A method for preparing gallium-based liquid metal ultrafine nanodroplets

Abstract

This invention relates to a method for preparing gallium-based liquid metal ultrafine nanodroplets, belonging to the field of nanomaterial preparation technology. The method involves ultrasonically cleaning the substrate surface to remove contaminants and drying it to obtain a clean substrate. The clean substrate undergoes surface modification treatment to obtain a modified substrate. The modified substrate is placed in a vacuum evaporation chamber, and a high-purity gallium-based liquid metal source is placed in the evaporation source container. The vacuum evaporation chamber is then evaporated to a working vacuum level. The temperature of the modified substrate in the vacuum evaporation chamber is controlled to a preset deposition temperature. The evaporation source container is heated to the evaporation temperature to evaporate the high-purity gallium-based liquid metal source, which is then deposited onto the modified substrate surface for in-situ condensation, nucleation, and growth into a discrete array of gallium-based liquid metal nanodroplets. The resulting gallium-based liquid metal ultrafine nanodroplet dispersion is obtained by physical peeling. This invention offers a simple, one-step process. By adjusting the substrate temperature and evaporation parameters, precise control over the size and distribution of the gallium-based liquid metal ultrafine nanodroplets can be achieved.

Description

Technical Field

[0001] This invention relates to a method for preparing gallium-based liquid metal ultrafine nanodroplets, belonging to the field of nanomaterial preparation technology. Background Technology

[0002] Gallium-based liquid metals possess unique rheological properties (high surface tension, low viscosity) and readily form surface oxide layers, posing significant challenges to achieving controllable, stable, and uniform formation at the nanoscale. Currently, the main methods for preparing gallium-based liquid metal nanodroplets include: (1) Ultrasonic fragmentation: Placing bulk liquid metal in a solvent and breaking it into nanodroplets through high-intensity ultrasonic treatment. Although this method is relatively simple, the resulting droplets have a wide particle size distribution (typically from tens of nanometers to several micrometers), and a large amount of surfactant is often required to obtain stable dispersion, which is difficult to remove and may affect the intrinsic properties of the material. (2) Emulsion method: Dispersing liquid metal in a carrier fluid to form an emulsion through mechanical stirring or microfluidic technology. This method is difficult to stably prepare uniform droplets at the sub-nanometer scale, and the yield is low. (3) Chemical synthesis method: Involving steps such as reduction or thermal decomposition of gallium salts. This type of method is complex, time-consuming, involves multiple chemical reagents, is not conducive to large-scale production, and the product may contain residual byproducts.

[0003] Therefore, there is a need to develop a method for preparing gallium-based liquid metal ultrafine nanodroplets that is simple to process, has precise and controllable dimensions, and can form stable structures in situ. Summary of the Invention

[0004] To address the technical problems of complex processes, difficulty in size control, strong substrate dependence, and insufficient product stability in existing technologies, this invention proposes a method for preparing gallium-based liquid metal ultrafine nanodroplets. The method employs vapor deposition to prepare gallium-based liquid metal ultrafine nanodroplets. By adjusting the substrate temperature and vapor deposition parameters, precise control of the nanodroplet size and distribution is achieved, resulting in gallium-based liquid metal ultrafine nanodroplets with narrow particle size distribution, excellent dispersibility, and stability. Under a constant vapor deposition rate, extending the vapor deposition time or increasing the substrate temperature promotes droplet coalescence and growth, thereby increasing the average particle size. Conversely, decreasing the substrate temperature increases the nucleation density, which is beneficial for obtaining a smaller average particle size.

[0005] A method for preparing gallium-based liquid metal ultrafine nanodroplets, the specific steps of which are as follows: (1) The substrate surface is ultrasonically cleaned to remove contaminants and dried to obtain a clean substrate; the clean substrate is then surface modified to obtain a modified substrate; (2) The modified substrate is placed in the vacuum evaporation chamber, the high-purity gallium-based liquid metal source is loaded into the evaporation source container, and the vacuum evaporation chamber is evacuated to the working vacuum level; (3) Control the temperature of the modified substrate in the vacuum evaporation chamber to the preset deposition temperature in order to regulate the surface diffusion and droplet nucleation dynamics of gallium-based liquid metal atoms; (4) Heat the vapor deposition source container to the evaporation temperature to evaporate the high-purity gallium-based liquid metal source, vapor deposit it onto the surface of the modified substrate for in-situ condensation, nucleation and growth into discrete gallium-based liquid metal nanodroplet arrays, or further physically peel off the gallium-based liquid metal nanodroplet arrays from the surface of the modified substrate into a solvent to obtain a gallium-based liquid metal ultrafine nanodroplet dispersion.

[0006] Preferably, the substrate in step (1) is carbon paper, silicon wafer, glass sheet, quartz sheet, sapphire sheet, polydimethylsiloxane, polyimide, polyethylene terephthalate or thermoplastic polyurethane.

[0007] Preferably, the surface modification treatment in step (1) is oxygen plasma treatment, ultraviolet ozone treatment, or silane coupling agent chemical functionalization treatment.

[0008] More preferably, the oxygen plasma treatment power is 30~80W, the plasma chamber pressure is 10~30Pa, and the time is 3~8min; the ultraviolet ozone treatment involves placing the clean substrate in an ultraviolet ozone cleaner and irradiating it with ultraviolet lamps with a main wavelength of 185nm and 254nm at room temperature for 15~30min; the silane coupling agent chemical functionalization treatment involves mixing γ-aminopropyltriethoxysilane (APTES), anhydrous ethanol, and deionized water at a volume ratio of 1~2:10:1 to obtain mixed solution A, adjusting the pH of mixed solution A to 4.0~5.0 with acetic acid and hydrolyzing it for 10~30min to obtain mixed solution B; at room temperature, immersing the clean substrate in mixed solution B for 15~100min, removing it, rinsing it with anhydrous ethanol, drying it with nitrogen, and then curing it at 100~120℃ for 10~30min.

[0009] Preferably, the high-purity gallium-based liquid metal source in step (2) is gallium, gallium indium, gallium tin, or gallium indium tin, and the working vacuum degree is not higher than 1×10⁻⁶. -4 Pa.

[0010] Preferably, the deposition temperature in step (3) is preset to be -40~80℃.

[0011] Preferably, the evaporation temperature in step (4) is 700~1400℃, and the evaporation rate is 0.1~1.0. / s, and the evaporation time is 1~300s.

[0012] Preferably, the physical stripping method in step (4) is mechanical vibration separation, liquid phase ultrasonic separation, or liquid phase centrifugal separation.

[0013] Preferably, the particle size of the gallium-based liquid metal ultrafine nanodroplet dispersion in step (4) is 10~400nm.

[0014] The preparation mechanism of gallium-based liquid metal ultrafine nanodroplets in this invention: Based on vacuum evaporation technology in physical vapor deposition, gallium-based liquid metal is heated and evaporated in a high-vacuum environment, causing its atoms to deposit, condense, nucleate, and grow into discrete nanodroplets on a surface-modified substrate. The nucleation and growth behavior of the entire process follows the classical thin-film nucleation theory and is closely related to the substrate surface state, atomic diffusion kinetics, and deposition flux. This invention achieves precise control over the average particle size, size distribution, and areal density of the nanodroplets by synergistically regulating substrate surface modification, substrate temperature, and evaporation parameters (rate and time).

[0015] (1) Mechanism of action of substrate modification The surface chemical composition and surface energy of the substrate determine the initial adsorption capacity of gallium-based liquid metal atoms, the density of nucleation sites, and the subsequent growth mode. Surface energy modulation: After treatment with oxygen plasma, ultraviolet ozone or silane coupling agents, polar functional groups (such as -OH, -Si-OH, -NH2, etc.) will be generated on the substrate surface, which significantly increases the surface free energy. High surface energy substrates are conducive to atomic adsorption, increase nucleation density, and promote the formation of uniform, small-sized droplets. Conversely, untreated low surface energy substrates (such as PDMS, PI) have strong atomic migration and diffusion capabilities, which easily lead to droplet coalescence, resulting in increased droplet size and sparse distribution.

[0016] Nucleation site control: Surface modification can introduce a large number of sub-nanometer-scale active sites (such as dangling bonds, hydroxyl groups, etc.) on the substrate. These sites serve as preferential nucleation centers, reducing the nucleation barrier and enabling high-density uniform nucleation of deposited atoms at low deposition amounts, thus avoiding the formation of continuous films or macroscopic agglomerations.

[0017] By adjusting the modification method (such as processing time, power, and type of chemical reagents), the surface energy of the substrate can be flexibly customized to meet the requirements of different substrates (rigid / flexible) and different droplet sizes.

[0018] (2) The mechanism by which substrate temperature regulates atomic diffusion and droplet growth Substrate temperature directly determines the diffusion coefficient of adsorbed atoms on the substrate surface and the merging and ripening dynamics of droplets, and is a key parameter for controlling droplet size.

[0019] Low-temperature deposition: atomic surface diffusion is limited, nucleation rate is high, and droplets tend to "freeze" and grow near the nucleation site, forming a large number of dense, small-sized nanodroplets; the Ostwald ripening process is significantly suppressed, and the particle size distribution is narrow.

[0020] High-temperature deposition: The atomic diffusion rate increases, and droplets grow continuously through surface diffusion, collision merging, and Ostwald ripening; larger droplets absorb surrounding smaller droplets or isolated atoms, resulting in a decrease in the number of droplets and an increase in average particle size. At the same time, the high temperature keeps the droplets in a liquid or supercooled liquid state, which is conducive to sphericity.

[0021] The effect of temperature on droplet morphology: The melting point of gallium-based liquid metals varies depending on the alloy composition (pure gallium is about 29.8℃, while gallium indium tin alloy is below room temperature); by controlling the substrate temperature to be below or above its melting point, solid or liquid nanodroplets can be obtained respectively; liquid droplets have self-healing capabilities and are more likely to maintain their integrity during peeling or subsequent processing.

[0022] Therefore, under the same evaporation parameters, as the substrate temperature increases, the average particle size of the nanodroplets increases monotonically, achieving linear tunability of the size.

[0023] (3) Regulation mechanism of vapor deposition parameters (rate, time, deposition amount) The evaporation rate and evaporation time together determine the atomic flux and total deposition amount deposited on the substrate surface per unit time, thereby controlling the nucleation density and final volume of the droplets.

[0024] Evaporation rate: At low rates, atoms arrive at the substrate one by one, with enough time to migrate to the nucleation sites with the lowest energy, forming a sparse and uniform droplet array; at high rates, the instantaneous atomic flux is high and the surface atomic supersaturation is large, which can induce a large number of fresh nuclei, but the local concentration is too high, which can lead to a decrease in droplet spacing, an increase in the probability of merging, and even the formation of a quasi-continuous film.

[0025] Evaporation time: At a constant rate, the longer the time, the greater the total deposition. In the initial stage of deposition, nucleation is dominant, and the number of droplets increases rapidly. As the deposition amount increases, atoms are mainly captured by existing droplets, causing the droplet volume to increase. By precisely controlling the time, the droplet size can be continuously adjusted.

[0026] Deposition amount (equivalent film thickness): Deposition amount is the product of rate and time, and is a direct parameter controlling droplet volume. Under constant substrate temperature and rate, the average droplet radius is proportional to the cube root of the deposition amount Q, because the volume of atoms captured by each droplet matches its surface area growth.

[0027] This invention achieves precise control over the entire process of nanodroplet nucleation and growth by synergistically regulating the parameters of the above three dimensions.

[0028] Furthermore, because the entire preparation process is carried out in a high vacuum (≤1×10⁻⁶), -4The process is carried out at a pressure of Pa, avoiding the introduction of oxygen and effectively suppressing the formation of the oxide layer on the surface of the gallium-based liquid metal (or forming only an extremely thin primary oxide layer), ensuring the high purity of the droplets and excellent electrical / thermal properties.

[0029] In summary, this invention establishes a three-pronged preparation strategy—"substrate modification and pre-setting of nucleation sites - temperature-controlled diffusion - evaporation parameter adjustment and supply"—by combining physical vapor deposition technology with surface engineering and thermodynamic control. This fundamentally solves the problems of difficult size control, poor dispersion, and substrate limitations in existing methods. This working principle is applicable to various gallium-based liquid metals (Ga, GaIn, GaSn, GaInSn) and various rigid / flexible substrates, possessing universality and industrial scale-up potential.

[0030] The beneficial effects of this invention are: (1) This invention uses vacuum evaporation technology in physical vapor deposition. By precisely controlling the deposition parameters, a highly uniform gallium-based liquid metal nanodroplet array can be directly formed on the substrate surface in one step without any template, catalyst or surfactant. The entire preparation process is completed in a vacuum environment, avoiding chemical pollution. The process window is wide and it is easy to scale up production. (2) By synergistically controlling the evaporation parameters (substrate temperature, evaporation rate, deposition amount), the present invention can achieve precise linear adjustment of the average particle size of gallium-based liquid metal nanodroplets from 10 to 250 nm, with a narrow particle size distribution, and can independently control their areal density. (3) This invention is not only applicable to traditional rigid substrates such as silicon wafers and glass, but also to various flexible polymer substrates such as PDMS, PI, and PET. Through simple surface modification treatment, the nucleation behavior on different substrates can be effectively controlled, showing strong substrate universality and providing a general platform for integrating gallium-based liquid metal nanostructures on various functional surfaces. (4) The gallium-based liquid metal nanodroplet array loaded on the substrate of the present invention can be used directly as a functional device component, and stable nanodroplets can be efficiently collected by a simple ultrasonic dispersion method. It has good dispersibility, no agglomeration, and can be transferred to various solvents to form a stable colloidal dispersion. It greatly facilitates the subsequent integration with solution processing technology (such as spin coating, inkjet printing, 3D printing, etc.) and broadens its application scenarios. Attached Figure Description

[0031] Figure 1 Here is a SEM image of the gallium nanodroplet array from Example 1; Figure 2 This is a statistical diagram of the particle size distribution of gallium nanodroplets in Example 1; Figure 3 Here is a SEM image of the gallium indium tin nanodroplet array from Example 2; Figure 4 This is a statistical diagram of the particle size distribution of gallium indium tin nanodroplets in Example 2; Figure 5 SEM comparison images of gallium indium nanodroplet arrays prepared at different substrate temperatures in Example 3. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0033] Example 1: A method for preparing gallium-based liquid metal ultrafine nanodroplets, the specific steps of which are as follows: (1) The surface of the substrate (10mm×10mm carbon paper) was ultrasonically cleaned with acetone, anhydrous ethanol and deionized water respectively to remove contaminants, and dried with high-purity nitrogen to obtain a clean substrate; the clean substrate was then subjected to surface modification treatment (oxygen plasma surface treatment, power of 50W, plasma chamber pressure of 20Pa, time of 5min) to obtain a modified substrate. (2) The modified substrate is placed in the vacuum evaporation chamber, the high-purity gallium metal source is loaded into the evaporation source container (tungsten boat evaporation source), and the vacuum evaporation chamber is evacuated to the working vacuum level (5×10). -5 Pa); (3) The temperature of the modified substrate in the vacuum evaporation chamber is controlled to the preset deposition temperature (40℃) in order to regulate the surface diffusion and droplet nucleation dynamics of gallium-based liquid metal atoms; (4) Heat the evaporation source container to the evaporation temperature (1000℃) at a heating rate of 5℃ / min to stabilize the high-purity gallium metal source. Monitor the evaporation rate in real time using a quartz crystal microbalance (QCM) (stabilize to 1℃). / s), evaporated onto the surface of the modified substrate, where it undergoes in-situ condensation, nucleation, and growth into a discrete array of gallium nanodroplets. Physical peeling (mechanical vibration) disperses the gallium nanodroplet array from the surface of the modified substrate into a solvent to obtain a gallium metal ultrafine nanodroplet dispersion. In this embodiment, the evaporation time is 10s. The SEM image of the gallium nanodroplet array in this embodiment is shown below. Figure 1 Highly uniform and discretely distributed gallium nanodroplets were formed on the surface of the modified substrate (carbon paper), without agglomeration or continuous film formation. The particle size distribution histogram of over 1000 nanodroplets was obtained using image analysis software. Figure 2 As shown, the average particle size of the gallium nanodroplets in this embodiment is 11.7 nm, and the particle size distribution is narrow.

[0034] Example 2: A method for preparing gallium-based liquid metal ultrafine nanodroplets, the specific steps of which are as follows: (1) The surface of the substrate (10mm×10mm flexible PDMS substrate) was ultrasonically cleaned with acetone, anhydrous ethanol and deionized water respectively to remove contaminants, and dried with high-purity nitrogen to obtain a clean substrate; the clean substrate was subjected to surface modification treatment (oxygen plasma surface treatment, power of 30W, plasma chamber pressure of 15Pa, time of 3min) to introduce hydrophilic silanol (Si-OH) groups to obtain a modified substrate; (2) The modified substrate is placed in the vacuum evaporation chamber, the high-purity gallium indium tin source is loaded into the evaporation source container (tungsten boat evaporation source), and the vacuum evaporation chamber is evacuated to the working vacuum level (8×10). -5 Pa); (3) Control the temperature of the modified substrate in the vacuum evaporation chamber to the preset deposition temperature (40℃) to regulate the surface diffusion and droplet nucleation dynamics of high-purity gallium indium tin; (4) The high-purity gallium indium tin source was heated to the evaporation temperature (950℃) at a heating rate of 5℃ / min to ensure stable evaporation. The evaporation rate was monitored in real time using a quartz crystal microbalance (QCM) (stabilized to 0.5℃). / s), evaporated onto the surface of the modified substrate, where it undergoes in-situ condensation, nucleation, and growth into a discrete array of gallium indium tin nanodroplets. Physical exfoliation (liquid-phase ultrasonic separation) disperses the gallium indium tin nanodroplet array from the surface of the modified substrate into a solvent to obtain a gallium indium tin ultrafine nanodroplet dispersion. In this embodiment, the evaporation time is 300s. The SEM image of the gallium indium tin nanodroplet array in this embodiment is shown below. Figure 3 Highly dispersed gallium indium tin nanodroplets with an average particle size of about 318 nm were formed on the surface of the modified substrate (PDMS) and were uniformly distributed. The particle size distribution histogram of over 1000 nanodroplets was obtained using image analysis software. Figure 4 As shown, the average particle size of the gallium indium tin nanodroplets in this embodiment is 318 nm, and the particle size distribution is narrow.

[0035] Example 3: A method for preparing gallium-based liquid metal ultrafine nanodroplets, the specific steps of which are as follows: (1) The surfaces of 7 substrates (10mm×10mm carbon paper) were ultrasonically cleaned with acetone, anhydrous ethanol and deionized water respectively to remove contaminants, and dried with high-purity nitrogen to obtain clean substrates; the clean substrates were then subjected to surface modification treatment (oxygen plasma surface treatment, power of 50W, plasma chamber pressure of 10Pa, time of 5min) to obtain modified substrates A1, A2, A3, A4, A5, A6 and A7; (2) Modified substrates A1, A2, A3, A4, A5, A6, and A7 are placed in vacuum evaporation chambers, respectively. High-purity gallium indium sources are loaded into evaporation source containers (tungsten boat evaporation sources), and the vacuum evaporation chambers are evacuated to the working vacuum level (5×10⁻⁶).-5 Pa); (3) Control the temperature of the modified substrate in the vacuum evaporation chamber to the preset deposition temperature (-40℃, -20℃, 0℃, 10℃, 25℃, 50℃, 80℃ respectively) to regulate the surface diffusion and droplet nucleation dynamics of high-purity gallium indium; (4) Heat the evaporation source container to the evaporation temperature (1000℃) at a heating rate of 5℃ / min to stabilize the high-purity gallium indium source. Monitor the evaporation rate in real time using a quartz crystal microbalance (QCM) (stabilizing to 1). / s), evaporated onto the surface of the modified substrate, where it undergoes in-situ condensation, nucleation, and growth into a discrete array of gallium indium nanodroplets. Physical peeling (liquid-phase ultrasonic separation) disperses the gallium indium nanodroplet array from the surface of the modified substrate into a solvent to obtain a gallium indium ultrafine nanodroplet dispersion. In this embodiment, the evaporation time is 30s. The SEM image of the gallium-indium nanodroplet array in this embodiment is shown below. Figure 5 Highly dispersed gallium-indium nanodroplets were formed on the surface of the modified substrate (carbon paper), and the distribution was uniform. Image analysis software was used to perform particle size statistics on more than 1,000 nanodroplets at different substrate temperatures, and a particle size distribution histogram was obtained. The average particle size of the gallium indium nanodroplets in this embodiment is shown. In this embodiment, when the temperature of the modified substrate is -40°C, the average particle size of the gallium indium nanodroplets is approximately 12 nm. In this embodiment, when the temperature of the modified substrate is -20°C, the average particle size of the gallium indium nanodroplets is approximately 21 nm. In this embodiment, when the temperature of the modified substrate is 0°C, the average particle size of the gallium indium nanodroplets is about 28 nm, with high nucleation density, small droplet size, and extremely uniform distribution. In this embodiment, when the temperature of the modified substrate is 10°C, the average particle size of the gallium indium nanodroplets is approximately 37 nm. In this embodiment, when the temperature of the modified substrate is 25°C, the average particle size of the gallium indium nanodroplets is approximately 52 nm. In this embodiment, when the temperature of the modified substrate is 50°C, the average particle size of the gallium indium nanodroplets is approximately 115 nm. In this embodiment, when the temperature of the modified substrate is 80°C, the average particle size of the gallium indium nanodroplets is approximately 240 nm. Therefore, the temperature of the modified substrate is a key parameter for controlling the average particle size of gallium indium nanodroplets. As the substrate temperature increases, the surface diffusion coefficient of deposited gallium indium increases, and the Oswald ripening and merging growth between droplets intensifies, leading to a monotonically increasing average particle size.

[0036] Example 4: A method for preparing gallium-based liquid metal ultrafine nanodroplets, the specific steps of which are as follows: (1) The surfaces of 6 substrates (10mm×10mm polyimide) were ultrasonically cleaned with acetone, anhydrous ethanol and deionized water respectively to remove contaminants, and dried with high-purity nitrogen to obtain clean substrates; the clean substrates were treated with ultraviolet ozone on the surface (the clean substrates were placed in an ultraviolet ozone cleaner and irradiated with ultraviolet lamps with a main wavelength of 185nm and 254nm for 15min at room temperature) to obtain modified substrates B1, B2, B3, B4, B5 and B6; (2) Modified substrates B1, B2, B3, B4, B5, and B6 were placed in the vacuum evaporation chamber, and the high-purity gallium source was loaded into the evaporation source container (tungsten boat evaporation source). The vacuum evaporation chamber was then evacuated to the working vacuum level (5×10⁻⁶). -5 Pa); (3) Control the temperature of the modified substrate in the vacuum evaporation chamber to the preset deposition temperature (10℃) to regulate the surface diffusion and droplet nucleation dynamics of high-purity gallium; (4) The high-purity gallium indium source container was heated to the evaporation temperature (1000℃) at a heating rate of 10℃ / min to ensure stable evaporation. The evaporation rate was monitored in real time using a quartz crystal microbalance (QCM) (stabilized to 0.1℃). / s, 0.2 / s, 0.4 / s, 0.6 / s, 0.8 / s, 1.0 / s), evaporated onto the surface of the modified substrate, where it undergoes in-situ condensation, nucleation, and growth into a discrete array of gallium nanodroplets. Physical peeling (liquid phase centrifugation) disperses the gallium nanodroplet array from the surface of the modified substrate into a solvent to obtain a gallium ultrafine nanodroplet dispersion. In this embodiment, the evaporation time is 100s. In this embodiment, highly dispersed gallium nanodroplets were formed on the surface of the modified substrate (polyimide), and the distribution was uniform. Image analysis software was used to perform particle size statistics on more than 1,000 nanodroplets at different evaporation rates, and a particle size distribution histogram was obtained. The average particle size of the gallium nanodroplets in this embodiment is shown. In this embodiment, the evaporation rate is stabilized at 0.1. At / s, the average particle size of gallium nanodroplets is approximately 17nm; In this embodiment, the evaporation rate is stabilized at 0.2. At / s, the average particle size of gallium nanodroplets is approximately 29nm; In this embodiment, the evaporation rate is stabilized at 0.4. At / s, the average particle size of gallium nanodroplets is approximately 44nm; In this embodiment, the evaporation rate is stabilized at 0.6. At / s, the average particle size of gallium nanodroplets is approximately 53nm; In this embodiment, the evaporation rate is stabilized at 0.8. At / s, the average particle size of gallium nanodroplets is approximately 71nm; In this embodiment, the evaporation rate is stabilized at 1.0. At / s, the average particle size of gallium nanodroplets is approximately 124nm; The results show that the particle size of the liquid metal nanodroplets on the surface increases with the increase of the evaporation rate. This is due to the increased particle size caused by droplet coalescence caused by excessively high local concentration. Therefore, the size of the liquid metal nanodroplets can be effectively adjusted by controlling the evaporation rate.

[0037] Example 5: A method for preparing gallium-based liquid metal ultrafine nanodroplets, the specific steps of which are as follows: (1) The surfaces of 7 substrates (10mm×10mm quartz sheets) were ultrasonically cleaned with acetone, anhydrous ethanol and deionized water respectively to remove contaminants, and dried with high-purity nitrogen to obtain clean substrates; the clean substrates were chemically functionalized with surface silane coupling agent: γ-aminopropyltriethoxysilane (APTES), anhydrous ethanol and deionized water were mixed in a volume ratio of 1:10:1 to obtain mixed solution A. The pH of mixed solution A was adjusted to 4.0~5.0 with acetic acid and hydrolyzed for 20min to obtain mixed solution B; at room temperature, the clean substrates were immersed in mixed solution B for 50min, and after being taken out, they were rinsed with anhydrous ethanol, dried with nitrogen, and then cured at 120℃ for 20min to obtain modified substrates C1, C2, C3, C4, C5, C6 and C7; (2) Modified substrates C1, C2, C3, C4, C5, C6, and C7 were placed in a vacuum evaporation chamber. A high-purity gallium source was placed into the evaporation source container (tungsten boat evaporation source), and the vacuum evaporation chamber was evacuated to a working vacuum level (6×10⁻⁶). -5 Pa); (3) Control the temperature of the modified substrate in the vacuum evaporation chamber to the preset deposition temperature (10℃) to regulate the surface diffusion and droplet nucleation dynamics of high-purity gallium; (4) The high-purity gallium indium source container was heated to the evaporation temperature (1000℃) at a heating rate of 10℃ / min to ensure stable evaporation. The evaporation rate was monitored in real time using a quartz crystal microbalance (QCM) (stabilized to 0.6℃). The gallium nanoparticles were vapor-deposited onto the modified substrate surface, where they underwent in-situ condensation, nucleation, and growth into a discrete array of gallium nanoparticles. Physical exfoliation (liquid-phase centrifugation) dispersed the gallium nanoparticle array from the modified substrate surface into a solvent to obtain a gallium ultrafine nanoparticle dispersion. In this embodiment, the vapor deposition times were 10s, 50s, 100s, 150s, 200s, 250s, and 300s, respectively. In this embodiment, highly dispersed gallium nanodroplets were formed on the surface of the modified substrate (quartz sheet), and the distribution was uniform. Image analysis software was used to perform particle size statistics on more than 1,000 nanodroplets at different evaporation rates, and a particle size distribution histogram was obtained. The average particle size of the gallium nanodroplets in this embodiment is shown. In this embodiment, when the evaporation time is 10s, the average particle size of gallium nanodroplets is approximately 23nm. In this embodiment, when the evaporation time is 50s, the average particle size of gallium nanodroplets is approximately 72nm. In this embodiment, when the evaporation time is 100s, the average particle size of gallium nanodroplets is approximately 96nm. In this embodiment, when the evaporation time is 150s, the average particle size of gallium nanodroplets is approximately 117nm. In this embodiment, when the evaporation time is 200s, the average particle size of gallium nanodroplets is approximately 137nm. In this embodiment, when the evaporation time is 250s, the average particle size of gallium nanodroplets is approximately 215nm. In this embodiment, when the evaporation time is 300s, the average particle size of gallium nanodroplets is approximately 240nm. The results show that the particle size of the liquid metal nanodroplets on the surface increases with increasing evaporation time, as atoms are mainly captured by the existing droplets, leading to an increase in droplet volume. Continuous adjustment of droplet size can be achieved by precisely controlling the time.

[0038] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for preparing gallium-based liquid metal ultrafine nanodroplets, characterized in that, The specific steps are as follows: (1) The substrate surface is ultrasonically cleaned to remove contaminants and dried to obtain a clean substrate; the clean substrate is then surface modified to obtain a modified substrate; (2) The modified substrate is placed in the vacuum evaporation chamber, the high-purity gallium-based liquid metal source is loaded into the evaporation source container, and the vacuum evaporation chamber is evacuated to the working vacuum level; (3) Control the temperature of the modified substrate in the vacuum evaporation chamber to the preset deposition temperature; (4) Heat the vapor deposition source container to the evaporation temperature to evaporate the high-purity gallium-based liquid metal source, vapor deposit it onto the surface of the modified substrate for in-situ condensation, nucleation and growth into discrete gallium-based liquid metal nanodroplet arrays, or further physically peel off the gallium-based liquid metal nanodroplet arrays from the surface of the modified substrate into a solvent to obtain a gallium-based liquid metal ultrafine nanodroplet dispersion.

2. The method for preparing gallium-based liquid metal ultrafine nanodroplets according to claim 1, characterized in that: Step (1) The substrate is carbon paper, silicon wafer, glass sheet, quartz sheet, sapphire sheet, polydimethylsiloxane, polyimide, polyethylene terephthalate or thermoplastic polyurethane.

3. The method for preparing gallium-based liquid metal ultrafine nanodroplets according to claim 1, characterized in that: Step (1) Surface modification treatment is self-oxygen plasma treatment, ultraviolet ozone treatment or silane coupling agent chemical functionalization treatment.

4. The method for preparing gallium-based liquid metal ultrafine nanodroplets according to claim 1, characterized in that: Step (2) The high-purity gallium-based liquid metal source is gallium, gallium indium, gallium tin, or gallium indium tin, and the working vacuum degree is not higher than 1×10⁻⁶. -4 Pa.

5. The method for preparing gallium-based liquid metal ultrafine nanodroplets according to claim 1, characterized in that: Step (3) The preset deposition temperature is -40~80℃.

6. The method for preparing gallium-based liquid metal ultrafine nanodroplets according to claim 1, characterized in that: Step (4) involves an evaporation temperature of 700~1400℃ and an evaporation rate of 0.1~1.

0. / s, and the evaporation time is 1~300s.

7. The method for preparing gallium-based liquid metal ultrafine nanodroplets according to claim 1, characterized in that: Step (4) Physical stripping methods include mechanical vibration separation, liquid phase ultrasonic separation, or liquid phase centrifugal separation.

8. The method for preparing gallium-based liquid metal ultrafine nanodroplets according to claim 1, characterized in that: Step (4) The particle size of the gallium-based liquid metal ultrafine nanodroplet dispersion is 10~400nm.

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