A cold-resistant, acid- and alkali-resistant, conductive, tough hydrogel and its preparation method

Abstract

The present invention provides a cold-resistant, acid-resistant, and alkali-resistant conductive and tough hydrogel and a preparation method thereof. A preparation method of a cold-resistant, acid-resistant, and alkali-resistant conductive and tough hydrogel comprises: using an alkaline urea system to dissolve carbon nanofibers at ‑22°C to ‑16°C to obtain solution A, freezing solution A at ‑22°C to ‑16°C for 22‑28 hours to obtain solution B, wherein the alkaline urea system is an aqueous solution containing alkali and urea; adding polyvinyl alcohol and a water-soluble ionic liquid to deionized water, heating and stirring at 95‑100°C for 1‑2 hours to obtain solution C; returning solution B to room temperature and mixing with solution C for 1‑2 seconds, and then subjecting the solution to multiple cycles of freezing and thawing to obtain a high-performance hydrogel. OH in the alkaline urea system ‑ It can induce the reconstruction of the ionic bonds of water-soluble ionic liquids to form large ionic bond clusters. The alkaline urea system interacts with the water-soluble ionic liquid. The prepared hydrogel can be quickly formed, has good low-temperature resistance, excellent acid and alkali resistance, and is conductive in a variety of solvents.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogels, and in particular to a cold-resistant, acid- and alkali-resistant, conductive and tough hydrogel and a preparation method thereof. Background Art

[0002] Current methods for preparing high-strength hydrogels typically employ a double- or multi-network crosslinking strategy. However, due to their high water content, the hydrogels freeze at temperatures below 0°C, rendering them impractical. Currently, most researchers use water-binding solvents such as glycerol or dimethyl sulfoxide (DMSO) to partially or completely replace water to achieve resistance to lower temperatures (around -20°C). However, this not only complicates the hydrogel preparation process but also compromises its mechanical properties or other functionalities. Professor Wu Peiyi and Researcher Jiao Yucong of Donghua University published a paper titled "Anti-freezing hydrogel electrolyte with ternary hydrogen bonding for high-performance zincion batteries" in Advanced Materials. This work exploits the Hofmeister effect of low-concentration Zn(ClO₄)₂ salts to create highly flexible polysaccharide hydrogels in situ for zinc-ion batteries, achieving cryogenic resistance down to -30°C. Therefore, the development of a novel hydrogel to address these challenges is urgently needed. Summary of the Invention

[0003] The present invention provides a cold-resistant, acid-resistant, and alkali-resistant conductive and tough hydrogel and a preparation method thereof. The specific implementation methods are as follows:

[0004] A method for preparing a cold-resistant, acid-resistant, and alkali-resistant conductive and tough hydrogel, the preparation method comprising:

[0005] (1) dissolving carbon nanofibers at -22°C to -16°C using an alkali-urea system to obtain a solution A, freezing the solution A at -22°C to -16°C for 22-28 hours to obtain a solution B, wherein the alkali-urea system is an aqueous solution containing an alkali and urea;

[0006] (2) adding polyvinyl alcohol and a water-soluble ionic liquid to deionized water, heating and stirring at 95-100° C. for 1-2 hours to obtain solution C;

[0007] (3) After returning solution B to room temperature, mixing it with solution C and stirring for 1-2 seconds, and then subjecting it to multiple cycles of freezing and thawing, a high-performance hydrogel can be obtained;

[0008] There is no time sequence restriction for steps (1) and (2);

[0009] Furthermore, the ratio of the alkali urea system, carbon nanofibers, polyvinyl alcohol, water-soluble ionic liquid and deionized water is 100:1-5:10-40:1-8:70-85 in parts by mass;

[0010] Furthermore, the ratio of the alkali urea system, carbon nanofibers, polyvinyl alcohol, water-soluble ionic liquid and deionized water is 100:1:20:5:80 by mass;

[0011] Furthermore, the alkaline urea system in step (1) is composed of 7%-20% NaOH, 12%-40% urea and 40%-81% H2O by mass fraction;

[0012] Furthermore, the preparation process of solution A in step (1) is specifically as follows: freezing the alkaline urea system at -22°C to -16°C for 22-28 hours, then adding the carbon nanofibers to the alkaline urea system and stirring and dissolving them in a 0°C ice water bath to obtain solution A;

[0013] Furthermore, the water-soluble ionic liquid in step (2) is 1-butyl-3-methylimidazolium tetrafluoroborate;

[0014] Furthermore, in step (3), the freezing temperature each time is between -24°C and -18°C, and the thawing temperature each time is at room temperature;

[0015] Furthermore, in step (3), the freezing time is 8-28 hours each time, and the thawing time is 3-8 hours each time;

[0016] Furthermore, the number of freeze-thaw cycles in step (3) is 3 times.

[0017] In addition, the present invention also provides a hydrogel prepared by the above method.

[0018] Due to the adoption of the above technical solution, the beneficial technical effects of the present invention are:

[0019] 1. The present invention provides a method for preparing a cold-resistant, acid-resistant, and alkali-resistant conductive and tough hydrogel. - It can induce the reconstruction of the ionic bonds of the ionic liquid to form large ionic bond clusters, which form the initial skeleton of the hydrogel. Therefore, the hydrogel of the present invention can be quickly formed within 1-2 seconds.

[0020] 2. Compared with the prior art, although the present invention uses water as the medium, the alkaline urea system can break the hydrogen bonds of water and significantly reduce the amount of free water, so that the hydrogel of the present invention still has good low-temperature resistance, and the low-temperature resistance can reach -60°C;

[0021] 3. Traditional hydrogels have poor compressive resistance. High pressure can damage the hydrogel structure and reduce its performance. However, the polyvinyl alcohol of the present invention forms a large number of crystals after freezing, and the crystal structure is more dense. In addition, carbon nanofibers can be used as reinforcing fillers. Therefore, the prepared hydrogel can withstand repeated vehicle crushing and maintain its structural integrity.

[0022] 4. The present invention forms large ionic bond clusters that cooperate with the frozen crystals of polyvinyl alcohol, so that the hydrogel has the special properties of being acid and alkali resistant and still conductive in solvents. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The hydrogel prepared in Example 1 was placed in different solvents for conductivity testing. A and B represent water, ethanol, n-hexane, petroleum ether, and tetrahydrofuran solvents, respectively.

[0024] Figure 2 Graphs showing the states of the hydrogel prepared in Example 1 at -60°C, -40°C, and -20°C, respectively;

[0025] Figure 3 The mass change rates of the hydrogels obtained in Example 1, Example 2, Example 4 and Comparative Example 1 after being immersed in different solvents for 60 days are shown in FIG. 5 , and ad represent the hydrogels in Comparative Example 1, Example 2, Example 4 and Example 1, respectively. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] A method for preparing a cold-resistant, acid-resistant, and alkali-resistant conductive and tough hydrogel, the preparation method comprising:

[0028] (1) dissolving carbon nanofibers in an alkali-urea system at -22°C to -16°C to obtain solution A, freezing solution A at -22°C to -16°C for 22-28 hours to obtain solution B, wherein the alkali-urea system is an aqueous solution containing alkali and urea;

[0029] (2) adding polyvinyl alcohol and a water-soluble ionic liquid to deionized water, stirring at 95-100° C. for 1-2 hours to obtain solution C;

[0030] (3) Solution B is returned to room temperature and then mixed with solution C and stirred for 1-2 seconds. The mixture is then frozen and thawed three times to obtain a hydrogel.

[0031] There is no time sequence restriction for steps (1) and (2).

[0032] Specifically, polyvinyl alcohol reacts with water-soluble ionic liquid to form H bonds, and the ionic liquid is adsorbed on the polyvinyl alcohol; when solution B returns to room temperature and is mixed with solution C, the OH in the alkaline urea system - It can induce the reconstruction of the ionic bonds of the ionic liquid to form large ionic bond clusters. The ionic bond clusters wrap the polyvinyl alcohol, and the ionic bond clusters form the initial skeleton of the hydrogel. The hydrogel can be quickly formed within 1-2 seconds. At this time, the ionic bonds form a preliminary skeleton to provide strength for the hydrogel; after three cycles of freezing and thawing, the polyvinyl alcohol crystallizes, and the number of crystals formed is large and the crystal form is very dense. At this time, a high-performance hydrogel with a supramolecular network structure that does not require cross-linking can be obtained.

[0033] Furthermore, the ratio of the alkali-urea system, carbon nanofibers, polyvinyl alcohol, water-soluble ionic liquid, and deionized water is 100:1-5:10-40:1-8:70-85 by weight. By adjusting the amounts of each component, the alkali-urea system induces the ionic bonds of the ionic liquid to form large ionic clusters, which in turn encapsulate the polyvinyl alcohol. The resulting hydrogel exhibits not only excellent low-temperature resistance, but also acid and alkali resistance, solvent resistance, and electrical conductivity.

[0034] Further, the alkaline urea system is composed of 7%-20% NaOH, 12%-40% urea and 40%-81% H2O;

[0035] Further, the water-soluble ionic liquid can be 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium hydrogen sulfate, 1-butyl-3-methylimidazolium methanesulfonate, 1-butyl-3-methylimidazolium dibutyl phosphate, 1-butyl-3-methylimidazolium dicyanamide, 1-butyl-3-methylimidazolium nitrate, 1-butyl-3-methylimidazolium octanesulfonate, 1-butyl-3-methylimidazolium thiocyanate, 1-butyl-3-methylimidazolium p-toluenesulfonate, 1-hexyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium bromide, 1-hexyl-3-methylimidazolium iodide, and one or more of 1-hexyl-3-methylimidazolium trifluoromethanesulfonate.

[0036] Example 1

[0037] The alkaline urea system consists of 7% NaOH, 12% urea and 81% H2O.

[0038] (1) Using 100 parts of an alkaline urea system to dissolve carbon nanofibers at -18°C: first, stir the alkaline urea system into a transparent solution and then place it in a refrigerator and freeze it at -18°C for 24 hours. Then, add 1 part of carbon nanofibers to the alkaline urea system and stir it at high speed in a 0°C ice water bath for 2 hours to fully dissolve the carbon nanofibers to obtain solution A. The obtained solution A is placed in a refrigerator and frozen at -18°C for 24 hours to obtain a transparent and viscous solution B.

[0039] (2) 20 parts of polyvinyl alcohol and 5 parts of 1-butyl-3-methylimidazolium tetrafluoroborate were added to 80 parts of water in a certain proportion, and the mixture was heated and stirred at 98° C. in an oil bath for 1 h at a stirring speed of 130 rpm until the solution became transparent to obtain solution C;

[0040] (3) Solution B was restored to room temperature and then added to solution C. The hydrogel was quickly prepared by stirring with a glass rod for 1-2 seconds.

[0041] (4) The hydrogel obtained in step (3) can obtain a high-performance hydrogel after three cycles of freezing and thawing, wherein the freezing temperature of each cycle is -20°C, the freezing time of each cycle is 20 hours, the thawing temperature of each cycle is room temperature, and the thawing time of each cycle is 5 hours.

[0042] Example 2

[0043] The alkaline urea system consists of 20% NaOH, 40% urea and 40% H2O.

[0044] (1) 100 parts of an alkaline urea system was used to dissolve carbon nanofibers at -22°C: the alkaline urea system was first stirred into a transparent solution and then frozen at -22°C for 22 hours. Then, 5 parts of carbon nanofibers were added to the alkaline urea system and stirred at high speed in a 0°C ice water bath for 3 hours to fully dissolve the carbon nanofibers to obtain solution A. The obtained solution A was placed in a refrigerator and frozen at -22°C for 28 hours to obtain a transparent and viscous solution B.

[0045] (2) 10 parts of polyvinyl alcohol and 1 part of 1-butyl-3-methylimidazole chloride were added to 70 parts of water in a certain proportion, and the mixture was heated and stirred at 95° C. in an oil bath for 2 h at a stirring speed of 130 rpm until the solution became transparent to obtain solution C;

[0046] (3) Solution B was restored to room temperature and then added to solution C, and the mixture was stirred with a glass rod for 1-2 seconds to quickly prepare a hydrogel;

[0047] (4) The hydrogel obtained in step (3) can obtain a high-performance hydrogel after two cycles of freezing and thawing, wherein the freezing temperature of each cycle is -24°C, the freezing time of each cycle is 8 hours, the thawing temperature of each cycle is room temperature, and the thawing time of each cycle is 3 hours.

[0048] Example 3

[0049] The alkaline urea system consists of 15% NaOH, 15% urea and 70% H2O.

[0050] (1) 100 parts of an alkaline urea system was used to dissolve carbon nanofibers at -16°C: the alkaline urea system was first stirred into a transparent solution and then frozen at -16°C for 28 hours. Then, 3 parts of carbon nanofibers were added to the alkaline urea system and stirred at high speed for 2 hours in a 0°C ice water bath to fully dissolve the carbon nanofibers to obtain solution A. The obtained solution A was placed in a refrigerator and frozen at -16°C for 22 hours to obtain a transparent and viscous solution B.

[0051] (2) 40 parts of polyvinyl alcohol and 8 parts of 1-hexyl-3-methylimidazolium trifluoromethanesulfonate were added to 85 parts of water in a proportion, and heated and stirred at 100° C. in an oil bath for 2 h at a stirring speed of 130 rpm until the solution became transparent to obtain solution C;

[0052] (3) Solution B was restored to room temperature and then added to solution C, and the mixture was stirred with a glass rod for 1-2 seconds to quickly prepare a hydrogel;

[0053] (4) The hydrogel obtained in step (3) can obtain a high-performance hydrogel after four cycles of freezing and thawing, wherein the freezing temperature of each cycle is -18°C, the freezing time of each cycle is 28 hours, the thawing temperature of each cycle is room temperature, and the thawing time of each cycle is 8 hours.

[0054] Example 4

[0055] Compared with Example 1, the amount of 1-butyl-3-methylimidazolium tetrafluoroborate used in Example 4 is 3 parts,

[0056] The other parts are the same as those in Example 1.

[0057] Comparative Example 1

[0058] Compared with Example 1, Comparative Example 1 does not add 1-butyl-3-methylimidazolium tetrafluoroborate, and other parts are the same as Example 1.

[0059] Comparative Example 2

[0060] Compared with Example 1, Comparative Example 2 uses dimethyl sulfoxide instead of the alkaline urea system, and other parts are the same as Example 1.

[0061] Comparative Example 3

[0062] Compared with Example 1, Comparative Example 3 was subjected to one freezing-thawing process, and other parts were the same as those of Example 1.

[0063] Mechanical properties tests were performed on the hydrogels prepared in Examples 1-4 and Comparative Examples 1-3, respectively.

[0064] Table 1 Test results of mechanical properties of hydrogels obtained in Examples 1-4 and Comparative Examples 1-3

[0065]

[0066]

[0067] It can be seen from the data in Table 1 above that when the amount of water-soluble ionic liquid is 5 parts and the alkali urea system is 100 parts, the ratio of water-soluble ionic liquid to alkali urea system is optimal, a supramolecular network is formed, and the resulting hydrogel has the best mechanical properties, with an elongation at break of 380% and a breaking strength of 9.7 MPa. Comparing the data of Comparative Example 1 and Comparative Example 2, when no water-soluble ionic liquid or alkali urea system is added, the mechanical properties of the prepared hydrogel do not meet the requirements at all. This also shows that the water-soluble ionic liquid and the alkali urea system are indispensable components of the present invention.

[0068] The hydrogels prepared in Examples 1-4 and Comparative Examples 1-3 were subjected to freezing resistance tests.

[0069] Table 2 Test results of the freezing resistance of hydrogels obtained in Examples 1-4 and Comparative Examples 1-3

[0070] Freezing temperature resistance (℃) Example 1 -60 Example 2 -55 Example 3 -56 Example 4 -52 Comparative Example 1 -5 Comparative Example 2 -5 Comparative Example 3 -20

[0071] According to the data in Table 2 above and Figure 2 It can be seen that the hydrogel prepared by the present invention has excellent low-temperature resistance and can continue to be used at a low temperature of -60°C. Although the present invention uses water as a medium, it still has good low-temperature resistance. Compared with the prior art and comparative examples 1-3, the low-temperature resistance is at least improved by 2 times.

[0072] The hydrogel prepared in Example 1 was placed in different solvents for conductivity testing. The hydrogel prepared in Example 1 was conductive in water, ethanol, n-hexane, petroleum ether and tetrahydrofuran. The test results are shown in FIG. Figure 1 As shown by Figure 1 It can be seen that the hydrogel prepared in the present invention has the special property of being conductive in a solvent.

[0073] The mechanical properties of the hydrogels prepared in Example 1, Example 2, Example 4 and Comparative Example 1 were tested under different acid and alkaline conditions. The test results are shown in Table 3.

[0074] Table 3 Mechanical properties test results of hydrogels obtained in Example 1, Example 2, Example 4 and Comparative Example 1 under different acid and alkaline conditions

[0075]

[0076] The test results in Table 3 show that, first, the elongation at break and the breaking strength of the hydrogels of each embodiment do not change much under different acid and alkaline conditions, while the elongation at break and the breaking strength of the hydrogel in Comparative Example 1 decrease by about 50% and about 80% respectively under different acid and alkaline conditions, indicating that the present invention has excellent acid and alkali resistance. Secondly, when the amount of water-soluble ionic liquid is 5 parts, the mechanical properties still maintain the best performance.

[0077] The hydrogels prepared in Example 1, Example 2, Example 4 and Comparative Example 1 were immersed in different solvents for 60 days to test their mass change rates. Figure 3 It can be seen that the mass change rate of the hydrogel prepared in Example 1 in each solvent is the smallest, while the mass change rate of the hydrogel prepared in Comparative Example 1 in each solvent is the largest.

[0078] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for preparing a cold-resistant, acid-resistant, and alkali-resistant conductive and tough hydrogel, characterized in that: The preparation method comprises: (1) dissolving carbon nanofibers at -22°C to -16°C using an alkali-urea system to obtain a solution A, freezing the solution A at -22°C to -16°C for 22-28 hours to obtain a solution B, wherein the alkali-urea system is an aqueous solution containing an alkali and urea; (2) adding polyvinyl alcohol and a water-soluble ionic liquid to deionized water, heating and stirring at 95-100° C. for 1-2 hours to obtain solution C; (3) After returning solution B to room temperature, mixing it with solution C and stirring for 1-2 seconds, and then subjecting it to multiple cycles of freezing and thawing, a high-performance hydrogel can be obtained; There is no time sequence restriction for steps (1) and (2).

2. The method for preparing a cold-resistant, acid-resistant, and alkali-resistant conductive and tough hydrogel according to claim 1, characterized in that: Calculated by mass, the usage ratio of the alkali urea system, carbon nanofiber, polyvinyl alcohol, water-soluble ionic liquid and deionized water is 100:1-5:10-40:1-8:70-85.

3. The method for preparing a cold-resistant, acid-resistant, and alkali-resistant conductive and tough hydrogel according to claim 1 or 2, characterized in that: Calculated by mass, the usage ratio of the alkali urea system, carbon nanofiber, polyvinyl alcohol, water-soluble ionic liquid and deionized water is 100:1:20:5:

80.

4. The method for preparing a cold-resistant, acid-resistant, and alkali-resistant conductive and tough hydrogel according to claim 1 or 2, characterized in that: Calculated by mass fraction, the alkaline urea system in step (1) is composed of 7%-20% NaOH, 12%-40% urea and 40%-81% H2O.

5. The method for preparing a cold-resistant, acid-resistant, and alkali-resistant conductive and tough hydrogel according to claim 1, characterized in that: The preparation process of solution A in step (1) is specifically as follows: freezing the alkaline urea system at -22°C to -16°C for 22-28 hours, then adding carbon nanofibers to the alkaline urea system and stirring and dissolving them in a 0°C ice water bath to obtain solution A.

6. The method for preparing a cold-resistant, acid-resistant, and alkali-resistant conductive and tough hydrogel according to claim 1, characterized in that: The water-soluble ionic liquid in step (2) is 1-butyl-3-methylimidazolium tetrafluoroborate.

7. The method for preparing a cold-resistant, acid-resistant, and alkali-resistant conductive and tough hydrogel according to claim 1, characterized in that: In the step (3), the freezing temperature each time is between -24°C and -18°C, and the thawing temperature each time is room temperature.

8. The method for preparing a cold-resistant, acid-resistant, and alkali-resistant conductive and tough hydrogel according to claim 1, characterized in that: In the step (3), the freezing time is 8-28 hours each time, and the thawing time is 3-8 hours each time.

9. The method for preparing a cold-resistant, acid-resistant, and alkali-resistant conductive and tough hydrogel according to claim 1, characterized in that: The number of freeze-thaw cycles in step (3) is 3 times.

10. A hydrogel prepared by the method for preparing a hydrogel according to any one of claims 1 to 9.

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