A polydopamine-coated emulsion-type shape-stabilized phase change material and a preparation method thereof

Abstract

The present application relates to a kind of polydopamine coated expanded graphite-polyethylene glycol / polyacrylamide emulsion type fixed phase change material and its preparation method, first respectively preparation includes acrylamide aqueous phase, molten polyethylene glycol as oil phase, expanded graphite solution, then using these raw materials preparation expanded graphite-polyethylene glycol / polyacrylamide fixed phase change material, afterwards in Tris-HCl buffer solution containing dopamine hydrochloride, dopamine hydrochloride is oxidized and polymerized in situ in PAM shell Deposition polydopamine layer, obtain polydopamine coated expanded graphite-polyethylene glycol / polyacrylamide emulsion type fixed phase change material.The present application utilizes polyacrylamide to be coated to polyethylene glycol, form stable emulsion type phase change material, then through the synergy of polydopamine and expanded graphite makes that emulsion type phase change material realizes solar energy utilization efficiency and heat conduction effect Double promotion, the obtained fixed phase change material has heat storage and light absorption performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of organic solid-liquid phase change materials, and relates to a polydopamine-coated emulsion type fixed shape phase change material and a preparation method thereof, in particular to a polydopamine-coated expanded graphite-polyethylene glycol / polyacrylamide emulsion type fixed shape phase change material and a preparation method thereof. BACKGROUND

[0002] To achieve the double carbon goal of China, reduce the use of fossil fuels, solar energy as an ideal renewable energy source to replace fossil fuels has many outstanding advantages. The entire wavelength range of the solar spectrum can generate heat energy through photo-thermal conversion. As an important solar heat storage medium, phase change materials (PCMs) have become an indispensable material in energy-saving systems, among which polyethylene glycol (PEG) has been studied for the manufacture of high-performance and multifunctional composite PCMs due to its high energy storage density, non-toxicity, wide melting temperature range, less phase separation and ideal cycle stability. However, factors such as liquid leakage, inherent low thermal conductivity and weak light absorption capacity seriously hinder its development in solar energy storage systems.

[0003] The application uses polyacrylamide (PAM) emulsion to encapsulate polyethylene glycol to form a core-shell structure, which can achieve the purpose of loading as many original PCMs as possible without leakage, but the inherent low thermal conductivity of organic materials is still a major challenge for application. Therefore, expanded graphite is introduced into the shell structure of the above emulsion particles, on the one hand, the strong adsorption of the porous structure of expanded graphite can further avoid leakage, on the other hand, the high thermal conductivity of expanded graphite can provide a continuous heat transfer channel for PEG, which is beneficial to improve the heat transfer efficiency of the composite PCMs. In addition, the application takes advantage of the strong light absorption capacity of polydopamine (PDA) in the ultraviolet, visible and near-infrared ranges, and attaches it to the surface of the polyacrylamide shell to improve the light absorption and heat conversion capacity of the core-shell structure. SUMMARY

[0004] To solve the above problems, the purpose of the present application is to provide a polydopamine-coated expanded graphite-polyethylene glycol / polyacrylamide emulsion type fixed shape phase change material and a preparation method thereof. The preparation method uses polyacrylamide to coat polyethylene glycol to form a stable emulsion type phase change material, and then uses the synergy of polydopamine and expanded graphite to realize the dual improvement of solar utilization efficiency and heat conduction effect of the emulsion type fixed shape phase change material.

[0005] To achieve the above purpose, a preparation method of a polydopamine-coated expanded graphite-polyethylene glycol / polyacrylamide emulsion type fixed shape phase change material is disclosed, which comprises the following steps:

[0006] (1) Preparation of aqueous phase

[0007] A certain amount of N, N-methylenebisacrylamide, acrylamide, polyvinylpyrrolidone and Tween 85 were weighed respectively, then the four substances were transferred into a beaker, then a certain volume of deionized water was poured into the beaker, then the beaker was ultrasonicated, after the ultrasonic treatment was completed, the aqueous solution in the beaker was used as the water phase and was prepared for use;

[0008] (2) Preparation of oil phase

[0009] A certain amount of polyethylene glycol was weighed and poured into a beaker, then the beaker was heated to melt the polyethylene glycol, and the melted polyethylene glycol was used as the oil phase and was prepared for use;

[0010] (3) Preparation of expanded graphite solution

[0011] (4) Preparation of expanded graphite-polyethylene glycol / polyacrylamide shape-stabilized phase change material

[0012] (5) Preparation of expanded graphite-polyethylene glycol / polyacrylamide emulsion type shape-stabilized phase change material coated with polydopamine.

[0013] Further, in step (3), a certain amount of expanded graphite (EG) was uniformly ground, and the uniformly ground expanded graphite was weighed at 1% to 5% of the amount of polyethylene glycol (PEG) used in step (2) and was added to anhydrous ethanol, then ultrasonic treatment was performed at 60°C, and after the ultrasonic treatment was completed, an expanded graphite solution was obtained.

[0014] Further, in step (4),

[0015] (4-1) The beaker containing the water phase in step (1) was placed in a rotor and was placed in a water bath constant temperature shaker, the water bath temperature and stirring speed were set, the oil phase obtained in step (2) was added to the stirring water phase, after the dropwise addition was completed, an O / L emulsion was obtained, stirring was continued, then the expanded graphite solution obtained in step (3) was added, and then stirring was continued, and an expanded graphite-polyethylene glycol / emulsion was obtained.

[0016] (4-2) Ammonium persulfate was added to the expanded graphite-polyethylene glycol / emulsion, and stirring was performed until uniform, then the emulsion was quickly poured into a beaker, then N, N, N, N-tetramethyl ethylenediamine was added dropwise, and after rapid stirring until uniform, the beaker was sealed and was placed in a blast constant temperature drying oven for drying, so that the acrylamide was polymerized and solidified;

[0017] (4-3) After the drying was completed, product A was obtained, product A was taken out and was placed in a vacuum freeze dryer for freezing, after the freezing was completed, product A was placed on filter paper and was placed in an oven, so that all the unencapsulated polyethylene glycol in product A flowed out, and an expanded graphite-polyethylene glycol / polyacrylamide shape-stabilized phase change material was obtained.

[0018] Further, in step (5), a certain mass of expanded graphite-polyethylene glycol / polyacrylamide shaped phase change material, dopamine hydrochloride, and a certain volume of Tris-HCl buffer solution are weighed, respectively, and then added to a flask, which is then mechanically stirred at room temperature. After stirring, the mixture obtained in the flask is centrifuged, and the supernatant is discarded to obtain a precipitate. The precipitate is washed with deionized water by centrifugation, and then dried at room temperature to obtain a polydopamine-coated expanded graphite-polyethylene glycol / polyacrylamide emulsion-shaped phase change material.

[0019] Further, in step (1), 0.4 g of N, N-methylene bisacrylamide, 1.6 g of acrylamide, 0.1 g of polyvinylpyrrolidone, and 0.3 g of Tween 85 are weighed, respectively, and then transferred to a beaker. 5 mL of deionized water is then added to the beaker, and the beaker is ultrasonicated for 30 min. After ultrasonication, the aqueous solution in the beaker is used as the water phase and is ready for use.

[0020] Further, in step (2), 5 g of polyethylene glycol with a molecular weight of 2000 is weighed and poured into a beaker. The beaker is then placed in a 65°C air-circulating constant-temperature drying oven for heating. The molten polyethylene glycol after heating is used as the oil phase and is ready for use.

[0021] Further, in step (3), the volume of anhydrous ethanol is 10 mL, and the ultrasonic treatment time is 30 min.

[0022] Further, in step (4),

[0023] (4-1) The beaker containing the water phase in step (1) is placed in a rotor and placed in a water bath constant-temperature shaker. The water bath temperature is set to 65°C, and the stirring speed is set to 1500 r / min. The oil phase obtained in step (2) is added dropwise to the stirring water phase. After the dropwise addition is completed, the beaker is sealed with plastic wrap and continues to stir for 30 min. Then, the expanded graphite solution obtained in step (3) is added dropwise while stirring. After the dropwise addition is completed, the stirring speed is kept unchanged, and the temperature is set to 65°C. Continue to stir for 30 min to obtain an expanded graphite-polyethylene glycol / emulsion.

[0024] (4-2) 0.03 g of ammonium persulfate is added to the expanded graphite-polyethylene glycol / emulsion and stirred uniformly. Then, the emulsion is quickly poured into a beaker, and 3 drops of N, N, N, N-tetramethyl ethylenediamine are added dropwise. After rapid stirring, the beaker is sealed and placed in a 50°C air-circulating constant-temperature drying oven for drying for 10 min, so that the acrylamide is polymerized and solidified.

[0025] (4-3) After drying, product A is obtained. Product A is taken out and placed on a culture dish, which is then placed in a vacuum freeze dryer and frozen for 12 hours. After freezing, product A is placed on filter paper and placed in an oven at 65°C to allow all unencapsulated polyethylene glycol in product A to flow out. During this period, the filter paper is continuously replaced until there is no wet stain on the replaced filter paper, thereby finally obtaining an expanded graphite-polyethylene glycol / polyacrylamide shape-stabilized phase change material.

[0026] Further, in step (5), a three-necked flask is taken, a stirring rod is placed into the three-necked flask from one of the connecting ports of the three-necked flask, the other connecting port is connected to a condenser, condensed water is passed through the condenser, and then 3g of expanded graphite-polyethylene glycol / PAM shaped phase change material and 1g of dopamine hydrochloride are weighed respectively, 300mL of trishydroxymethylaminomethane-hydrochloric acid (Tris-HCl) buffer solution with a pH of 8.4 is measured, and these three substances are added to the three-necked flask, and then mechanically stirred at room temperature for 24h at a stirring speed of 200-600r / min; after the stirring is completed, the mixture obtained in the above flask is centrifuged at 5000rpm for 5min, and then the supernatant is discarded to obtain a lower precipitate, the precipitate is centrifuged and washed with deionized water, and then dried at room temperature for 24h to obtain a polydopamine-coated expanded graphite-polyethylene glycol / polyacrylamide emulsion-type shaped phase change material.

[0027] In step (1), acrylamide is used as a polymerization monomer, N,N-methylenebisacrylamide plays a cross-linking role, Tween 85 is used as an oil-in-water emulsifier, and polyvinylpyrrolidone is used as a co-emulsifier; ultrasound is used to completely dissolve the solute in deionized water.

[0028] In step (3), the ultrasonic treatment is to uniformly disperse the expanded graphite in the anhydrous ethanol.

[0029] In step (4-1), the purpose of continuing stirring after the oil phase is added dropwise is to make the resulting O / L emulsion, i.e., the oil-in-water emulsion, more uniform and stable; the purpose of continuing stirring after adding the expanded graphite solution is to uniformly disperse the expanded graphite in the emulsion.

[0030] In step (4-2), the emulsion in the beaker is dried to allow the acrylamide to polymerize and solidify, thereby obtaining a shape-stable phase change material.

[0031] In step (4-3), the purpose of freezing the product A in a vacuum freeze dryer is to freeze-dry the water in the shape-fixed phase change material.

[0032] In step (5), the expanded graphite-polyethylene glycol / PAM shaped phase change material and dopamine hydrochloride are oxidatively polymerized in a Tris-HCl buffer solution; during the above-mentioned oxidative polymerization process, the viscosity of the solution is relatively large, so mechanical stirring is adopted, and the stirring speed is controlled to be 200-600 r / min. If the speed is too low, the polymer is likely to stick together, and if the speed is too high, it is easy to cause the reactants to splash.

[0033] In step (5), one of the connection ports of the three-necked flask is connected to a condenser. The purpose of passing condensed water through the condenser is to prevent overheating during the polymerization process, which would affect the final product generated by the polymerization reaction.

[0034] The present invention also aims to provide a polydopamine-coated expanded graphite-polyethylene glycol / polyacrylamide emulsion-type shape-fixed phase change material prepared according to any one of the above preparation methods.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention uses polyacrylamide to coat polyethylene glycol. The inner layer of polyacrylamide acts as a protective shell to provide tight packaging and good protection for the PCMs core, effectively preventing leakage in its molten state. The synergy of polydopamine and graphite enables the emulsion-type phase change material to achieve a dual improvement in solar energy utilization efficiency and heat conduction effect, promoting solar energy absorption and photothermal conversion of the microcapsule system. Specifically, by adding expanded graphite to the emulsion and coating it with dopamine hydrochloride, the resulting fixed-shape phase change material has both heat storage and light absorption properties. While expanding graphite enhances the thermal stability and material strength of the fixed-shape phase change material, it can reduce the leakage of the fixed-shape phase change material and significantly improve the thermal conductivity of the fixed-shape phase change material. The photothermal conversion ability of the fixed-shape phase change material is improved by coating with polydopamine, and the thermal conductivity path of the emulsion shell is formed in collaboration with expanded graphite, so that the fixed-shape phase change material has excellent light absorption capacity and photothermal storage performance.

[0037] (2) The preparation cost of the present invention is low and it is easy to promote and use as a heat storage fluid. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a technical roadmap for the preparation of a polydopamine-coated expanded graphite-polyethylene glycol / polyacrylamide emulsion-type shape-fixed phase change material (PDA@EG-PEG / PAM) according to an embodiment of the present invention;

[0039] Figure 2 Fourier transform infrared spectra of EG-PEG / PAM and PDA@EG-PEG / PAM prepared in Example 2 and PEG / PAM prepared in Comparative Example 1;

[0040] Figure 3XRD patterns of EG-PEG / PAM and PDA@EG-PEG / PAM prepared in Example 2;

[0041] Figure 4 Figure 2 shows the thermal stability of PDA@EG-PEG / PAM prepared in Example 2, where (a) shows the endothermic enthalpy diagram after 1 cycle and 100 cycles, and (b) shows the exothermic enthalpy diagram after 1 cycle and 100 cycles.

[0042] Figure 5 Thermal infrared images of polyethylene glycol and PDA@EG-PEG / PAM prepared in Example 2 under different sunlight exposure times. In each image, the upper image is PEG, and the lower image is PDA@EG-PEG / PAM. DETAILED DESCRIPTION

[0043] In order to better understand the content of the present invention, the present invention will be further described below in conjunction with specific examples and drawings. The following examples are implemented based on the technology of the present invention and provide detailed implementation methods and operating steps, but the scope of protection of the present invention is not limited to the following examples.

[0044] Example 1:

[0045] (1) Preparation of aqueous phase

[0046] Use an electronic balance to weigh 0.4 g of N,N-methylenebisacrylamide, 1.6 g of acrylamide, 0.1 g of polyvinylpyrrolidone, and 0.3 g of Tween 85, respectively. Then transfer the above four substances into a 100 mL beaker. Use a graduated cylinder to measure 5 mL of deionized water and pour it into the beaker. Finally, place the beaker in an ultrasonic cleaner and ultrasonically dissolve it for 30 minutes to completely dissolve the solutes in the deionized water. The aqueous solution after ultrasonic dissolution in the beaker is used as the aqueous phase for later use.

[0047] (2) Preparation of oil phase

[0048] 5 g of polyethylene glycol with a molecular weight of 2000 was weighed and poured into a 100 mL beaker. The beaker was then placed in a 65° C. forced air constant temperature drying oven to heat the polyethylene glycol to melt the polyethylene glycol. The melted polyethylene glycol was used as the oil phase for later use.

[0049] (3) Preparation of expanded graphite solution

[0050] A certain amount of expanded graphite (EG) was ground uniformly in a mortar, and the ground expanded graphite was weighed according to 1% of the amount of polyethylene glycol in step (2) and added to 10 mL of anhydrous ethanol. The mixture was then ultrasonically treated at 60° C. for 30 min to obtain an expanded graphite solution for later use.

[0051] (4) Preparation of expanded graphite-polyethylene glycol / polyacrylamide shaped phase change material

[0052] (4-1) Put the beaker containing the water phase in step (1) into the rotor and place it in a water bath constant temperature oscillator, set the stirring speed to 1500 r / min and the temperature to 65°C, add the oil phase obtained in step (2), i.e. the molten polyethylene glycol, drop by drop into the above-mentioned stirring water phase with a rubber bulb dropper, after the dropwise addition is completed, an oil-in-water emulsion is obtained, which is recorded as O / L emulsion, the beaker mouth is wrapped with plastic wrap and continues to stir for 30 min, then the expanded graphite solution obtained in step (3) is added drop by drop while stirring, after the dropwise addition is completed, the speed is kept unchanged, the temperature is set to 65°C, and stirring is continued for 30 min, so that the expanded graphite is uniformly dispersed in the O / L emulsion, and finally the expanded graphite-polyethylene glycol / emulsion is obtained, which is recorded as EG-PEG / emulsion.

[0053] (4-2) Add 0.03 g of ammonium persulfate to the EG-PEG / emulsion and stir uniformly, then quickly pour the emulsion into a 50 mL beaker, add 3 drops of N,N,N,N-tetramethyl ethylenediamine dropwise, stir uniformly quickly, then wrap the beaker with plastic wrap and place it in a 50°C air constant temperature drying oven for drying for 10 min, so that the acrylamide is polymerized and solidified to obtain a shaped phase change material with stable shape.

[0054] (4-3) After drying, product A is obtained, take out product A and transfer it to a culture dish, place the culture dish in a vacuum freeze dryer and freeze for 12 h, after freezing is completed, place product A on filter paper and put it in a 65°C oven, so that all the unencapsulated polyethylene glycol in product A flows out, during which the filter paper is replaced constantly until there is no wet spot on the replaced filter paper, finally the expanded graphite-polyethylene glycol / polyacrylamide shaped phase change material is obtained, which is recorded as EG-PEG / PAM shaped phase change material.

[0055] (5) Preparation of polydopamine-coated expanded graphite-polyethylene glycol / polyacrylamide emulsion-type shaped phase change material

[0056] Take a three-necked flask, put a stirring rod into the three-necked flask from one of the connecting ports of the three-necked flask, connect a condenser tube to the other connecting port, pass cold water through the condenser tube, then respectively take 3 g of the EG-PEG / PAM shape-changing phase change material obtained in step (4) of the preparation process, 1 g of dopamine hydrochloride, and 300 mL of Tris-HCl buffer solution with pH = 8.4, and add the three substances into the three-necked flask, then mechanically stir at room temperature for 24 h at a stirring speed of 500 r / min; after the stirring is completed, centrifuge the mixture obtained in the three-necked flask at 5000 rpm for 5 min in a table-type high-speed centrifuge, discard the supernatant, obtain the precipitate, centrifugally wash the precipitate with deionized water, and then dry at room temperature for 24 h to obtain a polydopamine-coated expanded graphite-polyethylene glycol / polyacrylamide emulsion type shape-changing phase change material, denoted as PDA@EG-PEG / PAM, which is a gray-black powder.

[0057] Example 2:

[0058] According to the preparation process of Example 1, 3% of the amount of polyethylene glycol in step (2) of the preparation process is weighed as uniformly ground expanded graphite in step (3), and the rest is the same as Example 1.

[0059] Example 3:

[0060] According to the preparation process of Example 1, 5% of the amount of polyethylene glycol in step (2) of the preparation process is weighed as uniformly ground expanded graphite in step (3), and the rest is the same as Example 1.

[0061] Example 4:

[0062] According to the preparation process of Example 1, 7% of the amount of polyethylene glycol in step (2) of the preparation process is weighed as uniformly ground expanded graphite in step (3), and the rest is the same as Example 1.

[0063] Comparative Example 1:

[0064] (1) Preparation of aqueous phase

[0065] An electronic balance is used to respectively weigh 0.4 g of N, N-methylene bisacrylamide, 1.6 g of acrylamide, 0.1 g of polyvinylpyrrolidone, and 0.3 g of Tween 85, then the above four substances are transferred into a 100 mL beaker, 5 mL of deionized water is measured into the beaker with a cylinder, and finally the beaker is placed in an ultrasonic cleaning instrument for ultrasonic dissolution for 30 min until the solute in the beaker is completely dissolved in the deionized water, and the ultrasonic dissolution of the aqueous solution in the beaker is stopped. The water solution after ultrasonic dissolution is used as the aqueous phase.

[0066] (2) Preparation of oil phase

[0067] Take 5 g of polyethylene glycol with a molecular weight of 2000, pour it into a 100 mL beaker, and then place the beaker in a 65°C air-circulating constant-temperature drying oven for heating to melt the polyethylene glycol. The molten polyethylene glycol is used as the oil phase and is ready for use.

[0068] (3) Preparation of polyethylene glycol / polyacrylamide shape-stabilized phase change material

[0069] The beaker containing the water phase in step (1) is placed in a rotor and placed in a water bath constant-temperature shaker, the stirring speed is set to 1500 r / min, and the temperature is set to 65°C. The oil phase obtained in step (2), i.e. the molten polyethylene glycol, is added dropwise into the above-mentioned stirring water phase using a rubber bulb dropper. After the dropwise addition is completed, an oil-in-water emulsion is obtained, which is denoted as O / L emulsion. The beaker is wrapped with a plastic wrap and continues to be stirred for 1 h. 0.03 g of ammonium persulfate is added to the O / L emulsion and stirred uniformly. Then, the emulsion is quickly poured into a 50 mL beaker, and 3 drops of N, N, N, N-tetramethyl ethylenediamine are added dropwise. After rapid stirring, the beaker is wrapped with a plastic wrap and placed in a 50°C air-circulating constant-temperature drying oven for drying for 10 min, so that the acrylamide is polymerized and solidified to obtain a shape-stabilized phase change material. After the drying is completed, the product A is taken out and transferred to a petri dish. The petri dish is placed in a vacuum freeze dryer for freezing for 12 h, so as to freeze-dry the water in the product A. After the freezing is completed, the product A is placed on filter paper and placed in a 65°C oven, so that the excess polyethylene glycol in the product A flows out. During this period, the filter paper is replaced constantly until there is no wet spot on the replaced filter paper. Finally, a shape-stabilized polyethylene glycol / polyacrylamide shape-stabilized phase change material is obtained, which is denoted as PEG / PAM shape-stabilized phase change material.

[0070] The preparation method used in Comparative Example 1 and Example 1 is the same, except that no expanded graphite is added during the preparation process and no subsequent polydopamine coating is performed.

[0071] Figure 1 The technical roadmap of the preparation method of the polydopamine-coated expanded graphite-polyethylene glycol / polyacrylamide emulsion type shape-stabilized phase change material (PDA@EG-PEG / PAM) of the present application is shown in the following figure.

[0072] The chemical reaction equation of the PAM polymerization reaction is as follows:

[0073]

[0074] The chemical reaction equation of the PDA polymerization reaction is as follows:

[0075]

[0076] Figure 2The Fourier infrared spectra of EG-PEG / PAM prepared in Example 2, PDA@EG-PEG / PAM, and PEG / PAM prepared in Comparative Example 1 were obtained from Figure 2 It can be seen that the O-H, C-H and other functional groups of the EG-PEG / PAM composite added with graphite are not changed, indicating that the addition of graphite does not change the structure of the polymer emulsion; after the EG-PEG / PAM is further coated with PDA, the N=N functional group appears in the PDA@EG-PEG / PAM, indicating that the PDA has been successfully coated.

[0077] Figure 3 The XRD patterns of the EG-PEG / PAM prepared in Example 2 and the PDA@EG-PEG / PAM, wherein the diffraction peaks at 2θ=19.4 and 2θ=23.6 are PEG crystal peaks, since PAM and PDA are both amorphous, it indicates that a large amount of PEG is coated in the EG-PEG / PAM prepared in Example 2 and the PDA@EG-PEG / PAM.

[0078] Figure 4 The thermal stability diagram of the PDA@EG-PEG / PAM prepared in Example 2, wherein Fig. (a) is the endothermic diagram of the PDA@EG-PEG / PAM after 1 cycle and 100 cycles, Fig. (b) is the exothermic diagram of the PDA@EG-PEG / PAM after 1 cycle and 100 cycles; wherein the material to be tested is heated from room temperature to 70℃, and then cooled from 70℃ to room temperature, which is recorded as 1 cycle, and the endothermic enthalpy and exothermic enthalpy values of the material after 1 cycle and 100 cycles are tested by a DSC analyzer; from Figure 4 It can be seen that the thermal stability of the PDA@EG-PEG / PAM composite shape-stabilized phase change material is good, and after 100 cycles, the endothermic enthalpy and exothermic enthalpy only decrease by 5.1% and 9.8%, indicating that the material has the ability of long-term application.

[0079] Polyethylene glycol and PDA@EG-PEG / PAM prepared in Example 2 were respectively pressed into small round pieces with a diameter of 0.8 cm and a height of 0.4 cm, and placed on the same culture dish, and then the culture dish was exposed to simulated sunlight with an irradiation intensity of 300 mW / cm 2 The temperature change of the two materials was recorded by an infrared thermal imager every 60 s.

[0080] Figure 5 The thermal infrared imaging real object diagrams of polyethylene glycol and PDA@EG-PEG / PAM prepared in Example 2 under different sunlight irradiation times, wherein in each diagram, the upper part is PEG, and the lower part is PDA@EG-PEG / PAM, Figure 5The middle picture (1) is the initial thermal infrared imaging image, and the pictures (1) to (8) are the thermal infrared imaging images taken at intervals of 60 seconds. Figure 5 It can be seen that as time goes by, the temperature of PEG increases slowly, while PDA@EG-PEG / PAM has obvious brightness changes. This is because the light absorption effect of PDA and the strong heat conduction ability of EG make the overall heating rate of the composite material faster, which can achieve rapid heat conduction and storage.

[0081] Table 1 shows the emulsion encapsulation efficiency (E) of EG-PEG / PAM prepared in Examples 1 to 4 of the present invention and PEG / PAM prepared in Comparative Example 1. en ) data, where ΔH m,PCM is the endothermic enthalpy of PEG / PAM in Comparative Example 1 and EG-PEG / PAM in different embodiments; ΔH m,PEG is the endothermic enthalpy of PEG.

[0082]

[0083] Table 1 Emulsion encapsulation efficiency

[0084] E en (%)]] PEG / PAM (Comparative Example 1) 61.23％ EG-PEG / PAM (Example 1) 71.01％ EG-PEG / PAM (Example 2) 71.64％ EG-PEG / PAM (Example 3) 57.22％ EG-PEG / PAM (Example 4) 48.50％

[0085] As can be seen from Table 1, the encapsulation efficiency of Examples 1 and 2 is greater than that of Comparative Example 1, indicating that the pores formed by adding a small amount of EG can form capillary force in the polyacrylamide shell, and can encapsulate more PEG than the pure PAM shell; with the increase of the amount of expanded graphite added, the encapsulation of EG-PEG / PAM first increases and then decreases. This is because the expanded graphite is mostly a macroporous structure, and an increase in the proportion will cause partial through-holes in the shell, resulting in the loss of PEG in the pores.

[0086] Table 2 shows the endothermic enthalpy and exothermic enthalpy data of the composite materials with different compositions prepared in PEG, Examples 1 to 4 of the present invention, and Comparative Example 1.

[0087] Table 2 Endothermic and exothermic enthalpies of composite materials with different compositions

[0088] Endothermic enthalpy (J / g) Exothermic enthalpy (J / g) PEG 209.8 207.36 PEG / PAM (Comparative Example 1) 128.47 129.85 EG-PEG / PAM (Example 1) 148.99 110.94 EG-PEG / PAM (Example 2) 150.32 141.52 EG-PEG / PAM (Example 3) 120.06 113.94 EG-PEG / PAM (Example 4) 101.77 97.768 PDA@EG-PEG / PAM (Example 2) 153.69 148.14

[0089] As shown in Table 2, under the synergistic effect of expanded graphite and polydopamine, the heat storage capacity of the material is significantly improved. In Example 2, 3% of expanded graphite and polydopamine-coated emulsion system are added, and the endothermic enthalpy reaches 153.69 J / g, which is 19.6% higher than the endothermic enthalpy of PEG / PAM. At the same time, its exothermic enthalpy reaches 148.14 J / g, which is 14.1% higher than the exothermic enthalpy of PEG / PAM. This is because the heat transfer rate of the carrier is increased, which is conducive to the rapid transfer of heat flow, thereby increasing the enthalpy value.

[0090] The above merely illustrates the embodiments of the present application, and does not limit the present application in any form, and the present application can have other forms of embodiments according to the above structure and function, and does not list them one by one. Therefore, any skilled person in the art, without departing from the technical solution range of the present application, according to the technical essence of the present application, any simple modification, equivalent change and modification of the above embodiments, still belongs to the range of the technical solution of the present application.

Claims

1. A method for preparing a polydopamine-coated expanded graphite-polyethylene glycol / polyacrylamide emulsion-type shape-stabilized phase change material, characterized by Specifically comprising the following steps: (1) Preparation of aqueous phase A certain amount of N, N-methylene bisacrylamide, acrylamide, polyvinylpyrrolidone and Tween 85 were weighed respectively, then the above four substances were transferred into a beaker, then a certain volume of deionized water was poured into the beaker, and the beaker was ultrasonicated. After the ultrasonic treatment was completed, the aqueous solution in the beaker was used as the aqueous phase and was prepared for use; (2) Preparation of oil phase A certain amount of polyethylene glycol was weighed and poured into a beaker, and the beaker was heated to melt the polyethylene glycol. The melted polyethylene glycol was used as the oil phase and was prepared for use; (3) Preparation of expanded graphite solution A certain amount of expanded graphite was ground uniformly, and the ground expanded graphite was weighed at 1% to 5% of the amount of polyethylene glycol in step (2) and was added to anhydrous ethanol. Then, the mixture was ultrasonically treated at 60°C. After the ultrasonic treatment was completed, an expanded graphite solution was obtained. (4) Preparation of expanded graphite-polyethylene glycol / polyacrylamide shape-stabilized phase change material (4-1) The beaker containing the aqueous phase in step (1) was placed in a rotor and was placed in a water bath constant temperature shaker. The water bath temperature and stirring speed were set. The oil phase obtained in step (2) was added to the stirring aqueous phase. After the dropwise addition was completed, an O / L emulsion was obtained. Then, the expanded graphite solution obtained in step (3) was added, and the mixture was continuously stirred to obtain an expanded graphite-polyethylene glycol / emulsion. (4-2) Ammonium persulfate was added to the expanded graphite-polyethylene glycol / emulsion, and the mixture was stirred uniformly. Then, the emulsion was quickly poured into a beaker, and N, N, N, N-tetramethyl ethylenediamine was added dropwise. After the mixture was quickly stirred uniformly, the beaker was sealed and was placed in a blast constant temperature drying oven for drying, so that the acrylamide was polymerized and solidified. (4-3) After the drying was completed, the product A was taken out and was placed in a vacuum freeze dryer for freezing. After the freezing was completed, the product A was placed on filter paper and was placed in an oven, so that the unencapsulated polyethylene glycol in the product A flowed out completely. Thus, an expanded graphite-polyethylene glycol / polyacrylamide shape-stabilized phase change material was obtained. (5) Preparation of expanded graphite-polyethylene glycol / polyacrylamide emulsion type shape-stabilized phase change material coated with polydopamine A certain amount of expanded graphite-polyethylene glycol / polyacrylamide shape-stabilized phase change material, dopamine hydrochloride and Tris-HCl buffer solution were weighed respectively, and were added to a flask. Then, the mixture was mechanically stirred at room temperature. After the stirring was completed, the mixture obtained in the flask was centrifuged, and the supernatant was discarded. Thus, a precipitate was obtained. The precipitate was washed with deionized water by centrifugation. After the precipitate was dried at room temperature, an expanded graphite-polyethylene glycol / polyacrylamide emulsion type shape-stabilized phase change material coated with polydopamine was obtained.

2. The method for preparing the polydopamine-coated expanded graphite-polyethylene glycol / polyacrylamide emulsion-type shape-fixed phase change material according to claim 1, wherein: In step (1), 0.4g of N, N-methylene bisacrylamide, 1.6g of acrylamide, 0.1g of polyvinylpyrrolidone and 0.3g of Tween 85 were weighed respectively, and were transferred into a beaker. Then, 5mL of deionized water was measured and was poured into the beaker. Finally, the beaker was ultrasonicated for 30min. After the ultrasonic treatment was completed, the aqueous solution in the beaker was used as the aqueous phase and was prepared for use.

3. The method for preparing the polydopamine-coated expanded graphite-polyethylene glycol / polyacrylamide emulsion-type shape-fixed phase change material according to claim 1, characterized in that: In step (2), 5 g of polyethylene glycol with a molecular weight of 2000 was weighed and poured into a beaker, and the beaker was placed in a blast constant temperature drying oven at 65 ℃ for heating. The molten polyethylene glycol after heating was used as the oil phase and was prepared for use.

4. The method for preparing the polydopamine-coated expanded graphite-polyethylene glycol / polyacrylamide emulsion-type shape-fixed phase change material according to claim 1, wherein: In step (3), the volume of anhydrous ethanol was 10 mL, and the ultrasonic treatment time was 30 min.

5. The method for preparing the polydopamine-coated expanded graphite-polyethylene glycol / polyacrylamide emulsion-type shape-fixed phase change material according to claim 1, wherein: In step (4), (4-1) The beaker containing the water phase in step (1) was placed in a rotor and placed in a water bath constant temperature oscillator, the water bath temperature was set to 65 ℃, the stirring speed was 1500 r / min, the oil phase obtained in step (2) was added dropwise into the stirring water phase, after the dropwise addition was completed, an O / L emulsion was obtained, the beaker mouth was wrapped with a preservative film and continued to stir for 30 min, then the expanded graphite solution obtained in step (3) was added dropwise while stirring, after the dropwise addition was completed, the speed was kept unchanged, the temperature was set to 65 ℃, and the stirring was continued for 30 min, and finally the expanded graphite-polyethylene glycol / emulsion was obtained; (4-2) 0.03 g of ammonium persulfate was added to the expanded graphite-polyethylene glycol / emulsion and stirred uniformly, then the emulsion was quickly poured into a beaker, 3 drops of N,N,N,N-tetramethyl ethylenediamine were added dropwise, and after rapid stirring, the beaker was sealed and placed in a blast constant temperature drying oven at 50 ℃ for drying for 10 min, so that the acrylamide was polymerized and solidified; (4-3) After drying, the product A was taken out and transferred to a culture dish, the culture dish was placed in a vacuum freeze dryer and frozen for 12 h, after the freezing was completed, the product A was placed on filter paper and placed in an oven at 65 ℃, so that all the unencapsulated polyethylene glycol in the product A flowed out, during which the filter paper was replaced constantly until there was no wet spot on the replaced filter paper, and finally the expanded graphite-polyethylene glycol / polyacrylamide shaped phase change material was obtained.

6. The method for preparing the polydopamine-coated expanded graphite-polyethylene glycol / polyacrylamide emulsion-type shape-fixed phase change material according to claim 1, characterized in that: In step (5), a three-necked flask was taken, a stirring rod was put into the three-necked flask from one of the connection ports of the three-necked flask, a condenser tube was connected to the other connection port, cold water was passed through the condenser tube, then 3 g of expanded graphite-polyethylene glycol / polyacrylamide shaped phase change material, 1 g of dopamine hydrochloride, and 300 mL of Tris-HCl buffer solution with pH=8.4 were weighed, and the three substances were added to the three-necked flask, then mechanical stirring was carried out at room temperature for 24 h, and the stirring speed was 200-600 r / min; after the stirring was completed, the mixture obtained in the above flask was centrifuged at 5000 rpm for 5 min, then the supernatant was discarded, and the precipitate was washed by centrifugation with deionized water, then the precipitate was dried at room temperature for 24 h to obtain the polydopamine-coated expanded graphite-polyethylene glycol / polyacrylamide emulsion-type shaped phase change material.

7. The polydopamine-coated expanded graphite-polyethylene glycol / polyacrylamide emulsion-type shaped phase change material prepared by the preparation method of any one of claims 1-6.

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