Preparation method of a shell-mimicking liquid metal-sodium alginate-aragonite nanoplate nanocomposite bulk material

Abstract

The present invention relates to a method for preparing a shell-mimicking liquid metal-sodium alginate-aragonite nanocomposite bulk material. The present invention combines a doctor blade coating method and a hot pressing method, and utilizes the synergistic effect of interfacial action and shear force to prepare a shell-mimicking liquid metal-sodium alginate-aragonite nanocomposite bulk material (conductive shell), thereby improving the degree of orientation and increasing the density of the composite material, and synergistically improving the stress transfer efficiency. Therefore, the shell-mimicking liquid metal-sodium alginate-aragonite nanocomposite bulk material prepared by the present invention has a flexural strength of 231 MPa and a fracture toughness of 5.09 MPa·m<supgt;1 / 2< / supgt;. In addition, the electrical conductivity of the composite bulk material reaches 9×10<supgt;‑< / supgt;<supgt;4< / supgt; Sm<supgt;‑1< / supgt>, and it can be used for in-situ monitoring of the structural integrity of the composite material. The artificial shell preparation strategy proposed by the present invention is simple and efficient, the material source is simple, and it is easy to realize large-scale preparation.

Description

Technical Field

[0001] The present invention relates to a preparation method of a nacre-mimicking liquid metal-sodium alginate-aragonite nanocomposite bulk material, belonging to the field of preparation of nanocomposites. Background Art

[0002] Natural nacre is composed of 95 vol% aragonite-phase calcium carbonate platelets and 5 vol% bioorganic polymers stacked alternately. Due to the multi-scale highly ordered "brick-mortar" layered structure and the synergistic interfacial interaction, the crack propagation is effectively blocked, endowing nacre with excellent toughness. Due to the mechanical property difference between natural nacre and aragonite platelets, it has attracted extensive attention of researchers. At present, researchers have prepared calcium carbonate (CaCO3) / polymer layered structure composites through biomineralization, but their poor mechanical properties make it difficult for the film to be self-supporting (Angew. Chem. Int. Edit. 2005, 44, 6571 - 6575). In order to further mimic the structure of nacre, an organic scaffold was obtained by etching CaCO3 in nacre and remineralized to obtain a layered composite material, but its mechanical properties were still low (Cryst. Growth Des. 2011, 11, 729 - 734). Until recently, researchers combined layer-by-layer assembly and biomineralization techniques to prepare a series of self-supporting layered composites. For example, Finnemore et al. used a porous film obtained by layer-by-layer deposition as an organic matrix to mediate the growth of CaCO3 and successfully fabricated an artificial nacre with iridescence. However, since these calcium carbonates are calcite-type or polycrystalline, their mechanical properties are lower than those of natural nacre (Nat. Commun. 2012, 3, 966). Different from the in-situ growth of calcium carbonate single crystals, Li et al. synthesized sheet-like CaCO3 single crystals and obtained CaCO3 / gelatin composite film materials by evaporation-induced self-assembly method, but their tensile strength and Young's modulus are still lower than those of natural nacre (Adv. Mater. 2012, 24, 6277 - 6282). Mao et al. used the ice-templating method to assemble chitosan into a layered structure, then acetylated it and mimicked the biomineralization process to mineralize the skeleton, and obtained an artificial nacre bulk material with structural and mechanical properties close to those of natural nacre by hot pressing (Science, 2016, 354, 107 - 110). On this basis, Meng et al. introduced iron oxide particles to balance the residual stress in the platelets and improve the fracture toughness of the artificial nacre bulk (~3.5 MPa·m 1 / 2 )(Adv. Mater. 2022, 34, 2108267). In addition, most of these preparation processes are difficult to control the crystal form of calcium carbonate and are relatively cumbersome, which is not conducive to sustainable development. At the same time, the weak interfacial interaction leads to poor mechanical properties, especially the lack of functional characteristics, which greatly limits their development and practical applications.

[0003] Currently, the relevant patents on shell-mimicking composite materials include: a sodium alginate-cellulose nanocrystal-calcium carbonate ternary nanocomposite material and its preparation method (CN113265091A), a biomimetic ceramic matrix material based on the optimization of nanoscale residual strain and its preparation method (CN110408087B), a nanocellulose-mica sheet composite board and its preparation method (CN112094439A), a three-dimensional shell-mimicking structural material and its preparation method (CN108912602B), a composite material with a shell-mimicking nacreous layer structure and its preparation method and application (CN105774182A), a bulk biomimetic material and its preparation method and application (CN105079887A), a shell-mimicking lightweight and high-strength composite material and its preparation method (CN112266497B), a wood fiber-based composite material with a shell-mimicking nacreous layer structure and its preparation method (CN110978679B), etc. However, these patents have problems such as complex preparation processes, high costs, weak interfacial interactions, and lack of functional characteristics. Therefore, developing a large-scale preparation strategy for shell-mimicking structure-functional integrated materials with rich and sustainable raw material sources is of great significance for the practical applications in this field. Summary of the Invention

[0004] The technical problem to be solved by the present invention: Overcoming the deficiencies of the prior art, providing a preparation method for a shell-mimicking liquid metal-sodium alginate-aragonite sheet nanocomposite block material, which can successfully prepare a shell-mimicking liquid metal-sodium alginate-aragonite sheet nanocomposite block material with high strength, high toughness, and electrical conductivity.

[0005] The present invention provides a bottom-up assembly method. Through the shear force generated by the doctor blade method, the aragonite sheets are induced to be oriented and arranged, and the ionic bond interfacial synergistic effect between the gallium ions of the liquid metal nanoparticles and the sodium alginate molecules is used to prepare a shell-mimicking liquid metal-sodium alginate-aragonite sheet nanocomposite block material with electrical conductivity and high mechanical properties. The flexural strength of the composite block material is 172 - 231 MPa, the fracture toughness is 4.52 - 5.54 MPa·m 1 / 2 , and the electrical conductivity is 1×10 -4 -9×10 -4 S m -1 . The improvement of the mechanical properties and electrical conductivity is mainly due to the high degree of orientation of the aragonite sheets (orientation factor is 0.893) and the ionic bond interaction between sodium alginate and gallium ions. At the same time, focused ion beam scanning electron microscopy (FIB-SEM) and wide-angle X-ray scattering (WAXS) tests show that the combination of liquid metal and SA improves the orientation of the aragonite sheets and reduces the voids between the aragonite sheets.

[0006] The present invention is realized through the following technical solutions: First, raw aragonite platelets are efficiently prepared from natural abalone shell nacre by a chemical exfoliation method; Second, a series of aragonite platelet-sodium alginate composite bulk materials with different aragonite platelet and sodium alginate contents are prepared by combining doctor blading and hot pressing techniques; Then, liquid metal nanoparticles are introduced through interfacial action, and the content of the liquid metal nanoparticles is regulated to prepare a shell-inspired liquid metal-sodium alginate-aragonite platelet nanocomposite bulk material with high mechanical properties and electrical conductivity characteristics.

[0007] The specific implementation steps of the present invention are as follows:

[0008] A preparation method of a shell-inspired liquid metal-sodium alginate-aragonite platelet nanocomposite bulk material, comprising the following steps:

[0009] (1) Raw aragonite platelets are exfoliated from abalone shell nacre using an alkali / urea / water system and dispersed in an aqueous solution; Then, the aragonite platelets are surface-modified with coupling agent molecules, and the modified aragonite platelets are added to deionized water to obtain an aragonite platelet aqueous dispersion.

[0010] (2) Weigh sodium alginate and dissolve it in deionized water to prepare a sodium alginate solution.

[0011] (3) Bulk liquid metal is ultrasonically treated in an aqueous solution containing hydrochloric acid dopamine to obtain a stable aqueous dispersion of polydopamine-coated liquid metal nanoparticles.

[0012] (4) The aragonite platelet aqueous dispersion, the polydopamine-coated liquid metal nanoparticle aqueous dispersion, and the sodium alginate solution obtained in step (1) are mixed and stirred to obtain a liquid metal-sodium alginate-aragonite platelet homogeneous dispersion.

[0013] (5) The liquid metal-sodium alginate-aragonite platelet mixed solution obtained in step (4) is assembled by doctor blading and then dried to obtain a composite film.

[0014] (6) The composite film obtained in step (5) is cut and stacked, wetted, crosslinked, and then hot pressed to obtain a shell-inspired liquid metal-sodium alginate-aragonite platelet nanocomposite bulk material.

[0015] In the present invention, the alkali / urea / water system refers to a mixture of alkali, urea, and water.

[0016] Further, in the step (1), the preparation process of the aragonite sheet aqueous dispersion is as follows: Use a cutting machine and sandpaper to grind off the horny layer and prismatic layer of the nacre of the abalone shell to obtain nacre. After crushing the nacre, add it to an aqueous solution containing a certain proportion of urea / sodium hydroxide / water, and control the mass ratio of sodium hydroxide to urea between 30 - 80%. Stir for 1 - 5 days, filter to obtain a precipitate, then wash and filter the precipitate repeatedly with deionized water, and vacuum dry to obtain aragonite sheet powder; among them, the mass ratio of sodium hydroxide to urea is controlled at 50%, and the stirring time is 2 days; Use a silane coupling agent to modify the surface of the aragonite sheet, where the concentration of the silane coupling agent is 0.5wt% - 10wt%, the solvent is a mixed solution of ethanol and water, and the reaction time is 4 - 24 hours; among them, the selected silane coupling agent is 3-aminopropyltriethoxysilane, the concentration is 5wt%, and the reaction time is 10 hours. Finally, add the aragonite sheet powder to deionized water, and obtain the aragonite sheet aqueous dispersion through ultrasonic treatment and stirring.

[0017] Further, in the step (2), dissolve sodium alginate in deionized water with a concentration of 50mg / mL.

[0018] Further, in the step (3), add a liquid metal block to an aqueous solution of hydrochloric acid dopamine with a concentration of 2mg / mL, where the liquid metal is a gallium-indium alloy (EGaIn). By setting the ultrasonic power to 200 - 500W and the ultrasonic time to 1 - 4 hours, and then stirring at room temperature for 12 - 24 hours, obtain polydopamine-coated liquid metal nanoparticles with a particle size distribution of 200nm - 900nm and a concentration of the liquid metal nanoparticles of 0.5 - 1.5wt%.

[0019] Further, in the step (4), the concentration of the liquid metal-sodium alginate-aragonite sheet homogeneous dispersion is 60mg / mL - 120mg / mL, the mass ratio of the aragonite sheet to sodium alginate is 4:6 - 7:3, the content of the liquid metal nanoparticles is 0.5 - 3wt% of the total mass, and the stirring reaction time is 2 - 8 hours to make the reaction sufficient. Among them, the concentration of the liquid metal-sodium alginate-aragonite sheet homogeneous dispersion is 90mg / mL, the mass ratio of the aragonite sheet to sodium alginate is 6:4, and the content of the liquid metal nanoparticles is 2wt% of the total mass.

[0020] Further, in the step (5), prepare a composite film on a polyethylene terephthalate substrate by the doctor blade method, with a doctor blade speed of 10 - 200mm / s, a drying temperature of 30 - 60°C, a doctor blade height of 50 - 500μm, a doctor blade width of 4 - 20cm, and a length of 12 - 50cm. After drying, a composite film with a thickness of 5 - 20μm can be obtained.

[0021] Further, in step (6), the composite film is cut into films of the same size and stacked into multiple layers of films. After being wetted with an aqueous solution, it is preheated and pressed at a pressure of 1 - 10 MPa and a temperature of 30 - 60 °C for 0.5 - 6 hours to form a prefabricated block; the prefabricated block is soaked in a calcium chloride solution with a concentration of 1 - 10 mol / L for crosslinking for 1 - 8 hours. After the prefabricated block is washed with water, it is hot-pressed at a pressure of 25 - 100 MPa and a temperature of 60 - 100 °C for 8 - 72 hours to obtain a nacre-like liquid metal-sodium alginate-aragonite nanocomposite block material; wherein, in step (6), preferably, the pressure of the preheating and pressing is 5 MPa, the temperature is 60 °C, and the time is 1 hour. The hot-pressing pressure for obtaining the final block material is 75 MPa, the temperature is 90 °C, and the time is 24 hours.

[0022] Further, in step (6), a universal mechanical testing machine is used to test the flexural strength and fracture toughness of the block material. The flexural strength and fracture toughness of the nacre-like liquid metal-sodium alginate-aragonite nanocomposite block material are 231 MPa and 5.09 MPa·m 1 / 2 .

[0023] Further, a sample with a prefabricated notch is prepared from the nacre-like liquid metal-sodium alginate-aragonite nanocomposite block material obtained in step (6). The conductive copper wire is fixed at both ends of the sample with silver glue. By using a two-point probe device, the change in resistance of the prefabricated notch sample during the bending process is monitored in-situ to evaluate the structural integrity of the nanocomposite material.

[0024] Principle of the present invention: The present invention first uses natural aragonite sheets, which are rich in sources and sustainable, as assembly units, and constructs a nacre-like liquid metal-sodium alginate-aragonite nanocomposite block material through the interfacial synergistic effect by means of doctor blade coating and hot pressing techniques. The shear force induces the oriented arrangement of aragonite sheets, and the synergistic effect of the crosslinking of gallium ions and sodium alginate molecules between layers improves the degree of orientation and reduces the voids, thereby increasing the density of the composite material, synergistically improving the stress transfer efficiency. The flexural strength of the obtained block material reaches 231 MPa, and the fracture toughness reaches 5.09 MPa·m 1 / 2 . At the same time, since the conductivity of the block material is 9×10 -4 S m -1 , it can be used to monitor the structural integrity of the composite material in-situ.

[0025] Advantages of the present invention compared with the prior art:

[0026] (1) Developed a simple and efficient bionic multi-level assembly strategy to prepare a nacre-like liquid metal-sodium alginate-aragonite nanocomposite block material with high mechanical properties and functional characteristics;

[0027] (2) Compared with elementary materials such as graphene oxide or transition metal carbides / nitrides, the aragonite flakes used as the elementary material in the present invention are derived from the nacre of natural abalone shells. While increasing the added value of the shells, large-scale preparation can be achieved, promoting the further development and practical application of shell-mimicking materials; in addition, this strategy is also applicable to natural materials such as mussel shells, conch shells, scallop shells, etc., as well as mica and clay.

[0028] (3) Based on the electrical conductivity of the shell-mimicking liquid metal-sodium alginate-aragonite flake nanocomposite bulk material, the present invention can evaluate the structural integrity of the shell-mimicking composite material by real-time monitoring of the change in resistance, thereby monitoring the safety of the nanocomposite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of a preparation method of a shell-mimicking liquid metal-sodium alginate-aragonite flake nanocomposite bulk material according to the present invention. First, aragonite flakes are exfoliated from the nacre of natural abalone shells using an alkali / urea / water system; liquid metal nanoparticles coated with polydopamine are obtained by ultrasonic treatment of bulk liquid metal in an aqueous solution containing hydrochloric acid dopamine; then the aragonite flakes, polydopamine-coated liquid metal nanoparticles and sodium alginate solution are mixed evenly, and a large-area composite film is prepared by a doctor blade method; the film is cut into the same size and stacked into multiple layers, and a preform is obtained through wetting and pre-pressing; finally, it is cross-linked with calcium ions and hot-pressed to obtain a shell-mimicking liquid metal-sodium alginate-aragonite flake nanocomposite bulk material.

[0030] Figure 2 It is the morphology and structure characterization of aragonite flakes in the preparation method of a shell-mimicking liquid metal-sodium alginate-aragonite flake nanocomposite bulk material according to the present invention. a, Digital photograph of large-scale exfoliated aragonite flake powder; b, X-ray diffraction (XRD) pattern of aragonite flakes; c, Scanning electron microscope (SEM) image of aragonite flakes; d, Atomic force microscope (AFM) image of aragonite flakes and its thickness.

[0031] Figure 3This invention relates to the microstructure and mechanical properties of natural shells and a shell-mimicking liquid metal-sodium alginate-aragonite nanocomposite bulk material in the preparation method of the shell-mimicking liquid metal-sodium alginate-aragonite nanocomposite bulk material. a, Scanning electron microscope photograph of the fracture surface of natural nacre; b, Scanning electron microscope photograph of the fracture surface of the shell-mimicking liquid metal-sodium alginate-aragonite nanocomposite bulk material (conductive shell); c, Flexural stress-strain curves of natural shells, shell-mimicking sodium alginate-aragonite nanocomposite bulk materials (artificial shells), and shell-mimicking liquid metal-sodium alginate-aragonite nanocomposite bulk materials (conductive shells); d, R curve of fracture toughness versus crack length of natural shells, shell-mimicking sodium alginate-aragonite nanocomposite bulk materials (artificial shells), and shell-mimicking liquid metal-sodium alginate-aragonite nanocomposite bulk materials (conductive shells).

[0032] Figure 4 This invention relates to the electrical conductivity of natural shells and conductive shells and the self-monitoring application of conductive shells in the preparation method of a shell-mimicking liquid metal-sodium alginate-aragonite nanocomposite bulk material. a, Electrical conductivity of natural shells and conductive shells; b, In the first loading test of the conductive shell, when cracks began to form and expand, the resistance increased rapidly from a slow rise, and the load was removed before the sample was damaged; c, In the second loading test of the conductive shell, since cracks had already occurred in the sample during the first loading, the resistance increased sharply as the cracks expanded. Detailed implementation mode

[0033] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the protection scope of the present invention should include all the contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement all the contents of the claims of the present invention.

[0034] Figure 1 This invention relates to a schematic diagram of a preparation method of a shell-mimicking liquid metal-sodium alginate-aragonite nanocomposite bulk material. First, aragonite sheets are peeled from natural abalone nacre using an alkali / urea / water system; stable dispersed liquid metal nanoparticles coated with polydopamine are obtained by ultrasonic treatment of bulk liquid metal in an aqueous solution containing hydrochloric acid dopamine; then the aragonite sheets, polydopamine-coated liquid metal nanoparticles, and sodium alginate solution are mixed evenly, and a large-area composite film is prepared by a doctor blade method; the film is cut into the same size and stacked into multiple layers, and a preform is obtained through wetting and pre-pressing; after calcium ion cross-linking and cleaning, finally, a shell-mimicking liquid metal-sodium alginate-aragonite nanocomposite bulk material is obtained by hot pressing.

[0035] Example 1

[0036] The horny layer and prismatic layer of abalone shells were removed by using a cutting machine and a grinding and polishing machine to obtain nacre. After crushing the nacre, 100 g of nacre fragments were weighed and added to a mixed solution containing 80 g of sodium hydroxide, 160 g of urea, and 1000 mL of deionized water, and stirred for 2 days. After standing for 2 hours, the upper liquid was poured off, washed with deionized water, and the precipitate was obtained by suction filtration. This was repeated 5 - 6 times. The obtained precipitate was vacuum dried at 60 °C for 24 hours, and the resulting powder was as Figure 2 shown in a. The powder was aragonite platelets. As Figure 2 shown in b, a typical aragonite - type peak of (221) appeared in the X - ray diffraction (XRD, Bruker D8 Advance) pattern, and no calcite characteristic peak of (104) appeared. These results confirmed that the powder was aragonite - type calcium carbonate. Tests by scanning electron microscopy (SEM, HITACHI SU8010) and atomic force microscopy (AFM, MultiMode 8) showed that the aragonite platelet - type calcium carbonate powder was a single calcium carbonate sheet ( Figure 2 shown in c, d), with a thickness of ∼450 nm, which was close to the thickness of natural aragonite platelets. These results confirmed that the structure and morphology of the aragonite platelets after peeling did not change, further indicating that the aragonite platelets were successfully peeled by this method of the present invention.

[0037] Example 2

[0038] The aragonite flakes prepared in Example 1 were surface-modified with 3-aminopropyltriethoxysilane to enhance the interfacial interaction between the aragonite flakes and the polymer. Specifically: First, 3-aminopropyltriethoxysilane was dispersed in a mixed solution of ethanol and water (volume ratio 12:1). Based on the total mass of ethanol and water, the content of 3-aminopropyltriethoxysilane was 5 wt%. It was stirred and hydrolyzed for 1 h to obtain a hydrolysis solution. Then, the aragonite flakes prepared in Example 1 were dispersed in ethanol at a concentration of 10 wt%. The ethanol dispersion of aragonite flakes was added to the hydrolysis solution, and the mass ratio of aragonite flakes to 3-aminopropyltriethoxysilane was 10:1. It was stirred at 50 °C for 10 h; centrifuged at 3000 rpm for 10 min to obtain a precipitate, washed 5 times with ethanol, and the precipitate was obtained by centrifugation. The precipitate was vacuum-dried at 60 °C for 24 h to obtain modified aragonite flakes. 10 g of sodium alginate was weighed and added to 200 mL of water, and stirred to obtain a 50 mg / mL sodium alginate solution. Liquid metal blocks were added to an aqueous solution of hydrochloric acid dopamine with a concentration of 2 mg / mL. The liquid metal was a gallium-indium alloy (EGaIn) with a mass ratio of gallium to indium of 9:1. By setting the ultrasonic power to 300 W and the ultrasonic time to 2 h, and then stirring at room temperature for 24 h, polydopamine-coated liquid metal nanoparticles were obtained. The particle size distribution of the nanoparticles was 200 - 900 nm, and the concentration of the liquid metal nanoparticles was ~1 wt%. To prepare a biomimetic shell-like liquid metal-sodium alginate-aragonite flake nanocomposite bulk material (conductive shell), the modified aragonite flakes were dispersed in deionized water to obtain an aragonite flake aqueous solution with an aragonite flake content of 10 wt%. Then, the aragonite flake aqueous solution, the sodium alginate solution, and the polydopamine-coated liquid metal nanoparticle aqueous solution were mixed and stirred to obtain a uniformly dispersed solution of polydopamine-coated liquid metal nanoparticles-sodium alginate-aragonite flakes, where the total solute concentration was 90 mg / mL; the mass ratio of aragonite flakes to sodium alginate was 6:4, and the content of liquid metal nanoparticles was 2 wt% of the total mass. After the liquid metal-sodium alginate-aragonite flake uniformly dispersed solution was ultrasonicated and degassed under vacuum, it was cast on a polyethylene terephthalate (PET) substrate, dried at 50 °C, and a biomimetic shell-like liquid metal-sodium alginate-aragonite flake nanocomposite thin film material was obtained. The film thickness was ~15 μm. The large-sized films were cut into films of the same size and stacked into multiple layers. Further, the multilayer films were wetted with deionized water, pre-pressed at a pressure of 5 MPa and a temperature of 60 °C for 1 h to form a preform; the preform was soaked in a 5 mol / L calcium chloride solution for crosslinking for 4 h. After the preform was washed with water multiple times, it was hot-pressed at a pressure of 75 MPa and a temperature of 90 °C for 24 h to obtain a biomimetic shell-like liquid metal-sodium alginate-aragonite flake nanocomposite bulk material (conductive shell), and the thickness of the bulk was ~2 mm. As Figure 3As shown in a and b, the fracture morphology of the conductive shell presents a "brick-mud" layered structure, which is extremely similar to the microstructure of natural shells. In addition, three-point bending tests and single-edge notch bending (SENB) tests were carried out on natural shells and conductive shells using a TSMate mechanical testing machine (EM6.103-T, TSMate mechanical testing machine), and the results are as Figure 3 shown in c and d. The bending strength of the conductive shell is 231 MPa and the fracture toughness is 5.09 MPa·m 1 / 2 , which are much greater than the bending strength (~179 MPa) and fracture toughness (~3.83 MPa·m 1 / 2 ) of natural shells.

[0039] Example 3

[0040] The aragonite flakes prepared in Example 1 were surface modified with 3-aminopropyltriethoxysilane to enhance the interfacial interaction between the aragonite flakes and the polymer. Specifically: First, 3-aminopropyltriethoxysilane was dispersed in a mixed solution of ethanol and water (volume ratio 12:1). Based on the total mass of ethanol and water, the content of 3-aminopropyltriethoxysilane was 5 wt%. It was stirred and hydrolyzed for 1 h to obtain a hydrolysis solution. Then, the aragonite flakes prepared in Example 1 were dispersed in ethanol with a concentration of 10 wt%. The ethanol dispersion of aragonite flakes was added to the hydrolysis solution, and the mass ratio of aragonite flakes to 3-aminopropyltriethoxysilane was 10:1. It was stirred at 50 °C for 10 hours; centrifuged at 3000 rpm for 10 minutes to obtain a precipitate, washed 5 times with ethanol, and the precipitate was obtained by centrifugation. The precipitate was vacuum dried at 60 °C for 24 hours to obtain modified aragonite flakes. Weighed 10 g of sodium alginate and added it to 200 mL of water, and stirred to obtain a 50 mg / mL sodium alginate solution. To prepare an artificial shell, an alginate-aragonite nanoparticle composite material, the modified aragonite flakes were dispersed in deionized water to obtain an aragonite aqueous solution with an aragonite content of 10 wt%. Then, the aragonite aqueous solution was mixed and stirred with the sodium alginate solution, and the mass ratio of aragonite to sodium alginate was 4:6 to obtain a uniformly dispersed alginate-aragonite solution, where the total solute concentration was 90 mg / mL. After the alginate-aragonite uniformly dispersed solution was ultrasonicated and degassed under vacuum, it was cast on a polyethylene terephthalate (PET) substrate, dried at 50 °C to obtain an alginate-aragonite nanoparticle composite thin film material with a film thickness of 20 μm. The large-sized film was cut into films of the same size and stacked into multiple layers of films. Further, the multiple layers of films were wetted with deionized water, pre-pressed at a pressure of 5 MPa and a temperature of 60 °C for 1 hour to form a preform; the preform was soaked in a 5 mol / L calcium chloride solution for crosslinking for 4 hours. After the preform was washed with water multiple times, it was hot pressed at a pressure of 75 MPa and a temperature of 90 °C for 24 hours to obtain an alginate-aragonite nanoparticle composite material (artificial shell), and the thickness of the block was ~2 mm. The mechanical properties of natural shells and artificial shells were tested by three-point bending. As Figure 3 shown in c, d, the flexural strength of the artificial shell (~172 MPa) is comparable to that of the natural shell (~179 MPa). At the same time, the fracture toughness of the artificial shell (~3.83 MPa·m 1 / 2 ) is greater than that of the natural shell (~3.81 MPa·m 1 / 2 ).

[0041] Example 4

[0042] The aragonite flakes prepared in Example 1 were surface-modified with 3-aminopropyltriethoxysilane to enhance the interfacial interaction between the aragonite flakes and the polymer. Specifically: First, 3-aminopropyltriethoxysilane was dispersed in a mixed solution of ethanol and water (volume ratio 12:1). Based on the total mass of ethanol and water, the content of 3-aminopropyltriethoxysilane was 5 wt%. It was stirred and hydrolyzed for 1 h to obtain a hydrolysis solution. Then, the aragonite flakes prepared in Example 1 were dispersed in ethanol at a concentration of 10 wt%. The ethanol dispersion of aragonite flakes was added to the hydrolysis solution, and the mass ratio of aragonite flakes to 3-aminopropyltriethoxysilane was 10:1. It was stirred at 50 °C for 10 h; centrifuged at 3000 rpm for 10 min to obtain a precipitate, washed 5 times with ethanol, and the precipitate was obtained by centrifugation. The precipitate was vacuum-dried at 60 °C for 24 h to obtain modified aragonite flakes. 10 g of sodium alginate was weighed and added to 200 mL of water, and stirred to obtain a 50 mg / mL sodium alginate solution. Liquid metal blocks were added to an aqueous solution of hydrochloric acid dopamine with a concentration of 2 mg / mL. The liquid metal was a gallium-indium alloy (EGaIn) with a mass ratio of gallium to indium of 9:1. By setting the ultrasonic power to 300 W and the ultrasonic time to 4 h, and then stirring at room temperature for 24 h, polydopamine-coated liquid metal nanoparticles were obtained. The particle size distribution of the nanoparticles was 200 nm - 900 nm, and the concentration of the liquid metal nanoparticles was ~1 wt%. To prepare a biomimetic shell-like liquid metal-sodium alginate-aragonite flake nanocomposite bulk material (conductive shell), the modified aragonite flakes were dispersed in deionized water to obtain an aragonite flake aqueous solution with an aragonite flake content of 10 wt%. Then, the aragonite flake aqueous solution, the sodium alginate solution, and the polydopamine-coated liquid metal nanoparticle aqueous solution were mixed and stirred to obtain a uniformly dispersed solution of polydopamine-coated liquid metal nanoparticles-sodium alginate-aragonite flakes, where the total solute concentration was 90 mg / mL; the mass ratio of aragonite flakes to sodium alginate was 6:4, and the content of liquid metal nanoparticles was 2 wt% of the total mass. After the liquid metal-sodium alginate-aragonite flake uniformly dispersed solution was ultrasonicated and vacuum-degassed, it was spin-coated on a polyethylene terephthalate (PET) substrate and dried at 50 °C to obtain a biomimetic shell-like liquid metal-sodium alginate-aragonite flake nanocomposite thin film material with a film thickness of 5 μm. The large-sized films were cut into films of the same size and stacked into multiple layers of films. Further, the multiple layers of films were wetted with deionized water, and pre-pressed at a pressure of 5 MPa and a temperature of 60 °C for 1 h to form a preform; the preform was soaked in a 5 mol / L calcium chloride solution for crosslinking for 4 h. After the preform was washed with water multiple times, it was hot-pressed at a pressure of 75 MPa and a temperature of 90 °C for 24 h to obtain a biomimetic shell-like liquid metal-sodium alginate-aragonite flake nanocomposite bulk material (conductive shell), and the thickness of the bulk was ~2 mm. As Figure 4As shown in Fig. a, compared with the natural shell with a conductivity of 0, the conductivity of the conductive shell prepared in the present invention reaches 9×10 -4 S m -1 , so the structural integrity of the artificial shell bulk material can be self-monitored. By using a two-point probe device to in-situ monitor the change of resistance during the bending process of the pre-notched sample, the structural integrity of the nanocomposite material is evaluated. As Figure 4 shown in Figs. b and c, during the first cycle, a load is continuously applied to the sample. Before crack initiation, the resistance slowly rises. When the load is applied to the maximum value, since the crack begins to propagate, the force gradually decreases. The crack propagation causes the destruction of the conductive skeleton of the material, resulting in a significant increase in resistance. The resistance change rate (ΔR / R0) reaches ~15%. Before the sample fractures, the load is released and the resistance recovers. During the second cycle, since there are already fine cracks in the sample, as the load increases, the resistance rises faster than the first time. Due to further crack propagation, the resistance increases sharply, and its ΔR / R0 reaches ~30%, while the load also decreases. Therefore, this phenomenon of the conductive shell composite material can be used to monitor the integrity of the material itself, thereby monitoring the safety of the nanocomposite material.

[0043] It should be noted that according to the above-mentioned embodiments of the present invention, those skilled in the art can fully implement the entire scope of claims 1 and its dependent claims of the present invention. The implementation process and method are the same as those of the above-mentioned embodiments; and the parts not elaborated in detail in the present invention belong to the well-known technology in the art.

[0044] The above is only a partial specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those familiar with the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A preparation method of a shell-mimicking liquid metal-sodium alginate-aragonite nanoplate nanocomposite bulk material, characterized in that, It includes the following steps: (1) Using an alkali / urea / water system to exfoliate raw aragonite sheets from abalone shell nacre and disperse them in an aqueous solution; then using coupling agent molecules to modify the surface of the aragonite sheets, adding the modified aragonite sheets to deionized water to prepare an aragonite sheet aqueous dispersion; (2) Weigh sodium alginate and dissolve it in deionized water to prepare a sodium alginate solution; (3) Ultrasonically treating bulk liquid metal in an aqueous solution containing hydrochloric acid dopamine to obtain a stable dispersion of polydopamine-coated liquid metal nanoparticles aqueous dispersion; the liquid metal is a gallium-indium alloy; (4) Mixing and stirring the aragonite sheet aqueous dispersion, polydopamine-coated liquid metal nanoparticles aqueous dispersion and sodium alginate solution obtained in step (1) to obtain a liquid metal-sodium alginate-aragonite sheet homogeneous dispersion; (5) Assembling the liquid metal-sodium alginate-aragonite sheet homogeneous dispersion obtained in step (4) by a doctor blade method, and then drying to obtain a composite film; (6) Stacking and cutting the composite film obtained in step (5), wetting, cross-linking, and then hot-pressing to obtain a shell-like liquid metal-sodium alginate-aragonite sheet nanocomposite bulk material.

2. The preparation method of a nacre-mimicking liquid metal-sodium alginate-aragonite nanocomposite bulk material according to claim 1, characterized in that: In step (1), the preparation process of the aragonite sheet aqueous dispersion is as follows: Using a cutting machine and sandpaper to remove the horny layer and prismatic layer of the abalone shell nacre to obtain nacre, crushing the nacre and adding it to an aqueous solution containing urea and sodium hydroxide, controlling the mass ratio of sodium hydroxide to urea between 30-80%, stirring for 1-5 days, filtering by suction to obtain a precipitate, repeatedly washing with deionized water, and vacuum drying to obtain aragonite sheet powder; using a silane coupling agent to modify the surface of the aragonite sheets, where the concentration of the silane coupling agent is 0.5 wt%-10 wt%, the solvent is a mixed solution of ethanol and water, and the reaction time is 4-24 hours.

3. The preparation method of an artificial shell liquid metal - sodium alginate - aragonite nanoplate nanocomposite bulk material according to claim 1, wherein: In step (2), in the sodium alginate solution, the concentration of sodium alginate is 30 mg / mL - 80 mg / mL.

4. The preparation method of an artificial shell liquid metal - sodium alginate - aragonite nanoplate nanocomposite bulk material according to claim 1, characterized in that: In step (3), the particle size distribution of the polydopamine-coated liquid metal nanoparticles is 200 nm - 900 nm, the concentration of the liquid metal nanoparticles in the dispersion is 0.5-1.5 wt%, the ultrasonic power is 200-500 W, and the ultrasonic time is 1-4 hours.

5. The preparation method of an artificial shell-like liquid metal-sodium alginate-aragonite nanoplatelet nanocomposite bulk material according to claim 1, characterized in that: In step (4), the concentration of the liquid metal-sodium alginate-aragonite sheet homogeneous dispersion is 60 mg / mL - 120 mg / mL, the mass ratio of aragonite sheets to sodium alginate is 4:6 - 7:3, and the content of liquid metal nanoparticles is 0.5-3 wt% of the total mass.

6. The preparation method of an artificial shell liquid metal-sodium alginate-aragonite nanocomposite bulk material according to claim 1, characterized in that: In step (5), a composite film is prepared on a polyethylene terephthalate substrate by the doctor blade method, the doctor blade speed is 10-200 mm / s, the drying temperature is 30-60 °C, the doctor blade height is 50-500 μm, the width of the doctor blade coating is 4-20 cm, the length is 12-50 cm, and a composite film with a thickness of 5-20 μm can be obtained after drying.

7. The preparation method of an artificial shell-like liquid metal-sodium alginate-aragonite nanocomposite bulk material according to claim 1, wherein: In the step (6), the composite film is cut into films of the same size and stacked into multiple layers of films. After being wetted by an aqueous solution, it is formed into a prefabricated block under a pressure of 1 - 10 MPa, a temperature of 30 - 60 °C, and preheating and pressing for 0.5 - 6 hours; the prefabricated block is soaked in a calcium chloride solution with a concentration of 1 - 10 mol / L for crosslinking for 1 - 8 hours. After the prefabricated block is washed with water, under the conditions of a pressure of 25 - 100 MPa and a temperature of 60 - 100 °C, hot pressing is carried out for 8 - 72 hours to obtain a nacre-like liquid metal-sodium alginate-aragonite nanocomposite block material.

8. Use of the imitation shell liquid metal-sodium alginate-aragonite nanoplate nanocomposite bulk material prepared by the preparation method according to any one of claims 1-7 in electric induction, characterized in that: Samples with prefabricated notches are prepared from the nacre-like liquid metal-sodium alginate-aragonite nanocomposite block material obtained in the step (6). Conductive copper wires are fixed at both ends of the samples with silver glue, and the change in resistance of the prefabricated notch samples during the bending process is in-situ monitored by using a two-point probe device to evaluate the structural integrity of the nanocomposite material.

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