Liquid metal hydrogel and preparation method and use thereof

Abstract

The present application relates to the field of hydrogel materials, and particularly relates to a liquid metal hydrogel as well as a preparation method and application thereof. The present application is prepared by using liquid metal microspheres to initiate copolymerization of vinyl monomers, and using hydrophobic association to form a physical crosslinking network; meanwhile, the liquid metal microspheres are coordinated and complexed with a polymer matrix rich in hydroxyl groups to form another physical crosslinking network, thereby obtaining a hydrogel with double physical crosslinking networks. The liquid metal hydrogel has multiple physical crosslinking centers, and the liquid metal microspheres can be deformed, so that the liquid metal hydrogel has excellent mechanical properties, self-recovery performance, self-healing performance and notch resistance. In addition, the liquid metal hydrogel has excellent electrical conductivity and photothermal properties, and the sensitivity coefficient (GF) is 7.21 after stretching more than 400%. The liquid metal hydrogel of the present application can be used in the fields of intelligent sensing, human-computer interaction and infrared camouflage.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of hydrogel materials, in particular to a liquid metal hydrogel and a preparation method and use thereof. BACKGROUND

[0002] Hydrogel is a kind of soft material with three-dimensional network structure composed of hydrophilic polymer chains and a large number of water molecules (50%-90%), which is a kind of cross-linked polymer with three-dimensional network structure. By introducing ions, conductive polymers or conductive fillers, hydrogel can realize conductivity, and is expected to be used in intelligent sensors, electronic skin, wearable devices and implantable devices. However, due to the inherent rigidity of the conjugated structure of the conductive polymer, the incompatibility of the conductive filler with the hydrogel matrix, and the salting-out effect, the mechanical properties of most current conductive hydrogels are poor, for example, poor toughness, low tensile strength, and poor self-healing performance, which greatly limits the application fields of hydrogels, such as intelligent sensors and electronic skin.

[0003] The current effective way to toughen the conductive hydrogel is to construct a double network, introduce sacrificial bonds or add rigid fillers. Rong Ran group (RSC Advances, Volume 6, November 2016, Pages 11268-112476) uniformly mixed polyvinyl alcohol and polyacrylamide in one pot, and used the strong hydrogen bond between polyvinyl alcohol and polyacrylamide and the microcrystals after freezing and thawing of polyvinyl alcohol to improve the mechanical strength of the hydrogel. The double network hydrogel prepared has excellent self-healing performance, but the toughness is general. Guanghui Gao group (Chemistry of Materials, Volume 31, November 2019, Pages 9522-9531) added mixed latex particles to the physically cross-linked hydrogel, introducing dynamic physical cross-linking centers, and the prepared hydrogel has excellent mechanical properties, but the self-healing performance is general, and the softness of the soft material is sacrificed. SUMMARY

[0004] One of the purposes of the present application is to provide a preparation method of liquid metal hydrogel, which uses the initiation effect of liquid metal microspheres on vinyl monomers and the coordination complexation of the surface oxides of liquid metal microspheres with hydroxyl groups to solve the structural defects of hydrogel, and designs and prepares a liquid metal hydrogel with multiple physical cross-linking, which has excellent mechanical properties, self-recovery performance, self-healing performance, notch resistance and conductivity.

[0005] To achieve the above purpose, the technical scheme adopted by the present application is as follows: a preparation method of liquid metal hydrogel, comprising the following steps:

[0006] S1. A hydroxyl-rich polymer matrix is ​​uniformly dispersed in deionized water to obtain a polymer aqueous solution with a concentration of 5-20 wt%.

[0007] S2. Sodium dodecyl sulfate and sodium chloride are added to water to obtain an amphiphilic solution. Liquid metal microspheres are then added and uniformly dispersed to obtain a liquid metal microsphere dispersion. The mass ratio of sodium dodecyl sulfate, sodium chloride and liquid metal microspheres is (2-3):1:(1-3). The concentration of liquid metal microspheres in water is 34-86 mg / mL.

[0008] S3. Mix and stir the polymer aqueous solution from step S1, the liquid metal microsphere dispersion from step S2, the hydrophobic monomer, and the vinyl monomer (excluding the hydrophobic monomer) to obtain a hydrogel solution; the mass ratio of the hydroxyl-rich polymer matrix, the hydrophobic monomer, and the vinyl monomer (excluding the hydrophobic monomer) in the hydrogel solution is (3-21):1:(20-21), and the mass ratio of the hydroxyl-rich polymer matrix to the liquid metal microspheres is 10:(6-15);

[0009] S4. The hydrogel solution is pre-cured and cured sequentially, and then the freeze-thaw cycle is repeated to obtain liquid metal hydrogel.

[0010] Steps S1 and S2 are not in any particular order.

[0011] Further improvements to the preparation method of liquid metal hydrogels:

[0012] Preferably, the hydroxyl-rich polymer matrix in step S1 is one or a combination of two or more of polyvinyl alcohol, gelatin, starch, gum arabic, and carboxymethyl cellulose.

[0013] Preferably, the hydroxyl-rich polymer matrix in step S1 is one or a combination of two or more of polyvinyl alcohol, gelatin, starch, gum arabic, and carboxymethyl cellulose.

[0014] Preferably, the liquid metal microspheres in step S2 are one or a combination of two or more of gallium indium alloy microspheres, gallium microspheres, and gallium indium tin microspheres.

[0015] Preferably, the hydrophobic monomer in step S3 is one or a combination of two or more of octadecyl methacrylate, lauryl methacrylate, and hexadecyl dimethyl allyl ammonium chloride, and the vinyl monomer other than the hydrophobic monomer is one or a combination of two or more of acrylamide, methacrylamide, acrylic acid, and methacrylic acid.

[0016] Preferably, the temperature of the hydroxyl-rich polymer matrix in step S1 is 65-95℃, and the time is 3-5 hours; the temperature of the amphiphilic solution in step S2 is 30-45℃, and the time is 1-3 hours; the liquid metal microspheres are uniformly dispersed in the amphiphilic solution by ultrasonic dispersion, the ultrasonic power is 30-90W, and the ultrasonic time is 10-30 minutes.

[0017] Preferably, the speed of mixing and stirring in step S3 is 300-700 rad / min, and the time is 7-20 minutes.

[0018] Preferably, the temperature of the pre-solidification in step S4 is 30-60℃, and the time is 7-20 minutes; the temperature of the solidification is 30-45℃, the humidity is 75-95%, and the time is 24-48 hours.

[0019] Preferably, the temperature of the freezing in step S4 is -5 to -20℃, and the time is 12-21 hours; the temperature of the thawing is 30-45℃, and the time is 3-6 hours; one freezing and one thawing is one cycle, and the cycle number is 2-6.

[0020] The second object of the present application is to provide a liquid metal hydrogel prepared by the above preparation method.

[0021] The third object of the present application is to provide a use of the above liquid metal hydrogel in the fields of intelligent sensing, human-computer interaction and infrared camouflage.

[0022] The present application has the following beneficial effects compared with the prior art:

[0023] 1) Compared with the traditional two-step method for preparing double-network hydrogels, the present application uses a one-pot method to design and prepare a liquid metal hydrogel with multiple physical cross-linking, which is simpler to operate and easier to control. The specific steps include:

[0024] The hydroxyl-rich polymer matrix is uniformly dispersed in deionized water to obtain a polymer aqueous solution. The hydroxyl groups can coordinate and chelate with Ga 3+ on the surface of the liquid metal microspheres, and the polymer will be adsorbed on the surface of the liquid metal microspheres, as shown in Figure 2 (a);

[0025] Sodium dodecyl sulfate and sodium chloride are uniformly dispersed in water to obtain an amphiphilic solution that can dissolve hydrophobic monomers, and then liquid metal is added and dispersed by ultrasonic dispersion to obtain a liquid metal dispersion;

[0026] The high molecular aqueous solution, liquid metal microsphere dispersion, hydrophobic monomer octadecyl methacrylate copolymerization and vinyl monomer except hydrophobic monomer are mixed and stirred uniformly, pre-solidified, poured into a mold and then solidified. During the pre-solidification process, the hydroxyl group can coordinate with Ga in the oxide layer on the surface of the liquid metal microsphere 3+ , the high molecule will be adsorbed on the surface of the liquid metal microsphere to form a physical cross-linking Figure 2 (a). At the same time, the liquid metal microsphere initiates the copolymerization of the vinyl monomer and the hydrophobic monomer octadecyl methacrylate, as shown in Figure 1 . A large number of high molecular chains grow on the surface of the liquid metal microsphere, so that cross-linking is formed in situ. In addition, sodium dodecyl sulfate and the hydrophobic segment form hydrophobic association, which further cross-links the high molecular chains obtained by copolymerization Figure 2 (b). Therefore, the viscosity of the hydrogel solution increases after pre-solidification, which improves the stability of the liquid metal microspheres in the hydrogel solution. The solidification makes the monomers fully polymerize, improves the degree of polymerization and cross-linking, and improves the mechanical properties of the liquid metal hydrogel.

[0027] Then the freeze-thaw cycle is carried out again, and the freeze-thaw cycle can promote the formation of hydrogen bonds of the high molecular chain rich in hydroxyl groups, further improve the performance of the liquid metal hydrogel, and finally obtain the liquid metal hydrogel.

[0028] 2) Compared with traditional toughening fillers (carbon materials, ceramic nanoparticles, rigid metal particles), the liquid metal microspheres used in the application can in situ initiate copolymerization of vinyl monomers while toughening, and form a cross-linking network by cooperating with hydrophobic association; the oxide on the surface of the liquid metal microsphere can coordinate with the hydroxyl group in the high molecular matrix rich in hydroxyl groups to form another physical cross-linking network in the high molecular rich in hydroxyl groups.

[0029] The multiple physical cross-linking gives the liquid metal hydrogel excellent tensile properties, with an elongation at break of 2000%, which exceeds most of the reported hydrogels. In addition to the multiple physical cross-linking, the liquid metal microspheres also need to consume energy when deforming, so the liquid metal hydrogel has excellent toughness (3.00 MJ / m 3 ) and notch resistance. The physical cross-linking can be rebuilt after being destroyed, and the deformed liquid metal microspheres can also restore to the original state, so the liquid metal hydrogel has excellent self-recovery and self-healing properties. The liquid metal hydrogel stretched by 400% recovers by 70% at room temperature for 1 hour; the cut liquid metal hydrogel heals by more than 99% at room temperature for 24 hours. The liquid metal hydrogel has a sensitivity coefficient of 7.21 after being stretched by 400%, which exceeds most of the reported hydrogels.

[0030] 3) Compared with traditional photoinitiator, the liquid metal microspheres used in the present application can be used in composite hydrogel system. Traditional photoinitiator can only be used for the preparation of transparent hydrogel, while the addition of nanofiller often changes the color of hydrogel, and the photoinitiator cannot play a role. Compared with conventional rigid particles, the liquid metal microspheres of the present application can maintain the soft characteristics of soft materials while toughening the hydrogel, and the conventional rigid particles often affect the modulus of the hydrogel while toughening the hydrogel. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 Chemical equation for liquid metal microspheres to initiate copolymerization of vinyl monomers.

[0032] Figure 2 Structure diagram of two networks in liquid metal hydrogel, wherein figure (a) is the crosslinked network formed by hydroxyl-rich polymers and liquid metal microspheres, and figure (b) is the crosslinked network formed by in-situ crosslinking of liquid metal to initiate copolymerization of vinyl monomers and hydrophobic association.

[0033] Figure 3 Stress-strain curves of polyvinyl alcohol / polyacrylamide double network hydrogel prepared in the comparative example and liquid metal hydrogel prepared in examples 1-4.

[0034] Figure 4 Stress-strain curves of liquid metal hydrogel prepared in example 3 after healing at 25℃ and 95% humidity for different times.

[0035] Figure 5 Relationship curve between resistance change and strain of liquid metal hydrogel prepared in example 3.

[0036] Figure 6 Relationship between photothermal temperature and laser power of liquid metal hydrogel prepared in example 3.

[0037] Figure 7 Use display diagram of liquid metal hydrogel prepared in example 3. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the present application more clear and obvious, the present application will be further described in detail below in combination with examples. All other examples obtained by those skilled in the art without creative labor on the basis of the examples in the present application belong to the scope of protection of the present application.

[0039] Comparative example

[0040] The present comparative example provides a preparation method of polyvinyl alcohol / polyacrylamide double network hydrogel, comprising the following steps:

[0041] S1, uniformly disperse polyvinyl alcohol in deionized water to obtain a polyvinyl alcohol aqueous solution with a concentration of 10 wt%;

[0042] S2, add 0.8000 g of sodium dodecyl sulfate and 0.2923 g of sodium chloride to 10 ml of water to obtain an amphiphilic solution;

[0043] S3, add 5.7250 g of the polyvinyl alcohol aqueous solution obtained in step S1, 0.1364 g of hydrophobic monomer octadecyl methacrylate, 2.8636 g of acrylamide, and 0.0913 g of photoinitiator 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropanone to the amphiphilic solution, and stir to disperse uniformly to obtain a hydrogel solution;

[0044] S4, place the hydrogel solution under a 1 KW 395 nm ultraviolet lamp for curing for 30 minutes, then freeze at -15°C for 12 hours, take out and thaw at 95% humidity and 35°C for 3 hours; repeat the freezing and thawing process twice to obtain a liquid metal hydrogel.

[0045] Example 1

[0046] The present embodiment provides a method for preparing a liquid metal hydrogel, which specifically comprises the following steps:

[0047] S1, uniformly disperse polyvinyl alcohol in deionized water to obtain a polyvinyl alcohol aqueous solution with a concentration of 10 wt%;

[0048] S2, add 0.8000 g of sodium dodecyl sulfate and 0.2923 g of sodium chloride to 10 ml of water to obtain an amphiphilic solution; then add 0.3435 g of gallium-indium alloy and ultrasonically disperse for 15 minutes at a power of 75 W to obtain a gallium-indium alloy microsphere dispersion liquid;

[0049] S3, take 5.7250 g of the polyvinyl alcohol aqueous solution prepared in step S1, and add 0.1364 g of hydrophobic monomer octadecyl methacrylate and 2.8636 g of acrylamide thereto, and add the gallium-indium alloy microsphere dispersion liquid during stirring to obtain a hydrogel solution;

[0050] S4, pre-cure the hydrogel solution at 45°C for 15 minutes, then pour it into a mold and cure at 95% humidity and 35°C for 24 hours; freeze the cured sample at -15°C for 12 hours, take it out and thaw at 95% humidity and 35°C for 3 hours, repeat the freezing and thawing process twice to obtain liquid metal hydrogel 1.

[0051] wherein Figure 1 is the chemical equation for the copolymerization of the vinyl monomer initiated by the liquid metal microspheres. Figure 2Schematic diagram of two networks in liquid metal hydrogel, in which (a) is the crosslinked network formed by hydroxyl-rich polymer and liquid metal microspheres. (b) is the crosslinked network formed by in-situ copolymerization of liquid metal triggered vinyl monomer and hydrophobic association.

[0052] Example 2

[0053] This example provides a preparation method of liquid metal hydrogel, and the specific steps refer to Example 1, and the only difference is that “0.4580 g of gallium-indium alloy is added” in step S1, and liquid metal hydrogel 2 is prepared.

[0054] Example 3

[0055] This example provides a preparation method of liquid metal hydrogel, and the specific steps refer to Example 1, and the only difference is that “0.5725 g of gallium-indium alloy is added” in step S1, and liquid metal hydrogel 3 is prepared.

[0056] Example 4

[0057] This example provides a preparation method of liquid metal hydrogel, and the specific steps refer to Example 1, and the only difference is that “0.8588 g of gallium-indium alloy is added” in step S1, and liquid metal hydrogel 4 is prepared.

[0058] The polyvinyl alcohol / polyacrylamide double network hydrogel prepared in the comparative example and the liquid metal hydrogels prepared in Examples 1-4 are cut into samples with a length of 60 mm, a width of 5 mm, and a thickness of 2 mm, and stretched at a speed of 50 mm / min under an electronic universal testing machine to obtain the stress-strain curves of each group of samples, as shown in Figure 3 Figure 3 In the above table, LM Hydrogel-0 is the polyvinyl alcohol / polyacrylamide double network hydrogel prepared in the comparative example; LM Hydrogel-n is the liquid metal hydrogel prepared in Examples 1-4, and n is the mass ratio of liquid metal to polyvinyl alcohol. As the mass of the liquid metal microspheres increases, the Young's modulus and the breaking strength of the liquid metal hydrogel decrease, and the liquid metal hydrogel becomes softer and softer, which is caused by the flexibility of the liquid metal; however, the breaking elongation of the liquid metal hydrogel first increases and then decreases, and when the mass ratio of the liquid metal to the polyvinyl alcohol is 1.0, the breaking elongation of the liquid metal hydrogel reaches 2000%, and the toughness reaches 3.00 MJ / m 3 , which is due to the good interaction between the liquid metal microspheres and the hydrogel network.

[0059] The liquid metal hydrogel prepared in Example 3 has the most excellent mechanical properties when the mass ratio of the liquid metal to the polyvinyl alcohol is 1.0. The secondary group of liquid metal hydrogels is used to characterize the self-healing performance, as shown in​Figure 4 As shown, under the condition of temperature 25℃ and humidity 95%, the liquid metal hydrogel gradually healed with the extension of time, and the stress-strain curve gradually recovered. After 24 hours, the healing efficiency of the liquid metal hydrogel was more than 99%. The liquid metal hydrogel was mainly physically cross-linked, and the broken physical cross-linking points could recombine after the sample pieces contacted with each other; at the same time, due to the fluidity of the liquid metal, the broken liquid metal microspheres could also recombine, so the liquid metal hydrogel had excellent self-healing performance.

[0060] The liquid metal hydrogel prepared in Example 3 was cut into a sample piece with a length of 60 mm, a width of 5 mm and a thickness of 2 mm, and the gauge factor (GF) of the liquid metal hydrogel in the tensile process was tested, as shown in Figure 5 As shown, within 400% stretching, the GF of the liquid metal hydrogel was 3.42; after stretching more than 400%, the GF of the liquid metal hydrogel was 7.21, which exceeded most of the reported hydrogels. In addition, the liquid metal microspheres endowed the hydrogel with good photothermal effect, as shown in Figure 6 As shown, with the increase of the power of 808 nm near-infrared laser, the temperature after irradiation for 30 seconds also increased. In summary, the liquid metal hydrogel was expected to be used in the fields of intelligent sensing, human-computer interaction and infrared camouflage, as shown in Figure 7

[0061] Those skilled in the art should understand that the above description is only some specific embodiments of the present application, not all embodiments. It should be noted that many modifications and improvements can also be made by those skilled in the art, and all modifications and improvements that do not exceed the scope of the claims should be considered as the protection scope of the present application.​

Claims

1. A method for preparing a liquid metal hydrogel, characterized in that, The method comprises the following steps: S1, uniformly dispersing a hydroxyl-rich polymer matrix in deionized water to obtain a polymer aqueous solution with a concentration of 5-20 wt%; S2, adding sodium dodecyl sulfate and sodium chloride to water to obtain an amphiphilic solution, and then uniformly dispersing liquid metal microspheres to obtain a liquid metal microsphere dispersion, wherein the mass ratio of sodium dodecyl sulfate, sodium chloride and liquid metal microspheres is (2-3):1:(1-3), and the addition concentration of the liquid metal microspheres in water is 34-86 mg / mL; the liquid metal microspheres are one of gallium-indium alloy microspheres, gallium microspheres and gallium-indium-tin microspheres or a combination of two or more thereof; S3, mixing and uniformly stirring the polymer aqueous solution of step S1, the liquid metal microsphere dispersion of step S2, a hydrophobic monomer and a vinyl monomer other than the hydrophobic monomer to obtain a hydrogel solution; the mass ratio of the hydroxyl-rich polymer matrix, the hydrophobic monomer and the vinyl monomer other than the hydrophobic monomer in the hydrogel solution is (3-21):1:(20-21), and the mass ratio of the hydroxyl-rich polymer matrix and the liquid metal microspheres is 10:(6-15); S4, sequentially performing pre-curing and curing on the hydrogel solution, and then cyclically performing freezing and thawing to obtain a liquid metal hydrogel; Steps S1 and S2 are not in a specific order.

2. The method of claim 1, wherein the liquid metal hydrogel is prepared by the steps of: The hydroxyl-rich polymer matrix in step S1 is one of polyvinyl alcohol, gelatin, starch, gum arabic and carboxymethyl cellulose or a combination of two or more thereof.

3. The method for preparing liquid metal hydrogel according to claim 1, characterized in that, The hydrophobic monomer in step S3 is one of octadecyl methacrylate, lauryl methacrylate and hexadecyl dimethyl allyl ammonium chloride or a combination of two or more thereof, and the vinyl monomer other than the hydrophobic monomer is one of acrylamide, methacrylamide, acrylic acid and methacrylic acid or a combination of two or more thereof.

4. The method of claim 1, wherein the liquid metal hydrogel is prepared by the steps of: The temperature for dispersing the hydroxyl-rich polymer matrix in deionized water in step S1 is 65-95°C, and the time is 3-5 hours; the temperature for preparing the amphiphilic solution in step S2 is 30-45°C, and the time is 1-3 hours; the liquid metal microspheres are uniformly dispersed in the amphiphilic solution by ultrasonic treatment in step S2, the ultrasonic power is 30-90 W, and the ultrasonic time is 10-30 minutes.

5. The method for preparing liquid metal hydrogel according to claim 1, characterized in that, The mixing and stirring speed for preparing the hydrogel solution in step S3 is 300-700 rad / min, and the time is 7-20 minutes.

6. The method of claim 1, wherein the liquid metal hydrogel is prepared by the steps of: The pre-curing temperature in step S4 is 30-60°C, and the time is 7-20 minutes; the curing temperature is 30-45°C, the humidity is 75-95%, and the time is 24-48 hours.

7. The method of claim 1, wherein the liquid metal hydrogel is prepared by the steps of: a) providing a liquid metal; b) providing a polymer solution; c) mixing the liquid metal and the polymer solution to form a liquid metal hydrogel. The freezing temperature in step S4 is -5 to -20°C, the time is 12-21 hours; the thawing temperature is 30-45°C, and the time is 3-6 hours; one cycle of freezing and thawing is one cycle of freezing and thawing, and the cycle number is 2-6.

8. A liquid metal hydrogel prepared by the method of any one of claims 1-7.

9. Use of the liquid metal hydrogel of claim 8 in the fields of intelligent sensing, human-computer interaction and infrared camouflage.

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