A method for preparing camouflaged microcapsules of chlorophyll derivatives coated with silica and its application

Abstract

This invention discloses a method for preparing silica-coated chlorophyll derivative camouflage microcapsules and their applications. A stable water-in-oil emulsion system is prepared using a sodium copper chlorophyll salt solution and an organic solution as the dispersed and continuous phases, respectively. Two silicon source precursors are then added to the emulsion in a specific ratio, causing hydrolysis and condensation to form a silica capsule wall of controllable thickness, thereby achieving the coating of the sodium copper chlorophyll salt aqueous solution. The microcapsules prepared by this invention delay the photoaging of sodium copper chlorophyll salt while mimicking the water absorption peak of leaves. Stable microcapsules with good coating capacity can be prepared through appropriate raw material ratios and processes, and can be applied in the field of optical camouflage, showing high application potential.

Description

Technical Field

[0001] This invention belongs to the field of military camouflage materials, specifically relating to a method for preparing camouflage microcapsules of chlorophyll derivatives coated with silica and their application, particularly a method for preparing chlorophyll copper sodium salt@silica core-shell structure camouflage microcapsules and their application in military camouflage materials. Background Technology

[0002] Green plants, serving as a typical environmental background for camouflage targets, are a key focus of hyperspectral research. The formation of the reflectance spectrum of plant leaves is mainly related to chlorophyll, water content, and a loose, porous structure. Camouflage materials prepared with natural pigments suffer from aging issues; therefore, encapsulating natural pigments can, to some extent, improve the photoaging properties of sodium copper chlorophyll.

[0003] Microencapsulation technology refers to the use of natural or polymeric compounds to encapsulate solid, liquid, or gaseous materials, forming tiny containers isolated from the external environment. The substance encapsulated within the microcapsule is called the core material, and the material used to encapsulate the core material is called the wall material. Silica is an important inorganic material widely used in the production of glass, refractory materials, optical fibers, coatings, ceramics, and other industries. It possesses properties such as chemical stability, low cost, high temperature resistance, and unique optical transparency, making it a common wall material for microcapsule manufacturing. Silica microcapsules are mostly encapsulated using silica or polymeric substances as the silicon source through physicochemical methods. Physicochemical methods reduce the solubility of the polymer by altering pH, temperature, etc., causing it to deposit on the surface of the core material to form a shell; the sol-gel method is frequently used. Summary of the Invention

[0004] This invention proposes a method for preparing camouflage microcapsules of chlorophyll derivatives coated with silica and their applications. By utilizing the water-carrying capacity of the microcapsules encapsulating sodium copper chlorophyll salt and silica, the photoaging characteristics of sodium copper chlorophyll salt are improved, while ensuring a certain water content in the microcapsules. This allows the microcapsules to potentially mimic the solar spectral reflectance characteristics of leaves, achieving optical camouflage.

[0005] This invention is achieved through the following technical solution, and the specific operation steps are as follows:

[0006] Step 1: Mix the lipophilic nonionic surfactant with cyclohexane as the continuous phase;

[0007] Step 2: Mix the hydrophilic surfactant with deionized water, and add the metallochlorophyll derivative while heating and stirring, and mix evenly to form the dispersed phase;

[0008] Step 3: Add the dispersed phase from Step 2 to the continuous phase from Step 1, and heat and stir simultaneously to form a stable water-in-oil (W / O) emulsion.

[0009] Step 4: Slowly add a mixture of silicon source precursor triethoxysilane and tetraethyl orthosilicate to the W / O emulsion in Step 3, and react while heating and stirring to obtain microcapsules of silica-coated metallochlorophyll derivatives.

[0010] Step 5: Wash the microcapsules obtained in Step 4 with cyclohexane more than 3 times, and then air dry to obtain disguised microcapsules with a metallochlorophyll derivative@silica core-shell structure.

[0011] Furthermore, the lipophilic nonionic surfactant mentioned in step one includes Span 80; the mass percentage of the lipophilic nonionic surfactant contained in the continuous phase is 0.9-1.4%.

[0012] Furthermore, in step two, the hydrophilic surfactant is a nonionic surfactant or anionic surfactant, wherein the nonionic surfactant is Tween 80, and the anionic surfactant includes sodium dodecylbenzene sulfonate or sodium dodecyl sulfate.

[0013] Furthermore, the mass percentage of the hydrophilic surfactant contained in the dispersed phase in step two is 0.6-1%; the mass percentage of the chlorophyll derivative contained in the dispersed phase in step two is 0.07-1.9%; the heating temperature in step two is 50-70℃, the stirring time is 5-10 min, and the rotation speed is 400-500 r / min.

[0014] Furthermore, the metal chlorophyll derivative mentioned in step two is a water-soluble transition metal chlorophyll derivative or a water-soluble rare earth chlorophyll complex; even further, the metal chlorophyll derivative mentioned in step two is a water-soluble transition metal chlorophyll sodium or potassium salt, including chlorophyll copper sodium salt, chlorophyll zinc sodium salt, chlorophyll iron sodium salt, chlorophyll chromium sodium salt, chlorophyll cobalt sodium salt, chlorophyll zinc potassium salt, etc.

[0015] Furthermore, the heating temperature in step three is preferably 50-70℃, the stirring time is preferably 1-2h, and the rotation speed is 800r / min; the volume ratio of the dispersed phase to the continuous phase in step three is 4.3%-6%.

[0016] Furthermore, in step four, the volume ratio of triethoxysilane to tetraethyl orthosilicate in the silicon source precursor is 5:9; the heating temperature in step four is 50-80℃, the stirring time is 6-8h, and the rotation speed is 800r / min; the volume ratio of W / O emulsion to silicon source precursor in step four is 5%-10%.

[0017] The camouflaged microcapsules with a metallochlorophyll derivative@silica core-shell structure prepared by the above method have a particle size of 20-80 nm.

[0018] This invention also provides the application of the above-mentioned metal chlorophyll derivative@silica core-shell structured camouflage microcapsules in the preparation of military camouflage materials. The microcapsules synthesized by this invention can be cast into films, which can not only simulate the selective absorption of sunlight by chlorophyll and water, but also have scattering properties that can simulate the multiple reflection effects of sunlight by the loose and porous structure of leaves, which meets the needs of green camouflage materials.

[0019] In some specific embodiments, the reflectance of the prepared metal chlorophyll derivative@silica core-shell camouflage microcapsules did not change significantly after two months of storage; compared with commercially available silica, the silica shell prepared by the method of the present invention has a water absorption characteristic peak; indicating that the metal chlorophyll derivative@silica camouflage microcapsules prepared by the method of the present invention have the effect of delaying the photoaging of sodium copper chlorophyll salt; and have good water absorption capacity, which meets the requirements of green camouflage materials for reflectance spectrum.

[0020] This invention utilizes an interfacial polymerization method within a W / O system to prepare silica-encapsulated sodium copper chlorophyllin microcapsules. Through natural drying, a core-shell structure of sodium copper chlorophyllin@silica camouflage microcapsules is ultimately produced. This method utilizes the silica shell to encapsulate the photo-aging-prone sodium copper chlorophyllin, reducing the impact of photoaging, while also allowing the silica shell to carry water. Adding this to polyvinyl alcohol and casting it into a film further enhances its water absorption characteristics, meeting the needs of green camouflage materials. The preparation process of this invention is economical, simple, practical, and highly controllable. The low-speed, low-temperature process is more suitable for mass production and is also safer. The prepared products have excellent morphology and uniform dimensions, making them well-suited for applications in military camouflage and other fields, such as military camouflage films and incorporation into textiles to create camouflage clothing. Attached image description:

[0021] Figure 1 This is a schematic diagram of the preparation process of chlorophyll copper sodium salt@silica core-shell structure camouflage microcapsules.

[0022] Figure 2 These are scanning electron microscope (SEM) images and XRD patterns of the chlorophyll copper sodium salt@silica core-shell structure camouflage microcapsules prepared in Example 1.

[0023] Figure 3 These are particle size distribution diagrams and physical images of the chlorophyll copper sodium salt@silica core-shell structure camouflage microcapsules prepared in Example 2, and physical images of Example 2 / PVA / TD.

[0024] Figure 4 These are reflectance diagrams of Examples 1, 2, 3, and 4 and Osmanthus fragrans leaves in the 300-2500nm range.

[0025] Figure 5The images show the reflectance of the camouflage film and osmanthus leaves in the 300-2500nm range after PVA / TD was added and dried in Examples 2 and 3.

[0026] Figure 6 This is a comparison chart of the reflectance of Example 2 in August, Example 2 after drying in October, and Example 2 after 8 hours of moisture absorption in October, in the range of 300-2500nm.

[0027] Figure 7 The reflectance diagrams for Example 2 are in the range of 300-2500nm after complete drying and after absorbing moisture in a constant temperature and humidity chamber for 2h, 4h, and 8h respectively.

[0028] Figure 8 The image shows the reflectance of the chlorophyll copper sodium salt@silica core-shell structure camouflage microcapsules prepared in Example 2 and commercially available silica powder in the 300-2500 nm range.

[0029] Figure 9 The image shows the reflection and absorption spectra of the chlorophyll copper sodium salt@silica core-shell structure camouflage microcapsules prepared in Example 2 in the range of 300-2500 nm. Detailed Implementation

[0030] The following specific examples illustrate the preparation process of chlorophyll copper sodium salt@silica core-shell structure camouflage microcapsules. Figure 1 As shown.

[0031] Example 1

[0032] (1) Mix 0.6g of lipophilic nonionic surfactant Span 80 with 65mL of organic solvent cyclohexane as a continuous phase;

[0033] (2) Mix 0.1g Tween 80 with 15mL deionized water, heat at 50℃ and stir for 10min, add 0.01g sodium copper chlorophyllin, and mix at 400r / min to form a uniform dispersion phase;

[0034] (3) Add the dispersed phase from step (2) to the continuous phase from step (1), heat and stir at 50°C for 1.5 h to disperse, and rotate at 800 r / min to form a stable W / O emulsion.

[0035] (4) Slowly add 5 mL of silicon source precursor triethoxysilane and 9 mL of tetraethyl orthosilicate to the W / O emulsion in step (3), heat and stir at 50°C for 8 h at a speed of 800 r / min, and the reaction yields chlorophyll copper sodium salt@silica microcapsules.

[0036] (5) The microcapsules were washed with cyclohexane more than three times and then dried naturally to obtain chlorophyll copper sodium salt@silica core-shell structure disguised microcapsules.

[0037] Example 2

[0038] In this embodiment, the amount of sodium copper chlorophyllin added is 0.1g, and the remaining steps are the same as in Example 1.

[0039] Example 3

[0040] In this embodiment, the amount of sodium copper chlorophyllin added is 0.3g, and the remaining steps are the same as in Example 1.

[0041] Example 4

[0042] In this embodiment, the amount of sodium copper chlorophyllin added is 0.2g, and the remaining steps are the same as in Example 1.

[0043] Figure 2 These are scanning electron microscope and XRD images of the chlorophyll copper sodium salt@silica core-shell structure camouflage microcapsules prepared under the conditions of Example 1. It can be seen that a silica shell is formed outside the chlorophyll copper sodium salt molecule. Figure 3 These are particle size distribution diagrams and physical images of the chlorophyll copper sodium salt@silica core-shell structure camouflage microcapsules prepared under the conditions of Example 2, and physical images of Example 2 / PVA / TD. Combined with... Figure 2 and Figure 3 It can be seen that the microcapsules are dark green, and the color is due to the sodium copper chlorophyll salt molecules.

[0044] Figure 4 The reflectance of Examples 1, 2, 3, and 4 and Osmanthus fragrans leaves in the 300-2500 nm range is calculated. The correlation coefficients between Example 1 and Osmanthus fragrans leaves are 0.8997; 0.5986; 0.4701; and 0.4686. Since the reflectance differences between Examples 1 and 4 and Osmanthus fragrans leaves in the 300-680 nm range are too large, Examples 2 and 3 are closer to the reflectance of Osmanthus fragrans leaves in this range. Therefore, Examples 2 and 3 were selected for further experimentation.

[0045] Preparation of the camouflage film: Polyvinyl alcohol and lithium chloride were dispersed in deionized water and stirred at 90°C for about 2 hours to form a homogeneous polyvinyl alcohol aqueous solution. Then, microcapsules were added to the solution cooled to room temperature and stirred for about 0.5 hours to form a homogeneous casting solution. After standing and defoaming, the casting solution was coated onto a petri dish. To improve the overall reflectivity of the camouflage film, titanium dioxide (TD) was added, and the dish was placed in the dark at room temperature for about 24 hours to allow for natural drying. Finally, after most of the water in the casting solution evaporated into the air, the preparation of the camouflage film was completed. Notably, due to thorough stirring during the preparation process and the certain viscosity of the casting solution, the microcapsule powder was uniformly distributed in the camouflage film. The sodium copper chlorophyllin@silica microcapsules, though insoluble in water, were uniformly dispersed in the PVA film, further demonstrating that the sodium copper chlorophyllin was coated with silica.

[0046] Figure 5 The data represents the reflectance of the camouflage films (added to PVA / TD in Examples 2 and 3) and osmanthus leaves after casting and drying, within the 300-2500 nm range. The correlation coefficient between the PVA / TD film in Example 2 and the osmanthus leaves is 0.9200; the correlation coefficient between the PVA / TD film in Example 3 and the osmanthus leaves is 0.9173. Example 2 was selected for further experimentation.

[0047] Figure 6 This is a comparison chart of the reflectance of the microcapsules in Example 2 after 2 months of storage. It can be seen that the reflectance of Example 2 after 8 months and 8 hours of moisture absorption in October is very similar around 550nm. This indicates that the sodium copper chlorophyllin salt was not significantly affected during these two months, and the actual change was not significant. This suggests that the silica shell has the effect of delaying the photoaging of the sodium copper chlorophyllin salt.

[0048] Figure 7 The values ​​for the microcapsules in Example 2 after absorbing moisture in a constant temperature and humidity chamber are within the range of 1300-2500 nm. This represents the change in the water content of the silica shell. The higher the water content, the lower the reflectivity at 1490 nm and 1940 nm, indicating that silica acts as a water-carrying shell and can be used as a characteristic peak for water absorption in camouflage materials. The weight difference before and after water absorption is 0.01 g, which is the mass of water absorbed, proving that it has good water absorption capacity.

[0049] Figure 8 The reflectance diagrams of Example 2 and commercially available silica powder in the 300-2500nm range demonstrate that the silica shell prepared by the method of the present invention can carry water, making the water absorption characteristic peaks at 1490nm and 1940nm more obvious, which meets the requirements of green camouflage materials for reflectance spectra.

[0050] Figure 9The images show the reflection and absorption spectra of the chlorophyll copper sodium salt@silica core-shell structure camouflage microcapsules prepared in Example 2 in the range of 300-2500nm. The reflection absorption rate at around 550nm shows that it has a good effect of camouflaging the "green peak" of the leaf. The peaks at 1490nm and 1940nm can simulate the water absorption band of the leaf.

Claims

1. A method for preparing a metallochlorophyll derivative@silica core-shell structure camouflage microcapsule, characterized in that: The metal chlorophyll derivative@silica core-shell structure camouflage microcapsules have a particle size of 20-80 nm; specifically, the following steps are included: Step 1: Mix the lipophilic nonionic surfactant with the organic solvent cyclohexane as the continuous phase; Step 2: Mix the hydrophilic surfactant with deionized water, and add the metallochlorophyll derivative while heating and stirring, mixing thoroughly to form the dispersed phase; wherein, the heating temperature is 50-70℃, the stirring time is 5-10 min, and the stirring speed is 400-500 r / min; the metallochlorophyll derivative is a water-soluble transition metal chlorophyll sodium salt, which includes chlorophyll copper sodium salt, chlorophyll zinc sodium salt, and chlorophyll iron sodium salt; Step 3: Add the dispersed phase from Step 2 to the continuous phase from Step 1, and heat and stir simultaneously to form a stable water-in-oil emulsion; wherein the heating temperature is 50-70℃, the stirring time is 1-2 h, and the stirring speed is 800 r / min. Step 4: Add silicon source precursor dropwise to the water-in-oil emulsion from Step 3, and react while heating and stirring to obtain silica-coated metallochlorophyll derivative microcapsules; wherein the heating temperature is 50-80℃, the stirring time is 6-8 h, and the rotation speed is 800 r / min. Step 5: Wash the microcapsules obtained in Step 4 with cyclohexane and air dry to obtain metallochlorophyll derivative@silica core-shell structure camouflaged microcapsules.

2. The method for preparing the metallochlorophyll derivative@silica core-shell structure camouflage microcapsules according to claim 1, characterized in that: In step one, the lipophilic nonionic surfactant includes Span 80; the mass percentage of the lipophilic nonionic surfactant contained in the continuous phase is 0.9-1.4%.

3. The method for preparing the metallochlorophyll derivative@silica core-shell structure camouflage microcapsules according to claim 1, characterized in that: The mass percentage of hydrophilic surfactants in the dispersed phase described in step two is 0.6-1%; the mass percentage of metallochlorophyll derivatives is 0.07-1.9%.

4. The method for preparing the metallochlorophyll derivative@silica core-shell structure camouflage microcapsules according to claim 1, characterized in that: In step two, the hydrophilic surfactant is either a nonionic surfactant or anionic surfactant. The nonionic surfactant is Tween 80, and the anionic surfactant includes sodium dodecylbenzene sulfonate or sodium dodecyl sulfate.

5. The method for preparing the metallochlorophyll derivative@silica core-shell structure camouflage microcapsules according to claim 1, characterized in that: The silicon source precursor mentioned in step four is a mixture of triethoxysilane and tetraethyl orthosilicate in a volume ratio of 5:

9.

6. An application of a metallochlorophyll derivative@silica core-shell structure camouflage microcapsule prepared by the method according to any one of claims 1-5, characterized in that: The metallochlorophyll derivative@silica core-shell structured camouflage microcapsules are used to prepare military camouflage materials.

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