Liquid metal nanodroplet self-sintering composite film preparation method and application thereof

Abstract

The present application relates to liquid metal composite film, and in particular to a preparation method of liquid metal nanodroplet spontaneous sintering composite film and application thereof. In the dispersion liquid, the liquid metal micro-nano droplet is spontaneously sintered in the evaporation process by using the conductive two-dimensional material Mxene, and a liquid metal composite film is formed. The liquid metal / MXene composite film obtained by the present application has a continuous self-oscillation function under a humidity gradient. The continuous self-oscillation function can be used to cut the magnetic induction lines in the magnetic field to generate an induced current. The liquid metal / MXene composite dispersion liquid prepared by the method can be used as conductive 'ink', and can induce the spontaneous sintering of liquid metal micro-nano droplets during the solvent evaporation process. Meanwhile, the liquid metal / MXene composite dispersion liquid can be used to prepare conductive self-oscillation power generation devices. The method has wide application prospects in the fields of printed electronics technology, sensors, flexible actuation, self-powered devices and environmental micro-energy collection.

Description

Technical Field

[0001] This invention relates to liquid metal composite films, specifically a method for preparing spontaneously sintered composite films of liquid metal nanodroplets and its application. Background Technology

[0002] Liquid metals are metals or alloys that exhibit excellent fluidity, readily deform under external forces, and remain liquid at room temperature. Furthermore, their good electrical conductivity and low viscosity make them promising candidates for applications in flexible electronic devices, conductive inks, conductive composite materials, and flexible sensors, and they are a hot research topic in the field of new materials.

[0003] Due to the high surface tension of liquid metals (e.g., the surface tension of gallium-indium alloy is 624 mN / m), -1 Liquid metals have poor affinity with many materials and substrates. Therefore, they are subjected to micro- and nano-processing such as ultrasound. However, the liquid metal micro- and nano-droplet dispersions obtained after ultrasound often require pressure sintering or laser sintering, which are energy-intensive and complicated (Adv. Funct. Mater. 2018, 28, 1804197).

[0004] Studies have found that a 0-10 nm thick oxide shell easily forms on the surface of liquid metal micro / nanodroplets. Therefore, only by increasing the surface tension and breaking down the oxide shell can the liquid metal micro / nanodroplets fuse to achieve the sintering process (Nat. Comm. 2019, 10:3514). Literature reports that liquid metal micro / nanodroplet dispersions obtained with the assistance of biomass nanofibers can generate high capillary forces during drying at room temperature and pressure, thereby breaking down the outer shell of the liquid metal micro / nanodroplets and allowing the internal liquid metal to flow out and fuse. However, biomass nanofibers are electronic insulators, and residual biomass nanofibers inevitably remain inside the sintered liquid metal, leading to a decrease in overall conductivity (Nat. Comm. 2019, 10:3514).

[0005] A search of existing technologies revealed that patent application CN 112538290 A, published on March 23, 2021, discloses a method for inducing the sintering of liquid metal micro / nanodroplets using nanoclay. The method includes: adding liquid metal to a nanoclay dispersion and ultrasonically breaking it down into nanoparticles to obtain a suspension of liquid metal nanoparticles; then drying the suspension to allow the liquid metal to fuse and sinter under capillary forces. However, this technology has limitations because the nanoclay used is not a conductive two-dimensional material, and it can only be used as a conductive coating or ink, making it difficult to obtain a complete flexible film material and hindering subsequent material applications. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a method for preparing spontaneously sintered composite thin films of liquid metal nanodroplets that is simple to operate, low in cost, and easy to industrialize, as well as its application.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a liquid metal nanodroplet spontaneously sintered composite film: using conductive two-dimensional material Mxene in a dispersion to spontaneously sinter liquid metal micro- and nano-droplets during evaporation, forming a liquid metal composite film.

[0009] To elaborate further:

[0010] 1) Prepare an aqueous solution of anionic surfactant;

[0011] 2) Add the liquid metal to the solution from step 1);

[0012] 3) In an ice-water bath atmosphere, liquid metal is split by ultrasonic cavitation to form a micro-nano droplet dispersion;

[0013] 4) Add the dispersion obtained by ultrasonication in step 3) to the MXene nanosheet dispersion and mix evenly; after uniform mixing, dry to form a film to obtain a conductive MXene / liquid metal heterogeneous thin film material.

[0014] The concentration of the anionic surfactant in the aqueous solution is 0.02-0.06 wt%; wherein,

[0015] The anionic surfactant is one or more of sodium alkyl sulfonate, sodium alkyl aryl sulfonate, sodium alkyl sulfate, sodium alginate (SA), hyaluronic acid (HA), sodium carboxymethyl cellulose (CMC), and quaternized chitosan (Qch).

[0016] The role of the added anionic surfactant is to form a protective layer on the surface of liquid metal micro- and nano-droplets, thereby improving their chemical and colloidal stability.

[0017] The aqueous solution is water or a mixture of water and an organic solvent; wherein the water volume content in the mixture is ≥50%, and the organic solvent is ethanol, DMF, DMSO, or ethyl acetate.

[0018] The concentration of the liquid metal added to the solution in step 1) is 0.5-1 wt%.

[0019] The liquid metal is a metal that is liquid at room temperature and has a melting point between 0 and 100°C.

[0020] The metal is selected from one or more of gallium (Ga), indium (In), tin (Sn), and alloys of the aforementioned metals.

[0021] Step 3) involves using the solvent cavitation effect induced by ultrasound at 0–40°C and with an ultrasonic power ≥200W to split the liquid metal and form a micro-nano liquid metal droplet dispersion with a diameter of 50–300 nm.

[0022] The MXene nanosheet dispersion was obtained by adding MXene nanosheets to an aqueous solution, and the concentration of MXene in the dispersion was 0.001-30 mg / mL. -1 The MXene nanosheets are 1 to 4 atomic layers thick, with a total thickness of ≤3 nm. Preferably, the MXene nanosheets can be obtained by chemical etching of the MAX phase, for example, by etching away the Al phase of the Ti3AlC2 intermediate layer with HCl+LiF, and then ultrasonically exfoliating to obtain the MXene nanosheets.

[0023] The aqueous solution in the MXene nanosheet dispersion and the aqueous solution in the anionic surfactant can be the same or different, selected from water or a mixture of water and an organic solvent; wherein, the water volume content in the mixture is ≥50%, and the organic solvent is ethanol, DMF, DMSO, or ethyl acetate. The aqueous solution or dispersion is mixed by natural diffusion or external stirring.

[0024] In step 4), the mass ratio of MXene to liquid metal droplets is 1 to 4.

[0025] In step 4), the water content of the dispersion system is ≥50%.

[0026] The functions of the aforementioned conductive two-dimensional material MXene are: firstly, to increase its capillary force during the evaporation and drying process, thereby promoting the sintering and fusion of liquid metal micro- and nano-droplets; secondly, as a hydrophilic and conductive two-dimensional material, MXene can be used to obtain thin film materials that are conductive on both sides and possess the intelligent function of continuous oscillation.

[0027] An application of the self-sintering composite thin film of liquid metal nanodroplets prepared by the method described above, specifically its application in electromagnetic induction.

[0028] Principle of this invention:

[0029] This invention involves uniformly mixing anionic surfactants with water before adding liquid metal and then ultrasonically dispersing it. The anions can cross-link with metal ions on the particle surface to form a protective layer in the form of a microgel, thereby improving the colloidal stability of the liquid metal micro / nano droplets and enhancing the dispersion stability of the system after the addition of MXene nanosheets. During the evaporation and drying process, MXene nanosheets tend to accumulate in the upper liquid layer, generating a huge capillary force, which helps the sintering and fusion of the liquid metal micro / nano droplets.

[0030] Advantages of this invention:

[0031] This invention utilizes the conductive two-dimensional material MXene to assist in the sintering of liquid metal micro / nanodroplets. The aqueous dispersion of the liquid metal micro / nanodroplets spontaneously fuses and sintersects during evaporation. The added MXene nanosheets tend to accumulate in the upper layer, ultimately forming a bilayer structure with an upper MXene-rich layer and a lower layer rich in sintered liquid metal micro / nanodroplets. The resulting liquid metal / MXene composite film exhibits continuous self-oscillation under a humidity gradient. This continuous self-oscillation can be used to cut magnetic field lines in a magnetic field, thereby generating an induced current. The liquid metal / MXene composite dispersion prepared by this method possesses good flexibility and high conductivity on both sides, making it suitable for use as conductive "ink." It can also induce spontaneous sintering of liquid metal micro / nanodroplets during solvent evaporation and can be used to fabricate conductive self-oscillating power generation devices. This method has broad application prospects in printed electronics, sensors, flexible actuators, self-powered devices, and environmental micro-energy harvesting. Attached Figure Description

[0032] Figure 1 This is a scanning electron microscope image of the nanoparticles in the liquid metal dispersion obtained in Example 1;

[0033] Figure 2 The image shows a transmission electron microscope (TEM) image of the nanoparticle-coated structure in the liquid metal dispersion obtained in Example 1.

[0034] Figure 3 This is a scanning electron microscope cross-sectional image of the liquid metal / MXene dispersion obtained in Example 1 on a glass substrate;

[0035] Figure 4 Image showing the metallic luster on the reverse side of the liquid metal / MXene dispersion obtained in Example 1 after sintering on a glass substrate;

[0036] Figure 5 This is a photograph of the liquid metal / MXene flexible self-supporting conductive film obtained in Example 1.

[0037] Figure 6 The liquid metal / MXene thin film obtained in Example 1 is used as a smart device for continuous oscillation (representing the braking angular velocity at the thin film endpoint);

[0038] Figure 7 The liquid metal / MXene thin film obtained in Example 1 is used as an electromagnetic induction power generation device (the dotted line represents the braking amplitude of the film endpoint, and the square dotted line represents the current generated between the front and rear ends of the film during braking). Detailed Implementation

[0039] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0040] This invention utilizes MXene, a two-dimensional material, to induce the spontaneous fusion and sintering of liquid metal micro / nanodroplets. During the evaporation of the aqueous dispersion of the liquid metal micro / nanodroplets, the added MXene nanosheets tend to accumulate in the upper layer, ultimately forming a bilayer structure with an upper MXene-rich layer and a lower layer rich in sintered liquid metal micro / nanodroplets. The resulting liquid metal / MXene composite film exhibits continuous self-oscillation under a humidity gradient, which can be used to cut magnetic field lines in a magnetic field, thereby generating an induced current. Simultaneously, anionic surfactants are used during the preparation process to protect the microgel shell, improving its colloidal stability. Furthermore, MXene, as a hydrophilic and conductive two-dimensional material, increases the capillary force during solvent evaporation. The liquid metal / MXene composite dispersion prepared by this method can be used as a conductive "ink" and can induce the spontaneous sintering of liquid metal micro / nanodroplets during solvent evaporation. It can also be used to prepare conductive self-oscillating power generation devices. This method has broad application prospects in printed electronics, sensors, flexible actuators, self-powered devices, and environmental micro-energy harvesting.

[0041] In the method described in this invention, the ultrasonic power is ≥150W, such as 150W, 200W, 250W, 300W, 400W, etc. The concentration of MXene in the dispersion is 0.001-30 mg / mL. -1 Preferably, a concentration of ≤20 mg / mL is used. -1 For example, 5mg / mL -1 10mg mL -1 15mg mL -1 The preferred mixing time is 1 min or 3 min.

[0042] The following examples illustrate the acquisition of MXene nanosheets:

[0043] MXene(Ti3C2T x The etching steps are as follows: 3g of Ti3AlC2 solid powder is slowly added to 3g of LiF and 60ml of 9mol L. -1In a hydrochloric acid solution, the mixture is stirred at 35°C for 24 hours, then the acid is washed away with deionized water, and then sonicated in a 400W water bath for 1 hour. After centrifugation at 3500 rpm for 1 hour, the supernatant is collected to obtain an aqueous dispersion of MXene. The above MXene nanosheets have a thickness of 1 to 4 atomic layers and a total thickness of ≤3 nm.

[0044] Example 1

[0045] A method for preparing self-sintering liquid metal thin films includes the following steps:

[0046] 1) Dissolve 240 mg of sodium alginate solution (3 wt%) in 15 mL of water and shake to mix thoroughly to obtain a sodium alginate aqueous solution with a mass fraction of 0.048 wt%.

[0047] 2) Add 150 mg of gallium-indium alloy to the above-mentioned sodium alginate aqueous solution, and sonicate for 15 min in a 20°C water bath using a 400 W ultrasonic disruptor (see [link to relevant documentation]). Figure 1 The resulting liquid metal droplets have an average diameter of approximately 100 nm.

[0048] 3) Add the gray solution obtained in step 2) to 20 mL of MXene dispersion (10 mg / mL). -1 After thorough mixing, one-third of the total volume of the mixture was poured into a 5.5cm diameter petri dish at room temperature (25℃) and evaporated to obtain a liquid metal / MXene flexible conductive film (see [link to product description]). Figure 3-5 ).

[0049] Depend on Figure 1-4 Analysis using scanning electron microscopy and transmission electron microscopy revealed that the average diameter of the particles in the liquid metal dispersion obtained in this example was ~100 nm. The surface of the liquid metal micro / nano droplets possessed an MXene coating structure. The introduction of the two-dimensional MXene material enhanced its capillary force during evaporation. Self-sintering of the liquid metal micro / nano droplets was achieved during solvent evaporation (temperature 25℃, relative humidity 50%) (see [link to relevant documentation]). Figure 3-5 ).

[0050] The liquid metal / MXene flexible conductive film (5.5 cm in diameter and 20 μm in thickness) obtained using the above embodiments was subjected to performance testing: under a humidity gradient of 40–50% relative humidity, its spontaneous actuation speed was approximately 200° / s (see [reference]). Figure 6 Microampere-level electrical energy can be obtained under a magnetic field strength of 0.2T (see [reference]). Figure 7 ).

[0051] Example 2

[0052] A method for preparing self-sintering liquid metal thin films includes the following steps:

[0053] 1) Dissolve 240 mg of sodium carboxymethyl cellulose (3 wt%) in 15 mL of water and shake to mix thoroughly to obtain a sodium carboxymethyl cellulose aqueous solution with a mass fraction of 0.048 wt%.

[0054] 2) Add 100 mg of gallium indium alloy to the above sodium carboxymethyl cellulose aqueous solution, and use an ultrasonic crusher with a power of 200 W to sonicate in a water bath at 20°C for 15 min.

[0055] 3) Add the gray solution obtained in step 2) to 20 mL of MXene dispersion (10 mg / mL). -1 After thoroughly mixing, the mixture is dropped onto a glass plate at room temperature (25°C).

[0056] Scanning electron microscopy and transmission electron microscopy revealed that the average diameter of the liquid metal dispersion obtained in this example was 250 nm, and its surface had an MXene nanosheet coating structure.

[0057] The mixed dispersion was evaporated and sintered on a glass substrate (temperature 25℃, relative humidity 50%). The bulk conductivity was measured using the two-probe method and the result was ~5*10. 5 S m -1 This dispersion can be used as electronic ink, and self-sintering printed circuits can be used as conductive paths.

[0058] Example 3

[0059] A method for preparing self-sintering liquid metal thin films includes the following steps:

[0060] 1) Dissolve 240 mg of sodium alginate solution (3 wt%) in 15 mL of water and shake to mix thoroughly to obtain a sodium alginate aqueous solution with a mass fraction of 0.048 wt%.

[0061] 2) Add 100 mg of gallium indium alloy to the above sodium alginate aqueous solution, and use an ultrasonic breaker with a power of 400 W to perform ultrasonic treatment in a water bath at 20°C for 10 min.

[0062] 3) Add the gray solution obtained in step 2) to 10 mL of MXene dispersion (10 mg / mL). -1 After repeated mixing, under ambient conditions (temperature 25℃, relative humidity 50%), 1 / 3 of the total volume of the mixture was poured into a petri dish (diameter 5.5cm) and evaporated to obtain a liquid metal / MXene flexible conductive film.

[0063] Analysis by scanning electron microscopy and transmission electron microscopy revealed that the average diameter of the particles in the liquid metal dispersion obtained in this example was ~200 nm. The surface of the liquid metal micro-nano droplets had an MXene coating structure. The introduction of MXene two-dimensional material improved its capillary force during evaporation, and the self-sintering of the liquid metal micro-nano droplets was achieved during solvent evaporation.

[0064] A composite flexible anisotropic thin film was obtained, consisting of a liquid metal-rich layer with a liquid metallic luster on one side and an MXene-rich layer on the other. Four-probe testing showed that both sides exhibited high conductivity (liquid metal layer conductivity ~6*10⁻⁶). 5 S m -1 The conductivity of the MXene layer is ~2*10 5 S m -1 ).

[0065] Example 4

[0066] A method for preparing self-sintering liquid metal thin films includes the following steps:

[0067] 1) Dissolve 240 mg of sodium alginate solution (3 wt%) in 15 mL of water and shake to mix thoroughly to obtain a sodium alginate aqueous solution with a mass fraction of 0.048 wt%.

[0068] 2) Add 100mg of gallium-indium alloy to the above sodium alginate aqueous solution, and use an ultrasonic disruptor with a power of 200W to perform ultrasonic treatment in a water bath at 20℃ for 30min.

[0069] 3) Add the gray solution obtained in step 2) to 20 mL of MXene dispersion (20 mg / mL). -1 After repeated mixing, under ambient conditions (temperature 25℃, relative humidity 50%), 1 / 3 of the total volume of the mixture was poured into a petri dish (diameter 5.5cm) and evaporated to obtain a flexible film.

[0070] Analysis using scanning electron microscopy and transmission electron microscopy revealed that the average particle diameter in the liquid metal dispersion obtained in this example was ~150 nm.

[0071] After uniform mixing and standing for a period of time, the dispersion forms a gel state, resulting in a flexible film with homogeneous liquid metal / MXene composite film on both sides (not exhibiting a liquid metal luster). Four-probe testing shows that both sides have high conductivity, and the conductivity is consistent (conductivity ~6*10⁻⁶). 5 S m -1 ).

[0072] Example 5

[0073] A method for preparing self-sintering liquid metal thin films includes the following steps:

[0074] 1) Dissolve 240 mg of sodium alginate solution (3 wt%) in 15 mL of water and shake to mix thoroughly to obtain a sodium alginate aqueous solution with a mass fraction of 0.048 wt%.

[0075] 2) Add 100 mg of gallium indium alloy to the above sodium alginate aqueous solution, and use an ultrasonic disruptor with a power of 300 W to perform ultrasonic treatment in a water bath at 20°C for 30 min.

[0076] 3) Add the gray solution obtained in step 2) to 100 mL of MXene dispersion (5 mg / mL). -1 After repeated mixing, under environmental conditions (temperature 25℃, relative humidity 50%), 1 / 3 of the total volume of the mixture is poured into a petri dish to evaporate and dry to form a film (diameter 5.5cm).

[0077] Analysis using scanning electron microscopy and transmission electron microscopy revealed that the average diameter of the particles in the liquid metal dispersion obtained in this example was ~100 nm. The introduction of MXene two-dimensional material enhanced the capillary force during the evaporation process, and the self-sintering of liquid metal micro- and nano-droplets was achieved during solvent evaporation.

[0078] The flexible liquid metal composite film obtained by evaporation sintering was tested for its self-driven and magnetic field line cutting power generation performance. The results showed that under a humidity gradient of 40-50% relative humidity, its spontaneous actuation angular velocity was about 20° / s, and it could obtain 0.1μA of electrical energy under a magnetic field strength of 0.2T.

[0079] The applicant declares that the detailed process equipment and process flow of the present invention are illustrated through the above embodiments, but the present invention is not limited to the above detailed process equipment and process flow, that is, it does not mean that the present invention must rely on the above detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a liquid metal nanodroplet self-sintered composite film, characterized in that: The application discloses a method for preparing a liquid metal nanodroplet self-sintering composite film by using a conductive two-dimensional material Mxene in a dispersion liquid during an evaporation process to make liquid metal micro-nano droplets self-sinter and form a liquid metal composite film. Specifically, 1) preparing an aqueous solution of an anionic surfactant; 2) adding liquid metal into the solution in step 1); 3) under the atmosphere of an ice water bath, the liquid metal is split by the method of ultrasonic cavitation to form a micro-nano droplet dispersion liquid; 4) the dispersion liquid obtained by ultrasonic cavitation in step 3) is added into a MXene nanosheet dispersion liquid and mixed uniformly; after uniform mixing, the film is dried to obtain a conductive MXene / liquid metal hetero thin film material; The MXene nanosheet dispersion liquid is obtained by adding MXene nanosheets into an aqueous solution, and the concentration of MXene in the dispersion liquid is 0.001-30 mg / mL -1 ; the MXene nanosheet has a thickness of 1-4 atomic layers, and a total thickness of ≤3 nm; The concentration of the anionic surfactant in the aqueous solution of the anionic surfactant is 0.02-0.06 wt%; wherein, The anionic surfactant is one or more of sodium alkyl sulfonate, sodium alkyl aryl sulfonate, sodium alkyl sulfate, sodium alginate (SA), hyaluronic acid (HA), sodium carboxymethyl cellulose (CMC) and quaternary aminated chitosan (Qch); The concentration of the liquid metal added into the solution in step 1) is 0.5-1 wt%; The liquid metal is a metal in liquid state at normal temperature, and the melting point of the metal is 0-100 ℃; The mass ratio of MXene to liquid metal droplets in step 4) is 1-4.

2. The method for preparing a liquid metal nanodroplet self-sintering composite film according to claim 1, wherein: The aqueous solution is water or a mixed liquid formed by water and an organic solvent; wherein the volume content of water in the mixed liquid is ≥50%, and the organic solvent is ethanol, DMF, DMSO or ethyl acetate.

3. The method for preparing liquid metal nanodroplet self-ignition sintered composite thin film according to claim 1, characterized in that: The metal is selected from one or more of gallium (Ga), indium (In), tin (Sn) and alloys of the aforementioned metals.

4. The method for preparing liquid metal nanodroplet self-ignition sintered composite thin film according to claim 1, characterized in that: Step 3) is to split the liquid metal to form a micro-nano liquid metal droplet dispersion liquid with a diameter of 50-300 nm by the solvent cavitation effect caused by ultrasonic under the condition that the ultrasonic power is ≥200 W and the temperature is 0-40 ℃.

5. The method for preparing a liquid metal nanodroplet self-sintering composite film according to claim 1, wherein: The aqueous solution in the MXene nanosheet dispersion liquid and the aqueous solution in the aqueous solution of the anionic surfactant can be the same or different and is selected from water or a mixed liquid formed by water and an organic solvent; wherein the volume content of water in the mixed liquid is ≥50%, and the organic solvent is ethanol, DMF, DMSO or ethyl acetate.

6. The method for preparing liquid metal nanodroplet self-ignition sintered composite thin film according to claim 1, characterized in that: The water content in the dispersion system in step 4) is ≥50%.

7. The use of the self-ignited sintered composite film of liquid metal nanodroplets prepared by the method of claim 1, characterized in that: The application of the composite film in electromagnetic induction.

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