Liquid metal foam composite ink for 3D printing of three-dimensional structures, preparation method and application thereof

Abstract

The present invention relates to the technical field of liquid metal functional composite materials, and specifically relates to a liquid metal foam composite ink for 3D three-dimensional structure printing, and a preparation method and application thereof. The method comprises the following steps: (1) taking an appropriate amount of liquid metal and inorganic fillers and mixing them by mechanical force to obtain a liquid metal composite material; (2) subjecting the liquid metal composite material obtained in step (1) to vacuum treatment to obtain a liquid metal foam composite ink. The preparation method does not require the addition of additives such as water, swelling agents, foaming agents, and skeleton materials, and does not require freeze assistance, and the complex reaction processes and equipment required for additional auxiliary forming technologies such as photocuring, sintering, and casting. It can simply, quickly, and in large quantities prepare a new type of liquid metal foam composite ink with low filler content, high injectability, and high strength, which can print high-precision and uniform 3D three-dimensional structures and can be applied in the fields of biomedicine, aerospace, electronics, and thermal interfaces, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid metal functional composite materials, and particularly relates to a liquid metal foam composite ink for 3D three-dimensional structure printing, its preparation method and application. Background Art

[0002] Liquid metal (LM) exhibits 3D printing potential in numerous applications due to its high thermal conductivity, high electrical conductivity, and flexible characteristics. However, currently, liquid metal is mainly applied to 2D planar pattern printing. Compared with planar patterns, 3D three-dimensional printing can create complex geometric shapes, meet customized requirements, and optimize material usage, and its importance in fields such as medical, aerospace, electronics, and architecture is becoming increasingly prominent. However, successfully printing a 3D three-dimensional structure requires the ink used to have appropriate rheological properties. Therefore, it is necessary to process and modify the ink and regulate its rheology.

[0003] Currently, the viscosity and mechanical properties of the ink can be increased by adding fillers. For example, patent document CN116555654A discloses a liquid metal composite material with high printing accuracy and fluidity, which can be used as a new generation of flexible electronic 3D printing material. Among them, continuously increasing the filler content can further increase the ink strength, but it will cause printing blockage and interruption. Another method is to prepare liquid metal foam by adding water, foaming agents, expandants, and the template method. By using the effect of the oxide layer on the bubble surface, the density of the material is reduced and its mechanical strength is enhanced. For example, patent document CN115341117B discloses a liquid metal foam, a liquid metal foam composite material, and its preparation method, in which hydrogen gas generated by the reaction of liquid metal oxide and water creates a porous structure inside the liquid metal.

[0004] However, these additional additives will cause problems such as structural instability, corrosion, and residue. For example, water-assisted spontaneous foaming will continue after printing, resulting in changes in the size of the printed structure and structural instability, and hardening over a long time will limit its flexible performance; the foaming agent is easily corroded by the liquid metal to form intermetallic compounds, affecting the performance of the liquid metal foam. Therefore, there is an urgent need to develop a new type of liquid metal ink with low filler content, high injectability, and high strength to meet the printing requirements of 3D three-dimensional structures. Summary of the Invention

[0005] Aiming at the problems existing in the application of liquid metal, the present invention provides a preparation method for a liquid metal foam capable of printing 3D three-dimensional structures. Through ink formulation and vacuum adjustment, a three-dimensional printing structure with programmable porosity and adjustable strength can be created.

[0006] In the present invention, the liquid metal composite material refers to a liquid metal composite material obtained by adding inorganic fillers to liquid metal.

[0007] In the present invention, the liquid metal foam composite ink refers to the liquid metal foam composite ink obtained by subjecting the liquid metal composite material to vacuum processing.

[0008] In the preparation process of the liquid metal composite material and the liquid metal foam composite ink in the present invention, no templates or other materials (such as water, expandable particles, foaming agents, templating agents, organic hollow framework materials, etc.) are required, and the preparation process, equipment, and operation are simple. The present invention manufactures the liquid metal foam composite ink through vacuum processing. Specifically, the microbubbles generated during the preparation of the liquid metal and the inorganic filler are used as nucleating agents, and a porous structure with a controllable porosity is generated inside the liquid metal composite material through the ink formulation and vacuum control.

[0009] The present invention is realized through the following technical solutions

[0010] A preparation method of a liquid metal foam composite ink for 3D stereoscopic structure printing, characterized by comprising the following steps:

[0011] (1) Take an inorganic filler with a volume fraction of 1.25 vol% - 15 vol% and mix it with the liquid metal by mechanical force to obtain a liquid metal composite material, where the liquid metal is one of gallium, gallium-indium alloy, gallium-indium-tin alloy, or a mixture of the above liquid metals, and the inorganic filler is at least one of zinc oxide, tungsten oxide, gallium oxide, or their graded mixture;

[0012] (2) Subject the liquid metal composite material obtained in step (1) to vacuum treatment to obtain a liquid metal foam composite ink; the use of water, expandable particles, foaming agents, templating agents, and organic hollow framework materials is not included in the preparation process of the liquid metal foam composite ink.

[0013] Among them, the particle size of the inorganic filler in step (1) is 10 nanometers - 20 micrometers;

[0014] Further, the mechanical force in step (1) is provided by ball milling, grinding, or sanding.

[0015] Further, the grinding time in step (1) is 10 - 60 min, and the rotation speed is 10 - 130 rpm, with the aim of uniformly mixing the liquid metal and the filler into a paste-like state.

[0016] Further, the vacuum treatment method in step (2) is at least one of a vacuum pump, a vacuum chamber, a vacuum mixer, and a vacuum freeze dryer.

[0017] Further, the vacuum degree in step (2) is 10 - 100 kPa, and the time is 10 - 300 s.

[0018] On the other hand, the present invention provides a liquid metal foam composite ink for 3D stereostructure printing, which is prepared by the aforementioned preparation method, and the liquid metal foam ink does not include water, swelling particles, foaming agents, templating agents, and organic hollow framework materials.

[0019] Furthermore, when using the liquid metal foam composite ink for 3D printing, no additional auxiliary forming techniques are required, and the additional auxiliary forming techniques include freeze assistance, photocuring, sintering, and casting.

[0020] Furthermore, the porosity and strength of the liquid metal foam composite ink are controlled according to the ink formula and vacuum regulation, presenting a porous structure with multiple internal bubbles.

[0021] On the other hand, the present invention provides an application of the liquid metal foam composite ink in the fields of biomedicine, aerospace, electronics, and thermal interfaces.

[0022] The present invention also provides an application of the above liquid metal foam composite ink in the fields of biomedicine, aerospace, electronics, and thermal interfaces.

[0023] The principle of the present invention is as follows: (1) In step (1), mechanical force mixing can enable the liquid metal and inorganic fillers to form lattice penetration and coordination, changing the liquid metal from a Newtonian fluid to a non-flowing fluid state of paste, and finally obtaining a liquid metal composite material; the porosity and strength of the liquid metal foam composite ink obtained in step (2) can be controlled according to the ink formula and vacuum regulation, presenting a porous structure with multiple internal bubbles. The reason is that the microbubbles generated during the mixing process can serve as nucleation points for bubbles in the liquid metal composite material. Under vacuum pumping, these microbubbles provide a low-pressure environment in the local area, prompting more gas to precipitate from the liquid metal or fillers to form new bubbles, thereby preparing a liquid metal foam composite material. Compared with the use of additives such as water, swelling particles, foaming agents, templating agents, and organic hollow framework material additives, this method can introduce air through the mechanochemical action during the preparation of the liquid metal composite ink, and then generate microbubbles, which are used as vacuum foaming nucleating agents to prepare the liquid metal foam composite ink. In the bubble structure of the liquid metal foam composite ink, the surface gallium oxide provides additional strength and support for the overall ink, laying a foundation for the printing of 3D stereostructures, so that when using the liquid metal foam composite ink for 3D printing, no additional auxiliary forming techniques including freeze assistance, photocuring, sintering, and casting are required.

[0024] The beneficial effects of the present invention include: providing a liquid metal foam composite ink and a preparation method thereof. The preparation method does not require the addition of additives such as water, expanders, foaming agents, and skeleton materials, nor does it require freezing assistance, and the complex reaction processes and equipment required by additional auxiliary forming technologies such as photocuring, sintering, and casting. It can simply, quickly, and in large quantities prepare the liquid metal foam composite ink. A new type of liquid metal ink with low filler content, high injectability, and high strength is obtained. The high-strength ink obtained by rheological regulation can print high-precision and uniform 3D three-dimensional structures. It can be applied in the fields of biomedicine, aerospace, electronics, and thermal interfaces, etc. Description of the Drawings

[0025] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not constitute a limitation to the embodiments of the present invention. In the drawings:

[0026] Figure 1 It is a flowchart for the preparation of the liquid metal foam composite ink. After adding inorganic fillers to the liquid metal, a liquid metal composite material is formed, and the liquid metal foam composite ink is further prepared by vacuum processing;

[0027] Figure 2 It is an image of the appearance and volume change of the liquid metal composite material with different filler volume fractions and the liquid metal foam composite ink after vacuum processing shown in Comparative Example 1 and Example 2;

[0028] Figure 3 It is an SEM image of the liquid metal foam composite ink with different filler volume fractions in Example 2;

[0029] Figure 4 It is an SEM image of the liquid metal foam composite ink obtained with different vacuum times in Example 3;

[0030] Figure 5 It is the viscosity test value of the liquid metal foam composite ink with different filler volume fractions in Example 2;

[0031] Figure 6 It is the comparison value of the viscosity test of the liquid metal composite material with different filler volume fractions and the liquid metal foam composite ink after vacuum processing shown in Comparative Example 1 and Example 2;

[0032] Figure 7 It is the test value of the storage modulus and loss modulus of the liquid metal foam composite ink with different filler volume fractions in Example 2;

[0033] Figure 8 It is the comparison value of the viscosity test of the liquid metal composite material with different filler volume fractions and the liquid metal foam composite ink after vacuum processing shown in Comparative Example 1 and Example 2;

[0034] Figure 9 For Comparative Example 2 and Example 2, the printed single-line structure and the changes after being placed for one day;

[0035] Figure 10 It is a 3D stereoscopic structure image printed with liquid metal foam. Detailed implementation manners

[0036] In order to make the objectives, technical solutions and advantages of the present invention clearer and more definite, the implementation details of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] It should be particularly noted that in the embodiments of the present invention, the intention of all uses of expressions such as "first" and "second" is only to distinguish two entities or parameters with the same name but different. Therefore, the use of "first" and "second" is only for the convenience of expression and should not be regarded as any limitation to the embodiments of the present invention. This will not be explained one by one in the subsequent embodiments.

[0038] It should be understood that the exemplary embodiments described herein are only illustrative examples of the present invention. Although several embodiments are described in detail in the text, for those skilled in the art, various modifications and changes are completely feasible without substantially departing from the subject matter of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

[0039] Comparative Example 1

[0040] 1.818 g of 20 nm tungsten oxide and 127.19 g of gallium-indium-tin liquid metal were placed in an agate automatic mortar and ground for 20 min in an air environment to obtain a paste-like LM-WO3 (1.25 vol%) composite material.

[0041] 3.635 g of 20 nm tungsten oxide and 125.38 g of gallium-indium-tin liquid metal were placed in an agate automatic mortar and ground for 20 min in an air environment to obtain a paste-like LM-WO3 (2.5 vol%) composite material.

[0042] 7.27 g of 20 nm tungsten oxide and 122.36 g of gallium-indium-tin liquid metal were placed in an agate automatic mortar and ground for 20 min in an air environment to obtain a paste-like LM-WO3 (5 vol%) composite material.

[0043] 10.905 g of 20 nm tungsten oxide and 119.14 g of gallium-indium-tin liquid metal were placed in an agate automatic mortar and ground for 20 min in an air environment to obtain a paste-like LM-WO3 (7.5 vol%) composite material.

[0044] 14.54 g of 20 nm tungsten oxide and 115.92 g of gallium-indium-tin liquid metal were placed in an automated agate mortar and ground for 20 min in an air environment to obtain a paste-like LM-WO3 (10 vol%) composite material.

[0045] 18.175 g of 20 nm tungsten oxide and 112.7 g of gallium-indium-tin liquid metal were placed in an automated agate mortar and ground for 20 min in an air environment to obtain a paste-like LM-WO3 (10 vol%) composite material.

[0046] Rheological tests were further carried out on them.

[0047] Comparative Example 2

[0048] 7.27 g of 20 nm tungsten oxide and 122.36 g of gallium-indium-tin liquid metal were placed in an automated agate mortar and ground for 20 min in an air environment to obtain a paste-like LM-WO3 (5 vol%) composite material. Subsequently, 6.48 g of water was added and grinding was continued for 5 min to obtain an H20-LM-WO3 (5 vol%) foam composite material. It was loaded into a 10 ml syringe and printed using a 0.7 mm nozzle through the program set by a direct-write 3D printer.

[0049] The accuracy of the printing ink was 0.7 mm. After standing for one day, the accuracy decreased to 1 mm, and unevenness and roughness appeared on the surface of the printing ink.

[0050] Example 1

[0051] 1.4 g of zinc oxide and 127.19 g of gallium-indium-tin liquid metal were placed in an automated agate mortar and ground for 40 min in an air environment to obtain a paste-like liquid metal composite material. Subsequently, it was placed in a vacuum chamber and evacuated at 10 kPa for 300 s to obtain a liquid metal-zinc oxide foam composite ink.

[0052] Example 2

[0053] Six liquid metal composite materials in Comparative Example 1 were respectively placed in a vacuum chamber and evacuated at 100 kPa for 60 s to obtain porous liquid metal-tungsten oxide foam composite inks. They were loaded into 10 ml syringes and printed using a 0.7 mm nozzle through the program set by a direct-write 3D printer.

[0054] The accuracy of the printing ink was about 0.7 mm. After standing for one day, the accuracy remained unchanged at 0.7 mm, and the surface of the printing ink was smooth.

[0055] Scanning electron microscope images were further taken of them, and their viscosity and modulus values were measured using a rotational rheometer. It was measured that as the filler content increased in the liquid metal-tungsten oxide foam composite ink, the total volume of bubbles first increased and then decreased. The viscosity and modulus of the liquid metal foam composite ink were greatly improved compared to the liquid metal composite material.

[0056] Example 3

[0057] Five equal portions of the LM-WO3 (5 vol%) composite material obtained in Example 2 were separated and placed in a vacuum chamber. They were evacuated for 0 s, 10 s, 60 s, 90 s, and 120 s respectively under a condition of 100 kPa to obtain liquid metal-tungsten oxide foam composite inks with different vacuum times.

[0058] Scanning electron microscope images were further taken of them. It was observed that under a vacuum condition of 100 kPa, as the vacuum time increased, the volume of cavities first increased and then decreased.

[0059] Figure 1 The preparation flow chart of the liquid metal foam composite ink is shown. The pure liquid metal presented a fluid state with low viscosity and spontaneously shrank into spherical droplets due to the action of high surface tension; after adding inorganic fillers, a uniform paste-like liquid metal composite material was formed; further vacuum processing formed a porous liquid metal foam composite ink with volume expansion.

[0060] Figure 2 The appearance and volume change images of the liquid metal composite materials with different filler volume fractions shown in Comparative Example 1 and Example 2 and the liquid metal foam composite ink after vacuum processing are shown. It can be seen from the figure that the volume of the liquid metal composite material increased significantly after vacuum processing, and as the filler volume fraction increased, the total volume of bubbles first increased and then decreased. Among them, the total volume of the liquid metal foam composite ink can reach up to 2.5 times the total volume of the liquid metal composite material.

[0061] Figure 3 The SEM images of the liquid metal foam composite inks with different filler volume fractions in Example 2 are shown. It can be seen from the figure that increasing the filler content led to an increase in the number of bubbles. The filler particles can act as nucleation sites to help gas precipitate from the liquid metal matrix to form bubbles. A higher filler content provides more nucleation sites, thus increasing the total number of bubbles.

[0062] Increasing the filler content also led to a decrease in the bubble size. This is because more filler particles mean that the bubble nucleation sites are more dispersed, and the available volume near each nucleation site is smaller, thus restricting the growth space of individual bubbles.

[0063] Figure 4The SEM images of the liquid metal foam composite inks obtained under different vacuum times in Example 3 are shown. It can be seen from the figure that under the vacuum condition of 100 kPa, as the vacuum time increases, the volume of cavities first increases and then decreases. In a short time, the original microbubbles serve as nucleation points and gradually expand under the low-pressure state, and the total volume of the foam pores increases. However, when the vacuum time is too long and exceeds 60 s, the continuous low pressure causes the pores to merge and collapse into a layered structure after the vacuum is withdrawn, and the total volume of the foam pores decreases.

[0064] Figure 5 The viscosity test values of the liquid metal foam composite inks with different filler volume fractions in Example 2 are shown. It can be seen from the figure that as the volume fraction of the filler increases, the viscosity value of the liquid metal foam composite ink gradually increases.

[0065] Figure 6 The viscosity test comparison values of the liquid metal composites with different filler volume fractions shown in Comparative Example 1 and Example 2 and the liquid metal foam composite ink after vacuum processing are shown. It can be seen from the comparison values that the viscosity of the liquid metal foam is significantly improved compared with the liquid metal ink before vacuum. The micro-pores play a key role in it, and the larger the total volume of the bubbles, the more obvious the influence on the rheological behavior of the liquid metal. The rheological behavior at a liquid metal filler volume fraction of 5% is close to the viscosity value of a liquid metal ink with a filler volume fraction of 10% before vacuum. It significantly reduces the filler volume fraction required to reach a high viscosity.

[0066] Figure 7 The storage modulus and loss modulus test values of the liquid metal foam composite inks with different filler volume fractions in Example 2 are shown. It can be seen from the figure that as the volume fraction of the filler increases, the storage modulus and loss modulus values of the liquid metal foam composite ink gradually increase.

[0067] Figure 8 The storage modulus and loss modulus value test comparison values of the liquid metal composites with different filler volume fractions shown in Comparative Example 1 and Example 2 and the liquid metal foam composite ink after vacuum processing are shown. It can be seen from the comparison values that the modulus of the liquid metal foam is significantly improved compared with the liquid metal ink before vacuum.

[0068] Figure 9Shows the printed single-line structure of Comparative Example 2 and Example 2 and the changes after one day of placement. The upper figure is the image of the H20-LM-WO3 (5 vol%) foam composite with water as an additive before and after placement. The accuracy of the printing ink is 0.7 mm. After one day of placement, the accuracy drops to 1 mm, and the surface of the printing ink becomes uneven. The lower figure is the image of the LM-WO3 (5 vol%) foam composite with vacuum foaming of the present invention before and after placement. The accuracy of the printing ink is about 0.7 mm. After one day of placement, the accuracy remains unchanged at 0.7 mm, and the surface of the printing ink is smooth.

[0069] Figure 10 Shows the 3D stereoscopic structure image printed with liquid metal foam, and the printing accuracy is 180 μm. It demonstrates the high strength, high viscosity and high modulus of liquid metal foam, which can achieve self-supporting three-dimensional forming without relying on any auxiliary forming means (such as freeze assistance, photocuring, sintering, casting, etc.) during the printing process, so as to construct a printed product with a 3D stereoscopic structure. By further designing the printing path, it can be applied to the manufacture of complex structures in the fields of biomedicine, aerospace, electronics and thermal interfaces.

[0070] The physical and chemical property detection of the liquid metal foam composite ink includes:

[0071] Rheology of the ink: The rheological properties of the ink were evaluated using an MCR302 rheometer (Anton Paar, Austria).

[0072] The measurement was carried out using a plate-plate geometry with a diameter of 8 mm and a gap of 1 mm, maintaining a constant temperature of 25°C.

[0073] Microstructural characterization: The liquid metal foam composite ink was frozen with liquid nitrogen and truncated, and then the cross-sectional morphology of the ink was characterized using a scanning electron microscope (SEM,

[0074] Hitachi S-4800).

[0075] In summary, to obtain a liquid metal foam composite material with the highest porosity, a moderate filler volume fraction (about 5%), a small particle size (20 nm), and a moderate vacuum time (60 s) can be selected. A higher porosity can increase the content of the gallium oxide layer spontaneously produced on the bubble surface, and the role of the oxide layer on the bubble surface can be used to reduce the density of the material and improve its mechanical strength. In the preparation process of the present invention, no templates or other materials (such as water, expandable particles, foaming agents, templating agents, organic hollow skeleton materials, etc.) are required, and its preparation process, equipment, and operation are simple. The adverse effects of additives on ink printing are avoided. For example, water-assisted spontaneous foaming will continue after printing, resulting in changes in the size of the printed structure and structural instability, and hardening over a long time will limit its flexible performance.

[0076] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing liquid metal foam composite ink for 3D structure printing, characterized in that: It consists of the following steps: (1) An inorganic filler having a volume fraction of 1.25 vol% to 15 vol% is mixed with a liquid metal by mechanical force to obtain a liquid metal composite material, wherein the liquid metal is one or a mixture of metal gallium, a gallium-indium alloy, a gallium-indium-tin alloy, and the inorganic filler is at least one of zinc oxide, tungsten oxide, and gallium oxide, or a graded mixture thereof; (2) The liquid metal composite material obtained in step (1) is subjected to vacuum treatment, the vacuum degree is 10-100 kPa, and the time is 10-300 s. The porosity and strength of the liquid metal foam composite ink are controlled by adjusting the ink formula and vacuum to obtain a liquid metal foam composite ink having a porous structure with multiple bubbles inside. The preparation process of the liquid metal foam composite ink does not include the use of water, expansion particles, foaming agent, template agent, and organic hollow skeleton material.

2. The method for preparing liquid metal foam composite ink for 3D structure printing according to claim 1, characterized in that: The particle size of the inorganic filler in step (1) is 10 nanometers to 20 micrometers.

3. The method for preparing liquid metal foam composite ink for 3D structure printing according to claim 2, characterized in that: The mechanical force in step (1) is provided by ball milling, grinding or sand milling.

4. The method for preparing liquid metal foam composite ink for 3D structure printing according to claim 3, characterized in that: The grinding time in step (1) is 10-60 min, and the rotation speed is 10-130 rpm, the purpose of which is to evenly mix the liquid metal and the filler into a paste.

5. The method for preparing liquid metal foam composite ink for 3D structure printing according to claim 4, characterized in that: The vacuum treatment method in step (2) is at least one of a vacuum pump, a vacuum box, a vacuum mixer, and a vacuum freeze dryer.

6. A liquid metal foam composite ink for 3D structure printing, characterized in that: The liquid metal foam composite ink is prepared by the preparation method described in any one of claims 1 to 5, and presents a porous structure with multiple bubbles inside. The liquid metal foam ink does not include water, expansion particles, foaming agent, template agent, and organic hollow skeleton material.

7. The liquid metal foam composite ink according to claim 6, characterized in that: When the liquid metal foam composite ink is used for 3D printing, no additional auxiliary molding technology is required. The additional auxiliary molding technology includes freezing assistance, light curing, sintering, and casting.

8. Application of the liquid metal foam composite ink according to any one of claims 6 to 7 in the fields of biomedicine, aerospace, electronics and thermal interface.

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