Slow-crystallization mechanical metamaterial with space-time programmable mechanical property and preparation method of slow-crystallization mechanical metamaterial

Abstract

The invention discloses a mechanical metamaterial with slow crystallization and space-time programmable mechanical property and a preparation method thereof, and belongs to the technical field of intelligent high polymer materials and mechanical metamaterials. The mechanical metamaterial provided by the invention has an amorphous micro-domain or crystalline micro-domain / amorphous micro-domain spatial distribution structure, and the amorphous micro-domain has a slow crystallization characteristic, so that the overall mechanical property of the material is regularly evolved along with time, and time dimension programming is realized. The mechanical metamaterial provided by the invention can also be subjected to repeated programming design for multiple times, breaks through the limitation that the traditional material cannot be subjected to repeated programming after being prepared and the performance is fixed, supports the customized design of spatial dimensions, and also has the characteristic that the mechanical property autonomously evolves along with the time rule. According to the present invention, the raw materials for preparing the crystallizable high-molecular polymer are subjected to slight cross-linking modification, the molecular chain movement is inhibited by using the cross-linked network, the material is endowed with the slow crystallization characteristic along with the time, and the accurate patterned distribution of the crystalline micro-domain and the amorphous micro-domain of the material is further achieved through the selective crystal region melting or the selective crystallization rate regulation and control.

Description

Technical Field

[0001] The present invention belongs to the technical field of intelligent polymer materials and mechanical metamaterials, and in particular relates to a mechanical metamaterial with slow crystallization and spatiotemporal programmable mechanical properties and a preparation method thereof. Background Art

[0002] Mechanical metamaterials, through artificially designed microstructural units (such as lattices and honeycombs), give materials extraordinary mechanical properties (such as negative Poisson's ratio and adjustable stiffness) that their natural components do not possess, showing great application potential in aerospace, intelligent protection, flexible electronics and other fields. However, traditional mechanical metamaterials rely on macroscopic geometric structure design, and their performance is fixed after preparation, making it difficult to meet the requirements of some complex application scenarios for customized material performance and dynamic adaptability. For example, in intelligent protective equipment, the ideal material should be able to provide differentiated protection in different parts, and automatically adjust its performance according to environmental changes during long-term use; in flexible wearable devices, the material needs to provide sufficient strength and support in certain key parts while ensuring overall flexibility to adapt to human movement and complex working environments.

[0003] The crystallization of polymer materials has a significant impact on their mechanical properties: the crystalline region usually has higher strength, modulus and hardness, while the amorphous region exhibits better flexibility and elongation at break. Therefore, it is feasible to use crystallization to control mechanical properties. However, traditional crystallization control methods (such as overall annealing) make it difficult to achieve the spatial programming distribution of crystalline / amorphous region microdomains in mechanical metamaterials, which limits the customized design of mechanical properties. In addition, once the material system is determined, the crystallization properties are fixed, making it difficult to achieve dynamic control of crystallinity and autonomous changes in customized mechanical properties without external stimulation. Therefore, existing technologies are still unable to achieve mechanical metamaterials with spatiotemporal programmable mechanical properties. Summary of the Invention

[0004] To address the aforementioned technical issues, the present invention proposes a slow-crystallizing mechanical metamaterial with spatiotemporally programmable mechanical properties, and a method for its preparation. This invention aims to impart slow crystallization properties to the material by lightly crosslinking the raw materials used to prepare the crystallizable polymer. Over time, changes in crystallinity lead to dynamic changes in mechanical properties, enabling the mechanical properties of the metamaterial to be customized to meet specific needs. Furthermore, by designing different crystalline / amorphous region distribution patterns, customized programming of the material's mechanical properties is possible.

[0005] To achieve the above objectives, the present invention provides the following technical solutions:

[0006] The present invention provides a mechanical metamaterial with slow crystallization and spatiotemporally programmable mechanical properties. The mechanical metamaterial has a spatially distributed structure of amorphous microdomains or crystalline microdomains / amorphous microdomains, and can be programmed to customize unconventional mechanical properties. The amorphous microdomains have slow crystallization characteristics, which allows the material's mechanical properties to evolve dynamically over time.

[0007] Technical Principle: The mechanical metamaterial provided by this invention possesses a spatially distributed structure of amorphous microdomains or crystalline / amorphous microdomains. The amorphous microdomains exhibit slow crystallization, enabling the overall mechanical properties of the material to evolve over time, enabling programming in the temporal dimension. The mechanical metamaterial provided by this invention can also be repeatedly programmed, overcoming the limitations of traditional materials that cannot be reprogrammed after fabrication and exhibit fixed properties. The mechanical metamaterial provided by this invention not only supports customized design in the spatial dimension but also possesses the characteristic of autonomous temporal evolution of mechanical properties.

[0008] Furthermore, the spatial distribution types of the crystalline microdomains / amorphous microdomains include grid, lattice, stripe, snake, Z-shape or convex shape.

[0009] Furthermore, the unconventional mechanical properties include one or more of adjustable modulus, adjustable stiffness, adjustable strength, and negative Poisson's ratio.

[0010] Furthermore, the complete crystallization time of the amorphous microdomain is 5-50 hours, and the complete crystallinity is 10-80%.

[0011] The present invention also provides a method for preparing the slow-crystallizing mechanical metamaterial with spatiotemporally programmable mechanical properties as described in the above technical solution, comprising the following steps:

[0012] Slightly cross-linking the raw materials for preparing the crystallizable high molecular polymer to obtain the slow-crystallizing mechanical metamaterial with spatiotemporally programmable mechanical properties; or

[0013] The raw materials for preparing the crystallizable high molecular polymer are lightly cross-linked to obtain a slow crystallizing material;

[0014] The slow-crystallizing material is subjected to selective crystal zone melting or selective crystallization rate regulation to obtain the slow-crystallizing mechanical metamaterial with spatiotemporally programmable mechanical properties.

[0015] Furthermore, the crystallizable high molecular polymer is at least one selected from polycarbonate, polycaprolactone, polytetramethylene terephthalate, polylactic acid, polyethylene terephthalate, polyamide, polyethylene, polypropylene, polystyrene, polyaryletherketone and polyether.

[0016] Furthermore, the reaction type of the slight cross-linking includes at least one of free radical cross-linking, ionic cross-linking, condensation cross-linking, addition cross-linking and epoxide cross-linking.

[0017] Furthermore, the selective melting crystal zone treatment includes laser engraving; and the selective crystallization rate control includes regionalized light irradiation or solvent treatment.

[0018] Furthermore, the parameters of the laser engraving include: engraving intensity 5-7%, engraving speed 300 mm / s, engraving accuracy 0.2-0.5 mm; and / or,

[0019] The parameters of the regionalized illumination include: illumination intensity 10-100mw / cm 2 , wavelength 365nm, time 0.1-2h; and / or,

[0020] The solvent for the solvent treatment is selected from one or more of ethanol, toluene and tetrahydrofuran, the temperature for the solvent treatment is 20-60° C., and the time for the solvent treatment is 0.5-10 h.

[0021] Furthermore, the slow-crystallizing mechanical metamaterial or slow-crystallizing material with spatiotemporally programmable mechanical properties is in the form of a fiber, a film or a three-dimensional shape.

[0022] Compared with the prior art, the present invention has the following advantages and technical effects:

[0023] (1) Traditional mechanical metamaterials rely on the design of macroscopic geometric structures. The present invention can achieve customized mechanical properties by flexible programming of the properties of the crystalline / amorphous regions. In addition, the crystal pattern distribution of the same material can be erased, and repeated programming design can be performed multiple times.

[0024] (2) The present invention realizes the spatiotemporal coordinated regulation of mechanical properties, which not only supports customized design in the spatial dimension, but also has the characteristics of autonomous evolution of mechanical properties over time. It breaks through the limitations of traditional materials that cannot be reprogrammed after preparation and have fixed performance, and gives the material dynamic adaptability to meet the needs of automatic performance adjustment during long-term use.

[0025] (3) The preparation method of the mechanical metamaterial of the present invention is simple and easy, the raw materials are common, and the means of regional programming crystallization distribution are diverse, such as solvent treatment, laser engraving and regional illumination. Among them, laser engraving has the characteristics of high precision and high flexibility, which is suitable for large-scale production and practical application, reducing costs.

[0026] (4) The material of the present invention can be processed into fibers, films, or three-dimensional shapes to meet the needs of different scenarios. The customizability and dynamic mechanical properties provide innovative material solutions for cutting-edge fields such as smart protection, flexible wearables, and biomedicine, and have broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0028] Figure 1 (a) The actual image and (b) stress-strain curve of the spline after different crystallization times in Example 1;

[0029] Figure 2 The actual image of the slow-crystallizing mechanical metamaterial with spatiotemporally programmable mechanical properties, prepared in Example 2, before and after stretching;

[0030] Figure 3 The actual images of the mechanical metamaterial with slow crystallization of rhombus shape and spatiotemporal programmable mechanical properties before stretching (a) and after stretching (b) in Example 3;

[0031] Figure 4 Schematic diagram of each pattern during the repetitive programming process of Example 4;

[0032] Figure 5 The physical image (a) and stress-strain curve (b) of the Z-shaped and convex-shaped slow-crystallizing mechanical metamaterials with spatiotemporal programmable mechanical properties prepared in Example 5;

[0033] Figure 6 The actual image (a) and stress-strain curve (b) of the thin film slow crystallization mechanical metamaterial with single horizontal stripes, multiple horizontal stripes, and multiple vertical stripes and spatiotemporally programmable mechanical properties in Example 6. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments 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.

[0035] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] Embodiments of the present invention provide a mechanical metamaterial with slow crystallization and spatiotemporally programmable mechanical properties. The metamaterial has a spatially distributed structure of amorphous microdomains or crystalline microdomains / (" / " represents sum) amorphous microdomains, allowing for programmable customization of unconventional mechanical properties. The amorphous microdomains exhibit slow crystallization properties, allowing the material's mechanical properties to evolve dynamically over time. The present invention utilizes the slowly crystallizing amorphous microdomains to allow the overall mechanical properties of the material to evolve regularly over time, achieving temporal programming. Furthermore, by designing different crystalline / amorphous region distribution patterns, customized programming of the material's mechanical properties can be achieved, resulting in a mechanical metamaterial that supports both customized design in the spatial dimension and the autonomous temporal evolution of mechanical properties.

[0037] In a preferred embodiment, the spatial distribution type of the crystalline microdomains / amorphous microdomains includes a grid, a lattice, a stripe, a serpentine, a zigzag or a convex shape. The spatial distribution type of the crystalline microdomains / amorphous microdomains in the present invention can be periodic or non-periodic.

[0038] In a preferred embodiment, the unconventional mechanical properties include one or more of adjustable modulus, adjustable stiffness, adjustable strength, and negative Poisson's ratio. The mechanical metamaterial provided by the present invention can customize its mechanical properties according to actual needs.

[0039] In a preferred embodiment, the complete crystallization time of the amorphous microdomain is 5-50 hours, more preferably 5-30 hours; the complete crystallinity of the amorphous microdomain is 10-80%.

[0040] The present invention also provides a method for preparing the slow-crystallizing mechanical metamaterial with spatiotemporally programmable mechanical properties as described in the above technical solution, comprising the following steps:

[0041] Slightly cross-linking the raw materials for preparing the crystallizable high molecular polymer to obtain the slow-crystallizing mechanical metamaterial with spatiotemporally programmable mechanical properties; or

[0042] The raw materials for preparing the crystallizable high molecular polymer are lightly cross-linked to obtain a slow crystallizing material;

[0043] The slow-crystallizing material is subjected to selective crystal zone melting or selective crystallization rate regulation to obtain the slow-crystallizing mechanical metamaterial with spatiotemporally programmable mechanical properties.

[0044] The present invention slightly cross-links the raw materials for preparing crystallizable polymers, uses the cross-linking network to inhibit the movement of molecular chains, and gives the material the characteristic of slow crystallization over time, thereby obtaining a mechanical metamaterial with a slow crystallization and spatiotemporal programmable mechanical properties with an amorphous microdomain structure; on this basis, further through selective melting of crystal areas or selective crystallization rate regulation, the patterned and precise distribution of crystalline microdomains and amorphous microdomains of the material is achieved, thereby realizing the spatial programming of customized unconventional mechanical properties.

[0045] In a preferred embodiment, the crystallizable high molecular polymer is selected from at least one of polycarbonate, polycaprolactone, polytetramethylene terephthalate, polylactic acid, polyethylene terephthalate, polyamide, polyethylene, polypropylene, polystyrene, polyaryletherketone and polyether, and is further preferably selected from at least one of polycarbonate, polycaprolactone and polyamide.

[0046] In a preferred embodiment, the slight crosslinking reaction type includes at least one of free radical crosslinking, ionic crosslinking, condensation crosslinking, addition crosslinking and epoxide crosslinking, and more preferably at least one of free radical crosslinking, condensation crosslinking and epoxide crosslinking.

[0047] In a preferred embodiment, when the crystallizable polymer is polycarbonate, the process of lightly crosslinking the raw materials for preparing the crystallizable polymer is as follows: 2 g of polycarbonate diol (molecular weight 2000) is dissolved in 5 g of tetrahydrofuran at 60°C under a nitrogen atmosphere to obtain a polycarbonate diol solution. 0.3364 g of hexamethylene diisocyanate and 0.03 g of dibutyltin dilaurate are sequentially added to the polycarbonate diol solution and reacted at 60°C for 4 hours to obtain a prepolymer solution. The resulting prepolymer solution is cooled to 25-30°C, 0.0894 g of trimethylolpropane (crosslinking agent) is added, and the mixture is stirred for 5 minutes to obtain a clear solution. The resulting clear solution is poured into an aluminum pan, heat-cured at 60°C for 10 hours, and vacuum-dried at 80°C for 10 hours to obtain a slowly crystallizable film.

[0048] In another preferred embodiment, when the crystallizable polymer is polycaprolactone, the process of slightly cross-linking the raw materials for preparing the crystallizable polymer is specifically as follows: 4 g of polycaprolactone diol (molecular weight 4000) is dissolved in 5 g of tetrahydrofuran under a nitrogen atmosphere at 60° C., and then 0.2822 g of ethyl isocyanate acrylate and 0.03 g of photoinitiator Irgacure 819 are added to obtain a prepolymer solution; the obtained prepolymer solution is poured into an aluminum pan, photocured under a UV lamp with a wavelength of 365 nm for 1 min, and vacuum dried at 80° C. for 10 h to obtain a slowly crystallizable film.

[0049] In another preferred embodiment, when the crystallizable polymer is polyamide, the process of lightly crosslinking the raw materials for preparing the crystallizable polymer is as follows: 2 g of double-terminated amino polyamide (molecular weight 2000) is dissolved in 5 g of tetrahydrofuran under a nitrogen atmosphere at 60° C., and then 0.2822 g of ethyl isocyanate acrylate and 0.03 g of dibutyltin dilaurate are added in sequence, and the mixture is reacted at 60° C. for 4 hours to obtain a prepolymer solution; the prepolymer solution is cooled to 25-30° C., 0.2163 g of pentaerythritol tetrathioglycolate (crosslinker) and 0.03 g of photoinitiator Irgacure 819 are added, and the mixture is stirred for 5 minutes to obtain a clear solution; the obtained clear solution is poured into an aluminum dish, photocured under a UV lamp with a wavelength of 365 nm for 2 minutes, and vacuum-dried at 80° C. for 10 hours to obtain a slowly crystallizable film.

[0050] In a preferred embodiment, the selective melting crystal region treatment includes laser engraving; and the selective crystallization rate control includes regionalized light irradiation or solvent treatment.

[0051] In a preferred embodiment, the laser engraving parameters include: engraving intensity 5-7%, engraving speed 300mm / s, and engraving accuracy 0.2-0.5mm. Laser engraving has the characteristics of high precision and high flexibility, is suitable for large-scale production and practical applications, and reduces costs.

[0052] In a preferred embodiment, the parameters of the regionalized illumination include: illumination intensity 10-100 mw / cm 2 , wavelength 365nm, time 0.1-2h.

[0053] In a preferred embodiment, the solvent for the solvent treatment is selected from one or more of ethanol, toluene and tetrahydrofuran; the temperature for the solvent treatment is 20-60° C., and the time for the solvent treatment is 0.5-10 h.

[0054] In a preferred embodiment, the slow-crystallizing mechanical metamaterial or slow-crystallizing material with spatiotemporally programmable mechanical properties is in the form of a fiber, a film or a three-dimensional shape.

[0055] The room temperature in the embodiments of the present invention refers to "25±2°C".

[0056] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources.

[0057] Example 1

[0058] A method for preparing a mechanical metamaterial with slow crystallization and spatiotemporally programmable mechanical properties, comprising the following steps:

[0059] Under a nitrogen atmosphere at 60°C, 2g of polycarbonate diol (molecular weight 2000) was dissolved in 5g of tetrahydrofuran to obtain a polycarbonate diol solution. 0.3364g of hexamethylene diisocyanate and 0.03g of dibutyltin dilaurate were sequentially added to the polycarbonate diol solution and reacted at 60°C for 4 hours to obtain a prepolymer solution. The resulting prepolymer solution was cooled to 25-30°C, 0.0894g of trimethylolpropane was added, and the mixture was stirred for 5 minutes to obtain a clear solution. The resulting clear solution was poured into an aluminum pan, heat-cured at 60°C for 10 hours, and vacuum-dried at 80°C for 10 hours to obtain a film that slowly crystallized for 30 hours. This is a slow-crystallizing mechanical metamaterial with spatiotemporally programmable mechanical properties.

[0060] The film prepared in Example 1 was cut into dumbbell-shaped splines, and the dumbbell-shaped splines were melted to obtain initial non-crystallized splines. The obtained initial non-crystallized splines were crystallized at room temperature for 0 h, 10 h, 20 h and 30 h, and the mechanical properties of the splines after different crystallization times were tested.

[0061] The physical picture (a) and stress-strain curve (b) of the spline after different crystallization times in Example 1 are shown in Figure 1 .from Figure 1 As can be seen from part a of the figure, as the crystallization time increases, the transparency of the spline decreases, indicating that the crystallinity of the spline increases. Therefore, the crystallinity of the material can be distinguished by observing the change in the transmittance of the spline. Figure 1 As can be seen from part b in FIG, the tensile modulus and tensile strength of the spline are significantly improved with the extension of crystallization time, indicating that the mechanical metamaterial prepared in Example 1 has dynamically evolving mechanical properties.

[0062] Example 2

[0063] A method for preparing a mechanical metamaterial with slow crystallization and spatiotemporally programmable mechanical properties, comprising the following steps:

[0064] Step (1) is the same as in Example 1;

[0065] (2) Cutting the film obtained in step (1) into strips and melting them to obtain initially non-crystallized strips; placing a portion of the initially non-crystallized strips in an ethanol solution and treating them at 40°C for 1 hour to accelerate crystallization, taking out the strips, and allowing the strips to crystallize after the ethanol on the surface of the strips evaporates. After being placed at room temperature for 1 hour, the degree of complete crystallization is close to 80%, thereby obtaining a mechanical metamaterial with slow crystallization, in which one portion is crystallized and the other portion is non-crystallized, and whose mechanical properties can be spatiotemporally programmed.

[0066] The actual pictures of the mechanical metamaterial with slow crystallization and spatiotemporal programmable mechanical properties before and after stretching prepared in Example 2 are shown in the figure below. Figure 2 .from Figure 2It can be seen that in the mechanical metamaterial with slow crystallization and spatiotemporal programmable mechanical properties prepared in Example 2, only the non-crystallized part is elongated and thinned, while the crystallized part has no obvious change, and the mechanical properties of the two parts are significantly different.

[0067] Example 3

[0068] A method for preparing a mechanical metamaterial with slow crystallization and spatiotemporally programmable mechanical properties, comprising the following steps:

[0069] Step (1) is the same as in Example 1.

[0070] (2) After the film obtained in step (1) is slowly crystallized at room temperature for 30 hours until it is completely crystallized, laser engraving is performed using a laser engraving machine. The laser intensity of the laser engraving machine is set to 5%, the engraving speed is set to 300 mm / s, the engraving accuracy is set to 0.5 mm, the engraving method is horizontal and bidirectional, and a diamond array pattern is engraved to obtain a mechanical metamaterial with a diamond-shaped slow crystallization and spatiotemporal programmable mechanical properties.

[0071] The actual pictures of the mechanical metamaterial with slow crystallization of rhombus shape and spatiotemporal programmable mechanical properties before stretching (a) and after stretching (b) in Example 3 are shown in FIG. Figure 3 .from Figure 3 As can be seen, because the film in the engraved area becomes transparent after melting, the mechanical metamaterial displays a crystalline / amorphous distribution pattern under natural light, namely, a spatial distribution structure of crystalline and amorphous microdomains. Furthermore, due to the spatial distribution of the crystalline regions, the mechanical metamaterial obtained in Example 3 exhibits an unconventional negative Poisson's ratio of -0.07 after stretching.

[0072] Example 4

[0073] A method for preparing a mechanical metamaterial with slow crystallization and spatiotemporally programmable mechanical properties, comprising the following steps:

[0074] Step (1) is the same as in Example 1.

[0075] (2) After the film obtained in step (1) is slowly crystallized at room temperature for 30 hours until it is completely crystallized, a laser engraving machine is used for laser engraving. The laser intensity of the laser engraving machine is set to 5%, the engraving speed is set to 300 mm / s, the engraving accuracy is set to 0.5 mm, and the engraving method is horizontal bidirectional. First, a long vertical stripe pattern is engraved. After the long vertical stripe pattern is completely slowly crystallized at room temperature, a short vertical stripe pattern is continued to be engraved. After the short vertical stripe pattern is completely slowly crystallized at room temperature, a horizontal stripe pattern is engraved again, thereby realizing repeated programming of mechanical metamaterials with slow crystallization and spatiotemporal programmable mechanical properties.

[0076] The schematic diagram of each pattern during the repetitive programming process of Example 4 is shown in Figure 4 .from Figure 4As can be seen, because the film in the engraved area becomes transparent after melting, the mechanical metamaterial displays a crystalline / amorphous distribution pattern under natural light, namely the spatial distribution structure of crystalline microdomains and amorphous microdomains. The amorphous region further slowly crystallizes, and after complete crystallization, the pattern disappears, allowing for reprogramming and engraving of new patterns.

[0077] Example 5

[0078] A method for preparing a mechanical metamaterial with slow crystallization and spatiotemporally programmable mechanical properties, comprising the following steps:

[0079] (1) 4 g of polycaprolactone diol (molecular weight 4000) was dissolved in 5 g of tetrahydrofuran at 60°C under a nitrogen atmosphere. 0.2822 g of ethyl isocyanate acrylate and 0.03 g of photoinitiator Irgacure 819 were then added to obtain a prepolymer solution. The resulting prepolymer solution was poured into an aluminum pan and photocured under a 365 nm UV lamp for 1 min. After vacuum drying at 80°C for 10 h, a film that slowly crystallized for 5 h was obtained.

[0080] (2) Place the Z-shaped hollow photomask and the convex-shaped hollow photomask on the surface of the film obtained in step (1), and then illuminate with ultraviolet light at an intensity of 60 mw / cm 2 The irradiation time was 0.1 h. The crosslink density in the illuminated area further increased, and the crystallization rate further decreased. After the irradiation, crystallization was continued at room temperature for 5 h, resulting in a zigzag-shaped mechanical metamaterial with slow crystallization and spatiotemporally programmable mechanical properties, and a convex-shaped mechanical metamaterial with slow crystallization and spatiotemporally programmable mechanical properties.

[0081] The physical image (a) and stress-strain curve (b) of the slow crystallization and spatiotemporal programmable mechanical metamaterials of Z-shaped and convex shapes prepared in Example 5 are shown in FIG. Figure 5 .from Figure 5 It can be seen that the moduli of the Z-shaped and convex-shaped mechanical metamaterials are similar, but the Z-shaped one has a higher tensile strength. This shows that the design of the selective melting crystal zone in the present invention can change the mechanical properties of the mechanical metamaterial, reflecting the sensitivity of the mechanical metamaterial of the present invention to the regulation of mechanical properties.

[0082] Example 6

[0083] A method for preparing a mechanical metamaterial with slow crystallization and spatiotemporally programmable mechanical properties, comprising the following steps:

[0084] (1) Under nitrogen atmosphere at 60°C, 2 g of double-terminated amino polyamide (molecular weight 2000) was dissolved in 5 g of tetrahydrofuran, followed by the addition of 0.2822 g of ethyl isocyanate acrylate and 0.03 g of dibutyltin dilaurate, and the mixture was reacted at 60°C for 4 h to obtain a prepolymer solution. The prepolymer solution was cooled to 25-30°C, and 0.2163 g of pentaerythritol tetramercaptoacetate and 0.03 g of photoinitiator Irgacure 819 were added and stirred for 5 min to obtain a clear solution. The obtained clear solution was poured into an aluminum pan and photocured under a UV lamp with a wavelength of 365 nm for 2 min. After vacuum drying at 80°C for 10 h, a film that could be slowly crystallized for 20 h was obtained.

[0085] (2) After the film obtained in step (1) is slowly crystallized at room temperature for 20 hours until it is completely crystallized, three 4*4 cm samples are cut and respectively engraved by a laser engraving machine. The laser intensity of the laser engraving machine is set to 7%, the engraving speed is set to 300 mm / s, the engraving accuracy is set to 0.2 mm, the engraving method is set to be horizontal and unidirectional, and the engraving patterns are single horizontal stripes, multiple horizontal stripes, and multiple vertical stripes, respectively. Thin-film slow crystallization and mechanical properties with spatiotemporal programmable mechanical metamaterials with single horizontal stripes, multiple horizontal stripes, and multiple vertical stripes are obtained.

[0086] The physical image (a) and stress-strain curve (b) of the thin film slow crystallization mechanical metamaterial with single horizontal stripes, multiple horizontal stripes, and multiple vertical stripes and whose mechanical properties can be programmed in time and space in Example 6 are shown in FIG. Figure 6 .from Figure 6 It can be seen that the single horizontal stripe mechanical metamaterial has a higher modulus than the multi-horizontal stripe mechanical metamaterial. This is because the single horizontal stripe mechanical metamaterial has more crystalline regions, resulting in a higher modulus. Compared to the multi-horizontal stripe mechanical metamaterial, the multi-vertical stripe mechanical metamaterial has non-crystalline regions perpendicular to the stretching direction. This allows the multi-vertical stripe mechanical metamaterial to achieve a higher modulus even if the distribution area of ​​crystalline and non-crystalline regions is the same. The experimental results of Example 6 demonstrate that the mechanical metamaterial provided by the present invention has programmable anisotropic mechanical properties.

[0087] The above are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A mechanical metamaterial with slow crystallization and spatiotemporal programmable mechanical properties, characterized by: The mechanical metamaterial has a spatial distribution structure of amorphous microdomains or crystalline microdomains / amorphous microdomains, and can be programmed to customize unconventional mechanical properties; the amorphous microdomains have slow crystallization characteristics, which allows the mechanical properties of the material to evolve dynamically over time.

2. The slow-crystallizing mechanical metamaterial with spatiotemporally programmable mechanical properties according to claim 1, characterized in that: The spatial distribution types of the crystalline microdomains / amorphous microdomains include grid, lattice, stripe, snake, Z-shape or convex shape.

3. The slow-crystallizing mechanical metamaterial with spatiotemporally programmable mechanical properties according to claim 1, characterized in that: The unconventional mechanical properties include one or more of adjustable modulus, adjustable stiffness, adjustable strength, and negative Poisson's ratio.

4. The slow-crystallizing mechanical metamaterial with spatiotemporally programmable mechanical properties according to claim 1, characterized in that: The complete crystallization time of the amorphous microdomain is 5-50 hours, and the complete crystallinity is 10-80%.

5. A method for preparing a mechanical metamaterial with slow crystallization and spatiotemporally programmable mechanical properties according to any one of claims 1 to 4, characterized in that: The following steps are involved: Slightly cross-linking the raw materials for preparing the crystallizable high molecular polymer to obtain the slow-crystallizing mechanical metamaterial with spatiotemporally programmable mechanical properties; or, The raw materials for preparing the crystallizable high molecular polymer are lightly cross-linked to obtain a slow crystallizing material; The slow-crystallizing material is subjected to selective crystal zone melting or selective crystallization rate regulation to obtain the slow-crystallizing mechanical metamaterial with spatiotemporally programmable mechanical properties.

6. The preparation method according to claim 5, characterized in that The crystallizable high molecular polymer is selected from at least one of polycarbonate, polycaprolactone, polytetrahydrofuran, polylactic acid, polyethylene terephthalate, polyamide, polyethylene, polypropylene, polystyrene, polyaryletherketone and polyether.

7. The preparation method according to claim 5, characterized in that The reaction type of the light crosslinking includes at least one of free radical crosslinking, ionic crosslinking, condensation crosslinking, addition crosslinking and epoxide crosslinking.

8. The preparation method according to claim 5, characterized in that The selective melting crystal zone processing includes laser engraving; the selective crystallization rate regulation includes regional light irradiation or solvent treatment.

9. The preparation method according to claim 8, characterized in that The parameters of the laser engraving include: engraving intensity 5-7%, engraving speed 300 mm / s, engraving accuracy 0.2-0.5 mm; and / or, The parameters of the regionalized illumination include: illumination intensity 10-100mw / cm 2 , wavelength 365nm, time 0.1-2h; and / or, The solvent for the solvent treatment is selected from one or more of ethanol, toluene and tetrahydrofuran, the temperature for the solvent treatment is 20-60° C., and the time for the solvent treatment is 0.5-10 h.

10. The preparation method according to claim 5, characterized in that The mechanical metamaterial or slow crystallization material with slow crystallization and spatiotemporally programmable mechanical properties is in the form of a fiber, a film or a three-dimensional shape.

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