A shape-stable paraffin / silica microcapsule phase change composite material and a preparation method thereof

Abstract

The application belongs to the technical field of ship electronic device heat management, and relates to a shape-stable paraffin-silicon dioxide microcapsule phase change composite material and a preparation method thereof. The phase change composite material takes high latent heat paraffin as an inner core and tetraethyl orthosilicate as a silicon source, a dense SiO2 shell layer is formed on the paraffin surface through a "two-step emulsification method", and a shape-stable paraffin-silicon dioxide microcapsule phase change composite material is synthesized. The microcapsule has a "organic core-inorganic shell" smooth and dense structure, is uniform in particle size, and presents a nanometer level. Compared with conventional microcapsules, the nanometer microcapsules increase the specific surface area, are beneficial to uniform wall material wrapping, and have an encapsulation rate of greater than 80%. Meanwhile, the high encapsulation rate enables the Pa@SiO2 microcapsule to have a high heat storage effect, a latent heat value of 210 J / g, and the Pa@SiO2 microcapsule shows excellent shape stability in a high-temperature leakage test.

Description

Technical Field

[0001] This invention belongs to the field of thermal management technology for marine electronic devices, specifically relating to a shape-stable paraffin@silica microcapsule phase change composite material and its preparation method. Background Technology

[0002] In recent years, my country's industrialization level has been continuously improving, and promoting the lightweighting and low-carbon development of ships is an important measure for us to implement policies. Electronic components on ships and submarines are developing towards digitalization, high frequency, high power, and high integration, with power density constantly increasing. Chips are the main players in these power electronics, and their lifespan decreases exponentially with increasing temperature. Thermal accumulation can significantly shorten the lifespan of chips, threatening the stable operation of ship electronic equipment and affecting navigation safety. The innovative development of efficient thermal management materials is a crucial guarantee for maintaining the efficiency, reliability, and continuous stability of electronic products.

[0003] Phase change materials (PCMs) cooling technology is an effective passive cooling method with excellent temperature control. For thermal management systems of some high-power devices, the high latent heat of PCMs can absorb the heat generated during electronic device operation, thus effectively buffering and regulating accumulated heat. Organic PCMs suffer from low inherent thermal conductivity and leakage during phase transition. To address the low thermal conductivity issue, the thermal conductivity of PCMs can be improved by adding high-thermal-conductivity materials, such as carbon fibers, expandable graphite, and other additives. However, leakage of the liquid phase above the melting point of solid-liquid PCMs can lead to environmental pollution, severely limiting their practical application. Currently, to address PCM leakage, existing technologies employ methods such as nanomaterial adsorption, chemical cross-linking networks, or impregnation of PCMs into porous support materials to prepare shape-stable PCMs.

[0004] Microencapsulation is a process of coating PCM with multiple layers of shell material, typically in the micrometer range, to prevent leakage of molten phase change material and reduce its reactivity with the external environment. Microencapsulated PCMs have been widely used in thermal management systems, solar energy storage systems, industrial refrigeration systems, and heat transfer fluids. Lei Kang et al. (2022; Composites Science and Technology; DOI: 10.1016 / j.compscitech.2022.109756) used a traditional emulsion-interface polymerization method with paraffin as the core and silica as the shell to prepare a series of paraffin@silica microcapsules with phase change function. However, their particle size distribution was uneven, and the particle size range remained between 1 and 2 micrometers. Min Li et al. (2025; Materials Science and Engineering: B; DOI:10.1016 / j.mseb.2025.117979) prepared a phase change microcapsule with paraffin as the core and graphene-silica composite as the shell material using the sol-gel method, but its microcapsule encapsulation efficiency was 70% and the size was about 20 micrometers. Luping Gu et al. (2025; Chemical Engineering & Technology; DOI:10.1002 / ceat.70038) prepared a phase change microcapsule with paraffin as the core and melamine-formaldehyde resin as the wall material through in-situ polymerization, but the microcapsule encapsulation efficiency was only 62.5%. However, due to the easy decomposition of organic matter at high temperatures, the microcapsule thermal stability was poor, which is not conducive to the recycling of phase change materials. Chinese patent CN115637135B provides a composite phase change material and its preparation method; wherein, the phase change microcapsule uses an organic phase change material as the core and silicon dioxide or polyethylene glycol as the shell, and then carbon nanotubes and silicon dioxide are sequentially coated on the surface of the phase change microcapsule to form a phase change microcapsule / carbon nanotube / SiO2 composite thermally conductive phase change material; the particle size of the composite structure is 20um-150um.

[0005] As can be seen from the existing technology, microencapsulation technology still has significant shortcomings and many areas that need improvement, such as low encapsulation efficiency, large particle size, and poor stability. Therefore, this invention provides a shape-stable paraffin@silica microcapsule phase change composite material and its preparation method. Summary of the Invention

[0006] In view of the above-mentioned technical problems, the present invention provides a shape-stable paraffin@silica microcapsule phase change composite material (Pa@SiO2) and its preparation method, so as to solve the technical problems of low encapsulation efficiency, large particle size and poor stability of existing microcapsule technology.

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

[0008] The first aspect of this invention provides a shape-stable paraffin@silica microcapsule phase change composite material, which uses high latent heat paraffin (OP44E) as the core and tetraethyl silicate (TEOS) as the precursor. A dense SiO2 shell is formed on the surface of paraffin through a high-speed pre-emulsification-homogenization-hydrolysis condensation reaction of tetraethyl silicate, thereby synthesizing a paraffin@silica (Pa@SiO2) microcapsule phase change composite material with a smooth and dense structure.

[0009] A second aspect of the present invention also provides a method for preparing a shape-stable paraffin@silica microcapsule phase change composite material, comprising the following steps: S1. Pretreatment: Ethanol is dissolved in water at a certain mass ratio to obtain an aqueous phase, and high latent heat paraffin is dissolved in tetraethyl silicate to obtain an oil phase. S2. Construct an oil-in-water emulsion; add the surfactant to the aqueous phase and fully dissolve and disperse it to obtain an aqueous mixed solution; then add the aqueous mixed solution to the oil phase and use a magnetic stirrer to mix it evenly to form an oil-in-water emulsion; S3. High-speed pre-emulsification: The oil-in-water emulsion system was pre-emulsified using a high-shear homogenizer to prepare a paraffin@silica (Pa@SiO2) microcapsule phase change composite emulsion with a wide particle size distribution and a smooth, dense structure. S4. Homogenization and emulsification: The above emulsion is homogenized and emulsified using a high-power ultrasonic cell disruptor to obtain stable microemulsion droplets. S5. Interfacial polymerization reaction: Slowly add an alkaline solution to the microemulsion to make the solution alkaline. Tetraethyl silicate undergoes hydrolysis and condensation reaction at the interface between the oil droplets and the aqueous phase. After the reaction is completed, the microcapsule suspension is obtained. S6. Curing, washing, and drying; after the reaction is complete, stirring is continued for a period of time; the mixture is washed multiple times with a mixture of ethanol and deionized water and dried to obtain the paraffin@silica microcapsule phase change composite material.

[0010] Further, in step S1, the stirring speed is 300rpm-500rpm, the stirring time is 10-30 minutes, the mass ratio of ethanol to water in the aqueous phase is 0.3-1.2, and the mass ratio of high latent heat paraffin to tetraethyl silicate in the oil phase is 0.5-2.

[0011] Furthermore, in step S2, the surfactant is hexadecyltrimethylammonium bromide; the magnetic stirrer speed is 500rpm-1000rpm, and the stirring time is 10-30 minutes.

[0012] Furthermore, in step S3, the high shear force homogenizing disperser operates at a speed of 5000 rpm to 30000 rpm and a dispersion time of 10 to 30 minutes.

[0013] Furthermore, in step S4, the ultrasonic dispersion time of the high-power ultrasonic cell disruptor is 30-60 minutes, and the ultrasonic power is 500W-1000W.

[0014] Furthermore, in step S5, the pH of the alkaline solution is 8-11.

[0015] Further, in step S6, the stirring speed is 500rpm-1000rpm, the stirring time is 30-60 minutes; the mass ratio of ethanol to deionized water is 0.2-1, the number of washing cycles is 3-10, and the drying temperature is 30℃-60℃.

[0016] The microcapsule suspension contains spherical Pa@SiO2 microcapsules formed by interfacial polymerization with high latent heat paraffin as the core and tetraethyl silicate as the precursor, with an encapsulation rate of >80%.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Using high latent heat paraffin (OP44E) as the core material and tetraethyl orthosilicate (TEOS) as the precursor, a dense SiO2 shell was formed on the surface of the paraffin through a two-step emulsification method of high-speed pre-emulsification-homogenization emulsification and the hydrolysis-condensation reaction of TEOS, thus synthesizing paraffin@silica (Pa@SiO2) phase change microcapsules with a smooth and dense structure.

[0018] 2. Based on the homogenization emulsification effect of the "two-step emulsification method", the emulsion is first dispersed into micron or submicron-sized fine droplets, and then further dispersed into stable droplets with small particle size and narrow distribution. The resulting microcapsules have a uniform particle size distribution between 100nm and 200nm, which makes them easy to disperse and improves their performance.

[0019] 3. The emulsion obtained through the "two-step emulsification" process exhibits stability, effectively preventing aggregation before wall formation. Simultaneously, the droplets produced by the combined effects of the "two-step emulsification" method are characterized by small and uniform particle size, increasing the specific surface area and facilitating uniform encapsulation of the wall material. These are prerequisites for achieving a high encapsulation efficiency (>80%) in the microcapsules. Furthermore, the high encapsulation efficiency gives the Pa@SiO2 microcapsules a highly efficient heat storage effect, resulting in a latent heat value of 210 J / g for the microcapsules prepared by the method of this invention.

[0020] 4. Compared with polymer materials, inorganic shell materials exhibit higher physical strength and greater stability. The SiO2 shell protects the core, effectively slowing down the decomposition process of the phase change material. The inorganic shell maintains the structural stability of the microcapsules, and Pa@SiO2 microcapsules demonstrate excellent shape stability in high-temperature leakage tests.

[0021] In summary, the preparation method of this invention forms a dense SiO2 shell on the surface of paraffin wax, resulting in a paraffin@silica microcapsule phase change composite material with high encapsulation efficiency, uniform nanoscale particle size, and strong stability. These nanoscale capsules increase the specific surface area, shorten the heat transfer path, fundamentally reduce thermal resistance, and significantly improve heat transfer efficiency. This has significant application value in dealing with dynamic thermal loads and transient thermal shocks in electronic devices, and improves the practical application performance of polymer phase change composite materials in the field of thermal management for marine electronic devices. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall method for preparing microcapsule phase change composite materials according to the present invention; Figure 2 The images show the microstructure of the microcapsule phase change composite materials prepared in various embodiments of the present invention (Figure a is Example 1, Figure b is Example 2, and Figure c is Example 3). Figure 3 The images show the microstructure of the microcapsule phase change composite materials prepared in the comparative examples of this invention (Figure a is comparative example 1, Figure b is comparative example 2). Figure 4 This is a microstructure diagram of the microcapsule phase change composite material prepared in Example 1 of the present invention; Figure 5 This is a comparison diagram of the phase change properties of the microcapsule phase change composite material prepared in Example 1 and Comparative Example 1 of the present invention and pure paraffin. Figure 6 This is a comparison of the thermogravimetric curves of the microcapsule phase change composite material prepared in Example 1 of the present invention and pure paraffin. Figure 7 To Figure 6 The differential weight loss rate comparison between the microcapsule phase change composite material prepared in Example 1 and pure paraffin was obtained by differentiating the thermogravimetric curves. Figure 8 This is a comparison diagram of the shape stability properties of the microcapsule phase change composite materials prepared in various embodiments of the present invention and commercial paraffin (Pa). Detailed Implementation

[0023] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0024] This invention provides a shape-stable paraffin@silica microcapsule phase change composite material, which uses high latent heat paraffin (OP44E) as the core and tetraethyl silicate (TEOS) as the precursor. A dense SiO2 shell is formed on the surface of paraffin through a high-speed pre-emulsification-homogenization-TEOS hydrolysis-condensation reaction, thus synthesizing a paraffin@silica (Pa@SiO2) microcapsule phase change composite material with a smooth and dense structure.

[0025] like Figure 1 As shown, this invention also provides a method for preparing a shape-stable paraffin@silica microcapsule phase change composite material. The ethanol, tetraethyl silicate (TEOS), and hexadecyltrimethylammonium bromide (CTAB) used in this embodiment are all analytical grade. The preparation method includes the following steps: S1, Preprocessing; Ethanol is dissolved in water to obtain an aqueous phase, and high latent heat paraffin is dissolved in tetraethyl silicate to obtain an oil phase. The stirring speed is 300 rpm-500 rpm, and the stirring time is 10-30 minutes. The mass ratio of ethanol to water in the aqueous phase is 0.3-1.2, and the mass ratio of high latent heat paraffin to tetraethyl silicate in the oil phase is 0.5-2. The aqueous phase and oil phase are mixed evenly under the action of a homogenizer to form an oil-in-water emulsion system.

[0026] S2. Construct an oil-in-water emulsion; The surfactant was added to the aqueous phase and fully dissolved and dispersed to obtain an aqueous mixed solution. This aqueous mixed solution was then added to the oil phase, and the mixture was homogeneously stirred using a magnetic stirrer to form an oil-in-water emulsion. The surfactant was hexadecyltrimethylammonium bromide (CTAB); the magnetic stirrer speed was 500-1000 rpm, and the stirring time was 10-30 minutes. As a cationic surfactant, CTAB contains hydrophilic head groups and hydrophobic tail groups, enabling it to form micellar structures in the emulsion, ensuring the uniform adhesion of TEOS subsequently.

[0027] S3, high-speed pre-emulsification; A high-shear homogenizer was used to pre-emulsify an oil-in-water emulsion system to prepare a paraffin@silica (Pa@SiO2) microcapsule phase change composite emulsion with a wide particle size distribution and a smooth, dense structure. The high-shear homogenizer operated at speeds of 5000 rpm to 30000 rpm for 10 to 30 minutes. Under high-speed shear, paraffin was dispersed into micron- or submicron-sized droplets. During high-speed emulsification, surfactants adsorbed at the oil-water interface, reducing interfacial tension and preventing droplet coalescence. The high-speed pre-emulsification resulted in a stable emulsion, ensuring droplet independence and stability before the addition of wall materials and the subsequent shell-forming reaction, creating favorable conditions for subsequent wall formation.

[0028] S4. Homogenization and emulsification; The emulsion was homogenized and emulsified using a high-power ultrasonic cell disruptor, uniformly dispersing molten paraffin in an aqueous solution containing a surfactant to obtain stable microemulsion droplets with small particle size and narrow distribution. The ultrasonic dispersion time of the high-power ultrasonic cell disruptor was 30-60 minutes, and the ultrasonic power was 500W-1000W. Based on the high-speed shear pre-emulsification and the homogenization emulsification effect of the high-power ultrasonic cell disruptor, the emulsion was first dispersed into micron or submicron-sized fine droplets, and then further dispersed into stable droplets with small particle size and narrow distribution. This resulted in a uniform particle size distribution of the microcapsules obtained after the interfacial polymerization reaction, with the particle size mainly distributed between 100nm and 200nm, facilitating dispersion and improving performance.

[0029] S5, interfacial polymerization reaction; An alkaline solution is slowly added dropwise to the microemulsion to make the solution alkaline, with a pH of 8-11. Once the reaction is complete, a microcapsule suspension is obtained. The alkaline environment causes TEOS to hydrolyze at the oil-water interface. Its ethoxy groups react with water to generate monosilicic acid and alcohols. Then, dehydration or de-alcoholization reactions occur between TEOS and silicic acid, or between silicic acid particles, initially forming Si-O-Si bonds. The resulting nascent silica particles are hydrophilic and tend to adsorb at the oil-water interface to reduce the interfacial energy of the entire system. In the subsequent hydrolysis-condensation reaction, the previously formed Si-O-Si bonds gradually elongate and cross-link to form a three-dimensional network structure. The silica wall layer gradually thickens along the surface of the oil droplets, eventually forming a dense SiO2 shell on the paraffin surface.

[0030] The emulsion obtained after the "two-step emulsification" is stable and can prevent aggregation before wall formation. At the same time, the droplets are small and uniform in size under the combined effect of high-speed shearing and homogeneous emulsification, which increases the specific surface area, facilitates uniform encapsulation of wall materials, improves the encapsulation rate of microcapsules, and the encapsulation rate of spherical Pa@SiO2 microcapsules obtained by interfacial polymerization is 80%-85%.

[0031] S6. Curing, washing, and drying; After the reaction is complete, continue stirring for a period of time to allow the polycondensation reaction to proceed fully, resulting in a higher degree of cross-linking and greater density of the silica wall layer. The stirring speed is 500-1000 rpm, and the stirring time is 30-60 minutes. The product is then washed multiple times with a mixture of ethanol and deionized water (mass ratio of ethanol to deionized water 0.2-1), and dried 3-10 times at a drying temperature of 30℃-60℃ to obtain the paraffin@silica microcapsule phase change composite material.

[0032] The microcapsule suspension contains spherical Pa@SiO2 microcapsules formed by interfacial polymerization with high latent heat paraffin as the core and tetraethyl silicate as the precursor, and the encapsulation rate is >80%.

[0033] Example 1 A method for preparing shape-stable paraffin@silica microcapsule phase change composite materials includes the following steps: S1. Thoroughly mix ethanol / water and high latent heat paraffin / TEOS to form an aqueous phase and an oil phase respectively; the stirring speed is 300 rpm and the stirring time is 10 minutes; the mass ratio of the two components in the aqueous phase is 0.3 and the mass ratio of the two components in the oil phase is 0.5. S2. The surfactant cetyltrimethylammonium bromide (CTAB) is added to the aqueous phase and fully dissolved and dispersed. Then, the aqueous phase mixture is added to the oil phase, and a magnetic stirrer is used to mix it evenly to form an oil-in-water emulsion. The magnetic stirrer speed is 500 rpm and the stirring time is 10 minutes. S3. The oil-in-water emulsion system is pre-emulsified using a high-shear homogenizer with a speed of 5000 rpm and a stirring time of 10 minutes. S4. A high-power ultrasonic cell disruptor is used to homogenize and emulsify the emulsion system to form a stable microemulsion; the ultrasonic dispersion time of the high-power ultrasonic cell disruptor is 30 minutes, and the ultrasonic power is 500W.

[0034] S5. Slowly add an alkaline solution dropwise to the microemulsion to make the solution alkaline, with a pH of 8; the microcapsule suspension contains spherical Pa@SiO2 microcapsules formed by interfacial polymerization with high latent heat paraffin as the core and TEOS as the precursor, with an encapsulation rate of 85%; S6. Stir with a magnetic stirrer at 500 rpm for 30 minutes; wash three times with ethanol and deionized water and dry at 30°C. The mass ratio of ethanol to deionized water is 0.2 to obtain the paraffin@silica microcapsule phase change composite material, denoted as Pa@SiO2-1.

[0035] Example 2 S1. Thoroughly mix ethanol / water and high latent heat paraffin / TEOS to form an aqueous phase and an oil phase, respectively; the stirring speed is 350 rpm and the stirring time is 15 minutes. The mass ratio of the two components in the aqueous phase is 0.9, and the mass ratio of the two components in the oil phase is 1.5. S2. The surfactant cetyltrimethylammonium bromide (CTAB) is added to the aqueous phase and fully dissolved and dispersed. Then, the aqueous phase mixture is added to the oil phase, and a magnetic stirrer is used to mix it evenly to form an oil-in-water emulsion. The magnetic stirrer speed is 650 rpm and the stirring time is 15 minutes. S3. The oil-in-water emulsion system is pre-emulsified using a high-shear homogenizer with a speed of 10,000 rpm and a stirring time of 15 minutes. S4. A high-power ultrasonic cell disruptor is used to homogenize and emulsify the emulsion system to form a stable microemulsion; the ultrasonic dispersion time of the high-power ultrasonic cell disruptor is 40 minutes, and the ultrasonic power is 600W. S5. Slowly add an alkaline solution dropwise to the microemulsion to make the solution alkaline, with a pH of 9; the microcapsule suspension contains spherical Pa@SiO2 microcapsules formed by interfacial polymerization with high latent heat paraffin as the core and TEOS as the precursor, with an encapsulation efficiency of 82%; S6. The magnetic stirrer was set at 800 rpm for 45 minutes. The mixture was washed five times with ethanol and deionized water and dried at 40°C. The mass ratio of ethanol to deionized water was 0.4. The resulting paraffin@silica microcapsule phase change composite material was denoted as Pa@SiO2-2.

[0036] Example 3 S1. Thoroughly mix ethanol / water and high latent heat paraffin / TEOS to form an aqueous phase and an oil phase respectively; the stirring speed is 400 rpm and the stirring time is 20 minutes; the mass ratio of the two components in the aqueous phase is 1.2 and the mass ratio of the two components in the oil phase is 2. S2. The surfactant cetyltrimethylammonium bromide (CTAB) is added to the aqueous phase and fully dissolved and dispersed. Then, the aqueous phase mixture is added to the oil phase, and a magnetic stirrer is used to mix it evenly to form an oil-in-water emulsion. The magnetic stirrer speed is 800 rpm and the stirring time is 10 minutes. S3. The oil-in-water emulsion system is pre-emulsified using a high-shear homogenizer with a speed of 15,000 rpm and a stirring time of 20 minutes. S4. A high-power ultrasonic cell disruptor is used to homogenize and emulsify the emulsion system to form a stable microemulsion; the ultrasonic dispersion time of the high-power ultrasonic cell disruptor is 50 minutes, and the ultrasonic power is 800W. S5. Slowly add an alkaline solution to the microemulsion to make the solution alkaline, with a pH of 10. The microcapsule suspension contains spherical Pa@SiO2 microcapsules formed by interfacial polymerization with high latent heat paraffin as the core and TEOS as the precursor, with an encapsulation rate of 80%.

[0037] S6. The magnetic stirrer was set at 1000 rpm and the stirring time was 60 minutes. The mixture was washed 8 times with ethanol and deionized water and dried at 50°C. The mass ratio of ethanol to deionized water was 0.6. The resulting paraffin@silica microcapsule phase change composite material was denoted as Pa@SiO2-3.

[0038] The preparation method of this invention forms a dense SiO2 shell on the surface of paraffin wax, resulting in a paraffin@silica (Pa@SiO2) microcapsule phase change composite material with high encapsulation efficiency, uniform nanoscale particle size, and strong stability. The stability of the emulsion obtained after the "two-step emulsification" process prevents aggregation before wall formation. The emulsion is first dispersed into micron or submicron-sized droplets, and then further dispersed into stable droplets with small particle size and narrow distribution, resulting in a uniform particle size distribution of the microcapsules after the interfacial polymerization reaction. Simultaneously, the combined effect of high-speed shearing and homogeneous emulsification leads to small and uniform droplet size, increasing the specific surface area and facilitating uniform encapsulation by the wall material, thereby improving the encapsulation efficiency of the microcapsules.

[0039] The results showed that the microcapsules had a uniform particle size distribution, mainly between 100nm and 200nm, making them easy to disperse and improving their performance. The spherical Pa@SiO2 microcapsules formed by interfacial polymerization had an encapsulation rate of 80%-85%, with a high encapsulation rate (>80%), resulting in efficient heat storage. The latent heat value of the Pa@SiO2-1 microcapsules reached 210J / g. The SiO2 shell protected the core, effectively slowing down the decomposition process of the phase change material. The inorganic shell maintained the structural stability of the microcapsules, and the Pa@SiO2 microcapsules exhibited excellent shape stability in high-temperature leakage tests.

[0040] Comparative Example 1 The difference from Example 1 is that a dense SiO2 shell is formed on the surface of high latent heat paraffin through a homogeneous emulsification-tetraethyl silicate hydrolysis condensation reaction step (omitting the high-speed pre-emulsification step), and a paraffin@silica (Pa@SiO2) microcapsule phase change composite material with a smooth and dense structure is synthesized, denoted as Pa@SiO2-4.

[0041] like Figure 3 As shown in (a), the microstructure results indicate that the microcapsule particle size is non-uniform; the high latent heat paraffin exists in the form of irregular droplets, resulting in inconsistent final microcapsule sizes and affecting the consistency of product performance. The surface of large-sized high latent heat paraffin droplets is difficult to be completely covered by the wall material, leading to pores in the wall layer and increasing the risk of leakage. This is because without high-speed pre-emulsification, a single homogenization emulsification step is insufficient to form a stable microemulsion, thus causing the microcapsule particle size to become uncontrolled.

[0042] Comparative Example 2 The difference from Example 1 is that a dense SiO2 shell is formed on the surface of high latent heat paraffin through a high-speed pre-emulsification-tetraethyl silicate hydrolysis condensation reaction step (omitting the homogenization emulsification step), and a paraffin@silica (Pa@SiO2) microcapsule phase change composite material with a smooth and dense structure is synthesized, denoted as Pa@SiO2-5.

[0043] like Figure 3 As shown in (b), the microstructure results indicate that the microcapsule particles are large and uneven in size. Furthermore, some shells are damaged due to incomplete encapsulation or uneven wall material coverage. The rough and uneven droplet surface results in a rough and porous microcapsule surface as well. This is because the microcapsules were only subjected to a one-step high-speed pre-emulsification process without homogenization, making it difficult to produce ultrafine and uniform emulsion droplets. Ultimately, this leads to larger microcapsule sizes, lower encapsulation efficiency, and poor product uniformity.

[0044] Comparative Example 3 The difference from Example 1 is that commercial paraffin, n-octadecane, and n-tetracosane were used as phase change materials, and a one-step high-speed emulsification-interfacial polycondensation process was employed to prepare phase change material@inorganic shell composite microcapsules. Although the prepared microcapsules possess shape stability, their particle size is all in the micrometer range, and their latent heat of phase change is all less than 200 J / g (specific data are shown in Table 1).

[0045] Table 1. Specific data on the preparation of stable phase change composite materials by microencapsulation method in Comparative Example 3.

[0046] To verify the performance of the composite materials obtained in the examples of this invention, the standard samples obtained after processing in Examples 1, 2, 3, Comparative Example 1, and Comparative Example 2 were tested. The test results are as follows: First, the microstructure of the phase change microcapsules was characterized using electron microscopy, such as... Figure 2 The figures show the microstructure of the paraffin@silica microcapsule phase change composite materials in each embodiment. The paraffin@SiO2 microcapsules have smooth surfaces, clear boundaries, and exhibit a distinct core-shell structure. Their particle size is mainly distributed between 100 nm and 200 nm, and the wall thickness is approximately 10 nm. These results indicate that uniform coating of SiO2 on the paraffin surface was achieved through the hydrolysis-condensation reaction of TEOS.

[0047] Figure 3 The microstructures of the microcapsule phase change composites prepared in Comparative Examples 1 and 2 are shown. The results indicate that the microcapsule particles are large and non-uniform, exhibiting micron-sized dimensions. The rough and non-uniform droplet surface leads to a rough and porous microcapsule surface as well. Paraffin exists in the form of irregular droplets, resulting in inconsistent final microcapsule sizes. Large paraffin droplets are difficult to completely cover with the wall material, leading to partial shell breakage and increasing the risk of leakage. This demonstrates that a single-step emulsification process is insufficient to produce ultrafine and uniform emulsion droplets, resulting in larger microcapsule sizes, lower encapsulation efficiency, and poor product uniformity.

[0048] Second, the microstructure of microcapsule phase change composite materials, such as Figure 4 As shown in the XRD pattern of SiO2 (corresponding to...) Figure 4 (Blue curve), at 2θ=22.4° ( Figure 4 A distinct broad diffraction peak (short and broad) appears at the location marked by the red circle, representing the amorphous structure of the SiO2 shell; in the XRD pattern of Pa (corresponding to...) Figure 4 The red curve shows multiple sharp diffraction peaks (high and thin peaks), indicating its high crystallinity; the XRD pattern of Pa@SiO2 (corresponding to...) Figure 4 The green curve contains almost all the characteristic peaks of both SiO2 and Pa, confirming that Pa was successfully encapsulated by the SiO2 shell.

[0049] Third, the phase transformation properties of Pa@SiO2 phase change composite materials, such as... Figure 5 As shown, the phase transition behavior of the two types of Pa@SiO2 microcapsules in Example 1 and Comparative Example 1 is similar to that of pure paraffin. The initial melting temperature T of Pa is... M The solidification temperature is 44.59℃, and the solidification temperature is T. C The initial melting temperature T of Pa@SiO2-1 after being coated with a SiO2 shell is 42.52℃. M The solidification temperature is 40.60℃, and the solidification temperature is T. C The temperature was 42.06℃, indicating that the SiO2 encapsulation shell had virtually no effect on the phase transition temperature of paraffin. The enthalpy of melting and solidification of pure paraffin were 258.7 J / g and 249.6 J / g, respectively. After being encapsulated with SiO2, the enthalpy of melting and solidification of Pa@SiO2-1 microcapsules were 214.9 J / g and 205.1 J / g, respectively. The inorganic shell lacks phase transition functionality, resulting in a reduction of approximately 15% in the latent heat of Pa@SiO2-1 microcapsules. For Pa@SiO2-4, the phase transition performance was severely reduced due to shell damage, with its enthalpy of melting and solidification being only 95 J / g and 87 J / g, respectively.

[0050] Fourth, the thermal stability of the product was examined by comparing thermal weight loss and differential weight loss rate. Figure 6 and Figure 7 It can be seen that both paraffin and Pa@SiO2-1 microcapsules exhibit one-step decomposition at high temperatures, corresponding to... Figure 7The curve shows only one peak; pure Pa completes its decomposition process entirely between 150℃ and 300℃, leaving no carbon residue. Paraffin begins to decompose at approximately 150℃, while the Pa@SiO2-1 microcapsules only begin to decompose at approximately 190℃, a 40℃ delay in decomposition temperature. The silica shell protects the core and, to some extent, hinders its volatilization, slowing down the decomposition process of the phase change material in the thermogravimetric experiment and delaying the decomposition temperature of the microcapsules by 40℃. This indicates that the successful encapsulation with the inorganic shell material effectively improves the thermal stability of the phase change material. Pa@SiO2 experiences a 90% mass loss at 800℃, with a final residual weight of approximately 10%. Therefore, with a SiO2 shell material content of 10%, the weight loss rate is essentially consistent with the microcapsule encapsulation efficiency.

[0051] Fifth, the commercial paraffin (Pa) and the three paraffin@silica microcapsules from the examples were placed in a constant temperature device at 100°C to examine the shape stability of the products. Figure 8 As shown, Figure 8 (a) and Figure 8 (c) are macroscopic morphology images of commercial paraffin and Pa@SiO2 microcapsules before the start of the experiment. Figure 8 (b) shows the morphology after the 60-minute high-temperature leakage test. It can be seen that the commercial paraffin completely melted into a liquid state after 60 minutes, while in reality, due to its low phase transition point (45°C), the commercial paraffin completely melted within the first 5 minutes of the experiment. Due to the barrier effect of the dense silica shell prepared in this invention, a dense SiO2 shell layer is formed on the surface of the paraffin through interfacial condensation reaction. The silica forms a hard inorganic network or shell, providing excellent structural support for the microcapsules and significantly improving their shape stability. Therefore, compared to… Figure 8 (c) and Figure 8 As shown in (d)-(f), none of the three Pa@SiO2 microcapsules showed any leakage during the entire test process as time increased. After the 60-minute high-temperature leakage experiment, the shape remained intact, indicating that the microcapsules prepared by this invention have excellent shape stability.

[0052] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A shape-stable paraffin@silica microcapsule phase change composite material, characterized in that: Using high latent heat paraffin as the core and tetraethyl silicate as the precursor, a dense silica shell is formed on the surface of paraffin through high-speed pre-emulsification-homogeneous emulsification-hydrolysis condensation reaction of tetraethyl silicate, thus synthesizing a paraffin@silica microcapsule phase change composite material with a smooth and dense structure.

2. A method for preparing a shape-stable paraffin@silica microcapsule phase change composite material, characterized in that, Includes the following steps: S1. Pretreatment: Ethanol is dissolved in water at a certain mass ratio to obtain an aqueous phase, and high latent heat paraffin is dissolved in tetraethyl silicate to obtain an oil phase. S2. Construct an oil-in-water emulsion; add the surfactant to the aqueous phase and fully dissolve and disperse it to obtain an aqueous mixed solution; then add the aqueous mixed solution to the oil phase and use a magnetic stirrer to mix it evenly to form an oil-in-water emulsion; S3. High-speed pre-emulsification: A high-shear homogenizer is used to pre-emulsify the oil-in-water emulsion system to prepare a stable emulsion with a wide particle size distribution. S4. Homogenization and emulsification: The above emulsion is homogenized and emulsified using a high-power ultrasonic cell disruptor to obtain stable microemulsion droplets. S5. Interfacial polymerization reaction: Slowly add an alkaline solution to the microemulsion to make the solution alkaline. Tetraethyl silicate undergoes hydrolysis and condensation reaction at the interface between the oil droplets and the aqueous phase. After the reaction is completed, the microcapsule suspension is obtained. S6. Curing, washing, and drying; after the reaction is complete, stirring is continued for a period of time; the mixture is washed multiple times with a mixture of ethanol and deionized water and dried to obtain the paraffin@silica microcapsule phase change composite material.

3. The preparation method according to claim 2, characterized in that: In step S1, the stirring speed is 300 rpm-500 rpm and the stirring time is 10-30 minutes; the mass ratio of ethanol to water in the aqueous phase is 0.3-1.2, and the mass ratio of high latent heat paraffin to tetraethyl silicate in the oil phase is 0.5-2.

4. The preparation method according to claim 2, characterized in that: In step S2, the surfactant is hexadecyltrimethylammonium bromide.

5. The preparation method according to claim 2, characterized in that: In step S2, the magnetic stirrer rotates at 500 rpm to 1000 rpm, and the stirring time is 10 to 30 minutes.

6. The preparation method according to claim 2, characterized in that: In step S3, the high shear force homogenizer rotates at 5000 rpm to 30000 rpm and the stirring time is 10 to 30 minutes.

7. The preparation method according to claim 2, characterized in that: In step S4, the ultrasonic dispersion time of the high-power ultrasonic cell disruptor is 30-60 minutes, and the ultrasonic power is 500W-1000W.

8. The preparation method according to claim 2, characterized in that: In step S5, the pH of the alkaline solution is 8-11.

9. The preparation method according to claim 2, characterized in that: In step S5, the microcapsule suspension contains spherical Pa@SiO2 microcapsules formed by interfacial polymerization with high latent heat paraffin as the core and tetraethyl silicate as the precursor, with an encapsulation rate >80%.

10. The preparation method according to claim 2, characterized in that: In step S6, the magnetic stirrer rotates at 500 rpm to 1000 rpm for 30 to 60 minutes; the mass ratio of ethanol to deionized water is 0.2 to 1; the washing is performed 3 to 10 times; and the drying temperature is 30°C to 60°C.

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