A toughened shell phase change capsule and a method of making the same

Abstract

The application discloses a kind of toughened shell phase change capsules and preparation method thereof, and the method steps are as follows: adding sodium alginate into polyvinyl alcohol solution, and dissolving sufficiently as outer phase fluid;The phase change material to be wrapped is heated to melt as inner phase fluid;Outer phase fluid and inner phase fluid are pumped into flow focusing microfluidic chip respectively with syringe pump, and composite emulsion precursor is generated at chip channel outlet;With calcium chloride solution as collection liquid, composite emulsion precursor is collected, and phase change capsule preparation is completed by chemical reaction to realize shell solidification;After prepared phase change capsule is frozen and thawed three times in liquid nitrogen, it can be used immediately.The application adopts microfluidic technology, and polyvinyl alcohol is introduced into calcium alginate shell, and then repeatedly frozen and thawed multiple times, to form polyvinyl alcohol and calcium alginate crosslinked crystal with polyvinyl alcohol crystal as crosslinking point, which can greatly improve the compression strength and toughness of phase change capsule, and significantly reduce the leakage risk of core phase change material during use.

Description

Technical Field

[0001] This invention relates to the field of composite material preparation technology, specifically to a phase change capsule with a strong and tough shell and its preparation method. Background Technology

[0002] Phase change capsules are phase change energy storage materials with a typical core-shell structure, using organic, inorganic, or organic-inorganic composite materials as the outer shell and phase change material as the core. Due to the protective effect of the outer shell on the internal phase change material, leakage, evaporation, and oxidation of the phase change material can be effectively prevented, improving its thermal stability and service life. Therefore, a stable, reliable, and durable outer shell is a necessary prerequisite for the long-term effective encapsulation of the core material inside the phase change capsule.

[0003] However, currently, the encapsulation process of phase change materials often faces problems such as poor controllability and low encapsulation success rate in shell preparation. In particular, many phase change capsule shells have poor mechanical properties and unreliable reliability, resulting in defects such as core material leakage and short service life in practical applications. Taking calcium alginate shells, which are commonly used in microfluidic phase change capsule preparation technology, as an example, although this material has advantages such as low cost, high curing efficiency, and environmental friendliness, calcium alginate shells have poor strength and are prone to deformation or even cracking in practical applications, thus seriously restricting the reliability, stability, and service life of phase change capsules.

[0004] Therefore, conducting research on strengthening the mechanical properties of calcium alginate, a commonly used but mechanically unsatisfactory phase change capsule shell material, and subsequently developing a method for preparing phase change capsules with a strong and tough shell, is of great practical significance for improving the reliability, stability, and service life of phase change capsules in practical applications and expanding their application fields. Summary of the Invention

[0005] Technical problem to be solved: In view of the problems existing in the prior art, the present invention proposes a phase change capsule with a strong and tough shell and its preparation method. The phase change capsule is prepared by microfluidic technology, and polyvinyl alcohol is introduced into the calcium alginate shell. After repeated freeze-thaw cycles, polyvinyl alcohol and calcium alginate cross-linked crystals are formed with polyvinyl alcohol crystals as cross-linking points, which can significantly improve the compressive strength and toughness of the phase change capsule.

[0006] Technical solution: One objective of this invention is to provide a method for preparing a phase change capsule with a strong and tough shell, the steps of which are as follows:

[0007] Step 1: Dissolve polyvinyl alcohol in deionized water and stir thoroughly to form solution A. Then add sodium alginate and stir thoroughly to form solution B, which serves as the external phase fluid.

[0008] Step 2: Dissolve calcium chloride in deionized water until fully dissolved to form solution C;

[0009] Step 3: Heat the phase change material to be coated until it melts, and add an oleophilic emulsifier as the internal phase fluid;

[0010] Step 4: Pump the external phase fluid and the internal phase fluid into the flow-focusing microfluidic chip using a syringe pump, and generate a composite emulsion precursor at the chip channel outlet.

[0011] Step 5: Using solution C as the collecting liquid, collect the composite emulsion precursor, and complete the phase change capsule preparation by solidifying the shell through a chemical reaction;

[0012] Step 6: After the phase change capsules prepared in step 5 are subjected to three freeze-thaw cycles in liquid nitrogen, phase change capsules with a strong and tough shell can be obtained.

[0013] In steps three through five, the phase change material needs to be kept in a molten state at a temperature higher than the melting temperature of the phase change material.

[0014] Preferably, in step one, the polyvinyl alcohol has a molecular weight of 13,000 to 23,000, a degree of alcoholysis of 87% to 89% and 98% to 99%, respectively, and a mass ratio of 1:4.5.

[0015] Preferably, in step one, 5% by mass of polyvinyl alcohol is dissolved in deionized water and stirred thoroughly to form solution A. Then, sodium alginate is added and stirred thoroughly to form solution B, which serves as the external phase fluid. The mass ratio of sodium alginate to polyvinyl alcohol is 1:2.45.

[0016] Preferably, in step two, calcium chloride with a mass fraction of 4-6% is dissolved in deionized water, and after complete dissolution, solution C is formed.

[0017] Furthermore, in step two, calcium chloride with a mass fraction of 5% is dissolved in deionized water, and after complete dissolution, solution C is formed.

[0018] Preferably, the phase change material in step three is paraffin wax.

[0019] Preferably, in step three, the phase change material is paraffin RT25, the lipophilic emulsifier is Span 80, and the mass fraction of the lipophilic emulsifier is 1-3%; the temperature in steps three to five is controlled at 28-30℃.

[0020] Furthermore, the mass fraction of the lipophilic emulsifier is 2%.

[0021] Preferably, in step four, the core glass channel of the flow-focusing microfluidic chip is made of an inner phase tube nested inside an outer phase tube, with the inner diameter ratio of the inner phase tube to the outer phase tube being 0.46 to 0.50, and it must be ensured that they are coaxially nested; the flow rate ratio of the inner phase to the outer phase fluid is 1:3.2 to 1:3.8.

[0022] Furthermore, the inner diameter ratio of the inner phase to the outer phase tube is 0.47, and they must be coaxially nested; the flow rate ratio of the inner phase to the outer phase fluid is 1:3.6.

[0023] Furthermore, in step five, solution C is used as the collecting liquid to collect the composite emulsion precursor. Specifically, the composite emulsion precursor is dripped into solution C, and the shell is solidified through a chemical reaction.

[0024] Preferably, the three-stage freeze-thaw process in step six is ​​as follows: quick-freezing with liquid nitrogen at -196℃ for 0.5 hours, followed by thawing for 1 hour to room temperature, and repeating this process three times.

[0025] Preferably, in step one, the solution A is formed after thorough stirring and dissolution as follows: the stirring temperature is 90-95℃, and the solution is continuously stirred with a magnetic stirrer at a speed of 700-900 rpm for 2-4 hours to form solution A, which is then cooled to room temperature; the solution B is formed after thorough stirring and dissolution as follows: the stirring temperature is 60-65℃, and the solution is continuously stirred with a magnetic stirrer at a speed of 700-900 rpm for 1-3 hours to form solution B, which is then cooled to room temperature.

[0026] Further, to form solution A after thorough stirring and dissolution: the stirring temperature is 90℃, and the mixture is continuously stirred with a magnetic stirrer at a speed of 700-900 rpm for 3 hours to form solution A, which is then cooled to room temperature; to form solution B after thorough stirring and dissolution: the stirring temperature is 60℃, and the mixture is continuously stirred with a magnetic stirrer at a speed of 700-900 rpm for 1 hour to form solution B, which is then cooled to room temperature.

[0027] Another object of the present invention is to provide a phase change capsule with a toughened shell prepared based on the above method.

[0028] The phase change capsule with a strong and tough shell provided by this invention uses polyvinyl alcohol-calcium alginate as the shell material, forming a polyvinyl alcohol-calcium alginate shell around the paraffin core, thereby successfully encapsulating the phase change material. The prepared phase change capsules have a particle size range of 500 μm to 700 μm.

[0029] Beneficial effects: (1) This invention uses microfluidic technology to prepare phase change capsules, and specifically introduces an appropriate amount of polyvinyl alcohol into the common calcium alginate shell. In this way, the network structure formed by polyvinyl alcohol and calcium alginate is interpenetrating, achieving double cross-linking. On this basis, after repeated freeze-thaw cycles, polyvinyl alcohol and calcium alginate cross-linked crystals are formed with polyvinyl alcohol crystals as cross-linking points. Moreover, after the formation of the complex, the hydrogen bonds in the molecular chain of polyvinyl alcohol are weakened, and the compactness of the network structure formed by polyvinyl alcohol and calcium alginate is enhanced. As a result, the compressive strength and toughness of the traditional calcium alginate shell are greatly improved. Compared with the conventional calcium alginate shell, the compressive strength of the phase change capsule prepared by this invention is increased by 20.5 times, and the toughness is increased by 31.18 times.

[0030] (2) The method provided by the present invention is simple, low-cost and environmentally friendly.

[0031] (3) The present invention uses microfluidic technology to prepare phase change capsules, which has the advantages of good controllability, high coating success rate and good monodispersity. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only the embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a flowchart of a method for preparing a phase change capsule with a strong and tough shell according to the present invention;

[0034] Figure 2 This invention provides a method for preparing a phase change capsule with a strong and tough shell, including a flowchart and a finished product image.

[0035] Figure 3 Scanning electron microscope (SEM) images of the surface and cross-section of a phase change capsule prepared using the prior art (Comparative Example 1) and a phase change capsule with a toughened shell prepared according to Example 1 of the present invention, wherein (a1) and (a2) are SEM images of the surface of a phase change capsule with 3% calcium alginate as the shell using the prior art; (a3) ​​is a cross-sectional SEM image of a phase change capsule with 3% calcium alginate as the shell using the prior art; (b1) and (b2) are SEM images of the surface of a phase change capsule with a toughened shell according to Example 1 of the present invention; and (b3) is a cross-sectional SEM image of a phase change capsule with a toughened shell according to Example 1 of the present invention.

[0036] Figure 4 Comparison of stress and strain between the phase change capsule prepared by the prior art (Comparative Example 1) and the phase change capsule with a toughened shell prepared by Example 1 of the present invention;

[0037] Figure 5 Comparison of compressive strength and compressive modulus between the phase change capsule prepared by the prior art (Comparative Example 1) and the phase change capsule with a toughened shell prepared by Example 1 of the present invention;

[0038] Figure 6 Comparison of stress and strain of phase change capsules prepared according to the prior art (Comparative Example 1) and phase change capsules with toughened shells prepared according to Examples 1-3 of the present invention;

[0039] Figure 7 Stress and strain comparison diagrams for phase change capsules with toughened shells prepared according to different freeze-thaw cycles (Example 1, Comparative Example 2, Comparative Example 3). Detailed Implementation

[0040] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the implementation of the present invention is not limited thereto.

[0041] Unless otherwise specified, all reagents used in the examples in this specification can be purchased from the market.

[0042] The molecular weight of polyvinyl alcohol is 13,000 to 23,000, and the degree of alcoholysis is 87% to 89% and 98% to 99%, respectively.

[0043] The core glass channel of the flow-focusing microfluidic chip is made of an inner phase tube nested inside an outer phase tube. The inner diameter ratio of the inner phase tube to the outer phase tube is 0.46 to 0.50, and they must be coaxially nested. The flow rate ratio of the inner phase to the outer phase fluid is 1:3.2 to 1:3.8.

[0044] Example 1

[0045] This embodiment describes a method for preparing a phase change capsule with a strong and tough shell. See [link to previous document]. Figure 1 and Figure 2 The specific steps are as follows:

[0046] (1) Weigh 1g of polyvinyl alcohol (degree of hydrolysis is 87% to 89%) and 4.5g of polyvinyl alcohol (degree of hydrolysis is 98% to 99%), dissolve them in 104.5mL of deionized water at room temperature, stir mechanically at 90℃ for 3 hours, cool to room temperature after complete dissolution, add 2.245g of sodium alginate and stir mechanically at 60℃ for 1 hour to dissolve, and obtain a polyvinyl alcohol aqueous solution of sodium alginate.

[0047] (2) Weigh 20g of calcium chloride and dissolve it in 380g of deionized water at room temperature with mechanical stirring.

[0048] (3) Weigh 1.12g of the lipophilic emulsifier Span 80 and dissolve it in 55g of paraffin (RT25) at 30℃.

[0049] (4) Insert the inner phase tube (outer diameter 2.5 mm, inner diameter 1.4 mm) of the flow-focusing microfluidic chip glass tube into another cylindrical capillary tube (outer diameter 4 mm, inner diameter 3 mm) coaxially; use epoxy resin glue for 5 minutes to connect the glue dispensing needle with an outer diameter of 1.8 mm and an inner diameter of 1.5 mm to the inner and outer phase tubes respectively and fix them on the glass slide. During this process, it is necessary to ensure that the concentricity of the inner and outer phase tubes is highly consistent, the epoxy resin glue connection is well sealed, and the glue dispensing needle is connected to the injection pump.

[0050] (5) The polyvinyl alcohol aqueous solution of paraffin (RT25) and sodium alginate was pumped into the flow focusing microfluidic chip as the internal and external phases respectively using an injection pump. The flow rate ratio was 1:3.6, and a composite emulsion precursor was generated at the chip channel outlet.

[0051] (6) The composite emulsion precursor obtained in (5) is dropped into an aqueous calcium chloride solution to solidify the shell and complete the preparation of the phase change capsule.

[0052] (7) The obtained phase change capsules were subjected to freeze-thaw cycles using liquid nitrogen (-196℃), i.e., quick-freezing for 0.5 hours and then thawing for 1 hour to room temperature, and this process was repeated three times.

[0053] Example 2

[0054] Same as Example 1, except that the amounts of deionized water and sodium alginate added in step (1) are different, as detailed below:

[0055] (1) Weigh 1g of polyvinyl alcohol (degree of hydrolysis is 87% to 89%) and 4.5g of polyvinyl alcohol (degree of hydrolysis is 98% to 99%), dissolve them in 177.83mL of deionized water at room temperature, stir mechanically at 90℃ for 3 hours, cool to room temperature after complete dissolution, add 3.74g of sodium alginate and stir mechanically at 60℃ for 1 hour to dissolve, and obtain a polyvinyl alcohol aqueous solution of sodium alginate.

[0056] (2) Weigh 20g of calcium chloride and dissolve it in 380g of deionized water at room temperature with mechanical stirring.

[0057] (3) Weigh 1.12g of the lipophilic emulsifier Span 80 and dissolve it in 55g of paraffin (RT25) at 30℃.

[0058] (4) Insert the inner phase tube (outer diameter 2.5 mm, inner diameter 1.4 mm) of the flow-focusing microfluidic chip glass tube into another cylindrical capillary tube (outer diameter 4 mm, inner diameter 3 mm) coaxially; use epoxy resin glue for 5 minutes to connect the glue dispensing needle with an outer diameter of 1.8 mm and an inner diameter of 1.5 mm to the inner and outer phase tubes respectively and fix them on the glass slide. During this process, it is necessary to ensure that the concentricity of the inner and outer phase tubes is highly consistent, the epoxy resin glue connection is well sealed, and the glue dispensing needle is connected to the injection pump.

[0059] (5) The polyvinyl alcohol aqueous solution of paraffin (RT25) and sodium alginate was pumped into the flow focusing microfluidic chip as the internal and external phases respectively using an injection pump. The flow rate ratio was 1:3.6, and a composite emulsion precursor was generated at the chip channel outlet.

[0060] (6) The composite emulsion precursor obtained in (5) is dropped into an aqueous calcium chloride solution to solidify the shell and complete the preparation of the phase change capsule.

[0061] (7) The obtained phase change capsules were subjected to freeze-thaw cycles using liquid nitrogen (-196℃), i.e., quick-freezing for 0.5 hours and then thawing for 1 hour to room temperature, and this process was repeated three times.

[0062] Example 3

[0063] Same as Example 1, except that the amounts of polyvinyl alcohol, deionized water, and sodium alginate added in step (1) are different, as detailed below:

[0064] (1) Weigh 2g of polyvinyl alcohol (degree of hydrolysis is 87% to 89%) and 9g of polyvinyl alcohol (degree of hydrolysis is 98% to 99%), dissolve them in 126.5mL of deionized water at room temperature, stir mechanically at 90℃ for 3 hours, cool to room temperature after complete dissolution, add 2.806g of sodium alginate and stir mechanically at 60℃ for 1 hour to dissolve, and obtain a polyvinyl alcohol aqueous solution of sodium alginate.

[0065] (2) Weigh 20g of calcium chloride and dissolve it in 380g of deionized water at room temperature with mechanical stirring.

[0066] (3) Weigh 1.12g of the lipophilic emulsifier Span 80 and dissolve it in 55g of paraffin (RT25) at 30℃.

[0067] (4) Insert the inner phase tube (outer diameter 2.5 mm, inner diameter 1.4 mm) of the flow-focusing microfluidic chip glass tube into another cylindrical capillary tube (outer diameter 4 mm, inner diameter 3 mm) coaxially; use epoxy resin glue for 5 minutes to connect the glue dispensing needle with an outer diameter of 1.8 mm and an inner diameter of 1.5 mm to the inner and outer phase tubes respectively and fix them on the glass slide. During this process, it is necessary to ensure that the concentricity of the inner and outer phase tubes is highly consistent, the epoxy resin glue connection is well sealed, and the glue dispensing needle is connected to the injection pump.

[0068] (5) The polyvinyl alcohol aqueous solution of paraffin (RT25) and sodium alginate was pumped into the flow focusing microfluidic chip as the internal and external phases respectively using an injection pump. The flow rate ratio was 1:3.6, and a composite emulsion precursor was generated at the chip channel outlet.

[0069] (6) The composite emulsion precursor obtained in (5) is dropped into an aqueous calcium chloride solution to solidify the shell and complete the preparation of the phase change capsule.

[0070] (7) The obtained phase change capsules were subjected to freeze-thaw cycles using liquid nitrogen (-196℃), i.e., quick-freezing for 0.5 hours and then thawing for 1 hour to room temperature, and this process was repeated three times.

[0071] Comparative Example 1

[0072] This comparative example demonstrates a prior art method for preparing phase change capsules, as detailed below:

[0073] (1) Weigh 7.5g of sodium alginate and dissolve it in 142.5g of deionized water under mechanical stirring at 60℃ for 1 hour to obtain sodium alginate aqueous solution.

[0074] (2) Weigh 20g of calcium chloride and dissolve it in 380g of deionized water at room temperature with mechanical stirring.

[0075] (3) Weigh 1.12g of the lipophilic emulsifier Span 80 and dissolve it in 55g of paraffin (RT25) at 30℃.

[0076] (4) Insert the inner phase tube (outer diameter 2.5 mm, inner diameter 1.4 mm) of the flow-focusing microfluidic chip glass tube into another cylindrical capillary tube (outer diameter 4 mm, inner diameter 3 mm) coaxially; use epoxy resin glue for 5 minutes to connect the glue dispensing needle with an outer diameter of 1.8 mm and an inner diameter of 1.5 mm to the inner and outer phase tubes respectively and fix them on the glass slide. During this process, it is necessary to ensure that the concentricity of the inner and outer phase tubes is highly consistent, the epoxy resin glue connection is well sealed, and the glue dispensing needle is connected to the injection pump.

[0077] (5) Paraffin (RT25) and sodium alginate aqueous solution were pumped into the flow focusing microfluidic chip as internal and external phases respectively using an injection pump at a flow rate ratio of 1:3.6, and a composite emulsion precursor was generated at the chip channel outlet.

[0078] (6) The composite emulsion precursor obtained in (5) is dropped into an aqueous solution of calcium chloride to solidify the shell, thus completing the preparation of a phase change capsule with calcium alginate as the shell.

[0079] Comparative Example 2

[0080] Similar to Example 1, except that step (7) is not used, that is, the obtained phase change capsule is not subjected to liquid nitrogen freeze-thaw, and the obtained composite emulsion precursor is dripped into calcium chloride aqueous solution to solidify the shell, thus completing the preparation of phase change capsule with polyvinyl alcohol-calcium alginate shell.

[0081] Comparative Example 3

[0082] Similar to Example 1, except that step (7) is not repeated three times with liquid nitrogen freeze-thaw, but only once. The phase change capsule to be obtained is subjected to freeze-thaw in liquid nitrogen (-196°C), that is, quick-freezing for 0.5 hours and then thawing for 1 hour to room temperature, and this is repeated once.

[0083] The products prepared in Examples 1-3 and Comparative Examples 1-3 were analyzed.

[0084] like Figure 3 As shown, the calcium alginate phase change capsules prepared by the existing method (Comparative Example 1) have a relatively smooth surface and a neat but sparse cross-section. The calcium alginate has a linear morphology without interlacing or a uniform network structure. The shell material of the toughened phase change capsule obtained in Example 1 is polyvinyl alcohol-calcium alginate. Compared with the existing method, the composite capsule containing polyvinyl alcohol has a more wrinkled and rough surface. Figure 3 (b1)(b2)(b3) all show a uniformly distributed network-like interwoven pattern.

[0085] Compression capsule experiments were conducted using an electronic universal testing machine. The mechanical properties of the phase change capsule with a strong and tough shell (polyvinyl alcohol-calcium alginate) prepared in Example 1 were compared with those of the phase change capsule with calcium alginate as the shell material prepared in Comparative Example 1. Figure 4 and Figure 5 As shown, the strain of the phase change capsule prepared in Example 1 increased from 27.57% to 80.40%, approximately 2.91 times higher than that of the calcium alginate shell, and the compressive strength increased from 0.042 MPa to 0.861 MPa, an increase of approximately 20.5 times. The compressive modulus decreased from 0.97 MPa to 0.48 MPa due to the weakening of hydrogen bonds in the polyvinyl alcohol molecular chain after the formation of the composite, but this did not affect its toughness, which increased from 0.498 J / m. 3 Increased to 15.526 J / m 3 This represents an increase of approximately 31.18 times. It is evident that the preparation method provided by this invention significantly improves the mechanical strength of the phase change capsule.

[0086] from Figure 6 As can be seen from Examples 1-3, the product prepared in Example 1 has the best mechanical properties.

[0087] from Figure 7 As can be seen, the mechanical properties of phase change capsules that have not undergone liquid nitrogen freeze-thaw cycles or have only undergone one liquid nitrogen freeze-thaw cycle are not as good as those that have undergone three freeze-thaw cycles. This is because after repeated freeze-thaw cycles, polyvinyl alcohol (PVA) crystals and calcium alginate cross-linked crystals are formed, with PVA crystals as the cross-linking points. Furthermore, after the formation of the complex, the hydrogen bonds in the PVA molecular chain are weakened, and the network structure formed by PVA and calcium alginate becomes more compact. As a result, the compressive strength and toughness of the traditional calcium alginate shell are significantly improved.

[0088] The above embodiments are the best embodiments of the present invention, but the preparation method of the present invention is not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a phase change capsule with a strong and tough shell, characterized in that, The steps are as follows: Step 1: Dissolve polyvinyl alcohol in deionized water and stir thoroughly to form solution A. Then add sodium alginate and stir thoroughly to form solution B, which serves as the external phase fluid. Step 2: Dissolve calcium chloride in deionized water until fully dissolved to form solution C; Step 3: Heat the phase change material to be coated until it melts, and add an oleophilic emulsifier as the internal phase fluid; Step 4: Pump the external phase fluid and the internal phase fluid into the flow-focusing microfluidic chip using a syringe pump, and generate a composite emulsion precursor at the chip channel outlet. Step 5: Using solution C as the collecting liquid, collect the composite emulsion precursor, and complete the phase change capsule preparation by solidifying the shell through a chemical reaction; Step 6: After the phase change capsules prepared in step 5 are subjected to three freeze-thaw cycles in liquid nitrogen, phase change capsules with a strong and tough shell can be obtained. In steps three through five, the phase change material needs to be kept in a molten state at a temperature higher than the melting temperature of the phase change material.

2. The method for preparing a phase change capsule with a strong and tough shell according to claim 1, characterized in that, In step one, the molecular weight of polyvinyl alcohol is 13,000 to 23,000.

3. The method for preparing a phase change capsule with a strong and tough shell according to claim 1, characterized in that, In step one, 5% polyvinyl alcohol by mass is dissolved in deionized water and stirred thoroughly to form solution A. Then, sodium alginate is added and stirred thoroughly to form solution B, which serves as the external phase fluid. The mass ratio of sodium alginate to polyvinyl alcohol is 1:2.

45.

4. The method for preparing a phase change capsule with a strong and tough shell according to claim 1, characterized in that, In step two, calcium chloride with a mass fraction of 4-6% is dissolved in deionized water. After complete dissolution, solution C is formed.

5. The method for preparing a phase change capsule with a strong and tough shell according to claim 1, characterized in that, The phase change material in step three is paraffin wax.

6. The method for preparing a phase change capsule with a strong and tough shell according to claim 5, characterized in that, In step three, the phase change material is paraffin RT25, the lipophilic emulsifier is Span 80, and the mass fraction of the lipophilic emulsifier is 1-3%; the temperature in steps three to five is controlled at 28-30℃.

7. The method for preparing a phase change capsule with a strong and tough shell according to claim 1, characterized in that, In step four, the core glass channel of the flow-focusing microfluidic chip is made of an inner phase tube nested inside an outer phase tube. The inner diameter ratio of the inner phase tube to the outer phase tube is 0.46~0.50, and it must be ensured that they are coaxially nested. The flow rate ratio of the inner phase to the outer phase fluid is 1:3.2~1:3.

8.

8. The method for preparing a phase change capsule with a strong and tough shell according to claim 1, characterized in that, The process of freezing and thawing three times with liquid nitrogen in step six specifically involves: quick freezing at -196℃ liquid nitrogen for 0.5 h, followed by thawing to room temperature for 1 h, and repeating this process three times.

9. The method for preparing a phase change capsule with a strong and tough shell according to claim 1, characterized in that, The process of fully stirring and dissolving to form solution A in step one specifically involves: stirring at a temperature of 90-95°C, continuously stirring with a magnetic stirrer at a speed of 700-900 rpm for 2-4 hours to form solution A, and then cooling to room temperature; and then fully stirring and dissolving to form solution B: stirring at a temperature of 60-65°C, continuously stirring with a magnetic stirrer at a speed of 700-900 rpm for 1-3 hours to form solution B, and then cooling to room temperature.

10. A phase change capsule with a toughened shell prepared according to the method of any one of claims 1-9.

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