Liquid metal composite hydrogel with magnetic response and thermal response self-healing performance, preparation method and application thereof

Abstract

This invention relates to a liquid metal composite magnetic hydrogel with magnetic and thermal self-healing properties, its preparation method, and its applications. It addresses the problems of poor flexibility, weak electrical and thermal conductivity, and insufficient environmental tolerance in existing hydrogels. The method of this invention comprises the following steps: 1) preparing a liquid metal dispersion; 2) preparing a magnetic precursor system; 3) preparing a carrageenan solution; 4) magnetic field-induced orientation and thermal cross-linking curing; and 5) low-temperature induced formation of a double network. The gel material prepared by this invention exhibits thermal self-healing properties, achieving flame retardancy and self-healing even in extreme environments such as high temperatures and combustion, thereby ensuring the structural integrity and continuous stable function of the material. Simultaneously, by introducing liquid metal, the electrical and thermal conductivity of the gel system is improved, and by introducing magnetic components, it acquires magnetic control capabilities, enabling continuous use in extreme environments.

Description

Technical Field

[0001] This invention relates to the field of magnetically driven soft materials and multifunctional hydrogel materials, specifically to a liquid metal composite magnetic hydrogel with magnetic and thermal self-healing properties, its preparation method, and its applications. Background Technology

[0002] Hydrogels are a class of three-dimensional network materials formed by the physical or chemical cross-linking of hydrophilic polymer chains. They can absorb and retain large amounts of water, thus possessing both the structural stability of solids and the transport properties of liquids. Due to their high water content, good flexibility, deformability, biocompatibility, and tunability, hydrogels show broad application prospects in biomedicine, environmental engineering, flexible electronics, smart sensing, and soft actuation. For example, in biomedicine, they can be used as tissue engineering scaffolds, drug delivery carriers, and wound dressings; in environmental engineering, they can be used for pollutant adsorption and oil-water separation; and in flexible electronics, they can be applied to flexible electrodes, wearable devices, and strain sensors.

[0003] In recent years, with the development of soft robots, biomimetic devices, and intelligent actuation materials, hydrogels have received increasing attention in the field of flexible actuation. Under external stimuli such as temperature, humidity, pH, electric fields, light fields, and magnetic fields, hydrogels can undergo changes in volume, shape, or mechanical properties, thereby mimicking the bending, stretching, contraction, grasping, and crawling movements of living organisms. Among them, magnetic hydrogels, due to their ability to achieve remote, non-contact manipulation under an applied magnetic field, possess advantages such as fast response, strong controllability, and flexible adjustment, showing significant application potential in soft actuators, micro-actuators, targeted delivery, biomimetic robots, and complex environment detection.

[0004] Magnetic hydrogels are typically composite functional materials formed by introducing magnetic particles into a hydrogel network. Patent application CN202210257597.2 discloses a "Magnetically Controllable Actuated Negative Temperature-Sensitive Hydrogel and its Preparation Method and Application." While this technology achieves controllable actuation of the hydrogel material under a magnetic field, it still faces challenges in balancing mechanical properties with magnetic response, and conductivity with self-healing properties. Specifically, in this approach, magnetic particles are directly encapsulated and dispersed within the hydrogel. The introduction of these magnetic particles affects the continuous network structure of the hydrogel, reducing its softness and elasticity, leading to performance degradation during long-term deformation and cyclic actuation. Furthermore, limited by the inherent environmental tolerance of the substrate material, this type of hydrogel is prone to embrittlement, thermal decomposition, hydrolysis, or excessive swelling under extreme conditions such as ultra-high temperatures, ultra-low temperatures, combustion, and acid / alkali corrosion, resulting in a rapid decline in its overall performance and making it difficult to meet the application requirements for stable service in complex environments.

[0005] Liquid metals are a class of metals or alloys that remain liquid at or near room temperature. Typical examples include gallium and gallium-based alloys, such as gallium-indium alloys and gallium-indium-tin alloys. Liquid metals are less prone to irreversible fracture when subjected to stretching, compression, bending, or other deformations. They can maintain the continuity of conductive pathways through their own flow and interface reconstruction, thus exhibiting significant advantages in flexible conductive materials, thermal management materials, stretchable electronic devices, and smart composite materials. Introducing liquid metals into magnetic hydrogel systems is expected to effectively overcome the following performance shortcomings of existing magnetic hydrogels.

[0006] Patent application number "CN2024106643319" discloses "An anisotropic composite fiber hydrogel and its preparation method," which is composed of multiple composite hydrogel fibers tightly stacked and cross-linked in an aligned manner. Each hydrogel fiber has a hollow porous structure, consisting of a porous shell and a hollow cavity. The shell of the hydrogel fiber is composed of a dual-network polymer chain and magnetic liquid metal (MLM) embedded therein. The polymer chain includes flexible polyvinyl alcohol (PVA) and rigid cellulose nanofibers (CNF), and the MLM is obtained by coating magnetic nanoparticles with room temperature liquid metal (LM). The problem with this method is:

[0007] 1. Since the dual-network polymer chains (flexible polyvinyl alcohol PVA and rigid cellulose nanofibers CNF) are formed only through physical cross-linking and lack self-healing mechanisms such as dynamic covalent bonds or reversible non-covalent bonds, their stability is poor. Therefore, the gel network cannot achieve self-repair after mechanical damage or breakage, resulting in the material losing its function after damage and being unable to be reused, which significantly shortens the service life of the material.

[0008] 2. Due to inherent limitations of wet spinning technology, such as low production efficiency, complex process parameter control, and difficulty in ensuring fiber diameter uniformity, and because this patent requires a multi-step process of preparing single hollow porous fibers and then stacking and cross-linking them, the overall preparation process is time-consuming, inefficient, and difficult to meet the needs of large-scale industrial production, and the cost is high, which limits its promotion and application in practical engineering.

[0009] 3. Due to the high surface tension of magnetic liquid metal (MLM), poor interfacial compatibility with PVA / CNF polymer matrix, and lack of effective dispersion stabilization strategies, MLM is prone to agglomeration and sedimentation in gel network. This results in uneven dispersion of magnetic functional fillers within the material, which in turn leads to insufficient magnetic response performance of the overall composite material when subjected to an external magnetic field, making it impossible to achieve efficient and precise remote drive control. Summary of the Invention

[0010] To address the problems of poor softness, weak electrical and thermal conductivity, and insufficient environmental tolerance of existing hydrogels, this invention provides a liquid metal composite magnetic hydrogel with magnetic and thermal self-healing properties, its preparation method, and its applications.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing a liquid metal composite magnetic hydrogel with magnetic and thermal self-healing properties, comprising the following steps:

[0012] Step 1, Preparation of liquid metal dispersion:

[0013] Polyvinylpyrrolidone (PVP) was added to deionized water and stirred until completely dissolved. Then, gallium-indium room temperature liquid metal was added and dispersed using a cell disruptor to obtain a liquid metal dispersion.

[0014] Step 2, constructing a magnetic precursor system:

[0015] Acrylamide, crosslinking agent and initiator are dissolved in deionized water, argon gas is introduced to reduce oxygen content, then nano iron oxide particles are added, stirred evenly, and then the liquid metal dispersion obtained in step one is added to obtain an acrylamide precursor mixture containing liquid metal and magnetic particles.

[0016] Step 3, Preparation of carrageenan solution:

[0017] Carrageenan and potassium chloride are added to deionized water and heated and stirred in a constant temperature water bath to fully dissolve the carrageenan and obtain a carrageenan solution.

[0018] Step 4, magnetic field-induced orientation and thermal cross-linking curing:

[0019] The precursor mixture obtained in step two is added to the carrageenan solution obtained in step three. After mixing evenly under constant temperature conditions, it is poured into a mold. A magnetic field is applied to both the upper and lower sides of the mold to cause the iron oxide particles to migrate in a directional manner during the gel formation process, forming an oriented structure and being evenly distributed in the gel network. Subsequently, a free radical polymerization reaction is carried out under heating conditions to cause the acrylamide to crosslink and cure, fixing the oriented structure in the gel network.

[0020] Step 5, Low-temperature induced formation of dual networks:

[0021] The gel obtained in step four was refrigerated and allowed to stand at low temperature, allowing carrageenan to undergo thermally reversible physical cross-linking under the action of potassium ions. This resulted in the formation of a dense carrageenan gel network on the basis of the chemically cross-linked polyacrylamide network, yielding a dual-network composite hydrogel with magnetic and thermal self-healing properties.

[0022] Furthermore, the amounts of each raw material used in the method are as follows: carrageenan 0.5-1.0 g; potassium chloride 0.1-0.5 g; acrylamide 3-6 g; crosslinking agent 0.0001-0.0015 g; initiator 0.015-0.028 g; nano iron oxide particles 1-4 g; polyvinylpyrrolidone 0.2-0.5 g; gallium indium room temperature liquid metal 0.5-3 g; deionized water 10-50 mL.

[0023] Furthermore, in step one, PVP is used as a liquid metal surface modification material. Its mixed solution is placed in a cell disruptor for dispersion treatment for 1-3 hours, and a 60% amplitude is applied using a pulse mode of "on for 3 seconds, off for 2-3 seconds".

[0024] Furthermore, in step four, during the gelation process, a bidirectional magnetic field is simultaneously applied to the upper and lower sides of the mold to drive the iron oxide particles to undergo controllable directional migration along the magnetic field lines during the gel formation stage, thereby constructing an anisotropic ordered orientation structure within the gel network and achieving uniform distribution of particles throughout the entire gel system.

[0025] Furthermore, in step two, the crosslinking agent is N,N'-methylenebisacrylamide, the initiator is ammonium persulfate, and the particle size of the nano-iron oxide particles is 60–80 nm.

[0026] Furthermore, in step three, the water bath temperature is 80-95℃, and the time is 2 hours.

[0027] Furthermore, in step four, the thermal crosslinking curing is carried out in an oven at a temperature of 80°C for 12 hours.

[0028] Furthermore, in step five, the refrigeration temperature is 4°C and the settling time is 12 hours.

[0029] The above preparation method yields a liquid metal composite magnetic hydrogel with magnetic and thermal response self-healing properties.

[0030] The above-mentioned liquid metal composite magnetic hydrogels are used in magnetically controlled drives, flexible sensing, intelligent grasping, soft robots, and electromagnetic response devices.

[0031] Compared with the prior art, the advantages of the present invention are as follows:

[0032] (1) This invention uses carrageenan and polyacrylamide to construct a dynamic dual-network structure with reversible cross-linking properties (a static physical cross-linking network that is not PVA / CNF). At the same time, liquid metal and magnetic nanoparticles are uniformly dispersed in the gel matrix as synergistic composite fillers. Macroscopic bulk gels are also constructed through an in-situ gel integrated molding process, which realizes the synergistic integration of magnetic response driving, electrical and thermal conduction and thermal triggering self-healing functions, endowing the material with magnetic control driving capability. Furthermore, the introduction of liquid metal significantly improves its conductivity and thermal response capability, thereby realizing multi-physics field coupling response and functional integration, and expanding the application range of hydrogels in complex environments.

[0033] (2) The liquid metal used in this invention can not only exist as a conductive filler in this invention, but also form continuous or quasi-continuous conductive and thermal conductive pathways in the hydrogel network. During the process of material being heated or damaged, on the one hand, the excellent thermal conductivity can quickly transfer external heat to the damaged area, promote the untangling and recombination of carrageenan molecular chains, and further enhance the thermal healing ability of the double network gel. On the other hand, the liquid metal, with its high fluidity, good conductivity, deformability and adaptability and interface reconstruction ability, can reconnect conductive pathways in the local fracture area, restore structural integrity and functional connectivity, thereby achieving the synchronous restoration of structure and function.

[0034] (3) The magnetic Fe3O4 nanoparticles of this invention undergo directional alignment under an applied magnetic field, constructing an anisotropic magnetic microstructure. This endows the hydrogel with excellent magnetic responsiveness and controllable driving capability, enabling remote control, real-time adjustment, and directional motion control. Simultaneously, liquid metal (LM), as a flexible functional phase with high electrical and thermal conductivity, not only forms a continuous conductive / thermal network itself but also exhibits a significant synergistic effect with the directional Fe3O4 particles: the magnetic field orientation of the Fe3O4 particles guides the liquid metal to preferentially distribute along the same direction in the gel matrix, further enhancing the electrothermal transfer performance and driving response efficiency of the composite material in the magnetic field direction. This synergistic effect allows the hydrogel to achieve rapid and precise deformation and movement even under low magnetic fields, while possessing efficient thermal management capabilities. It fully leverages the unique advantages of liquid metal's "fluid conductivity + dynamic deformation," significantly improving the material's comprehensive performance in multi-physics field coupling responses.

[0035] (4) The polyacrylamide raw material of this invention provides a stable chemical cross-linking framework, while the thermally reversible physical cross-linking of carrageenan forms a second network, constructing a dual-network hydrogel with heat-induced self-healing properties. This dual-network structure not only endows the material with flame-retardant properties and reversible recombination capabilities under extreme environments such as high temperature and combustion, realizing a rapid and efficient self-healing process, but also provides a unique advantage for the conductive electromagnetic drive function of liquid metal and magnetic particles: the dynamically reversible carrageenan network can adaptively accommodate the flow deformation of liquid metal and redirect the orientation distribution of magnetic particles after self-healing, thereby repairing the conductive / magnetic pathways and restoring the electromagnetic drive and thermal conductivity of the material. Compared with traditional static networks, this design effectively avoids functional failure caused by gel breakage, ensuring that the hydrogel continuously and stably exerts magnetic response and conductive and thermal conductivity capabilities under extreme environments, laying a structural foundation for the synergistic integration of self-healing behavior and multi-physics coupling functions.

[0036] (5) By precisely controlling the amount of potassium chloride, the crosslinking density of carrageenan is effectively adjusted, thereby enhancing the self-healing ability of the double network gel under heating conditions. The higher the potassium chloride content, the more complete the crosslinking, and the more significant the thermo-induced self-healing performance of the gel. It can achieve flame retardancy and self-healing in extreme environments such as high temperature, thereby ensuring the integrity of the material structure and the continuous and stable performance of its function. At the same time, by introducing liquid metal, the conductivity of the gel system is improved, and by introducing magnetic components, it is given magnetic control driving ability, enabling it to be used continuously in extreme environments.

[0037] (6) In this invention, polyvinylpyrrolidone (PVP) is used as a dispersant and interface stabilizer for liquid metal. By pulverizing cells and applying a 60% amplitude pulse mode with a "3-second on, 2-3-second off" pulse, a stable PVP@GaIn dispersion system is formed, which effectively inhibits the aggregation and sedimentation of liquid metal droplets and makes them uniformly distributed in the hydrogel system. This uniform dispersion structure not only ensures the continuity of the electrical and thermal conduction pathways, but also helps to reduce stress concentration and improve the structural stability and recyclability of the material during deformation.

[0038] (7) This invention adopts a preparation strategy that combines magnetic field-induced molding and thermal crosslinking. By applying a bidirectional magnetic field to the mold, the iron oxide particles undergo controllable directional migration along the magnetic field lines during gel solidification, resulting in an anisotropic orientation distribution structure within the gel network, thus achieving stable fixation of the particles in the dual-network system. This structural design not only significantly improves the magnetic response efficiency and driving stability, effectively avoiding the adverse effects of particle agglomeration on mechanical properties in traditional random dispersion systems, but also has the following unique advantages for composite magnetic gel systems incorporating liquid metal: On the one hand, the directional arrangement of iron oxide particles provides a "guide template" for the distribution of liquid metal in the gel matrix, prompting the liquid metal to form continuous conductive / thermal microchannels along the same direction, thereby significantly enhancing the anisotropic conductivity and thermal conductivity of the composite material; on the other hand, the oriented magnetic particles and liquid metal synergistically construct a more efficient electro-magnetic-thermal coupling network, which can achieve lower energy loss and faster thermal response speed under magnetic field drive, further improving the comprehensive performance of the material in fields such as flexible drive and intelligent sensing. This invention provides a feasible and efficient technical approach for preparing high-performance hydrogels with controllable structure and synergistic function.

[0039] (8) The raw materials used in the preparation method of the present invention are readily available, the steps are simple, and the reaction conditions are mild. The resulting material has good structural stability and versatility. The prepared composite hydrogel has good application prospects in the fields of soft robots, flexible electronic devices, intelligent sensing and complex environment driving systems. Attached Figure Description

[0040] Figure 1 Flowchart of the preparation process of the dual-network hydrogel of this invention.

[0041] Figure 2 The microstructure of the dual-network hydrogel of the present invention is shown in the scanning electron microscope image; wherein, (a) is the SEMN morphology and EDS test image of the liquid metal gallium indium alloy; and (b) is the SEM image of the liquid metal composite polyacrylamide-carrageenan dual-network gel.

[0042] Figure 3 Digital photographs and VSM test diagrams of the dual-network hydrogel of this invention; wherein, (a) is a magnetically driven migration diagram of the hydrogel along a specified path; (b) is a VSM curve of the liquid metal composite iron oxide polyacrylamide-carrageenan dual-network gel and its freeze-dried state and strong magnetic vibration test of iron oxide particles.

[0043] Figure 4The rheological test results of the dual-network hydrogel of this invention show the storage modulus and loss modulus. Among them, (a) is the test results of the storage modulus and loss modulus of the liquid metal composite polyacrylamide-carrageenan dual-network gel at different frequencies; (b) is the test results of the storage modulus and loss modulus of the liquid metal composite polyacrylamide-carrageenan dual-network gel at different strains.

[0044] Figure 5 Electrochemical impedance spectroscopy and electronic conductivity test results of the dual-network hydrogel of this invention.

[0045] Figure 6 The present invention provides a digital display diagram of the heat healing of the dual-network hydrogel and a test diagram of its mechanical properties after heat healing; wherein, (a) is a diagram of the carrageenan-polyacrylamide composite hydrogel after heat self-healing; and (b) is a diagram of the tensile strength of the carrageenan-polyacrylamide composite hydrogel after heat self-healing.

[0046] Figure 7 Low-field NMR 3D imaging of PVP-modified liquid metal dispersions of this invention. Detailed Implementation

[0047] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0048] Example 1:

[0049] like Figure 1 The preparation method of a liquid metal composite magnetic hydrogel with magnetic and thermal self-healing properties is shown in the figure.

[0050] Step 1, Preparation of liquid metal dispersion:

[0051] 0.4 g of polyvinylpyrrolidone (PVP) was added to 20 mL of deionized water and stirred until completely dissolved. Then, 2 g of room temperature liquid metal in gallium indium was added. The mixture was then subjected to high-energy dispersion treatment for 1 h using a cell disruptor with an amplitude of 60% and a pulse mode of "on for 3 seconds, off for 2 seconds" to break the liquid metal into micron-sized droplets. Under the action of polyvinylpyrrolidone, a stable dispersion system was formed, resulting in a liquid metal dispersion.

[0052] Step 2, constructing a magnetic precursor system:

[0053] 4 g of acrylamide, 0.001 g of N,N'-methylenebisacrylamide (crosslinking agent) and 0.026 g of ammonium persulfate (initiator) were added to a reaction vessel, along with 15 mL of deionized water. The mixture was magnetically stirred at room temperature (25°C) for 1 hour to obtain an acrylamide base solution. Argon gas was then introduced into the acrylamide solution to reduce the oxygen content. 2 g of nano-iron oxide particles with a particle size of 60–80 nm were added and stirred until homogeneous. The liquid metal dispersion obtained in step one was then added to obtain an acrylamide precursor mixture containing liquid metal and magnetic particles.

[0054] Step 3, Preparation of carrageenan solution:

[0055] Add 0.75 g of carrageenan and 0.2 g of potassium chloride to 20 mL of deionized water, and stir in an 80°C constant temperature water bath for 2 hours to fully dissolve the carrageenan and form a homogeneous solution.

[0056] Step 4, magnetic field-induced orientation and thermal cross-linking curing:

[0057] The precursor mixture obtained in step two is added to the carrageenan solution obtained in step three. After mixing evenly under constant temperature conditions, the mixture is poured into a mold (a circular mold with a diameter of 10 cm and 25 mL of solution in this embodiment). A bidirectional magnetic field is simultaneously applied to the upper and lower sides of the mold to drive the iron oxide particles to undergo controllable directional migration along the magnetic field lines during the gel formation stage. This constructs an anisotropic ordered orientation structure within the gel network, achieving uniform distribution of particles throughout the entire gel system. The mold is then placed in an oven for thermal crosslinking and curing. The oven temperature is set to 80°C, and the curing time is 12 hours, allowing the polyacrylamide network to fully crosslink and form a dense gel network. Simultaneously, the liquid metal is uniformly distributed within the network.

[0058] Step 5, Low-temperature induced formation of dual networks:

[0059] The gel obtained in step four was refrigerated and allowed to stand at 4°C for 12 h to allow carrageenan to undergo thermally reversible physical cross-linking under the action of potassium ions, thereby forming a dense carrageenan gel network on the basis of the chemically cross-linked polyacrylamide network, resulting in a dual-network composite hydrogel with magnetic and thermal self-healing properties.

[0060] The dual-network composite hydrogel prepared by this invention can be used in magnetically controlled actuation, flexible sensing, intelligent grasping, soft robots, and electromagnetic response devices.

[0061] Example 2:

[0062] A method for preparing a liquid metal composite magnetic hydrogel with magnetic and thermal self-healing properties includes the following steps:

[0063] Step 1, Preparation of liquid metal dispersion:

[0064] 0.3 g of polyvinylpyrrolidone (PVP) was added to 20 mL of deionized water and stirred until completely dissolved. Then, 1 g of room temperature liquid metal in gallium indium was added. The mixture was then subjected to high-energy dispersion treatment for 1 h using a cell disruptor with an amplitude of 60% and a pulse mode of "on for 3 seconds, off for 3 seconds" to break the liquid metal into micron-sized droplets. Under the action of polyvinylpyrrolidone, a stable dispersion system was formed, resulting in a liquid metal dispersion.

[0065] Step 2, constructing a magnetic precursor system:

[0066] 3 g of acrylamide, 0.001 g of N,N'-methylenebisacrylamide (crosslinking agent) and 0.027 g of ammonium persulfate (initiator) were added to a reaction vessel, along with 15 mL of deionized water. The mixture was magnetically stirred at room temperature (25°C) for 1 hour to obtain an acrylamide base solution. Argon gas was then introduced into the acrylamide solution to reduce the oxygen content. 3 g of 60 nm nano-iron oxide particles were then added and stirred until homogeneous. Finally, the liquid metal dispersion obtained in step one was added to obtain an acrylamide precursor mixture containing liquid metal and magnetic particles.

[0067] Step 3, Preparation of carrageenan solution:

[0068] Add 0.65g of carrageenan and 0.3g of potassium chloride to 20 mL of deionized water, and stir in a 90℃ constant temperature water bath for 2 hours to fully dissolve the carrageenan and form a homogeneous solution.

[0069] Step 4, magnetic field-induced orientation and thermal cross-linking curing:

[0070] The precursor mixture obtained in step two is added to the carrageenan solution obtained in step three. After mixing evenly under constant temperature conditions, the mixture is poured into a mold (a circular mold with a diameter of 10 cm and 25 mL of solution in this embodiment). A bidirectional magnetic field is simultaneously applied to the upper and lower sides of the mold to drive the iron oxide particles to undergo controllable directional migration along the magnetic field lines during the gel formation stage. This constructs an anisotropic ordered orientation structure within the gel network, achieving uniform distribution of particles throughout the entire gel system. The mold is then placed in an oven for thermal crosslinking and curing. The oven temperature is set to 80°C, and the curing time is 12 hours, allowing the polyacrylamide network to fully crosslink and form a dense gel network. Simultaneously, the liquid metal is uniformly distributed within the network.

[0071] Step 5, Low-temperature induced formation of dual networks:

[0072] The gel obtained in step four was refrigerated and allowed to stand at 4°C for 12 h to allow carrageenan to undergo thermally reversible physical cross-linking under the action of potassium ions, thereby forming a dense carrageenan gel network on the basis of the chemically cross-linked polyacrylamide network, resulting in a dual-network composite hydrogel with magnetic and thermal self-healing properties.

[0073] Example 3:

[0074] A method for preparing a liquid metal composite magnetic hydrogel with magnetic and thermal self-healing properties includes the following steps:

[0075] Step 1, Preparation of liquid metal dispersion:

[0076] 0.5 g of polyvinylpyrrolidone (PVP) was added to 20 mL of deionized water and stirred until completely dissolved. Then, 3 g of room temperature liquid metal in gallium indium was added. The mixture was then subjected to high-energy dispersion treatment for 1 h using a cell disruptor with an amplitude of 60% and a pulse mode of "on for 3 seconds, off for 2 seconds" to break the liquid metal into micron-sized droplets. Under the action of polyvinylpyrrolidone, a stable dispersion system was formed, resulting in a liquid metal dispersion.

[0077] Step 2, constructing a magnetic precursor system:

[0078] 6 g of acrylamide, 0.0015 g of N,N'-methylenebisacrylamide (crosslinking agent) and 0.026 g of ammonium persulfate (initiator) were added to a reaction vessel, along with 20 mL of deionized water. The mixture was magnetically stirred at room temperature (25°C) for 1 hour to obtain an acrylamide base solution. Argon gas was introduced into the acrylamide solution to reduce the oxygen content. Then, 3 g of 80 nm nano-iron oxide particles were added and stirred until homogeneous. Finally, the liquid metal dispersion obtained in step one was added to obtain an acrylamide precursor mixture containing liquid metal and magnetic particles.

[0079] Step 3, Preparation of carrageenan solution:

[0080] Add 0.8 g of carrageenan and 0.5 g of potassium chloride to 20 mL of deionized water, and stir in an 80°C constant temperature water bath for 2 hours to fully dissolve the carrageenan and form a homogeneous solution.

[0081] Step 4, magnetic field-induced orientation and thermal cross-linking curing:

[0082] The precursor mixture obtained in step two is added to the carrageenan solution obtained in step three. After mixing evenly under constant temperature conditions, the mixture is poured into a mold (a circular mold with a diameter of 10 cm and 25 mL of solution in this embodiment). A bidirectional magnetic field is simultaneously applied to the upper and lower sides of the mold to drive the iron oxide particles to undergo controllable directional migration along the magnetic field lines during the gel formation stage. This constructs an anisotropic ordered orientation structure within the gel network, achieving uniform distribution of particles throughout the entire gel system. The mold is then placed in an oven for thermal crosslinking and curing. The oven temperature is set to 80°C, and the curing time is 12 hours, allowing the polyacrylamide network to fully crosslink and form a dense gel network. Simultaneously, the liquid metal is uniformly distributed within the network.

[0083] Step 5, Low-temperature induced formation of dual networks:

[0084] The gel obtained in step four was refrigerated and allowed to stand at 4°C for 12 h to allow carrageenan to undergo thermally reversible physical cross-linking under the action of potassium ions, thereby forming a dense carrageenan gel network on the basis of the chemically cross-linked polyacrylamide network, resulting in a dual-network composite hydrogel with magnetic and thermal self-healing properties.

[0085] Comparative Example 1:

[0086] A method for preparing a carrageenan-polyacrylamide composite hydrogel (without adding liquid metal and iron oxide nanoparticles) includes the following steps:

[0087] Step 1: Prepare carrageenan solution and acrylamide precursor solution.

[0088] Weigh 0.75 g of carrageenan and 0.2 g of potassium chloride and add them to a reaction vessel. Add 20 mL of deionized water and stir in a 90°C water bath for 2 hours to obtain a homogeneous carrageenan solution. Weigh 4 g of acrylamide, 0.001 g of N,N'-methylenebisacrylamide (crosslinking agent), and 0.026 g of ammonium persulfate (initiator) and add them to 15 mL of deionized water. Stir magnetically at 25°C for 1 hour to obtain an acrylamide base solution.

[0089] Step 2: Mixing and thermal cross-linking curing.

[0090] Add the acrylamide solution to the carrageenan solution and stir in an 80°C water bath for 2 hours to ensure thorough mixing. Pour the mixture into a 10 cm diameter circular mold (25 mL of solution), without placing a magnet. Place the mold in an oven for thermal crosslinking and curing at 80°C for 12 hours to allow the polyacrylamide network to fully crosslink and form a dense gel network.

[0091] Step 3: Low-temperature settling and double network formation.

[0092] The gel obtained in step two was placed in a refrigerator at 4°C and left to stand for 12 hours. The carrageenan network underwent thermally reversible cross-linking in the presence of potassium ions, forming a dense carrageenan-polyacrylamide dual-network hydrogel.

[0093] The hydrogel prepared by the method in Comparative Example 1 has an overall thickness of 10 mm. Both the upper and lower layers are carrageenan-polyacrylamide network structures, without a magnetic driving layer or liquid metal conductive pathways. Compared to Example 1 of this invention, the gel lacks magnetic responsiveness and liquid metal conductivity and thermal healing capabilities. After damage, it cannot quickly restore its overall structure and conductivity, but it still retains basic flexibility and mechanical support properties.

[0094] Comparative Example 2:

[0095] A method for preparing a carrageenan-polyacrylamide-iron oxide composite hydrogel (without adding liquid metal, only adding iron oxide nanoparticles), comprising the following steps:

[0096] Step 1: Prepare carrageenan solution and acrylamide precursor solution.

[0097] Weigh 0.75 g of carrageenan and 0.2 g of potassium chloride and add them to a reaction vessel. Add 20 mL of deionized water and stir in a 90°C constant temperature water bath for 2 hours to obtain a homogeneous carrageenan solution. Weigh 4 g of acrylamide, 0.001 g of N,N'-methylenebisacrylamide (crosslinking agent), and 0.026 g of ammonium persulfate (initiator) and add them to 15 mL of deionized water. Simultaneously add 2 g of iron oxide nanoparticles and stir magnetically at room temperature (25°C) for 1 hour, followed by ultrasonic dispersion treatment to ensure uniform dispersion of the iron oxide particles, thus obtaining an acrylamide base solution containing iron oxide.

[0098] Step 2: Mixing and thermal cross-linking curing.

[0099] Add the acrylamide solution containing iron oxide to the carrageenan solution and stir in an 80°C water bath for 2 hours to ensure thorough mixing. Pour the mixture into a 10 cm diameter circular mold (25 mL of solution), without placing a magnet. Then, place the mold in an oven for thermal crosslinking and curing at 80°C for 12 hours to ensure full crosslinking of the polyacrylamide network and fixation of the iron oxide particles within the network structure, forming a homogeneous composite system.

[0100] Step 3: Low-temperature settling and double network formation.

[0101] The gel obtained in step two was placed in a refrigerator at 4°C and left to stand for 12 hours. The carrageenan network underwent thermal reversible cross-linking under the action of potassium ions, forming a carrageenan-polyacrylamide dual network structure. At the same time, iron oxide particles were uniformly distributed in the gel matrix.

[0102] The hydrogel prepared in Comparative Example 2 has an overall thickness of 10 mm and is a carrageenan-polyacrylamide composite network structure with uniformly dispersed iron oxide particles inside, exhibiting certain magnetic responsiveness. However, due to the lack of a liquid metal conductive phase, the system lacks a continuous conductive pathway, resulting in weak overall conductivity. Furthermore, this gel does not possess the electronic and thermal conductivity properties brought by liquid metal, only exhibiting basic flexibility and a certain mechanical reinforcement effect. Therefore, although Comparative Example 2 imparts certain magnetic responsiveness to the material by introducing iron oxide particles, due to the lack of a magnetic field-induced structure and a liquid metal conductive phase, it is significantly inferior to Example 1 of the present invention in terms of magnetic drive, conductivity, and self-healing ability, further verifying the synergistic enhancement effect of the technical solution of the present invention.

[0103] The following tests were performed on Example 1 and Comparative Example 2:

[0104] 1. Morphological characterization of Example 1 and gallium-indium liquid metal:

[0105] SEM images of the fracture surface of the lyophilized composite gel were obtained using scanning electron microscopy, as shown below. Figure 2 (a) shows the scanning electron microscope (SEM) image of the gallium-indium (GaIn) alloy and the corresponding energy-dispersive X-ray spectroscopy (EDS) analysis results. The SEM image shows that the surface of the GaIn alloy is relatively smooth and the boundaries are clear after dispersion. The EDS surface scanning analysis results show that the main elements in the sample are gallium (Ga) and indium (In), and their characteristic peak positions are consistent with the standard spectrum. Figure 1 No obvious impurity elements were detected, indicating that the prepared liquid metal system has high purity. Furthermore, Ga and In elements are uniformly distributed within the scanning area, without elemental segregation or localized enrichment, indicating that the gallium-indium alloy has formed a homogeneous liquid metal system. Figure 2 As shown in (b), the hydrogel of Example 1 observed under a scanning electron microscope exhibits a distinct porous structure, indicating that the liquid metal composite magnetically responsive carrageenan composite polyacrylamide hydrogel network is tightly cross-linked. Digital photographs demonstrate the stretchability, deformation recovery stability, and formability of the liquid metal composite magnetically responsive carrageenan composite polyacrylamide bilayer hydrogel network.

[0106] 2. The magnetic properties of the liquid metal composite magnetically responsive hydrogel from Example 1 were evaluated using a vibrating sample magnetometer (VSM). The specific testing method is as follows:

[0107] The prepared liquid metal composite magnetically responsive carrageenan-polyacrylamide hydrogel was cut into small pieces of approximately 2 mm × 2 mm × 2 mm to ensure uniform sample thickness and avoid the influence of volume effects on magnetic measurements. The measurement temperature was room temperature (25℃), and the applied magnetic field range was set to ±2,000 Oe (Oersted). The magnetic field scanning mode was set to continuous scanning with a step size of 50 Oe and an average of 3 samplings per point to ensure measurement stability. The sample amplitude was set to 1 mm, and the vibration frequency was set to 40 Hz. The test results are as follows: Figure 3 As shown in (a), the hydrogel exhibits a clear magnetic response behavior, allowing it to be magnetically driven and move along a specified path. Figure 3 As shown in (b), the magnetic saturation intensity (Ms) is approximately 22 emu / g, and the remanence (Mr) is approximately 3 emu / g. When the applied magnetic field changes from negative saturation to positive saturation, the hydrogel can rapidly respond to the change in magnetic field direction, achieving directional alignment of the magnetically driven layer. The iron oxide nanoparticles form an ordered structure along the magnetic field lines, enabling the hydrogel to produce controllable displacement and directional deformation under the action of an external magnetic field, demonstrating excellent magnetic response performance.

[0108] The VSM test results show that the liquid metal composite magnetically responsive hydrogel can generate controllable magnetic actuation under the action of an external magnetic field, ensuring the functionality and structural stability of the magnetic actuation layer, and providing reliable support for magnetically controlled flexible devices and micro soft robots.

[0109] 3. The rheological storage modulus and loss modulus of the liquid metal composite magnetic gel in Example 1 were evaluated using a rheometer. The specific testing method is as follows:

[0110] The hydrogel was cut into disc samples with a diameter of 14 mm and a thickness of 2 mm, ensuring that the upper and lower surfaces were flat. The samples were placed in a parallel plate rheometer measurement system with a parallel plate gap of 1 mm. Test conditions were set as follows: temperature control: 25℃ (thermostat). Frequency scan ranged from 0.1 to 100 rad / s, and shear strain was maintained at 1% to ensure it remained within the linear viscoelastic range (LVR). Strain scan ranged from 0.01% to 1%, with a fixed frequency of 1 Hz, to determine the linear and nonlinear intervals. Test results are as follows. Figure 4 As shown. Within 0~100 rad / s -1 High-frequency scanning test results Figure 4 (a) shows that G' increases slightly with frequency, indicating that the dual-network structure maintains stability under dynamic loads, with a maximum value of 16 kPa. Liquid metal and iron oxide nanoparticles enhance the network rigidity while retaining elastic properties. These rheological test results demonstrate that the liquid metal composite magnetic hydrogel possesses high storage modulus and moderate loss modulus, combining mechanical support with flexible buffering characteristics, providing a reliable network foundation for magnetically controlled actuation and thermal self-healing functions. Figure 4(b) shows that under strain variations of 0.001%–1%, in the low shear strain region, the storage modulus (G') and loss modulus (G'') are significantly greater than that of G', indicating that the hydrogel exhibits typical solid elastic behavior and a stable network structure. At a strain of 1%, the storage modulus G' is approximately 125 kPa, and the loss modulus G'' is approximately 6 kPa, demonstrating that the hydrogel possesses good mechanical support capabilities and also exhibits certain viscous buffering properties. As the shear strain increases, G' gradually decreases, while G'' first decreases and then increases, indicating that the hydrogel network begins to undergo localized damage, exhibiting typical shear thinning behavior.

[0111] 4. Evaluate the electrical conductivity of the liquid metal composite magnetic carrageenan-polyacrylamide hydrogel of Example 1, and compare it with that of Comparative Example 2 (without liquid metal). Electrochemical impedance spectroscopy (EIS) was used for testing, and the specific testing method is as follows:

[0112] The hydrogel was cut into circular pieces (10 mm in diameter and 2 mm in thickness). The hydrogel was sandwiched between two conductive electrodes, ensuring good contact. The electrode gap was kept consistent with the sample thickness to avoid poor electrode contact affecting impedance measurements. The measuring instrument was an electrochemical workstation (CHI660E), with the AC voltage amplitude set to 10 mV, the frequency range set to 0.1 Hz ~ 1 MHz, and the measurement temperature set to 25℃ (room temperature). The test results are as follows... Figure 5 As shown, the conductivity analysis is as follows: Example 1, a liquid metal composite hydrogel, exhibits low impedance with a conductivity of approximately 15.1 S / m, significantly higher than that of Comparative Example 2 hydrogel (approximately 3.2 S / m). Nyquist curves show that Example 1 has a good electronic conduction pathway; the low-frequency region shows a near-vertical line, indicating that the liquid metal forms a continuous conductive network, which is beneficial for the simultaneous transport of ions and electrons. Test results indicate that the liquid metal forms a continuous conductive pathway in the network, allowing the hydrogel to recover conductivity through thermal self-healing after damage, making it suitable for flexible sensors or self-healing conductive devices. The liquid metal composite magnetic hydrogel significantly outperforms the comparative hydrogel without liquid metal and iron oxide in terms of conductivity, verifying the role of the liquid metal in forming a continuous conductive network in the hydrogel, providing a reliable electronic pathway for magnetic actuation and self-healing functions.

[0113] 5. To evaluate the heat-healing performance of the liquid metal composite magnetic carrageenan-polyacrylamide hydrogel of Example 1, a tensile testing machine was used to test its mechanical properties, and the morphological recovery after heat healing was recorded. The specific testing methods are as follows:

[0114] The hydrogel was cut into standard tensile specimens, approximately 30 mm × 5 mm × 2 mm in size. A section of the specimen was longitudinally cut midway through the specimen to ensure a clearly fractured state before testing. For heat healing, the cut hydrogel specimens were aligned and placed in a constant temperature water bath or oven to 80°C for 60 minutes. During heating, the liquid metal formed a thermally conductive pathway in the polyacrylamide network, accelerating the network reorganization at the fracture interface. The carrageenan helical structure underwent reversible cross-linking, achieving heat-induced self-healing. After heat healing, the specimens were removed and allowed to stand for 5 minutes to reach room temperature. Tensile mechanical testing was performed using an electronic universal tensile testing machine (e.g., Instron 3345). The tensile speed was set to 10 mm / min, and the test temperature was room temperature (25°C). The mechanical properties of the undamaged original hydrogel and the heat-healed hydrogel were compared. The test results and heat healing behavior are shown below. Figure 6 As shown in (a) and (b), the hydrogel exhibits a tensile strain of 37% and a tensile strength of 90 kPa after heat healing, demonstrating significant thermal self-healing ability. The tensile stress-strain curves show that the elastic and extended regions of the heat-healed hydrogel largely retain their original morphology, indicating that the dual-network structure successfully re-crosslinks under heating. Digital photographs show that the fracture interface closes well, and the overall morphology of the hydrogel is restored to its complete state, indicating that the synergistic effect of the thermal conductivity of liquid metal and the reversible crosslinking of carrageenan enables rapid self-healing of the fractured area. This demonstrates that liquid metal plays a crucial role in thermal conductivity and structural support during the self-healing process. Example 1: The liquid metal composite magnetic hydrogel possesses excellent thermal healing ability, enabling rapid restoration of mechanical properties and morphology after damage through heating, providing a reliable guarantee for the application of self-healing flexible devices and magnetically controlled smart materials.

[0115] 6. Evaluation of the low-field NMR 3D imaging test of the PVP-modified liquid metal dispersion in Example 1: A low-field NMR instrument (VTMR20-010V-I, main frequency 21MHz, center frequency should be 21.04MHz, magnetic field strength 0.5T) was used for 3D imaging. Before the test, the obtained PVP-modified liquid metal mixture was thoroughly shaken and mixed, and about 2 mL was transferred to a 10 mm diameter NMR-specific glass sample tube. The sample was allowed to stand for 10 min to remove bubbles and reduce interference from air bubbles on the imaging signal. The test temperature was controlled at 25 ± 0.5 ℃. 3D spin-echo imaging was used, with a field of view (FOV) of 50 mm × 50 mm × 50 mm, an acquisition matrix of 128 × 128 × 64, and a reconstructed voxel resolution of approximately 0.23 mm × 0.23 mm × 0.47 mm. The repetition time (TR) was set to 800 ms, the echo time (TE) to 18 ms, the number of excitations (NEX) to 8, and 20 layers were used for observation. The total acquisition time was approximately 57 min.

[0116] After imaging, the instrument's built-in 3D reconstruction software was used to reconstruct and analyze the signal distribution within the sample. Since liquid metal itself provides almost no proton signal, it typically appears as a low-signal or signal-deficient region in NMR images, while the water / organic solvent phase in the continuous phase appears as a stronger signal region. Therefore, the dispersion stabilizing effect of PVP on liquid metal particles can be evaluated by the spatial distribution, size uniformity, and presence of significant aggregation or sedimentation in the low-signal region. The test results are as follows... Figure 7 As shown in the low-field NMR 3D imaging results, the PVP-modified liquid metal mixture prepared in Example 1 exhibits a relatively uniform spatial distribution throughout the entire detection volume, with no obvious local aggregation or bottom deposition. This indicates that PVP modification significantly improves the dispersion uniformity and storage stability of the liquid metal in the system. The low-signal regions corresponding to the liquid metal are small and dispersed, indicating that PVP can effectively reduce the interfacial tension between liquid metal droplets and inhibit their aggregation, thereby obtaining a stable mixture system with good dispersion. This may be attributed to the adsorption of PVP molecules on the surface of liquid metal droplets, forming a steric hindrance protective layer, reducing the probability of direct contact and fusion between droplets, thereby improving the colloidal stability and dispersion uniformity of the system.

[0117] Embodiment 1 of the present invention is the preferred embodiment.

[0118] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a liquid metal composite magnetic hydrogel with magnetic and thermal self-healing properties, characterized in that, Includes the following steps: Step 1, Preparation of liquid metal dispersion: Polyvinylpyrrolidone (PVP) was added to deionized water and stirred until completely dissolved. Then, gallium-indium room temperature liquid metal was added and dispersed using a cell disruptor to obtain a liquid metal dispersion. Step 2, constructing a magnetic precursor system: Acrylamide, crosslinking agent and initiator are dissolved in deionized water, argon gas is introduced to reduce oxygen content, then nano iron oxide particles are added, stirred evenly, and then the liquid metal dispersion obtained in step one is added to obtain an acrylamide precursor mixture containing liquid metal and magnetic particles. Step 3, Preparation of carrageenan solution: Carrageenan and potassium chloride are added to deionized water and heated and stirred in a constant temperature water bath to fully dissolve the carrageenan and obtain a carrageenan solution. Step 4, magnetic field-induced orientation and thermal cross-linking curing: Add the precursor mixture obtained in step two to the carrageenan solution obtained in step three. Mix evenly under constant temperature conditions and pour into a mold. Apply a magnetic field to both the upper and lower sides of the mold to cause the iron oxide particles to migrate in a directional manner during the gel formation process, forming an oriented structure and being evenly distributed in the gel network. Subsequently, a free radical polymerization reaction was carried out under heating conditions to crosslink and cure the acrylamide, fixing the oriented structure in the gel network; Step 5, Low-temperature induced formation of dual networks: The gel obtained in step four was refrigerated and allowed to stand at low temperature, allowing carrageenan to undergo thermally reversible physical cross-linking under the action of potassium ions. This resulted in the formation of a dense carrageenan gel network on the basis of the chemically cross-linked polyacrylamide network, yielding a dual-network composite hydrogel with magnetic and thermal self-healing properties.

2. The method for preparing the liquid metal composite magnetic hydrogel with magnetic and thermal self-healing properties according to claim 1, characterized in that: The amounts of each raw material used in the method are as follows: carrageenan 0.5-1.0 g; potassium chloride 0.1-0.5 g; acrylamide 3-6 g; crosslinking agent 0.0001-0.0015 g; initiator 0.015-0.028 g; nano iron oxide particles 1-4 g; polyvinylpyrrolidone 0.2-0.5 g; gallium indium room temperature liquid metal 0.5-3 g; deionized water 10-50 mL.

3. The method for preparing the liquid metal composite magnetic hydrogel with magnetic and thermal self-healing properties according to claim 1, characterized in that: In step one, PVP is used as a liquid metal surface modification material. Its mixed solution is placed in a cell disruptor for dispersion treatment for 1-3 hours, and a 60% amplitude is applied using a pulse mode of "on for 3 seconds, off for 2-3 seconds".

4. The method for preparing the liquid metal composite magnetic hydrogel with magnetic and thermal self-healing properties according to claim 1, characterized in that: In step four, during the gelation process, a bidirectional magnetic field is simultaneously applied to the upper and lower sides of the mold to drive the iron oxide particles to undergo controllable directional migration along the magnetic field lines during the gel formation stage, thereby constructing an anisotropic ordered orientation structure within the gel network and achieving uniform distribution of particles throughout the entire gel system.

5. The method for preparing the liquid metal composite magnetic hydrogel with magnetic and thermal self-healing properties according to claim 1, characterized in that: In step two, the crosslinking agent is N,N'-methylenebisacrylamide, the initiator is ammonium persulfate, and the particle size of the nano-iron oxide particles is 60-80 nm.

6. The method for preparing the liquid metal composite magnetic hydrogel with magnetic and thermal self-healing properties according to claim 1, characterized in that: In step three, the water bath temperature is 80-95℃ and the time is 2 hours.

7. The method for preparing the liquid metal composite magnetic hydrogel with magnetic and thermal self-healing properties according to claim 1, characterized in that: In step four, the thermal crosslinking curing is carried out in an oven at a temperature of 80°C for 12 hours.

8. The method for preparing the liquid metal composite magnetic hydrogel with magnetic and thermal self-healing properties according to claim 1, characterized in that: In step five, the refrigeration temperature is 4°C and the settling time is 12 hours.

9. A liquid metal composite magnetic hydrogel with magnetic and thermal self-healing properties prepared by any one of claims 1 to 8.

10. The application of the liquid metal composite magnetic hydrogel according to claim 9 in magnetically controlled drive, flexible sensing, intelligent grasping, soft robots and electromagnetic response devices.

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