogen bond donor are mixed at 100-150 °C for 0.5-2 h to obtain the dynamic deep eutectic solvent.

[0008] A dynamic deep eutectic solvent-based ionic gel material is prepared from the above-mentioned dynamic deep eutectic solvent, a stabilizer, a crosslinking agent, and a metal halide. The dynamic deep eutectic solvent of the present invention undergoes thermal-initiated ring-opening polymerization and is mixed with a stabilizer, a crosslinking agent, and a metal halide to prepare the dynamic deep eutectic solvent-based ionic gel material.

[0009] In the present invention, the stabilizer is one or more of tannic acid, acrylic acid, and itaconic acid; the crosslinking agent is one or more of polyethylene glycol diacrylate, divinylbenzene, 1,3-diisopropenylbenzene, and trimethylolpropane tris(3-mercaptopropionate); the metal halide includes one or more of ferric sulfate, ferric chloride hexahydrate, ferric nitrate, iron stearate, and aluminum chloride hexahydrate.

[0010] In the present invention, the mass ratio of the hydrogen bond donor, the hydrogen bond acceptor, the stabilizer, the crosslinking agent, and the metal halide is 1:(0.2-0.5):(0.01-0.03):(0.05-0.15):(0-0.016). For example, the mass ratio of the hydrogen bond donor, the hydrogen bond acceptor, the stabilizer, the crosslinking agent, and the metal source is 1:20 wt .%: 2 wt .%: 10 wt .%: (0~1.6) wt .%.

[0011] The present invention discloses the application of the above-mentioned dynamic deep eutectic solvent in the preparation of ionic gel materials; the application of the above-mentioned dynamic deep eutectic solvent-based ionic gel materials in the preparation of functional materials, such as multifunctional elastomer materials.

[0012] The present invention first provides a dynamic deep eutectic solvent (DDES), which is obtained by mixing a hydrogen bond acceptor and a hydrogen bond donor, and the mass ratio of the hydrogen bond acceptor to the hydrogen bond donor is not less than 20 wt .%.

[0013] As a preferred example, choline chloride is used as the hydrogen bond acceptor and lipoic acid is used as the hydrogen bond donor; choline chloride (ChCl) is used as the hydrogen bond acceptor, and its chemical structural formula is as follows:

[0014] .

[0015] The dynamic component is lipoic acid (LA), which is used as the hydrogen bond donor, and its chemical structural formula is as follows:

[0016] 。

[0017] The stabilizer is tannic acid (TA), which is dissolved in absolute ethanol during use. Its chemical structural formula is as follows:

[0018] 。

[0019] The crosslinking agent is 1,3 - diisopropenylbenzene (DIB). Its chemical structural formula is as follows:

[0020] 。

[0021] The metal halide is aluminum chloride hexahydrate (AlCl3·6H2O), which is dissolved in absolute ethanol during use.

[0022] The present invention also provides a preparation method of the above - mentioned dynamic eutectic solvent - based ion gel material. Under the condition of 100 - 150 °C, a stabilizer is added to the dynamic eutectic solvent. After heating and stirring, a small - molecule crosslinking agent is added to the mixture, and heating and stirring are continued. Then, a metal halide dissolved in an organic solvent is added, and heating and stirring are continued. After that, heating is stopped, and then the eutectic is poured into a mold and kept warm in an oven to obtain the target product.

[0023] Due to the adoption of the above - mentioned technical solution, the present invention has the following advantages:

[0024] The present invention selects zwitterionic hydrogen - bond acceptors and dynamic - component hydrogen - bond donors to prepare a metastable dynamic eutectic solvent, and is supplemented with a stabilizer, a crosslinking agent, and a metal source to prepare a stable dynamic eutectic solvent - based ion gel. The eutectic solvent raw materials have the advantages of wide sources, low cost, easy preparation, low toxicity, biodegradability, etc. At the same time, the reaction conditions are mild, and the atom utilization rate is 100%, meeting the requirements of green chemistry. The lipoic acid adopted is a natural small - molecule coenzyme, which also has the advantages of non - toxicity and wide sources. The ion gel obtained after polymerization contains dynamic covalent disulfide bonds, non - covalent hydrogen bonds, and metal coordination bonds at the same time. The combination of multiple interactions makes the system have advantages such as good mechanical properties, self - healing ability, adhesion, recyclability, and strain - sensing ability. The present invention provides a new idea for the preparation and application of novel eutectic solvents. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the appearance of the ion gel prepared in Example 3 of the present invention.

[0026] Figure 2 It is a schematic diagram of the infrared spectrum (FT - IR) of ChCl, LA, TA, and the ion gel prepared in Example 3 of the present invention.

[0027] Figure 3 Schematic diagram of the Raman spectrum of the ion gel prepared by LA and Example 3 of the present invention.

[0028] Figure 4 Schematic diagram of the UV-Vis spectrum of the ion gel prepared in Example 3 of the present invention.

[0029] Figure 5 Schematic diagram of the XRD of the ion gel prepared by LA and Example 3 of the present invention.

[0030] Figure 6 Schematic diagram of the SEM of the ion gel prepared by LA, TA and Example 3 of the present invention.

[0031] Figure 7 Schematic diagram of the EDS of the ion gel prepared in Example 3 of the present invention.

[0032] Figure 8 Stress-strain curve of uniaxial tension of the ion gel prepared in all examples of the present invention.

[0033] Figure 9 Stress-strain curve of cyclic tension of the ion gel prepared in Example 3 of the present invention.

[0034] Figure 10 Stress-strain curve of cyclic compression of the ion gel prepared in Example 3 of the present invention.

[0035] Figure 11 Stress-strain curve of uniaxial tension of the ion gel prepared in Example 3 of the present invention with different repair times.

[0036] Figure 12 Schematic diagram of the picture showing that the ion gel prepared in Example 3 of the present invention can adhere to the surface of different substrates.

[0037] Figure 13 (A) Lap shear stress-strain curve and (B) adhesion strength schematic diagram of the ion gel prepared in Example 3 of the present invention.

[0038] Figure 14 Stress-strain curve of uniaxial tension of the ion gel prepared in Example 3 of the present invention after being recycled twice.

[0039] Figure 15 Schematic diagram of the sensing performance of the ion gel prepared in Example 3 of the present invention. Detailed implementation manners

[0040] The present invention combines lipoic acid and choline chloride to form a eutectic solvent, which can break and reconnect S-S bonds under external conditions. The obtained material has both dynamic covalent bonds and non-covalent bonds at the same time. The disulfide five-membered ring end can undergo ring-opening polymerization to form a polymer main chain with dynamic disulfide bonds as the backbone, and the carboxyl end can generate non-covalent bond interactions such as coordination bonds and hydrogen bonds, supplemented by metal coordination bonds, making the system have good mechanical properties, self-healing properties, adhesion, recyclability, strain sensitivity, etc. Moreover, the raw materials of the present invention are widely sourced, inexpensive, and environmentally friendly, which will bring a new round of technological innovation to eutectic solvents.

[0041] To better understand the content of the present invention, the following further illustrates the content of the present invention in combination with specific implementation methods, but the protection scope of the present invention is not limited to the following examples; the reagents used in the present invention are existing products, and the specific preparation operations and performance tests are conventional technologies.

[0042] Example 1

[0043] Lipoic acid (5 g) and choline chloride (1 g) were mixed in a 50 mL round-bottom flask and heated to eutectic in an oil bath at 120 °C for 1 h to obtain a uniform, transparent orange-yellow metastable dynamic eutectic solvent. Then, 1,3-diisopropenylbenzene (0.5 g) was added to the above eutectic, and after stirring and reacting at 120 °C for 20 min, the obtained mixed molten liquid was poured into a polytetrafluoroethylene mold (4 cm × 2 cm × 0.1 cm) and placed in an oven at 35 °C for heat preservation for 24 h to obtain a dynamic eutectic solvent-based ion gel.

[0044] Example 2

[0045] Lipoic acid (5 g) and choline chloride (1 g) were mixed in a 50 mL round-bottom flask and heated to eutectic in an oil bath at 120 °C for 1 h to obtain a uniform, transparent orange-yellow metastable dynamic eutectic solvent. Then, tannic acid (0.1 g, dissolved in 0.5 mL of absolute ethanol) was added to the above eutectic, and after stirring and reacting at 120 °C for 20 min, 1,3-diisopropenylbenzene (0.5 g) was added to the above eutectic, and after stirring and reacting at 120 °C for 20 min, the obtained mixed molten liquid was poured into a polytetrafluoroethylene mold (4 cm × 2 cm × 0.1 cm) and placed in an oven at 35 °C for heat preservation for 24 h to obtain a dynamic eutectic solvent-based ion gel.

[0046] Example 3

[0047] Mix lipoic acid (5 g) and choline chloride (1 g) in a 50 mL round-bottom flask, place it in an oil bath at 120 °C and heat it to melt for 1 h to obtain a uniform, transparent orange-yellow metastable dynamic eutectic solvent. Then add tannic acid (0.1 g, dissolved in 0.5 mL of absolute ethanol) to the above-mentioned eutectic, maintain stirring at 120 °C and react for 20 min. Then add 1,3-diisopropenylbenzene (0.5 g) to the above-mentioned eutectic, maintain stirring at 120 °C and react for 20 min. Add aluminum chloride hexahydrate (0.01 g, dissolved in 0.5 mL of absolute ethanol) to the above-mentioned eutectic. After stirring and reacting for 20 min, pour the obtained mixed molten liquid into a polytetrafluoroethylene mold (4 cm × 2 cm × 0.1 cm), and place it in an oven at 35 °C for heat preservation for 24 h to obtain a dynamic eutectic solvent-based ion gel.

[0048] Examples 4 to 6

[0049] Except for changing the feeding mass of aluminum chloride hexahydrate, the remaining steps and conditions are the same as those in Example 3, and different dynamic eutectic solvent-based ion gels are obtained respectively. The numbers, components and contents of all the prepared ion gels are shown in Table 1:

[0050]

[0051] After the dynamic eutectic solvent-based ion gel is prepared, it is cooled to room temperature, and the product is in the form of a yellow transparent solid, as Figure 1 shown, which is PDDES 0.2 The physical picture of the ion gel.

[0052] Example 7

[0053] Perform structural characterization on the ion gel (taking PDDES 0.2 as an example), and the specific method is as follows:

[0054] Use Fourier transform infrared spectroscopy and Raman spectroscopy to determine the chemical structure of the ion gel, and the results are as Figure 2 、 Figure 3 shown. Among them, ChCl represents choline chloride, LA represents lipoic acid, and TA represents tannic acid. From Figure 2 , the hydrogen bond cross-linking effect formed inside the material was observed at 3360 cm -1 . The obvious stretching vibration absorption peak of carboxyl-Al -1 inside was observed at 1656 cm 3+ . In addition, the absorption peaks attributed to S-Ar at 1046 cm -1 and 1200 cm -1The vibration absorption peak attributed to S-CH2 indicates that the sulfur free radicals formed during the ring-opening of LA successfully reacted chemically with the benzene ring of TA and the double bond of DIB to form a cross-linked structure. From Figure 3 , 508 cm -1 and 525 cm -1 The doublet split from the macromolecular disulfide bond formed after ring-opening polymerization was observed, from which it can be inferred that the lipoic acid monomers have fully participated in the polymerization reaction during the reaction process.

[0055] Using an ultraviolet-visible spectrophotometer and a powder X-ray single crystal diffractometer, the physical properties such as the transmittance and crystal form of PDDES 0.2 were studied, and the test results are as Figure 4 , Figure 5 shown. Figure 4 It is shown that in the visible light wavelength range of 400 - 800 nm, the material exhibits strong absorption, and the optical transmittance can reach 88%. Figure 5 In , a very broad "bread-like" peak appears at around 20°, indicating that the monomer LA has undergone ring-opening polymerization and an amorphous polymer has been obtained.

[0056] Using a scanning electron microscope and an X-ray energy spectrometer to observe the morphology and surface elements of PDDES 0.2 , and the test results are as Figure 6 , Figure 7 shown. Figure 6 It shows the smooth and pore-free homogeneous morphology of the ion gel, which may be attributed to the existence of a stable cross-linked structure inside the ion gel, resulting in the formation of a dense three-dimensional network polymer skeleton. After performing area scanning analysis on the ion gel, the elemental mapping images were obtained. From Figure 7 it can be seen that each element is evenly dispersed on the surface of the ion gel, indicating the good homogeneous phase structure of the material.

[0057] Example 8 Mechanical property tests were carried out on different ion gels

[0058] Taking the above ion gel, placing both ends of the material on the tensile machine fixture, and stretching it at a speed of 50 mm min -1 , and observing its tensile properties, as Figure 8 shown. It can be seen from the figure that the material with only the DIB component added shows a soft and weak curve, while the material with the TA and DIB groups added shows similar characteristics and even weaker mechanical strength than the pure DIB group. In contrast, after adding AlCl3·6H2O, the fracture stress of the ion gel increases significantly, and with the increase of Al 3+With the increase in content, the fracture stress increased from 89 kPa to 241 kPa, while the elongation at break decreased from 1292% to 649%. Specifically, it showed a transformation of the material from flexible to rigid, with an increase in mechanical strength. Different Al 3+ The uniaxial tensile data of ionic gel materials with different Al 3+ contents are compared in Table 2. The increase in Al 0.2 content inevitably limits the flexibility of the material. Therefore, in order to coordinate the mechanical properties of all aspects of the material, the following tests mainly selected PDDES Figure 9 for exploration. The results of cyclic tensile and compression tests are shown in Figure 10 . Given the material a certain recovery time, the tensile strength can be restored to the initial state. After 250 cycles of compression, the material can still almost return to its original state, and the compression strength attenuation is very small. This shows that the self-recovery of reversible bonds in the material can well resist energy dissipation, thereby maintaining its mechanical properties and improving the fatigue resistance ability.

[0059]

[0060] The self-healing performance of the ionic gel (taking the PDDES 0.2 sample as an example) was tested.

[0061] The ionic gel was cut into two identical pieces with a knife, and then without any additional stimulation, it was placed in an oven at 35 °C to allow it to contact for different healing times. The repaired specimens were subjected to a tensile test with a tensile rate of 50 mm / min -1 , and its self-healing performance was observed. As can be seen from Figure 11 , the fracture strain of the original PDDES 0.2 was 1292%. After 24 h of repair, the strain recovered to 1258%, and the self-healing efficiency was as high as 97% at this time. Its stress also almost returned to the same level. The strength of the repaired ionic gel could lift a 200 g weight without breaking.

[0062] The adhesion performance of the ionic gel (taking the PDDES 0.2 sample as an example) was tested.

[0063] The ionic gel was placed between two glass slides (different substrates such as paper, iron sheet, plastic, etc.). The sample was evenly distributed between the two identical substrates, and the overlapping area was 2 cm × 2 cm. Then, it was pressed with fingers for 1 min to make it fully adhere to the substrate. A lap shear test was carried out on it using a universal tensile testing machine. The two glass slides were clamped between two clamps in the vertical direction, and the fixed tensile rate was 20 mm / min -1 , and its adhesion performance was observed. Figure 12 shows the instantaneous adhesion of the ionic gel to different substrates. Figure 13The adhesion strengths to paper, iron sheet, glass, and plastic are 47 kPa, 44 kPa, 28 kPa, and 27 kPa, respectively. In addition, a prepared ionic gel sample is sandwiched between two pieces of glass, and the glass adhered by the ionic gel can easily lift a 200 g weight, showing excellent adhesion performance.

[0064] The recyclability of the ionic gel (taking the PDDES 0.2 sample as an example) was tested

[0065] By simply heating the broken ionic gel at 120 °C for 10 min until the solid ionic gel completely melted into a uniform light red transparent liquid. Then the recovered liquid was poured into a polytetrafluoroethylene mold and placed in an oven at 35 °C for 24 h to obtain a newly prepared ionic gel. Tensile tests were carried out on it, as Figure 14 shown, the tensile stress and strain of the two recycled samples were basically the same as those of the original sample. This is attributed to the spontaneity and reversibility of interactions such as disulfide bonds, hydrogen bonds, and metal coordination bonds, thus ensuring the recyclability of the material.

[0066] The sensing performance of the ionic gel (taking the PDDES 0.2 sample as an example) was tested

[0067] The sensing performance of the ionic gel was tested using an LCR digital bridge tester (TH2830, Changzhou Tonghui Electronics). Take the ionic gel of the present invention, connect its two ends to copper wires respectively, and the other ends of the copper wires are connected to the test instrument. The ionic gel is assembled into a wearable sensor to detect corresponding changes, as Figure 15 shown, the ionic gel strain sensor can accurately detect large resistance change signals caused by artificial stretching in real time. When the ionic gel is stretched repeatedly, the peak values of the resistance signals are roughly the same. Attaching the ionic gel to the human finger joint can monitor the movement of the finger joint bending in real time. This shows that it has good stability and sensitivity as a strain sensor.

[0068] The above-described examples are only the preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above examples. All technical solutions falling within the idea of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, improvements and modifications made without departing from the principle of the present invention are still regarded as within the protection scope of the present invention.

Claims

1. A dynamic eutectic solvent, comprising a hydrogen bond acceptor and a hydrogen bond donor, characterized in that, Choline chloride serves as a hydrogen bond acceptor, and lipoic acid serves as a hydrogen bond donor.

2. The dynamic eutectic solvent according to claim 1, characterized in that, The mass of the hydrogen bond acceptor is more than 20% of the mass of the hydrogen bond donor.

3. A method for preparing the dynamic eutectic solvent according to claim 1, characterized in that, The hydrogen bond acceptor and the hydrogen bond donor are mixed to obtain a deep eutectic solvent.

4. A dynamic eutectic solvent-based ion gel material, characterized in that, The deep eutectic solvent-based ionic gel material is prepared from the deep eutectic solvent according to claim 1, a stabilizer, a crosslinking agent, and a metal halide.

5. The dynamic eutectic solvent-based ion gel material according to claim 4, characterized in that, The stabilizer is one or more of tannic acid, acrylic acid, and itaconic acid; the crosslinking agent is one or more of polyethylene glycol diacrylate, divinylbenzene, 1,3 - diisopropenylbenzene, and trimethylolpropane tris(3 - mercaptopropionate); the metal halide includes one or more of iron sulfate, ferric chloride hexahydrate, iron nitrate, iron stearate, and aluminum chloride hexahydrate.

6. The dynamic eutectic solvent-based ion gel material according to claim 4, characterized in that, The mass ratio of the hydrogen bond donor, the hydrogen bond acceptor, the stabilizer, the crosslinking agent, and the metal halide is 1∶(0.2 - 0.5)∶(0.01 - 0.03)∶(0.05 - 0.15)∶(0 - 0.016).

7. Use of the dynamic eutectic solvent-based ion gel material according to claim 4 in the preparation of functional materials.

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