A method for preparing a hydrogen-bonded organic framework-polyeutectic solvent composite hydrogel

Abstract

This invention discloses a method for preparing a hydrogen-bonded organic framework-polyeutectic solvent composite hydrogel. The method involves uniformly dispersing HOFs in a DES aqueous solution, followed by free radical polymerization to form a HOF / PDES composite hydrogel. The composite hydrogel obtained by this invention effectively integrates the advantages of HOFs and PDES. Furthermore, the polymerization of DES to form PDES solves the DES leakage problem and improves the tensile strength, toughness, compressive strength, and conductivity of the hydrogel.

Description

Technical Field

[0001] This invention belongs to the field of hydrogel preparation technology, specifically relating to a method for preparing a composite hydrogel of hydrogen-bonded organic frameworks (HOFs) and polyeutectic solvents (PDES). Background Technology

[0002] Wearable flexible strain sensors have shown great application potential in many fields such as human motion detection, human-computer interaction, and bioelectronics. Hydrogels, due to their excellent biocompatibility and tunable mechanical properties, are widely used in wearable flexible strain sensors. However, many hydrogels still suffer from problems such as low tensile strength, poor toughness, and weak conductivity, and optimizing these properties can be challenging. Introducing conductive nanofillers into hydrogels is an effective method to simultaneously improve their tensile strength, toughness, and conductivity. Yu et al. (Y.Li,D.Yang,Z.Wu,F.Gao,H.Zhao,X.Li,Z.Yu,Self-adhesive,self-healing,biocompatible and conductive polyacrylamidenanocomposite hydrogels for reliable strain and pressure sensors,Nano Energy2023,109,108324.) prepared carbon nanotube composite hydrogels by introducing polydopamine-modified carbon nanotubes into polyacrylamide hydrogels. The conductivity of this material was 2 mS / m. -1 With a tensile strength of 20 kPa and an elongation at break of 800%, it can be used as a strain sensor to monitor human movement. Lai et al. (Y.Ni,X.Zang,J.Chen,T.Zhu,Y.Yang,J.Huang,W.Cai,Y.Lai, Flexible MXene-based hydrogel enables wearable human-computer interaction for intelligent underwater communication and sensing rescue.Adv.Funct.Mat.2023,33,2301127.) prepared a composite hydrogel by incorporating MXene into polyacrylamide hydrogels. This composite hydrogel has a tensile strength of approximately 100 kPa and a toughness of 560 kJ / m. -3With an elongation at break of 1224%, it was used for underwater strain sensing. Although the tensile strength was improved by introducing conductive nanofillers into polymer hydrogels, the limited number of active sites in these nanoparticles led to problems such as uneven dispersion and discontinuous conductive networks, affecting the tensile strength, toughness, and conductivity of the hydrogel, thus limiting its application scope. Designing and synthesizing composite hydrogels of nanofillers with abundant organic groups and polymers is a necessary condition for improving tensile strength, toughness, and conductivity.

[0003] HOFs (Hypermeric Organic Foliar Materials) are porous crystalline supramolecular materials that self-assemble from organic building blocks through hydrogen bonding. They possess advantages such as high specific surface area, ordered pores, tunable structure, abundant functional groups, and good solution processability. Eutectic solvents (DES) are an emerging green solvent composed of hydrogen bond acceptors and donors. They offer advantages such as simple preparation, environmental friendliness, tunable performance, and high ionic conductivity, and are widely used in the research of conductive hydrogel sensors. Introducing HOFs into DES hydrogels allows the abundant organic functional groups on the HOF surface to form supramolecular interactions with the polymer and DES, improving the tensile strength and toughness of the hydrogel. The ordered pores of HOFs can promote ion transport and enhance ionic conductivity. However, leakage of DES solvent within the hydrogel severely affects its mechanical properties and conductivity. Designing and synthesizing novel hydrogel materials is crucial for improving tensile strength, toughness, and conductivity.

[0004] Currently, there are no reports on hydrogels that combine PDES and HOFs for wearable flexible strain sensors. Developing PDES and HOFs composite hydrogels with high strength, good toughness, strong conductivity, simple preparation, and low cost has become an urgent problem to be solved to expand their application in wearable flexible strain sensors. Summary of the Invention

[0005] This invention addresses the problems existing in hydrogels currently used in wearable flexible strain sensors by providing a method for preparing a HOFs-PDES composite hydrogel and applying it to strain sensors. The method involves uniformly dispersing HOFs in a DES aqueous solution, followed by free radical polymerization to form the HOFs-PDES composite hydrogel. The composite hydrogel obtained by this invention effectively integrates the advantages of HOFs and PDES. Furthermore, the polymerization of DES to form PDES solves the DES leakage problem and improves the tensile strength, toughness, compressive strength, and conductivity of the hydrogel. Compared with a single PDES hydrogel, the composite hydrogel obtained by this invention exhibits a 4.5-fold increase in tensile strength, a 4.5-fold increase in toughness, a 2.6-fold increase in compressive strength, and a 1.2-fold increase in conductivity.

[0006] The technical solution of this invention is as follows:

[0007] A method for preparing a hydrogen-bonded organic framework-polyeutectic solvent composite hydrogel, the method comprising the following steps:

[0008] HOFs and DES were added to deionized water and stirred for 1–24 hours. Then, polyethyleneimine aqueous solution was added and stirred for 2–15 minutes. Finally, an initiator was added and stirred for 0.1–3 minutes to obtain a hydrogen-bonded organic framework-polyeutectic solvent composite hydrogel.

[0009] The composition of HOFs is 0.01–30% of the mass of DES; the composition of deionized water is 10–300% of the mass of DES; the composition of polyethyleneimine is 0.1–50% of the mass of DES; and the composition of initiator is 0.03–10% of the mass of DES.

[0010] The concentration of the polyethyleneimine aqueous solution is 100–3000 mg / mL;

[0011] The initiator is potassium persulfate or sodium persulfate;

[0012] The method for preparing the HOFs includes the following steps:

[0013] The building blocks were added to the first organic solvent and stirred at 25–120°C for 0.5–48 hours. After cooling to room temperature, the second organic solvent was added and stirred for 0.1–24 hours. The synthesized solid was then centrifuged, washed, Soxhlet extracted, and dried to obtain HOFs.

[0014] The volume ratio of the first organic solvent to the second organic solvent is 1:1 to 100; 0.1 to 30 mg of building units are added to each 1 mL of the first organic solvent; the first organic solvent is N,N-dimethylformamide, ethanol, or tetrahydrofuran; the second organic solvent is any one or both of ethanol and ethyl acetate.

[0015] The building blocks are 1,3,6,8-tetracarboxypyrene, 1,3,6,8-tetra(4-carboxyphenyl)pyrene, 1,3,6,8-tetra(6-carboxy-2-naphthyl)pyrene, 4,4',4”,4”'-(pyrene-1,3,6,8-tetrayl)tetra(2-fluorobenzoic acid), 4,4',4”,4”'-(pyrene-1,3,6,8-tetrayl)tetra(2-aminobenzoic acid), 4,4',4”,4”'-(pyrene-1,3,6,8-tetrayl)tetra(2-methylbenzoic acid)aldehyde, or 2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine.

[0016] The method for preparing DES includes the following steps:

[0017] DES is obtained by mixing hydrogen bond donors and hydrogen bond acceptors and heating at 25–100°C for 5–60 minutes.

[0018] The molar ratio of hydrogen bond donor to hydrogen bond acceptor is 1:0.1 to 5;

[0019] The hydrogen bond donor is an olefin, or a mixture of olefins and non-olefins;

[0020] The olefinic substances are any one or more of acrylamide, acrylic acid, and hydroxyethyl methacrylate, and the non-olefinic substances are any one or more of glycerol, urea, benzoic acid, malonic acid, and 1,4-butanediol.

[0021] The hydrogen bond acceptor is any one or more of choline chloride, ammonium chloride, fluorinated choline, betaine, lithium bis(trifluoromethanesulfonylimide), glycine, histidine, and alanine.

[0022] The hydrogen-bonded organic framework-polyeutectic solvent composite hydrogel obtained by the method is used as an intermediate layer in wearable strain sensors. The specific steps are as follows:

[0023] A polyeutectic solvent-hydrogen bonded organic framework composite gel is used as the middle layer of a wearable strain sensor. Copper wires are wound around both ends of the gel and fixed between two pieces of adhesive tape to assemble the strain sensor. The sensor is then adhered to the skin, including the wrist joint, finger joint, and pulse point. A voltage of 1-3V is applied to both ends of the gel to monitor the resistance changes of the hydrogel at these locations during human movement.

[0024] The essential features of this invention are:

[0025] This invention involves uniformly dispersing HOFs in a DES aqueous solution and preparing a HOFs-PDES composite hydrogel via free radical polymerization. In this composite hydrogel, the organic functional groups on the surface of HOFs form supramolecular interactions with PDES, enhancing the tensile strength, toughness, and compressive strength of the hydrogel. The regular and ordered channels of HOFs facilitate ion transport and improve the conductivity of the hydrogel, which is superior to many existing hydrogel strain sensors.

[0026] The beneficial effects of this invention are as follows:

[0027] (1) This invention provides a method for preparing HOFs and PDES composite hydrogels. The well-defined structures of HOFs and PDES provide an ideal platform for understanding the relationship between hydrogel structure and strain sensing performance.

[0028] (2) The HOFs and PDES composite hydrogel provided by the present invention benefits from the supramolecular interaction formed between HOFs and PDES and the crystal structure of HOFs. The tensile strength is 135.23 kPa, which is 4.5 times higher than that of the PDES hydrogel alone (30.22 kPa).

[0029] (3) The HOFs and PDES composite hydrogel provided by this invention has a toughness of 2.69 MJ / m. -3 Compared with PDES hydrogel alone (0.6 MJ m -3 The composite hydrogel exhibits 4.5 times greater toughness.

[0030] (4) The HOFs and PDES composite hydrogel provided by the present invention has a strength of 0.89 MPa under 80% compression, which is 2.6 times higher than that of the PDES hydrogel alone (0.34 MPa).

[0031] (5) The HOFs and PDES composite hydrogel provided by this invention has an electrical conductivity of 4.33 ± 0.02 S m. -1 Compared with PDES hydrogel alone, (3.53 ± 0.07 S m) -1 The conductivity of the composite hydrogel was increased by 1.2 times.

[0032] (6) The HOFs and PDES composite hydrogel provided by the present invention, after being assembled into a strain sensor, can be adhered to the skin, including the wrist joint, finger joint, and pulse point, and can monitor the relative resistance change of the hydrogel strain sensor in these areas during movement in real time. Attached Figure Description

[0033] Figure 1 The stress-strain curves of the composite hydrogel and PDES hydrogel obtained in Example 1 and Comparative Example 1 are shown.

[0034] Figure 2 The stress-strain curves for the composite hydrogel and PDES hydrogel obtained in Example 1 and Comparative Example 1 are shown.

[0035] Figure 3 The ionic conductivity is the composite hydrogel and PDES hydrogel obtained in Example 1 and Comparative Example 1.

[0036] Figure 4 This is a schematic diagram of a strain sensor.

[0037] Figure 5The graph shows the relative resistance change of the composite hydrogel sensor obtained in Example 1 when it is attached to the wrist joint to monitor the wrist from straightening, bending downwards to bending upwards, for 19 cycles.

[0038] Figure 6 The graph shows the relative resistance change of the composite hydrogel sensor obtained in Example 1, which is attached to the finger joint to monitor the bending process of the finger from extension to bending downward at 45° for 10 cycles, and then from extension to bending downward at 90° for 13 cycles.

[0039] Figure 7 The graph shows the relative resistance change of the composite hydrogel sensor obtained in Example 1 when it is attached to the pulse point to monitor the pulse. Detailed Implementation

[0040] To further illustrate the method of the present invention, specific embodiments are described below with reference to the accompanying drawings. The following embodiments are merely specific preparation methods of the present invention and do not limit the scope of the invention.

[0041] Comparative Example 1

[0042] Acrylamide (1.8 g, 0.025 mol), acrylic acid (1.78 g, 0.025 mol), and choline chloride (3.49 g, 0.025 mol) were stirred at 80 °C for 15 minutes to obtain DES.

[0043] Add DES (7.07 g) to deionized water (7 mL), add polyethyleneimine (0.5 g), stir for 5 minutes, then add potassium persulfate (0.021 g), stir for 0.5 minutes to obtain PDES hydrogel;

[0044] Example 1

[0045] 200 mg of 4,4',4”,4”'-(pyrene-1,3,6,8-tetramethyl)tetra(2-fluorobenzoic acid) was added to 10 mL of N,N-dimethylformamide. The mixture was heated and stirred at 120 °C for 30 minutes. After cooling to room temperature, 200 mL of ethyl acetate was added and stirred for 12 hours. The synthesized solid was then centrifuged, washed, Soxhlet extracted, and dried to obtain HOFs.

[0046] Acrylamide (1.8 g, 0.025 mol), acrylic acid (1.78 g, 0.025 mol), and choline chloride (3.49 g, 0.025 mol) were stirred at 80 °C for 15 minutes to obtain DES.

[0047] HOFs (18 mg) and DES (7.07 g) were added to deionized water (6 mL) and stirred for 12 hours. Then, polyethyleneimine aqueous solution (500 mg / mL, 1 mL) was added and stirred for 5 minutes. Finally, potassium persulfate (0.021 g) was added and stirred for 0.5 minutes to obtain hydrogen-bonded organic framework-polyeutectic solvent composite hydrogel.

[0048] Figure 1 In this study, tensile stress-strain curves of the composite hydrogel and PDES hydrogel were obtained using a material tensile testing machine (CMT 6104). The maximum stress on the tensile stress-strain curve represents the tensile strength, and the area enclosed by the stress-strain curve and the horizontal axis represents the toughness. The tensile strength of the HOFs / PDES composite hydrogel was 135.23 kPa, which is 4.5 times higher than that of the PDES hydrogel alone (30.22 kPa). The toughness of the HOFs / PDES composite hydrogel was 2.69 MJ / m. -3 Compared with PDES hydrogel alone (0.6 MJ m -3 The composite hydrogel exhibits 4.5 times greater toughness.

[0049] Figure 2 In this study, the compressive stress-strain curves of the composite hydrogel and PDES hydrogel were obtained using a material tensile testing machine (CMT 6104). The maximum stress on the compressive stress-strain curve represents the compressive strength. The HOFs / PDES composite hydrogel exhibited a strength of 0.89 MPa at 80% compression, which is 2.6 times higher than that of the PDES hydrogel alone (0.34 MPa).

[0050] Figure 3 In this study, the ionic conductivity of the composite hydrogel and PDES hydrogel was measured using an electrochemical workstation (CHI 760E) and electrochemical impedance spectroscopy. The conductivity of the HOFs / PDES composite hydrogel was 4.33 ± 0.02 S m. -1 Compared with PDES hydrogel alone, (3.53 ± 0.07 S m) -1 The conductivity of the composite hydrogel was increased by 1.2 times.

[0051] Figure 4 In this process, a composite gel is used as the middle layer of a wearable strain sensor, with copper wires wrapped around both ends. The gel is then fixed between two pieces of adhesive tape to assemble the strain sensor.

[0052] Figure 5 In this study, a composite hydrogel sensor was attached to the wrist joint to monitor the relative resistance change curve during the process of the wrist going from straight, bending downwards to bending upwards, 19 times.

[0053] Figure 6 In this study, a composite hydrogel sensor was attached to the finger joint to monitor the relative resistance change curve during the bending process, from extension to bending downwards at 45° for 10 cycles and then from extension to bending downwards at 90° for 13 cycles.

[0054] Figure 7 In this study, a composite hydrogel sensor was attached to the pulse point to monitor the relative resistance change curve of the strain sensor during the pulse beat.

[0055] Example 2

[0056] 1,3,6,8-tetra(4-carboxyphenyl)pyrene (210 mg) was added to N,N-dimethylformamide (31.5 mL), stirred at 25 °C for 24 hours, cooled to room temperature, and then ethanol (174.3 mL) was added. After stirring for 10 minutes, the synthesized solid was centrifuged, washed, Soxhlet extracted, and dried to obtain HOFs.

[0057] Glycerol (4.6 g, 0.05 mol), acrylic acid (1.78 g, 0.025 mol), and choline chloride (3.49 g, 0.025 mol) were stirred at 80 °C for 20 minutes to obtain DES.

[0058] HOFs (0.99 mg) and DES (9.87 g) were added to deionized water (28.6 mL), and stirred for 1 hour. Then, polyethyleneimine aqueous solution (100 mg / mL, 1 mL) was added, and stirred for 2 minutes. Then, sodium persulfate (0.011 g) was added, and stirred for 0.1 minutes to obtain hydrogen-bonded organic framework-polyeutectic solvent composite hydrogel.

[0059] Example 3

[0060] 2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine (100 mg) was added to ethanol (100 mL), stirred at 90 °C for 48 hours, cooled to room temperature, and then ethanol (200 mL) was added. After stirring for 10 minutes, the synthesized solid was centrifuged, washed, Soxhlet extracted, and dried to obtain HOFs.

[0061] Acrylamide (1.48 g, 0.025 mol), acrylic acid (1.78 g, 0.025 mol), and ammonium chloride (1.34 g, 0.025 mol) were stirred at 60 °C for 30 minutes to obtain DES.

[0062] HOFs (0.1g) and DES (4.92g) were added to deionized water (4mL) and stirred for 24 hours. Then, polyethyleneimine aqueous solution (2000mg / mL, 1mL) was added and stirred for 15 minutes. Finally, potassium persulfate (0.05g) was added and stirred for 3 minutes to obtain hydrogen-bonded organic framework-polyeutectic solvent composite hydrogel.

[0063] Matters not covered in this invention are common knowledge.

Claims

1. A method for preparing a hydrogen-bonded organic framework-polyeutectic solvent composite hydrogel, characterized in that, The method includes the following steps: HOFs and DES were added to deionized water and stirred for 1 to 24 hours. Then, polyethyleneimine aqueous solution was added and stirred for 2 to 15 minutes. Finally, an initiator was added and stirred for 0.1 to 3 minutes to obtain hydrogen-bonded organic framework-polyeutectic solvent composite hydrogel. The composition of the HOFs is 0.01–30% of the DES mass; the composition of the deionized water is 10–300% of the DES mass; the composition of the polyethyleneimine is 0.1–50% of the DES mass; and the composition of the initiator is 0.03–10% of the DES mass. The concentration of the polyethyleneimine aqueous solution is 100~3000 mg / mL; The building blocks of the HOFs are 1,3,6,8-tetracarboxypyrene, 1,3,6,8-tetra(4-carboxyphenyl)pyrene, 1,3,6,8-tetra(6-carboxy-2-naphthyl)pyrene, 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetra(2-fluorobenzoic acid), 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetra(2-aminobenzoic acid), 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetra(2-methylbenzoic acid)aldehyde, or 2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine; The method for preparing DES includes the following steps: DES is obtained by mixing hydrogen bond donors and hydrogen bond acceptors and heating at 25~100 ℃ for 5~60 minutes. The molar ratio of hydrogen bond donor to hydrogen bond acceptor is 1:0.1~5; The hydrogen bond donor is an olefin, or a mixture of olefins and non-olefins; The olefinic substances are any one or more of acrylamide, acrylic acid, and hydroxyethyl methacrylate, and the non-olefinic substances are any one or more of glycerol, urea, benzoic acid, malonic acid, and 1,4-butanediol. The hydrogen bond acceptor is any one or more of choline chloride, ammonium chloride, fluorinated choline, betaine, lithium bis(trifluoromethanesulfonylimide), glycine, histidine, and alanine.

2. The preparation method of the hydrogen-bonded organic framework-polyeutectic solvent composite hydrogel as described in claim 1, characterized in that, The initiator is potassium persulfate or sodium persulfate.

3. The preparation method of the hydrogen-bonded organic framework-polyeutectic solvent composite hydrogel as described in claim 1, characterized in that, The method for preparing the HOFs includes the following steps: The building blocks were added to the first organic solvent and stirred at 25-120°C for 0.5-48 hours. After cooling to room temperature, the second organic solvent was added and stirred for 0.1-24 hours. The synthesized solid was then centrifuged, washed, Soxhlet extracted, and dried to obtain HOFs. The volume ratio of the first organic solvent to the second organic solvent is 1:1 to 100; 0.1 to 30 mg of building units are added to each 1 mL of the first organic solvent; the first organic solvent is N,N-dimethylformamide, ethanol, or tetrahydrofuran; the second organic solvent is one or both of ethanol and ethyl acetate.

4. The application of the hydrogen-bonded organic framework-polyeutectic solvent composite hydrogel obtained by the method described in claim 1, characterized in that, Used as an intermediate layer for wearable strain sensors.

5. The application as described in claim 4, characterized in that, Includes the following steps: A hydrogen-bonded organic framework-polyeutectic solvent composite hydrogel is used as the middle layer of a wearable strain sensor. Copper wires are wound around both ends of the hydrogel, which is then fixed between two pieces of adhesive tape to assemble the strain sensor.

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