Preparation method of hydrated salt phase change hydrogel proton force microscope sample

Abstract

The invention discloses a preparation method of a hydrous salt phase change hydrogel proton force microscope sample. The method comprises the following steps: dropwise adding a hydrogel polymer material into a quartz glass ring of which the bottom is cushioned with a newly cleaved mica sheet, and then immediately irradiating under ultraviolet light to carry out photocuring crosslinking, so as to obtain a hydrogel sheet; and cooling the hydrogel sheet to room temperature to obtain an atomic force microscope sample to be detected, inverting the quartz glass ring, removing the mica sheet, and performing subsequent microstructure characterization within 20 minutes. The problem that AFM characterization lacks a standardized hydrogel preparation method is solved, operation is easy, it can be guaranteed that a sample is kept stable within 24 hours while a flat detection surface is formed, high-resolution characterization of sample surface microtopography, quantitative height and mechanical performance can be obtained, the accuracy of sample characterization is improved, and the method is suitable for large-scale popularization and application. And the stability and reliability of test results are ensured.

Description

Technical Field

[0001] This invention relates to the field of atomic force microscopy sample technology, and in particular to a method for preparing hydrated salt phase change hydrogel atomic force microscopy samples. Background Technology

[0002] Hydrated salt phase change hydrogels, as a novel intelligent thermal management material, achieve synergistic optimization of latent heat storage and structural stability by combining hydrated salt phase change materials (such as Na₂SO₄·10H₂O, CaCl₂·6H₂O, CH₃COONa·3H₂O, etc.) with three-dimensional polymer networks (such as PVA and polyacrylamide). Their thermal regulation mechanism relies on the reversible crystallization / melting phase transition of the hydrated salt, while the hydrogel network effectively suppresses salt leakage and phase separation through physical confinement and chemical bonding.

[0003] Currently, the microstructure characterization of hydrated salt phase change hydrogels typically employs electron microscopy techniques, such as scanning electron microscopy (SEM) or transmission electron microscopy (TEM). However, conventional electron microscopy faces significant technical limitations. SEM's high-vacuum mode leads to irreversible dehydration of the hydrated salts, causing microstructural collapse and degradation of the phase change function. Furthermore, organic matrices (such as polyvinyl alcohol (PVA)) are prone to melting and pore formation artifacts under electron irradiation, affecting data reliability. While cryo-electron microscopy (Cryo-SEM) can preserve the original distribution of hydrated salt crystals in the gel network through freeze-drying and allows direct observation of the phase change interface, it relies on a helium cycle refrigeration system, resulting in high equipment costs and complex sample preparation. In contrast, TEM ultrathin sectioning process easily dissolves salt crystals, and electron beam irradiation causes cross-linking and degradation of the hydrogel network.

[0004] In contrast, atomic force microscopy (AFM) overcomes these limitations by offering in-situ analysis capabilities at the nanoscale and compatibility with liquid environments. It can non-destructively characterize aqueous samples without the need for vacuum or freezing, and simultaneously acquire multidimensional information on morphology, surface height, and mechanical properties.

[0005] However, existing research lacks a standardized hydrogel preparation method for AFM characterization, which restricts the widespread application of this technology. Therefore, developing a simple, rapid, and reproducible sample preparation scheme to optimize the AFM compatibility of hydrated salt phase change gels has become a key issue that urgently needs to be addressed in the field of phase change material characterization. Summary of the Invention

[0006] In view of the shortcomings of existing technologies, the purpose of this invention is to provide a method for preparing atomic force microscopy (AFM) samples of hydrated salt phase change hydrogels. This invention addresses the drawbacks of existing electron microscopy methods for characterizing hydrated salt phase change hydrogels, such as low resolution, susceptibility to sample changes, and high equipment costs due to freeze-drying operations requiring helium-cycle refrigeration systems. Instead, it provides a method for preparing AFM samples within a quartz glass ring with a newly cleaved mica sheet at the bottom. The technical solution of this invention is as follows: This invention provides a method for preparing hydrated salt phase transition hydrogel samples for atomic force microscopy, characterized by comprising: S1. The hydrated salt system phase change material is heated and stirred to melt under a sealed condition to obtain the molten hydrated salt system phase change material; S2. Add monomer, crosslinking agent and initiator sequentially to the above molten hydrated salt system phase change material in a certain mass ratio, heat and stir under sealed conditions to obtain polymer; S3. Take a certain amount of the above polymer and drop it into a quartz glass ring with a flat base at the bottom. Then immediately irradiate it under ultraviolet light to perform photocuring and crosslinking to obtain a hydrogel sheet. S4. Then, the above hydrogel sheet is cooled to room temperature to obtain the atomic force microscope sample to be tested. After the quartz glass ring is inverted and peeled off to flatten the substrate, subsequent microstructure characterization is carried out.

[0007] Preferably, the flat substrate is selected from one of the following: newly cleaved mica sheets, silicon wafers, silicon oxide wafers, and glass slides.

[0008] More preferably, the flat substrate is selected from newly cleaved mica sheets.

[0009] "Newly cleaved mica flakes" refer to thin flakes that have just been peeled off from bulk mica along the (001) plane and have not yet been in prolonged contact with the outside world. The cleavage plane is broken along the (001) plane of the crystal, the roughness is <0.3nm, and the surface K is high immediately after peeling. + It has not been replaced by atmospheric CO2 and H2O, and there is no potassium carbonate adsorption layer, ensuring the accuracy of characterization.

[0010] Preferably, in step S1, the heating is carried out by water bath heating or direct heating, and the heating temperature is 10℃-20℃ higher than the phase transformation temperature of the material.

[0011] Preferably, in step S3, the polymer thickness is lower than the height of the quartz glass ring to prevent sample overflow.

[0012] Preferably, the photocuring crosslinking under ultraviolet light in step S3 specifically involves photocuring crosslinking under 365nm ultraviolet light for 3-7 minutes.

[0013] Preferably, the mass ratio of the monomer to the crosslinking agent is 100:(1-5), and the initiator is 1%-2% of the monomer mass.

[0014] Preferably, the monomer is selected from acrylamide and acrylic acid.

[0015] Preferably, the crosslinking agent is selected from polyethylene glycol diacrylate and N,N'-methylenebisacrylamide.

[0016] Preferably, the initiator is selected from 1-hydroxycyclohexylphenyl ketone and 2,2-diethoxyacetophenone.

[0017] Another object of the present invention is to provide the application of the preparation method described herein in atomic force microscopy observation of the microstructure of hydrated saline gel materials.

[0018] The beneficial effects of this invention are as follows: This invention addresses the lack of standardized hydrogel preparation methods for AFM characterization by providing a method for preparing AFM samples using a quartz glass ring with a flat substrate at the bottom. The method is simple to operate, ensuring sample contact with the external environment while forming a flat detection surface, thus guaranteeing sample stability for 24 hours. It not only provides high-resolution characterization of sample surface microstructure, quantitative height, and mechanical properties, but also improves the accuracy of sample characterization, ensuring stable and reliable test results. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the AFM sample preparation process for the hydrated salt phase change hydrogel of the present invention; Figure 2 This is a photograph of the soft hydrogel obtained after photocuring and crosslinking in Example 1. Figure 3 This is a photograph of the hydrogel sample from Example 1, in which the quartz glass ring was inverted and the mica sheet was peeled off before AFM imaging. Figure 4 The AFM morphology height and mechanical properties of the 41.3% MgCl2·6H2O-58.7% Mg(NO3)2·6H2O eutectic hydrated brine gel of Example 1 are characterized; where a is the morphology height diagram of the flexible state; b is the morphology height diagram of the rigid state; a 、 The diagram shows the mechanical properties in the flexible state; b 、 The mechanical properties diagram is for a rigid state. Figure 5 The image shows the rigid hydrogel obtained by seeding the soft hydrogel of Example 1. Figure 6 The image shows the actual soft hydrogel obtained after photocuring and crosslinking in Example 2. Figure 7The AFM morphology and mechanical properties of the CH3COONa·3H2O hydrated saline gel in Example 2 are shown; where a is the morphology height diagram in the flexible state; b is the morphology height diagram in the rigid state; a 、 The diagram shows the mechanical properties in the flexible state; b 、 This is a diagram showing the mechanical properties under rigid conditions. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] In the description of this invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "top surface," "bottom surface," "inner," "outer," "inner side," and "outer side," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0022] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. Where the terms "first," "second," and "third" are used for descriptive purposes and to distinguish technical features, they should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the sequential relationship of the indicated technical features.

[0023] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. The embodiments of this invention will now be described according to its overall structure.

[0024] Figure 1This is a schematic diagram of the AFM sample preparation process for the hydrated salt phase change hydrogel of the present invention. (See attached diagram) Figure 1 This invention provides a method for preparing hydrated salt phase change hydrogel samples for atomic force microscopy, characterized by comprising: S1. The hydrated salt system phase change material is heated and stirred to melt under a sealed condition to obtain the molten hydrated salt system phase change material; The heating process employs either water bath heating or direct heating, with the heating temperature being 10℃-20℃ higher than the material's phase transformation temperature.

[0025] S2. Add monomer, crosslinking agent and initiator sequentially to the above molten hydrated salt system phase change material in a certain mass ratio, heat and stir under sealed conditions to obtain polymer; The mass ratio of the monomer to the crosslinking agent is 100:(1-5), and the initiator is 1%-2% of the monomer mass.

[0026] S3. A certain amount of the above polymer is dropped into a quartz glass ring with a flat base at the bottom. The thickness of the polymer is lower than the height of the quartz glass ring to prevent the sample from overflowing. Then, it is immediately irradiated under ultraviolet light to perform photocuring and crosslinking to obtain a hydrogel sheet.

[0027] S4. Then, the above hydrogel sheet is cooled to room temperature to obtain the atomic force microscope sample to be tested. After the quartz glass ring is inverted and peeled off to flatten the substrate, subsequent microstructure characterization is carried out.

[0028] In some embodiments, the photocuring crosslinking under ultraviolet light in step S3 specifically involves photocuring crosslinking under 365nm ultraviolet light for 3-7 minutes.

[0029] In some embodiments, the flat substrate is selected from one of newly cleaved mica sheets, silicon wafers, silicon oxide wafers, and glass slides.

[0030] In some embodiments, the flat substrate is preferably a newly cleaved mica sheet.

[0031] In some embodiments, the monomer is selected from acrylamide and acrylic acid, but the present invention is not limited thereto.

[0032] In some embodiments, the crosslinking agent is selected from polyethylene glycol diacrylate and N,N'-methylenebisacrylamide, but the present invention is not limited thereto.

[0033] In some embodiments, the initiator is selected from 1-hydroxycyclohexylphenyl ketone and 2,2-diethoxyacetophenone, but the present invention is not limited thereto.

[0034] In some embodiments, the hydrated salt may be selected from one or more of MgCl2·6H2O, Mg(NO3)2·6H2O, CH3COONa·3H2O, Na2SO4·10H2O, and CaCl2·6H2O, but the present invention is not limited thereto.

[0035] Another object of the present invention is to provide the application of the preparation method described herein in atomic force microscopy observation of the microstructure of hydrated saline gel materials.

[0036] Example 1: Sample preparation and AFM characterization of 41.3% MgCl2·6H2O -58.7% Mg(NO3)2·6H2O eutectic hydrated saline gel. 1. 41.3 g of MgCl2·6H2O and 58.7 g of Mg(NO3)2·6H2O were placed in a beaker, sealed, and stirred and melted on a precisely temperature-controlled magnetic stirrer. The heating was carried out in a water bath at a temperature of 80℃ to obtain a molten hydrated salt system phase change material. 2. At 80°C, monomers (acrylamide), crosslinking agents (polyethylene glycol dipropylene ester), and initiators (1-hydroxycyclohexylphenyl ketone) were added sequentially to the obtained molten hydrated salt system phase change material in a mass ratio of 100:2:2. The mixture was heated and stirred for 10 min under sealed conditions to obtain the polymer. 3. Then, using a dropper, take 1 ml of the above polymer and add it to a quartz glass ring with a freshly cleaved mica sheet at the bottom. Immediately move the ring to 365 nm ultraviolet light and irradiate it for 5 minutes to allow the polymer to photocur and crosslink to form a hydrogel (e.g., Figure 2 (As shown in the figure); the thickness of the polymer sample must always be lower than the height of the quartz glass ring to prevent sample overflow. 4. Then, cool the above hydrogel sample to room temperature to obtain the AFM test sample. Before AFM imaging, invert the quartz glass ring and peel off the mica sheet (e.g., Figure 3 As shown), and ensure that the surface morphology and mechanical properties of the sample are tested within 20 minutes of the mica sheet being removed (e.g. Figure 4 As shown), hydrogels exist in both flexible and rigid forms. Figure 2 The image shows a flexible hydrogel; rigidity requires seed induction during testing to transform it into a rigid hydrogel (e.g., Figure 5 (As shown).

[0037] Example 2: Sample preparation and AFM characterization of hydrated saline gel of CH3COONa·3H2O 1. Place 100 g of CH3COONa·3H2O in a beaker, seal it, and stir it on a precisely temperature-controlled magnetic stirrer until it melts. The heating is done in a water bath at a temperature of 80ºC to obtain a molten hydrated salt system phase change material. 2. At 80°C, monomers (polyacrylamide), crosslinking agents (N,N'-methylenebisacrylamide), and initiators (2,2-diethoxyacetophenone) were added sequentially to the molten hydrated salt phase change material in a mass ratio of 100:1:1. The mixture was heated and stirred for 10 minutes under sealed conditions to obtain the polymer. 3. Then, using a dropper, take 1 ml of the above polymer sample and add it to a quartz glass ring with a freshly cleaved mica sheet at the bottom. Immediately move the ring to 365 nm ultraviolet light and irradiate it for 5 minutes to allow the polymer to photocur and crosslink to form a hydrogel (e.g., Figure 6 (As shown); the sample thickness must always be lower than the height of the quartz glass ring to prevent sample overflow. 4. Then, cool the above hydrogel sample to room temperature to obtain the AFM test sample. Before AFM imaging, invert the quartz glass ring and peel off the mica sheet, ensuring that the sample surface morphology and mechanical properties are detected within 20 minutes of the mica sheet being peeled off (e.g., Figure 7 (As shown).

[0038] Depend on Figure 4 and Figure 7 As can be seen from Figures a and b of Examples 1 and 2, the sample surface morphology is highly uniform, indicating that the method of sample preparation within the quartz glass ring ensures contact between the sample and the external environment while forming a flat detection surface. Figures a of Examples 1 and 2 further illustrate this. 、 and b 、 The figure shows that the sample retains the in-situ microstructure information of the hydrogel material, exhibiting good mechanical properties without causing structural damage. This demonstrates that the present invention can ensure the sample remains stable for 24 hours under an AFM scanning microscope, and can detect the sample's morphology height with high resolution, accurately characterizing the microstructure information of the hydrogel material surface, and can also characterize the DMT modulus information with high resolution, thus achieving accurate characterization of mechanical properties.

[0039] In summary, this invention addresses the lack of standardized hydrogel preparation methods for AFM characterization by providing a method for preparing AFM samples within a quartz glass ring with a newly cleaved mica sheet at the bottom. This method is simple to operate, ensures sample contact with the external environment while forming a flat detection surface, and guarantees sample stability for 24 hours. It not only provides high-resolution characterization of sample surface microstructure, quantitative height, and mechanical properties, but also improves the accuracy of sample characterization, ensuring stable and reliable test results.

[0040] The above description is only a specific embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for preparing a hydrated salt phase change hydrogel atomic force microscope sample, characterized in that, include: S1. The hydrated salt system phase change material is heated and stirred to melt under a sealed condition to obtain the molten hydrated salt system phase change material; S2. Add monomer, crosslinking agent and initiator sequentially to the above molten hydrated salt system phase change material in a certain mass ratio, heat and stir under sealed conditions to obtain polymer; S3. Take a certain amount of the above polymer and drop it into a quartz glass ring with a flat base at the bottom. Then immediately irradiate it under ultraviolet light to perform photocuring and crosslinking to obtain a hydrogel sheet. S4. Then, the above hydrogel sheet is cooled to room temperature to obtain the atomic force microscope sample to be tested. After the quartz glass ring is inverted and peeled off to flatten the substrate, subsequent microstructure characterization is carried out.

2. The method for preparing a hydrated salt phase transition hydrogel atomic force microscope sample according to claim 1, characterized in that, The flat substrate is selected from one of the following: newly cleaved mica sheets, silicon wafers, silicon oxide wafers, and glass slides.

3. The method for preparing a hydrated salt phase transition hydrogel atomic force microscope sample according to claim 1, characterized in that, The flat substrate is selected from newly cleaved mica sheets.

4. The method for preparing a hydrated salt phase change hydrogel atomic force microscope sample according to claim 1, characterized in that, In step S3, the polymer thickness is lower than the height of the quartz glass ring to prevent sample overflow.

5. The method for preparing a hydrated salt phase change hydrogel atomic force microscope sample according to claim 1, characterized in that, In step S3, the photocuring crosslinking under ultraviolet light irradiation specifically involves irradiating with 365nm ultraviolet light for 3-7 minutes to perform photocuring crosslinking.

6. The method for preparing a hydrated salt phase change hydrogel atomic force microscope sample according to claim 1, characterized in that, The mass ratio of the monomer to the crosslinking agent is 100:(1-5), and the initiator is 1%-2% of the monomer mass.

7. The method for preparing a hydrated salt phase change hydrogel atomic force microscope sample according to claim 1, characterized in that, The monomer is selected from acrylamide and acrylic acid.

8. The method for preparing a hydrated salt phase change hydrogel atomic force microscope sample according to claim 1, characterized in that, The crosslinking agent is selected from polyethylene glycol diacrylate and N,N'-methylenebisacrylamide.

9. The method for preparing a hydrated salt phase transition hydrogel atomic force microscope sample according to claim 1, characterized in that, The initiator is selected from 1-hydroxycyclohexylphenyl ketone and 2,2-diethoxyacetophenone.

10. The application of the preparation method according to any one of claims 1 to 9 in atomic force microscopy observation of the microstructure of hydrated saline gel materials.

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