Cement-based composite material and method for producing same

Abstract

The application provides a cement-based composite material and a preparation method thereof, and belongs to the technical field of composite material preparation.The application comprises the following steps: step one, preparing heat-conducting and enhanced phase change energy storage microcapsules with uniform and controllable particle sizes; step two, preparing heat-conducting and enhanced phase change energy storage microcapsules with controllable wall thicknesses; and step three, preparing a phase change energy storage cement-based composite material test piece.The application prepares heat-conducting and enhanced phase change energy storage microcapsules with uniform and controllable particle sizes through a microfluidic chip, controls the wall thicknesses of the microcapsules through a layer-by-layer self-assembly method, and finally adds the heat-conducting and enhanced phase change energy storage microcapsules with controllable wall thicknesses into a cement paste, so that the microcapsules are dispersed in the cement paste, and a phase change energy storage cement-based composite material with good heat regulation capacity is prepared.

Description

Technical Field

[0001] This invention relates to the field of composite material preparation technology, and in particular to a cement-based composite material and its preparation method, especially to a cement-based composite material and its preparation method based on thermally conductive and energy-storing microcapsules with controllable wall thickness. Background Technology

[0002] Thermal energy storage technology, as a new energy-saving technology, plays an increasingly important role in energy conservation and environmental protection. It can be used to recover thermal energy, directly or indirectly reducing the consumption of natural resources and decreasing carbon emissions. Phase change energy storage, as a type of thermal energy storage technology, stores or releases energy through the principle that the temperature remains essentially constant during a phase change of the material. It features high energy density and minimal temperature change during the phase change process. To avoid direct contact between the phase change material and cement-based materials, which could affect their performance, the phase change material needs to be microencapsulated. However, existing cement-based materials prepared using phase change material microcapsules still have certain problems, mainly: existing phase change materials are mainly solid-liquid organic phase change materials, which are prone to leakage and volatilization, causing phase change material failure and shortening service life; existing phase change materials reduce the overall thermal conductivity of the prepared cement-based structure, and the decrease in thermal conductivity prolongs the phase change reaction time of the phase change microcapsules, thus affecting the energy storage effect; existing phase change materials have poor thermal conductivity, and the phase change energy storage microcapsules prepared by commonly used in-situ polymerization, emulsion polymerization and other methods have uneven particle size, resulting in uneven dispersion in cement-based materials, affecting energy storage efficiency and thus limiting their application. Summary of the Invention

[0003] In view of this, in order to overcome the above-mentioned shortcomings of existing phase change materials, on the one hand, the present invention provides a method for preparing cement-based composite materials. The method involves preparing phase change energy storage microcapsules with uniform and controllable particle size and enhanced thermal conductivity using a microfluidic chip, controlling the wall thickness of the microcapsules through a layer-by-layer self-assembly method, and finally adding the thermally conductive phase change energy storage microcapsules with controllable wall thickness to cement slurry to disperse the microcapsules in the cement slurry, thereby preparing a phase change energy storage cement-based composite material with good thermal regulation capability.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for preparing a cement-based composite material includes the following steps:

[0006] Step 1: Preparation of thermally enhanced phase change energy storage microcapsules with uniform and controllable particle size

[0007] The molten phase change energy storage material is mixed evenly with the thermally conductive material to form the inner phase solution; the sodium alginate aqueous solution is mixed evenly with the surfactant to form the outer phase solution.

[0008] The inner phase solution and the outer phase solution are injected into the microfluidic chip, forming oil-in-water microdroplets at the outlet of the microfluidic chip. The microdroplets are then dropped into the receiving liquid with gravity assistance, ultimately forming thermally enhanced phase change energy storage microcapsules with uniform and controllable particle size.

[0009] Step 2: Preparation of thermally enhanced phase change energy storage microcapsules with controllable wall thickness

[0010] The thermally conductive phase change energy storage microcapsules with uniform and controllable particle size prepared in step one are then self-assembled layer by layer to obtain thermally conductive phase change energy storage microcapsules with controllable wall thickness.

[0011] Step 3: Preparation of phase change energy storage cement-based composite material specimens

[0012] The thermally conductive and energy-saving phase change microcapsules with controllable wall thickness obtained in step two were mixed with cement slurry, oscillated multiple times, and then solidified to obtain a phase change energy-saving cement-based composite material specimen.

[0013] Preferably, in step one, the preparation method of the inner phase solution is as follows: the thermally conductive material is directly added to the molten phase change energy storage material at a temperature of 50-70°C and stirred for 1-2 hours, and then subjected to ultrasonic oscillation for 1-3 hours.

[0014] Preferably, the phase change energy storage material is a paraffin-based phase change material;

[0015] Preferably, the paraffinic phase change material includes at least one of n-tetradecane, n-hexadecane, n-octadecane, and n-eicosane;

[0016] Preferably, the thermally conductive material is a carbon-based material, and the carbon-based material is preferably at least one of graphite, graphene, graphene oxide, carbon nanotubes, and carbon quantum dots;

[0017] Preferably, the concentration of the thermally conductive material in the inner phase solution is 0.1–0.5 wt%.

[0018] Preferably, in step one, the preparation method of the external phase solution is as follows: at a temperature of 50-70°C, water, sodium alginate, and surfactant are mixed and stirred at a speed of 800-1000 r / min for 40-60 min.

[0019] Preferably, the surfactant is at least one selected from polysorbate 80, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and polyvinylpyrrolidone;

[0020] Preferably, the concentration of sodium alginate in the external phase solution is 3-5 wt%; and the concentration of surfactant in the external phase solution is 0.5-1 wt%.

[0021] Preferably, in step one, the internal phase solution and the external phase solution are injected into the microfluidic chip via a syringe pump, and the flow rate ratio of the internal phase solution and the external phase solution is controlled.

[0022] Preferably, the flow rate ratio of the internal phase solution to the external phase solution is 1 / 4 to 1 / 2;

[0023] Preferably, the receiving solution is a CaCl2 solution with a mass fraction of 2-5 wt%.

[0024] Preferably, the microfluidic chip is vertically suspended along the outlet direction;

[0025] Preferably, the distance between the outlet end of the microfluidic chip and the surface of the receiving liquid is 4-5 cm;

[0026] Preferably, the inner diameter of the inner phase glass capillary of the microfluidic chip is 100–500 μm, and the outer diameter is 500–900 μm;

[0027] Preferably, the outer phase glass capillary of the microfluidic chip has an inner diameter of 800–1200 μm and an outer diameter of 1500–3000 μm.

[0028] Preferably, in step two, the layer-by-layer self-assembly involves immersing the thermally enhanced phase change energy storage microcapsules with uniform and controllable particle size prepared in step one in a sodium alginate solution, and then washing them with ethanol to obtain pretreated thermally enhanced phase change energy storage microcapsules; subsequently, the pretreated thermally enhanced phase change energy storage microcapsules are immersed in a CaCl2 solution, removed, and washed with ethanol to obtain a cycle treatment.

[0029] Following the above cycle, thermally enhanced phase change energy storage microcapsules with controllable wall thickness were obtained;

[0030] Preferably, the layer-by-layer self-assembly involves immersing the thermally conductive enhanced phase change energy storage microcapsules with uniform and controllable particle size prepared in step one in a 3-5 wt% sodium alginate solution for 5-10 minutes, followed by washing with ethanol 3-5 times to obtain pretreated thermally conductive enhanced phase change energy storage microcapsules; subsequently, immersing the pretreated thermally conductive enhanced phase change energy storage microcapsules in a 2-5 wt% CaCl2 solution for 5-10 minutes, removing them, and washing them with ethanol 3-5 times to obtain a cycle-treated thermally conductive enhanced phase change energy storage microcapsules.

[0031] By following the above cycle, thermally enhanced phase change energy storage microcapsules with controllable wall thickness can be obtained.

[0032] Preferably, in step two, the particle size of the prepared thermally enhanced phase change energy storage microcapsules with controllable wall thickness is controllable in the range of 1500–3500 μm, and the wall thickness is controllable in the range of 100–1000 μm.

[0033] Preferably, step three specifically includes:

[0034] The thermally conductive enhanced phase change energy storage microcapsules with controllable wall thickness obtained in step two are placed in an oven at 40-60℃ and dried for 24-48 hours. Then, the thermally conductive enhanced phase change energy storage microcapsules with controllable wall thickness are mixed, stirred, and cured with cement slurry to obtain phase change energy storage cement-based composite material specimens.

[0035] Preferably, in step three, the thermally conductive enhanced phase change energy storage microcapsules with controllable wall thickness are added in multiple steps. Preferably, first, 1 / 4 of the thermally conductive enhanced phase change energy storage microcapsules with controllable wall thickness are added, then 1 / 4 of the mold height of cement and water is added to form a cement slurry, and the mixture is vibrated for 20-30 seconds. Then, 3 / 4 of the thermally conductive enhanced phase change energy storage microcapsules with controllable wall thickness and 1 / 2 of the mold height of cement slurry are added sequentially, and the mixture is vibrated for 20-30 seconds. Finally, the remaining cement slurry is added to the mold.

[0036] On the other hand, the present invention provides a cement-based composite material prepared by the above-described method for preparing cement-based composite materials.

[0037] Preferably, by weight, it includes: 100-200 parts cement, 45-90 parts water, and 10-15 parts thermally conductive phase change energy storage microcapsules with controllable wall thickness.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The microcapsules for thermally enhanced phase change energy storage with controllable wall thickness prepared by the present invention have high encapsulation efficiency, good monodispersity, uniform and controllable size, good thermal conductivity, and controllable wall thickness, which improves the strength of the outer wall of the microcapsules, so as to prevent the microcapsules from breaking in cement and causing leakage of phase change materials, and avoid direct contact between phase change materials and cement-based materials, which would lead to a decline in the performance of cement-based materials.

[0040] The particle size is controlled by the flow rate ratio, which is limited to the range of 1 / 4 to 1 / 2 in this invention. A higher flow rate ratio results in a larger particle size, and vice versa. Particle size uniformity is controlled by the flow rate. As long as the flow rate is constant, the produced microcapsules will be of uniform size.

[0041] This invention improves thermal conductivity by adding thermally conductive materials and enhances the dispersion of these materials through multiple layered oscillations, ensuring uniform dispersion and thus uniform thermal conductivity.

[0042] After the wall material is thickened, it will be dehydrated and dried. After drying, the overall density of the wall material increases, which has a negligible impact on thermal conductivity. The increase in wall thickness improves the strength of the outer wall of the microcapsule, which has a negligible impact on its thermal conductivity.

[0043] (2) The phase change energy storage cement-based composite material specimen prepared by the present invention has good thermal regulation performance, which can make full use of the heat absorption and release capacity of the phase change material, thereby reducing indoor temperature fluctuations and controlling indoor temperature. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the microfluidic chip used to prepare phase change microcapsules according to the present invention.

[0045] Figure 2 An apparatus for preparing thermally enhanced phase change microcapsules;

[0046] Figure 3 For thermally conductive phase change energy storage microcapsules with controllable wall thickness;

[0047] Figure 4 The phase change energy storage cement-based composite material specimen prepared according to the present invention;

[0048] In the figure, 1. Metal sleeve; 2. Inner phase glass capillary; 3. Outer phase glass capillary; 4. Conical transition tube; 5. Glass slide; 6. Outer phase solution with syringe connected to injection pump; 7. Inner phase solution with syringe connected to injection pump; 8. Polytetrafluoroethylene capillary tube; 9. Culture dish; 10. Receiver; 11. Heating source; 12. Core material; 13. Self-assembled wall material; 14. Thermally conductive material; 15. Cement-based material; 16. Thermally conductive phase change energy storage microcapsule with controllable wall thickness. Detailed Implementation

[0049] The method for preparing the above-mentioned cement-based composite material provided by the present invention includes the following steps:

[0050] Step 1: Preparation of thermally enhanced phase change energy storage microcapsules with uniform and controllable particle size

[0051] The molten phase change energy storage material and the thermally conductive material 14 are mixed evenly to form the inner phase solution; the sodium alginate aqueous solution and the surfactant are mixed evenly to form the outer phase solution.

[0052] The inner phase solution and the outer phase solution are injected into the microfluidic chip, forming an oil-in-water microdroplet at the outlet of the microfluidic chip. The microdroplet is then dropped into the receiving liquid 10 with gravity assistance, ultimately forming a thermally enhanced phase change energy storage microcapsule with uniform and controllable particle size.

[0053] Specifically as follows:

[0054] (1) The method for preparing the internal phase solution is as follows: According to the weight, preferably, 99.5 to 99.9 parts of molten phase change energy storage material and 0.1 to 0.5 parts of thermally conductive material 14 are poured into a glass beaker. The mixed solution is placed on a magnetic stirrer with a temperature preferably of 50 to 70°C and stirred at a speed of 800 to 1000 r / min for 1 to 2 hours. Preferably, it is sealed and placed in an ultrasonic oscillator for ultrasonic oscillation for 1 to 3 hours. The temperature during oscillation is maintained at 50 to 70°C. During this period, it is stirred once every 30 minutes to obtain the internal phase solution.

[0055] (2) The method for preparing the external phase solution is as follows: by weight, preferably, 3 to 5 parts of sodium alginate, 0.5 to 1 part of surfactant, and 96.5 to 94 parts of water are poured into a glass beaker, and the mixed solution is placed on a magnetic stirrer and stirred at a speed of 50 to 70°C and 800 to 1000 r / min for 40 to 60 min to obtain the external phase solution.

[0056] (3) Prepare the receiving solution 10: preferably take 2 to 5 parts of anhydrous calcium chloride and 95 to 98 parts of water by weight, mix and stir to prepare a CaCl2 solution with a mass fraction of preferably 2 to 5 wt%.

[0057] (4) The microfluidic chip is vertically suspended in the air along the outlet direction, and the distance between its outlet end and the surface of the receiving liquid 10 is preferably 4 to 5 cm.

[0058] (5) Using an injection pump, the inner and outer phase solutions are injected into the polytetrafluoroethylene capillary 8. The ratio of the inner and outer phase flow rates controlled by the injection pump is preferably 1 / 4 to 1 / 2. Different flow rate ratios can yield phase change energy storage microcapsules with different particle sizes, thus achieving the purpose of controlling the particle size. Thermally enhanced phase change energy storage microcapsules are formed at the outlet of the microfluidic chip. The microdroplets are then dropped into the receiving liquid 10 with gravity assistance, ultimately forming thermally enhanced phase change energy storage microcapsules with uniform and controllable particle size.

[0059] The phase change energy storage material is preferably a paraffinic phase change material; the paraffinic phase change material preferably includes at least one of n-tetradecane, n-hexadecane, n-octadecane and n-eicosane; the thermally conductive material 14 is preferably a carbon-based material, and the carbon-based material is preferably at least one of graphite, graphene, graphene oxide, carbon nanotubes and carbon quantum dots; in this invention, the concentration of the thermally conductive material 14 in the inner phase solution is preferably 0.1 to 0.5 wt%, wherein the thermally conductive material 14 can improve the thermal conductivity of the phase change microcapsules.

[0060] In this invention, the surfactant is at least one of polysorbate 80, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and polyvinylpyrrolidone.

[0061] In this invention, the concentration of sodium alginate in the external phase solution is 3-5 wt%; the concentration of surfactant in the external phase solution is 0.5-1 wt%.

[0062] The internal and external phase solutions are injected into the microfluidic chip via a syringe pump, and the flow rate ratio of the internal and external phase solutions is controlled; the flow rate ratio of the internal and external phase solutions is 1 / 4 to 1 / 2.

[0063] like Figure 1-2 As shown, this invention provides one embodiment of a microfluidic chip, the microfluidic chip comprising:

[0064] A glass slide 5 has an inner phase glass capillary 2 and an outer phase glass capillary 3 at its upper and lower ends, respectively. The outer phase glass capillary 3 is fitted over the inner phase glass capillary and is 1 / 3 to 1 / 2 the length of the inner phase glass capillary 2, with one end flush with the inner phase glass capillary 2. A tapered transition tube 4 is used to fasten the non-flush end, and all three are fixed to the glass slide 5 with sealant. A capillary metal sleeve 1 is fitted over the non-flush end of the inner phase glass capillary 2 and the outer phase glass capillary 3, thus protecting the end of the inner phase glass capillary 2.

[0065] The inlet end of the inner phase glass capillary 2 and the inlet end of the tapered transition tube 4 are respectively connected to the outer phase solution and the syringe and the injection pump 6 and 7 via polytetrafluoroethylene capillary tubes.

[0066] The outer phase glass capillary 3 has an inner diameter of 800–1200 μm and an outer diameter of 1600–3000 μm; or an inner diameter of 100–500 μm and an outer diameter of 500–900 μm; the outer phase glass capillary 3 and the inner phase glass capillary 2 are concentrically fitted together.

[0067] The receiving solution 10 is contained in the culture dish 9, and the microcapsules formed at the outlet of the microfluidic chip are dropped into the receiving solution 10.

[0068] A heating source 11 can also be set in the microfluidic chip to avoid the impact of temperature changes on the phase change energy storage material.

[0069] Step 2: Preparation of thermally enhanced phase change energy storage microcapsules with controllable wall thickness 16

[0070] The thermally conductive phase change energy storage microcapsules with uniform and controllable particle size prepared in step one are self-assembled layer by layer to obtain thermally conductive phase change energy storage microcapsules 16 with controllable wall thickness.

[0071] Layer-by-layer self-assembly involves immersing the thermally conductive phase change energy storage microcapsules with uniform and controllable particle size prepared in step one in a sodium alginate solution, followed by washing with ethanol to obtain pretreated thermally conductive phase change energy storage microcapsules; subsequently, the pretreated thermally conductive phase change energy storage microcapsules are immersed in a CaCl2 solution, removed, and washed with ethanol to obtain a cycle treatment.

[0072] According to the above cycle, the self-assembly cycle can gradually increase the wall thickness, thereby gradually improving the shell strength of the microcapsule and preventing the microcapsule from rupturing and causing leakage of the internal phase change material. Based on the wall thickness requirements, thermally enhanced phase change energy storage microcapsules 16 with controllable wall thickness can be obtained by repeating the cycle.

[0073] Specifically as follows:

[0074] (6) The prepared thermally enhanced phase change energy storage microcapsules were immersed in a 3-5 wt% sodium alginate solution for 5-10 min, and then washed with ethanol 3-5 times to obtain pretreated thermally enhanced phase change energy storage microcapsules. Subsequently, the pretreated thermally enhanced phase change energy storage microcapsules were immersed in a 2-5 wt% CaCl2 solution for 5-10 min, and then washed with ethanol 3-5 times to obtain a cycle-treated thermally enhanced phase change energy storage microcapsules. Following the above cycle, thermally enhanced phase change energy storage microcapsules with controllable wall thickness 16 were obtained.

[0075] The particle size of the thermally conductive enhanced phase change energy storage microcapsules 16 with controllable wall thickness prepared in step two is controllable in the range of 1500-3500 μm, and the wall thickness is controllable in the range of 100-1000 μm.

[0076] like Figure 3 As shown, the core material 12 of the thermally conductive phase change energy storage microcapsule 16 with controllable wall thickness is wrapped with a self-assembled wall material 13, and the self-assembled wall material 13 is wrapped with a thermally conductive material 14.

[0077] Step 3: Preparation of phase change energy storage cement-based composite material specimens

[0078] The thermally conductive and microcapsules 16 with controllable wall thickness obtained in step two were mixed with cement slurry, vibrated repeatedly, and then cured to obtain a phase change energy storage cement-based composite material specimen, as follows:

[0079] (7) After drying the thermally conductive enhanced phase change energy storage microcapsules 16 with controllable wall thickness in an oven at 40-60℃ for 24-48 hours, phase change energy storage cement-based composite material specimens were prepared. To avoid the microcapsules all floating on the surface of the cement paste after shaking, the microcapsules were added to the mold in layers multiple times and shaken multiple times.

[0080] The specific steps are as follows:

[0081] First, add 1 / 4 of the thermally conductive enhanced phase change energy storage microcapsule 16 with controllable wall thickness, then add 1 / 4 of the mold height of cement slurry, and vibrate for 20-30 seconds. Then, add 3 / 4 of the thermally conductive enhanced phase change energy storage microcapsule 16 with controllable wall thickness and 1 / 2 of the mold height of cement slurry, and vibrate for 20-30 seconds. Finally, add the remaining cement slurry to the mold to prepare a phase change energy storage cement-based composite material specimen. Multiple layered vibrations can improve the dispersion of the thermally conductive enhanced phase change energy storage microcapsule 16 with controllable wall thickness in cement, making it uniformly dispersed.

[0082] like Figure 4 As shown, in the cement-based composite material specimen, thermally conductive enhanced phase change energy storage microcapsules 16 with controllable wall thickness are uniformly dispersed in the cement-based material 15, giving the cement-based composite material specimen excellent thermal conductivity.

[0083] On the other hand, the present invention provides a cement-based composite material prepared by the above-described method for preparing cement-based composite materials.

[0084] In this invention, by weight, it includes: 100-200 parts of cement, 45-90 parts of water, and 1610-15 parts of thermally conductive phase change energy storage microcapsules with controllable wall thickness.

[0085] The technical solution of the present invention will be clearly and thoroughly described below with reference to specific embodiments.

[0086] Example 1

[0087] Step 1: Prepare thermally enhanced phase change energy storage microcapsules with uniform and controllable particle size.

[0088] Using a 10ml syringe, draw 10ml of the external phase solution, containing 3% sodium alginate and 0.5% polysorbate 80. Using another syringe of the same specifications, draw 10ml of the internal phase solution, containing 99.9% phase change paraffin (melting point 24℃) and 0.1% graphene. Figure 2 Connection device. A 2% (w / w) CaCl2 solution was poured into a 120 mm diameter culture dish and placed below the outlet of the microfluidic chip. The inner phase solution flowing through the channel was heated using a heat source to maintain it above 25°C. The outer phase flow rate was set to 1500 μL / min; the inner phase flow rate was set to 375 μL / min. The syringe pump was started, forming an oil-in-water droplet at the microfluidic chip outlet, which solidified in the culture dish to form thermally enhanced phase change energy storage microcapsules with a particle size of 2000-2400 μm.

[0089] Step 2: Prepare thermally enhanced phase change energy storage microcapsules with controllable wall thickness.

[0090] The prepared thermally enhanced phase change energy storage microcapsules were immersed in a 3% sodium alginate solution for 8 minutes, and then washed four times with ethanol to obtain pretreated thermally enhanced phase change energy storage microcapsules. Subsequently, the pretreated thermally enhanced phase change energy storage microcapsules were immersed in a 2% CaCl2 solution for 8 minutes, and then washed four times with ethanol to obtain a cycled thermally enhanced phase change energy storage microcapsules. The above steps were repeated three times, and then dried in a 50℃ oven for 36 hours to obtain thermally enhanced phase change energy storage microcapsules with a wall thickness of 160-200 μm.

[0091] Step 3: Prepare phase change energy storage cement-based composite material specimens.

[0092] The prepared thermally conductive enhanced phase change energy storage microcapsules were self-assembled layer by layer to obtain thermally conductive enhanced phase change energy storage microcapsules with controllable wall thickness. These microcapsules were then dried in a 50℃ oven for 36 hours. 100 parts of silicate cement, 45 parts of water, and 10 parts of the thermally conductive enhanced phase change energy storage microcapsules with controllable wall thickness were mixed together. The thermally conductive enhanced phase change energy storage microcapsules with controllable wall thickness were added to a mold in multiple batches and subjected to repeated vibrations. Specifically, 1 / 4 of the thermally conductive enhanced phase change energy storage microcapsules with controllable wall thickness were added first, followed by 1 / 4 of the mold height of cement slurry, and then vibrated for 20 seconds. Then, 3 / 4 of the thermally conductive enhanced phase change energy storage microcapsules with controllable wall thickness and 1 / 2 of the mold height of cement slurry were added sequentially, and vibrated for 20 seconds. Finally, the remaining cement slurry was added to the mold to prepare a phase change energy storage cement-based composite material specimen.

[0093] Example 2

[0094] Step 1: Prepare thermally enhanced phase change energy storage microcapsules with uniform and controllable particle size.

[0095] 10 ml of the external phase solution was drawn using a 10 ml syringe, containing 4% sodium alginate and 0.7% polysorbate 80. 10 ml of the internal phase solution was drawn using another syringe of the same specifications, containing 99.7% n-octadecane and 0.3% graphene as the phase change material. Figure 2 Connection device. A 4% (w / w) CaCl2 solution was poured into a 120 mm diameter culture dish and placed below the outlet of the microfluidic chip. The inner phase solution flowing through the channel was heated using a heat source and kept above 30°C. The outer phase flow rate was set to 1500 μL / min; the inner phase flow rate was set to 400 μL / min. The syringe pump was started, forming an oil-in-water droplet at the microfluidic chip outlet, which solidified in the culture dish to form thermally enhanced phase change energy storage microcapsules with a particle size of 2700-3000 μm.

[0096] Step 2: Prepare thermally enhanced phase change energy storage microcapsules with controllable wall thickness.

[0097] The prepared thermally enhanced phase change energy storage microcapsules were immersed in a 4% sodium alginate solution for 10 min, and then washed five times with ethanol to obtain pretreated thermally enhanced phase change energy storage microcapsules. Subsequently, the pretreated thermally enhanced phase change energy storage microcapsules were immersed in a 4 wt% CaCl2 solution for 10 min, and then washed five times with ethanol to obtain a cycled thermally enhanced phase change energy storage microcapsules. The above steps were repeated four times, and then the microcapsules were dried in a 50℃ oven for 36 h to obtain thermally enhanced phase change energy storage microcapsules with a wall thickness of 200-240 μm.

[0098] Step 3: Prepare phase change energy storage cement-based composite material specimens.

[0099] After drying thermally conductive phase change energy storage microcapsules with controllable wall thickness in a 60℃ oven for 24 hours, 150 parts of silicate cement, 58 parts of water, and 13 parts of the thermally conductive phase change energy storage microcapsules with controllable wall thickness were mixed. The thermally conductive phase change energy storage microcapsules with controllable wall thickness were added to the mold in multiple batches and shaken repeatedly. Specifically, 1 / 4 of the thermally conductive phase change energy storage microcapsules with controllable wall thickness were added first, followed by 1 / 4 of the mold height of cement slurry, and then shaken for 30 seconds. Then, 3 / 4 of the thermally conductive phase change energy storage microcapsules with controllable wall thickness and 1 / 2 of the mold height of cement slurry were added sequentially, and shaken for 30 seconds. Finally, the remaining cement slurry was added to the mold to prepare a phase change energy storage cement-based composite material specimen.

[0100] Example 3

[0101] Step 1: Prepare thermally enhanced phase change energy storage microcapsules with uniform and controllable particle size.

[0102] Using a 10ml syringe, draw 10ml of the external phase solution, containing 5% sodium alginate and 1% polysorbate 80. Using another syringe of the same specifications, draw 10ml of the internal phase solution, containing 99.5% n-octadecane and 0.5% graphene as the phase change material. Figure 2 Connection device. A 5% (w / w) CaCl2 solution was poured into a 120 mm diameter culture dish and placed below the outlet of the microfluidic chip. The inner phase solution flowing through the channel was heated using a heat source and kept above 30°C. The outer phase flow rate was set to 800 μL / min; the inner phase flow rate was set to 400 μL / min. The syringe pump was started, forming an oil-in-water droplet at the microfluidic chip outlet, which solidified in the culture dish to form thermally enhanced phase change energy storage microcapsules with a particle size of 3000-3200 μm.

[0103] Step 2: Prepare thermally enhanced phase change energy storage microcapsules with controllable wall thickness.

[0104] The prepared thermally enhanced phase change energy storage microcapsules were immersed in a 5% sodium alginate solution for 10 min, and then washed five times with ethanol to obtain pretreated thermally enhanced phase change energy storage microcapsules. Subsequently, the pretreated thermally enhanced phase change energy storage microcapsules were immersed in a 5 wt% CaCl2 solution for 10 min, and then washed five times with ethanol to obtain a cycled thermally enhanced phase change energy storage microcapsules. After repeating the above steps five times, they were dried in a 50℃ oven for 36 h to obtain thermally enhanced phase change energy storage microcapsules with a wall thickness of 240-280 μm.

[0105] Step 3: Prepare phase change energy storage cement-based composite material specimens.

[0106] After drying thermally conductive phase change energy storage microcapsules with controllable wall thickness in a 60℃ oven for 24 hours, 200 parts of silicate cement, 90 parts of water, and 15 parts of the thermally conductive phase change energy storage microcapsules with controllable wall thickness were mixed. The thermally conductive phase change energy storage microcapsules with controllable wall thickness were added to the mold in multiple batches and shaken repeatedly. Specifically, 1 / 4 of the thermally conductive phase change energy storage microcapsules with controllable wall thickness were added first, followed by 1 / 4 of the mold height of cement slurry, and then shaken for 30 seconds. Then, 3 / 4 of the thermally conductive phase change energy storage microcapsules with controllable wall thickness and 1 / 2 of the mold height of cement slurry were added sequentially, and shaken for 30 seconds. Finally, the remaining cement slurry was added to the mold to prepare a phase change energy storage cement-based composite material specimen.

[0107] Example 4

[0108] While keeping other parameters constant, the internal and external phase flow rates in Example 1 were set to 500 μL / min and 1200 μL / min, respectively. Thermally conductive phase change energy storage microcapsules with a particle size of 3000-3300 μm were prepared according to step one of Example 1.

[0109] By keeping the conditions of step two in Example 1 unchanged, thermally enhanced phase change energy storage microcapsules with a wall thickness of 160-200 μm that can be self-assembled for 3 cycles were prepared.

[0110] Example 5

[0111] While keeping other parameters constant, the mass fraction of graphene in Comparative Example 2 was increased to 0.3%, and thermally enhanced phase change energy storage microcapsules with a particle size of 3000-3300 μm were prepared according to step one in Example 1.

[0112] By keeping the conditions of step two unchanged, thermally enhanced phase change energy storage microcapsules with a wall thickness of 160-200 μm were prepared after three self-assembly cycles.

[0113] Example 6

[0114] While keeping other parameters constant, the mass fraction of graphene in Comparative Example 2 was increased to 0.5%, and thermally enhanced phase change energy storage microcapsules with a particle size of 3000-3300 μm were prepared according to step one in Example 1.

[0115] By keeping the conditions of step two unchanged, thermally enhanced phase change energy storage microcapsules with a wall thickness of 160-200 μm were prepared after three self-assembly cycles.

[0116] Example 7

[0117] While keeping the number of cycles in step two of comparative examples 2 and 3 unchanged (except for 4 and 5 cycles respectively), thermally enhanced phase change energy storage microcapsules with wall thicknesses in the ranges of 200-240 μm and 240-280 μm were obtained.

[0118] Comparative Example 1

[0119] 9.4 g of Span 80 was weighed as an emulsifier and poured into 375 ml of molten phase change paraffin with a melting point of 24 °C. The mixture was stirred at 1300 rpm for 20 min using a magnetic stirrer, maintaining the temperature at 60 °C. The solution was then added to 1500 ml of a 3% sodium alginate solution and stirred at 6000 rpm for 10 min using a high-speed homogenizer to form a stable oil-in-water emulsion. The prepared emulsion was poured into 3000 ml of a 2% CaCl2 solution and stirred at 50 °C with a magnetic stirrer at 500 rpm for 3 min. After polymerization, centrifugation yielded phase change energy storage microcapsules, which were washed twice with ethanol to remove unencapsulated paraffin. Finally, the microcapsules were dried in a 50 °C oven for 36 h to obtain the phase change energy storage microcapsules prepared by emulsion polymerization.

[0120] Comparative analysis revealed that microcapsules prepared by emulsion polymerization generally exhibited agglomeration, with particle sizes ranging from 1000 μm to 10 mm, resulting in uneven particle size and poor dispersibility.

[0121] Table 1 shows the performance comparison of the phase change microcapsules prepared for each example.

[0122]

[0123] Table 1 shows that, with a constant flow rate ratio, the particle size prepared by microfluidic technology is relatively uniform. When the internal / external flow rate ratio increases, the particle size of the prepared microcapsules also increases; with other parameters remaining constant, the thermal conductivity of the microcapsules increases with the increase of the proportion of thermally conductive material. However, increasing the number of self-assembly cycles has little effect on the thermal conductivity of the microcapsules.

[0124] Table 2 shows the rupture rate of each example phase change microcapsule (after self-assembly) at room temperature.

[0125] Examples of microcapsule preparation Particle size (before self-assembly) Self-assembled wall thickness Fragmentation rate % Example 1 2000-2400μm 160-200μm 23 Example 2 2700-3000μm 200-240μm 15 Example 3 3000-3200μm 240-280μm 9 Example 4 3000-3300μm 160-200μm 22 Example 5 3000-3300μm 160-200μm 23 Example 6 3000-3300μm 160-200μm 21 Example 7 (4 cycles) 3000-3300μm 200-240μm 17 Example 7 (5 cycles) 3000-3300μm 240-280μm 12 Comparative Example 1 1000μm-10mm — 72

[0126] As shown in Table 2, with the increase of self-assembly cycles, the wall thickness of the microcapsules also increases, while the rupture rate of the microcapsules decreases. Furthermore, compared with the microcapsules prepared by the conventional emulsion polymerization method in Comparative Example 1, their rupture rate is significantly reduced.

[0127] The thermally conductive enhanced phase change energy storage microcapsules prepared in the examples were used to prepare phase change energy storage cement-based composite material specimens according to step 3 in Examples 1, 2 and 3 respectively.

[0128] Thermal regulation experiments revealed that as the proportion of thermally conductive phase change energy storage microcapsules increases, a significant temperature control effect is observed when the specimen's temperature falls within the phase change temperature range. The specimen exhibited the best thermal regulation capability, with a temperature control effect reaching ±4℃, when the graphene content was 0.5%, the sodium alginate solution mass fraction was 5%, the CaCl2 solution mass fraction was 5%, and the cement-based material ratio was as shown in Example 3.

[0129] The technical solutions in the embodiments of the present invention have been clearly and completely described above. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

Claims

1. A method for preparing a cement-based composite material, characterized in that, Includes the following steps: Step 1: Preparation of thermally enhanced phase change energy storage microcapsules with uniform and controllable particle size The molten phase change energy storage material is mixed evenly with the thermally conductive material to form the inner phase solution; the sodium alginate aqueous solution is mixed evenly with the surfactant to form the outer phase solution. The internal and external phase solutions are injected into the microfluidic chip via a syringe pump. The flow rate ratio of the internal and external phase solutions is controlled to be 1 / 4-1 / 2. Water-in-oil microdroplets are formed at the outlet of the microfluidic chip. The microdroplets are then dropped into the receiving liquid with gravity assistance, ultimately forming thermally conductive phase change energy storage microcapsules with uniform and controllable particle size. Step 2: Preparation of thermally enhanced phase change energy storage microcapsules with controllable wall thickness The thermally conductive phase change energy storage microcapsules with uniform and controllable particle size prepared in step one are then self-assembled layer by layer to obtain thermally conductive phase change energy storage microcapsules with controllable wall thickness. Step 3: Preparation of phase change energy storage cement-based composite material specimens The thermally conductive and energy-saving phase change microcapsules with controllable wall thickness obtained in step two were mixed with cement slurry, oscillated multiple times, and then solidified to obtain a phase change energy-saving cement-based composite material specimen.

2. The method for preparing a cement-based composite material according to claim 1, characterized in that, In step one, the preparation method of the internal phase solution is as follows: the heat-conducting material is directly added to the molten phase change energy storage material at a temperature of 50~70℃ and stirred for 1~2 hours, followed by ultrasonic oscillation for 1~3 hours.

3. The method for preparing a cement-based composite material according to claim 2, characterized in that, The phase change energy storage material is a paraffin-based phase change material.

4. The method for preparing a cement-based composite material according to claim 3, characterized in that, Paraffinic phase change materials include at least one of n-tetradecane, n-hexadecane, n-octadecane, and n-eicosane.

5. The method for preparing a cement-based composite material according to claim 2, characterized in that, The thermally conductive material is carbon-based.

6. The method for preparing a cement-based composite material according to claim 5, characterized in that, Carbon-based materials are at least one of graphite, graphene, graphene oxide, carbon nanotubes, and carbon quantum dots.

7. The method for preparing a cement-based composite material according to claim 2, characterized in that, The concentration of the thermally conductive material in the inner phase solution is 0.1~0.5 wt%.

8. The method for preparing a cement-based composite material according to claim 1, characterized in that, In step one, the preparation method of the external phase solution is as follows: water, sodium alginate and surfactant are mixed at a temperature of 50~70℃ and stirred at a speed of 800~1000 r / min for 40~60 min.

9. The method for preparing a cement-based composite material according to claim 8, characterized in that, The surfactant is at least one of polysorbate 80, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and polyvinylpyrrolidone.

10. A method for preparing a cement-based composite material according to claim 8, characterized in that, The concentration of sodium alginate in the external phase solution is 3-5 wt%; the concentration of surfactant in the external phase solution is 0.5-1 wt%.

11. The method for preparing a cement-based composite material according to claim 1, characterized in that, The receiving solution is a CaCl2 solution with a mass fraction of 2~5 wt%.

12. The method for preparing a cement-based composite material according to claim 1, characterized in that, The microfluidic chip is suspended vertically along the outlet direction.

13. The method for preparing a cement-based composite material according to claim 1, characterized in that, The distance between the outlet end of the microfluidic chip and the surface of the receiving liquid is 4-5 cm.

14. The method for preparing a cement-based composite material according to claim 1, characterized in that, The inner diameter of the inner phase glass capillary in the microfluidic chip is 100~500 mm. μm The outer diameter is 500~900 μm.

15. The method for preparing a cement-based composite material according to claim 1, characterized in that, The outer glass capillary of the microfluidic chip has an inner diameter of 800~1200 mm. μm The outer diameter is 1600~3000 μm.

16. A method for preparing a cement-based composite material according to claim 1, characterized in that, In step two, the layer-by-layer self-assembly involves immersing the thermally enhanced phase change energy storage microcapsules with uniform and controllable particle size prepared in step one in a sodium alginate solution, and then washing them with ethanol to obtain pretreated thermally enhanced phase change energy storage microcapsules. Subsequently, the pretreated thermally enhanced phase change energy storage microcapsules were immersed in CaCl2 solution, removed and washed with ethanol to obtain a cycle treatment; By following the above cycle, thermally enhanced phase change energy storage microcapsules with controllable wall thickness can be obtained.

17. A method for preparing a cement-based composite material according to claim 16, characterized in that, Layer-by-layer self-assembly involves immersing the thermally conductive phase change energy storage microcapsules with uniform and controllable particle size prepared in step one in a sodium alginate solution with a mass fraction of 3-5 wt% for 5-10 minutes, and then washing them with ethanol 3-5 times to obtain pretreated thermally conductive phase change energy storage microcapsules. Subsequently, the pretreated thermally enhanced phase change energy storage microcapsules were immersed in a CaCl2 solution with a mass fraction of 2-5 wt% for 5-10 minutes, and then washed with ethanol 3-5 times to obtain a cycle-treated thermally enhanced phase change energy storage microcapsule.

18. A method for preparing a cement-based composite material according to claim 1, characterized in that, In step two, the particle size of the thermally enhanced phase change energy storage microcapsules with controllable wall thickness is between 1500 and 3500 μm. μm The range is controllable, and the wall thickness is between 100 and 1000 mm. μm The scope is controllable.

19. A method for preparing a cement-based composite material according to claim 1, characterized in that, Step three specifically involves: The thermally conductive enhanced phase change energy storage microcapsules with controllable wall thickness obtained in step two are placed in an oven at 40~60℃ and dried for 24~48h. Then, the thermally conductive enhanced phase change energy storage microcapsules with controllable wall thickness are mixed, stirred and cured with cement slurry to obtain phase change energy storage cement-based composite material specimens.

20. A method for preparing a cement-based composite material according to claim 1, characterized in that, In step three, the thermally conductive phase change energy storage microcapsules with controllable wall thickness are added in multiple steps.

21. A method for preparing a cement-based composite material according to claim 20, characterized in that, First, add 1 / 4 of the thermally conductive phase change energy storage microcapsule with controllable wall thickness, then add cement slurry formed by cement and water to 1 / 4 of the mold height, and vibrate for 20-30 seconds. Then, add 3 / 4 of the thermally conductive phase change energy storage microcapsule with controllable wall thickness and cement slurry to 1 / 2 of the mold height, and vibrate for 20-30 seconds. Finally, add the remaining cement slurry to the mold.

22. A cement-based composite material, characterized in that, It is prepared by any one of the methods for preparing a cement-based composite material according to claims 1-21.

23. A cement-based composite material according to claim 22, characterized in that, By weight, it includes: 100-200 parts cement, 45-90 parts water, and 10-15 parts thermally conductive phase change energy storage microcapsules with controllable wall thickness.

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