Solid-liquid phase change two-dimensional soft elastic metamaterial and preparation method thereof

Abstract

The invention discloses a solid-liquid phase change two-dimensional soft elastic metamaterial and a preparation method thereof, and relates to the field of materials. The plurality of liquid metal functional units are coated in the flexible polymer matrix; the rigid mass blocks are arranged in the flexible polymer matrix in a dispersed manner; wherein the liquid metal function units and the adjacent rigid mass blocks are associated and coupled in space to jointly form periodically arranged resonance unit cells; the melting point of the liquid metal ranges from 20 DEG C to 40 DEG C, and solid-liquid phase change of the liquid metal is triggered by changing the environment temperature, so that the equivalent stiffness of the resonance unit cells is changed, and active regulation and control of the elastic wave band gap of the metamaterial are achieved; according to the metamaterial, the rigidity of the material can be obviously changed within the second-level time by utilizing the rapid and reversible solid-liquid phase change of the liquid metal near the room temperature, so that the rapid switching of an elastic wave band gap is realized, and the regulation and control timeliness is greatly improved.

Description

Technical Field

[0001] This invention relates to materials technology, specifically to a solid-liquid phase change two-dimensional soft elastic metamaterial and its preparation method. Background Technology

[0002] Elastic wave metamaterials are functional materials with artificial periodic structures that can suppress the propagation of elastic waves (such as vibrations and sound waves) at specific frequencies through their "bandgap" characteristics, making them important for vibration isolation and noise control. To enable metamaterials to adapt to dynamic environments, researchers have developed active control techniques, among which temperature control has attracted attention due to its ability to operate without complex external fields and its wide applicability.

[0003] Currently, the mainstream approach to achieving temperature-controlled bandgap regulation is to use shape memory alloys (SMA) or shape memory polymers (SMP). While these materials can respond to temperature changes and alter their stiffness, their response speed is typically slow (on the order of minutes), and they are prone to material fatigue and performance degradation after repeated temperature cycles, limiting their application in applications requiring rapid and frequent temperature switching. Therefore, existing temperature-controlled elastic wave metamaterials generally suffer from technical drawbacks such as slow response speed and poor cycle durability. Summary of the Invention

[0004] The purpose of this invention is to provide a solid-liquid phase change two-dimensional soft elastic metamaterial and its preparation method, so as to solve the problems of slow response speed and insufficient cycle stability of temperature-controlled elastic wave metamaterials in the prior art due to their reliance on shape memory materials.

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

[0006] In a first aspect, the present invention provides a solid-liquid phase change two-dimensional soft elastic metamaterial, comprising:

[0007] Flexible polymer matrix;

[0008] Multiple liquid metal functional units are encapsulated within the flexible polymer matrix;

[0009] and multiple rigid mass blocks dispersed in the flexible polymer matrix;

[0010] The liquid metal functional unit is spatially coupled with the adjacent rigid mass block to form a periodically arranged resonant unit cell. The melting point of the liquid metal is between 20°C and 40°C. By changing the ambient temperature, its solid-liquid phase transition is triggered, thereby changing the equivalent stiffness of the resonant unit cell and realizing the active control of the elastic bandgap of the metamaterial.

[0011] Furthermore, the flexible polymer matrix is ​​polydimethylsiloxane (PDMS), which has good elasticity, flexibility and chemical stability. Its Young's modulus can be selected in the range of kPa to MPa to meet different vibration isolation frequency requirements.

[0012] Furthermore, the liquid metal is gallium or a gallium-based alloy, with a phase transition temperature of 25°C-35°C, to ensure a rapid and efficient solid-liquid phase transition response can be achieved in an environment close to room temperature.

[0013] Furthermore, the rigid mass block is a metal block (such as iron, copper, or aluminum), a ceramic block, or a polymer composite material block. Its main function is to form a local resonant unit with the surrounding flexible matrix and liquid metal functional units. Its mass size is one of the key parameters affecting the center frequency of the bandgap.

[0014] Furthermore, the liquid metal functional unit has a multi-branched curved topology and is arranged around the rigid mass block. This design (such as a curved quadrilateral or a radial star shape) can enhance the coupling between the liquid metal phase transition region and the rigid mass block, and effectively widen the band gap or achieve band gap merging by stimulating local resonance of multi-mode.

[0015] Furthermore, the multi-branched curved topology is a quadruple-symmetric curved tetrapod.

[0016] Furthermore, the bandgap modulation frequency range is 1Hz-1000Hz.

[0017] Secondly, the present invention provides a method for preparing a solid-liquid phase change two-dimensional soft elastic metamaterial as described above, comprising:

[0018] S1. A mold is provided, into which a flexible polymer prepolymer (such as PDMS mixture) is poured. After solidification, the mold is demolded to obtain a channel mold with a cavity of a preset topological shape. Molten liquid metal is injected into the cavity, and after cooling and shaping, the solid liquid metal functional unit is removed.

[0019] S2. Multiple liquid metal functional units and multiple rigid mass blocks are spliced ​​and fixed in a preset two-dimensional periodic arrangement (such as a square lattice or a hexagonal lattice) to form an unencapsulated resonant unit cell array.

[0020] S3. Place the unencapsulated resonant unit cell array in the final molding mold, pour in a flexible polymer prepolymer (such as PDMS) to completely encapsulate the array, and demold after heating and curing to obtain the solid-liquid phase change two-dimensional soft elastic metamaterial.

[0021] Furthermore, in step S1, after injecting liquid metal into the cavity, the channel mold or liquid metal is frozen to facilitate the solidification or demolding of the liquid metal.

[0022] Furthermore, the flexible polymer prepolymer is a mixture of polydimethylsiloxane as the main agent and a curing agent, wherein the mass ratio of the main agent to the curing agent is 8-12:1.

[0023] Compared with existing technologies, the present invention provides a solid-liquid phase transition two-dimensional soft elastic metamaterial and its preparation method, the main beneficial effects of which include:

[0024] By utilizing the rapid and reversible solid-liquid phase transition of liquid metals (such as gallium) near room temperature, significant changes in material stiffness can be achieved within seconds, thereby enabling rapid switching of elastic wave bandgap and greatly improving the control timeliness.

[0025] The phase transition of liquid metal is a physical change and is not prone to fatigue. At the same time, the use of flexible polymer materials (such as PDMS) to completely encapsulate it avoids metal oxidation and leakage, enabling the metamaterial to maintain stable controllability after multiple temperature cycles and significantly improving durability.

[0026] By designing the topological shape of the liquid metal functional unit (such as a curved quadrilateral), the parameters of the rigid mass block, and its two-dimensional periodic arrangement, the position and width of the bandgap can be flexibly designed and controlled within a wide frequency range of 1Hz-1000Hz.

[0027] The modular manufacturing method adopted, which involves prefabricating functional units and then assembling and packaging them, has clear process steps, good repeatability, and is conducive to ensuring product quality and achieving large-scale production. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0029] Figure 1 This is a schematic diagram of the overall structure provided for an embodiment of the present invention;

[0030] Figure 2 A schematic diagram of a resonant unit cell provided in an embodiment of the present invention;

[0031] Figure 3 This is a schematic diagram of the method flow provided in an embodiment of the present invention;

[0032] Figure 4The graphs are non-contact vibration velocity measurement results provided in Embodiment 4 of the present invention, where Figure A shows the array side excitation and Figure B shows the diagonal endpoint excitation.

[0033] Explanation of reference numerals in the attached figures:

[0034] 1. Flexible polymer matrix; 2. Liquid metal functional unit; 3. Rigid mass block. Detailed Implementation

[0035] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0036] As attached Figure 1 To be continued Figure 4 As shown:

[0037] Example 1:

[0038] This invention provides a solid-liquid phase transition two-dimensional soft elastic metamaterial, comprising:

[0039] The metamaterial is in the shape of a thin plate, and its functional core consists of multiple resonant unit cells arranged periodically in a square lattice within a flexible polymer matrix 1. The side length of each resonant unit cell is designed to be 20 mm.

[0040] Each resonant unit cell includes: a PDMS substrate serving as both a flexible matrix and an encapsulator; a cylindrical, rigid iron mass 3 located approximately at the center of the unit cell, with a diameter of about 6 mm and a height equal to the thickness of the PDMS substrate; and a curved quadrilateral gallium metal functional unit completely encapsulated by the PDMS substrate. This gallium metal functional unit exhibits a fourfold symmetrical curved quadrilateral topology, with its four curved "leaves" extending outwards from the central region and surrounding the central iron mass, but with minute gaps between them to ensure PDMS filling. Gallium, with a melting point of 29.8°C, is the phase-change functional material used in this embodiment.

[0041] Among them, the flexible polymer matrix 1 is PDMS, the liquid metal functional unit 2 is a gallium channel, and the rigid mass block 3 is a cylindrical iron block.

[0042] The preparation method of the metamaterial mainly includes three core stages, and the specific steps are as follows:

[0043] Phase 1: Prefabrication of bent quadrilateral gallium metal functional units

[0044] a) Design and fabricate a master mold with a cavity that is a curved four-leaf shaped protrusion.

[0045] b) Mix the PDMS base agent and curing agent at a mass ratio of 10:1 until homogeneous, degas under vacuum, and pour the mixture onto the master mold to cover the raised structure. Cur the mixture in an oven at 80°C for 2 hours.

[0046] c) After demolding, a flexible PDMS "channel mold" with a curved four-leaf-shaped recessed cavity is obtained.

[0047] d) Carefully inject molten gallium metal (heated to about 40°C) into the cavity using an injection device until it is filled.

[0048] e) Immediately place the entire gallium-filled mold into a -5°C freezer for 10 minutes to allow the gallium to solidify completely and shrink slightly for demolding.

[0049] f) Gently remove the solidified gallium metal functional unit with a curved tetrapod structure from the PDMS channel mold. Repeat this process to prepare a sufficient number of standardized functional units.

[0050] Phase Two: Assembling the Resonant Unit Cell Array

[0051] Multiple curved quadrilateral gallium functional units and multiple cylindrical iron blocks, fabricated in the first stage, were precisely arranged on a flat surface in a square grid spaced 20 mm apart. Each iron block was ensured to be located in the central blank area of ​​a gallium functional unit. A small amount of ephemeral adhesive was used for temporary fixation at critical contact points, forming a 5×5 "unencapsulated resonant unit cell array".

[0052] Phase 3: Overall Encapsulation and Curing

[0053] a) Place the assembled array into a shallow rectangular final molding mold.

[0054] b) Mix the new PDMS prepolymer (ratio 10:1), degas under vacuum, and slowly pour it into the mold until the PDMS liquid completely submerges the array, ensuring that the PDMS penetrates into all gaps.

[0055] c) Place the entire mold in an oven at 80°C and cure for 3 hours.

[0056] d) After curing, the material is removed from the mold to obtain a solid-liquid phase change two-dimensional soft elastic metamaterial product with an overall encapsulation of approximately 100mm × 100mm in size, which includes a PDMS matrix, gallium functional units, and an iron mass block.

[0057] Among them, the rigid mass block 3 has a thickness of 4mm and a radius of 3mm, and the total thickness of the entire device is 6mm. It covers the iron block and gallium channel with 1mm coverage on the top and bottom, and the metal gallium channel is arranged diagonally.

[0058] Working principle:

[0059] When the ambient temperature is below the melting point of gallium (e.g., 25°C), the gallium functional unit is in a solid state with high stiffness, forming a highly efficient local resonant unit together with the iron block and PDMS matrix. At this time, the metamaterial will generate a significant elastic wave bandgap in a specific low-frequency range (e.g., in the range of 150-450Hz through simulation optimization), and the vibration is strongly attenuated in this frequency band (bandgap open state).

[0060] When the ambient temperature rises above the melting point of gallium (e.g., 35°C), the gallium functional unit melts into a liquid state, and its effective stiffness decreases sharply. This fundamentally changes the resonant characteristics of the original resonant unit, causing the original bandgap to disappear or the center frequency to shift significantly (bandgap closure or shift). This process is a physical phase transition, therefore the response is rapid and completely reversible. Active and dynamic control of the vibration isolation frequency band of the metamaterial can be achieved through a simple temperature control device.

[0061] Example 2:

[0062] This embodiment is basically the same as Embodiment 1, except that the main difference lies in the topological configuration of the liquid metal functional unit 2, which aims to demonstrate the flexibility of the design of the present invention and its optimization effect on bandgap characteristics.

[0063] In this embodiment, the liquid metal functional unit 2 adopts a multi-branch star topology with eight curved, slender branches arranged radially symmetrically. This more complex topology provides a larger contact area between the liquid metal and the PDMS and may excite more higher-order local vibration modes.

[0064] The preparation method is similar to that in Example 1, except that in the first stage, the mother mold cavity used to make the channel mold needs to be processed into an eight-branch star-shaped protrusion structure.

[0065] Working principle and effects:

[0066] Finite element simulation comparisons revealed that, under the same unit cell size, iron block mass, and material parameters, the eight-branch star topology of this embodiment produces a bandgap that is approximately 15%-25% wider than the four-leaf topology of Embodiment 1, and also exhibits superior bandgap depth (attenuation coefficient). This demonstrates that by optimizing the topology design of the liquid metal functional unit 2, the performance indicators of the metamaterial can be further improved without altering its external dimensions and main materials.

[0067] Example 3:

[0068] This embodiment is basically the same as Embodiment 1, except that the performance is optimized for the application scenario of the vehicle-mounted precision instrument vibration isolation platform.

[0069] To meet the requirements of isolating vehicle body vibrations of 30-200Hz at room temperature and being able to quickly and temporarily shut down the vibration isolation, the following targeted design and process optimizations were carried out:

[0070] Bandgap positioning: Through simulation, the mass and unit cell size of the rigid iron block are adjusted to precisely design the bandgap center frequency at around 80Hz.

[0071] Fast-response design: After the third-stage encapsulation and curing, a micro-flexible thin-film heating element (belonging to the application system component) can be integrated on the back of the finished metamaterial. Combined with the rapid gallium phase transition, a second-level bandgap switching can be achieved.

[0072] Process optimization: In the first stage of freezing, programmed temperature control is used (first rapidly cooling to -10℃, then slowly rising to 0℃ before demolding) to reduce internal stress and microcracks in gallium functional units and improve cycle life.

[0073] Working principle: Under normal conditions, the heating element is not activated, the metamaterial is at room temperature, the gallium functional unit is solid-state, the bandgap is open, and vibrations around 80Hz are isolated. When the instrument needs to operate, the heating element is activated to heat up to above 35°C, the gallium functional unit melts, the bandgap closes, and vibrations can be transmitted for instrument operation. After completion, heating is stopped, and the bandgap returns to normal. This embodiment demonstrates the ability of the metamaterial of this invention to intelligently switch between vibration isolation states through temperature control.

[0074] Example 4: Experimental Testing and Verification of Metamaterial Bandgap Properties

[0075] This embodiment aims to verify the bandgap characteristics and temperature control adjustability of the solid-liquid phase change two-dimensional soft elastic metamaterial prepared by the present invention through experimental testing.

[0076] 1. Test Sample:

[0077] The metamaterial sample prepared by the method described in Example 1 has an overall size of approximately 100mm × 100mm, wherein the liquid metal functional unit 2 is a bent four-lobed gallium metal and the rigid mass block 3 is a cylindrical iron block.

[0078] 2. Test system setup:

[0079] The system mainly includes:

[0080] Excitation module: The signal generator produces a linear sweep frequency signal, which is amplified by the power amplifier and drives the piezoelectric ceramic actuator attached to the edge of the sample to excite a plane elastic wave in the sample.

[0081] Measurement module: A laser vibrometer is used to perform non-contact vibration velocity measurement at specific points on the sample surface (array sides and diagonal endpoints).

[0082] Control and acquisition module: The computer controls the signal generation and data acquisition system, and synchronously records the excitation signal and response signal.

[0083] 3. Testing process and results analysis:

[0084] a) Room temperature test (solid-state gallium, 25℃): Place the sample on a temperature-controlled platform and maintain it at 25℃. Perform frequency sweep excitation in the range of 1-1000Hz. Collect vibration response data and calculate the frequency response function (FRF) curve of the sample.

[0085] b) Temperature rise test (liquid gallium, 35°C): Raise the temperature control platform to 35°C and stabilize it to ensure that the gallium functional unit is completely melted. Repeat the frequency sweep test in step a) under the same conditions.

[0086] c) Simulation comparison: Using COMSOL Multiphysics software, a finite element model completely consistent with the experimental sample was established, and frequency domain analysis was performed to calculate the theoretical bandgap structure and frequency response.

[0087] 4. Test Conclusion:

[0088] The experimentally measured FRF curves were compared with the simulation results.

[0089] Consistency verification: Under the condition of 25℃ (solid gallium), the experimental curves show a significant vibration transmission attenuation valley (i.e., band gap) in the frequency range of 150-450Hz. The position and width of the band gap are in high agreement with the simulation prediction results, which proves that the design method and fabrication process of the present invention are accurate and feasible.

[0090] Verification of temperature control reversibility: Comparing the experimental curves at 25℃ and 35℃, it can be clearly observed that at 35℃ (liquid gallium), the original 150-450Hz bandgap basically disappears, and the vibration transmission level increases significantly. This change is completely reversible and repeats with temperature cycling.

[0091] Functional realization: The above experimental results directly confirm that the metamaterial of the present invention can trigger solid-liquid phase transition through temperature change (within the range of 25℃ to 35℃), thereby realizing active and reversible "switching" control of a specific elastic wave bandgap (such as 150-450Hz) in the range of 1-1000Hz, achieving the expected purpose of the present invention.

[0092] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A solid-liquid phase change two-dimensional soft elastic metamaterial, characterized in that, include: Flexible polymer matrix; Multiple liquid metal functional units are encapsulated within the flexible polymer matrix; and multiple rigid mass blocks dispersed in the flexible polymer matrix; The liquid metal functional unit is spatially coupled with the adjacent rigid mass block to form a periodically arranged resonant unit cell. The melting point of the liquid metal is between 20°C and 40°C. By changing the ambient temperature, its solid-liquid phase transition is triggered, thereby changing the equivalent stiffness of the resonant unit cell and realizing the active control of the elastic bandgap of the metamaterial.

2. The solid-liquid phase change two-dimensional soft elastic metamaterial according to claim 1, characterized in that, The flexible polymer matrix is ​​polydimethylsiloxane.

3. The solid-liquid phase change two-dimensional soft elastic metamaterial according to claim 1, characterized in that, The liquid metal is gallium or a gallium-based alloy, and the phase transition temperature is 25℃-35℃.

4. The solid-liquid phase change two-dimensional soft elastic metamaterial according to claim 1, characterized in that, The rigid mass block is a metal block, a ceramic block, or a polymer composite material block.

5. The solid-liquid phase change two-dimensional soft elastic metamaterial according to claim 1, characterized in that, The liquid metal functional unit has a multi-branched curved topology and is arranged around the rigid mass block.

6. The solid-liquid phase change two-dimensional soft elastic metamaterial according to claim 5, characterized in that, The multi-branched curved topology is a quadruple-symmetric curved tetrapod.

7. The solid-liquid phase change two-dimensional soft elastic metamaterial according to claim 1, characterized in that, The bandgap modulation frequency range is 1Hz-1000Hz.

8. A method for preparing a solid-liquid phase transition two-dimensional soft elastic metamaterial as described in any one of claims 1-7, characterized in that, include: S1. A mold is provided, into which a flexible polymer prepolymer is poured. After solidification, the mold is demolded to obtain a channel mold with a cavity of a preset topological shape. Molten liquid metal is injected into the cavity, and after cooling and shaping, the solid liquid metal functional unit is removed. S2. Multiple liquid metal functional units and multiple rigid mass blocks are spliced ​​and fixed in a preset two-dimensional periodic arrangement to form an unencapsulated resonant unit cell array. S3. Place the unencapsulated resonant unit cell array in the final molding mold, pour in a flexible polymer prepolymer to completely encapsulate the array, and demold after heating and curing to obtain the solid-liquid phase change two-dimensional soft elastic metamaterial.

9. The preparation method according to claim 8, characterized in that, In step S1, after injecting liquid metal into the cavity, the channel mold or liquid metal is frozen.

10. The preparation method according to claim 8, characterized in that, The flexible polymer prepolymer is a mixture of polydimethylsiloxane as the main agent and a curing agent, wherein the mass ratio of the main agent to the curing agent is 8-12:1.

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