Flexible composite phase change film capable of storing heat by using solar energy

Abstract

The application provides a flexible composite phase change film capable of storing heat by using solar energy, which comprises an upper layer film, a middle layer film and a lower layer film, the material constituting the upper layer film and the lower layer film comprises polyvinyl alcohol and graphene nanosheets, and the material constituting the middle layer film comprises polyvinyl alcohol, graphene nanosheets and phase change microcapsules. The composite phase change film has excellent flexibility, efficient light-heat conversion and heat storage functions, and can be used for preparing wearable warm-keeping materials or heat compress materials for treatment.

Description

Technical Field

[0001] This invention relates to a flexible composite phase change membrane, and more specifically, to a flexible composite phase change membrane that can utilize solar energy for thermal storage. Background Technology

[0002] In recent years, the frequent occurrence of extreme weather events and the development of thermal management, energy conversion, energy-efficient buildings, and renewable energy technologies have placed higher demands on the technology and functionality of constant-temperature thermal management. Traditional thermal management models utilize fossil fuels for building heating or cooling, resulting in high energy consumption. The resulting heat emissions exacerbate global warming and the urban heat island effect. Solar energy is a green and abundant renewable energy source. Achieving effective thermal management of human body temperature under cold outdoor temperatures and low light conditions is extremely challenging. Wearing thick clothing is one of the traditional strategies for keeping warm. However, due to the lack of a continuous heat source, it is difficult to maintain a constant body temperature in cold outdoor environments, and wearing heavy clothing can affect physical activity and reduce comfort. Maintaining a relatively constant and comfortable body temperature in cold outdoor areas is crucial for various bodily functions. Therefore, developing multifunctional flexible composite materials with solar-driven thermal management capabilities is of great significance. Phase change materials (PCMs) with high latent heat and storage density have been widely used for thermal energy storage and temperature regulation. CN107502296A discloses a material for solar thermal storage using paraffin phase change material; CN110372824A discloses a phase change material for room temperature thermal energy storage via solid-solid phase change. CN106281235A discloses a polyol composite phase change material that can be used for industrial waste heat recovery. Organic phase change materials have attracted widespread attention due to their good chemical stability, low supercooling, and weak chemical corrosion. However, organic phase change materials have low thermal conductivity, and their flow is severely hindered during the phase change process, which impedes their practical application. Microencapsulation technology is an effective method to solve the above problems. CN114773680A discloses a phase change microcapsule that effectively encapsulates paraffin phase change material using silica / modified illite powder, and the prepared phase change microcapsule can be used for thermal energy storage and insulation systems. CN115838586A discloses a phase change microcapsule with a mesh polyurethane hybrid shell structure, which can effectively prevent leakage of the phase change material. CN112251197A discloses a method for encapsulating phase change materials with polydopamine, which has full-spectrum absorption of sunlight, to obtain a phase change microcapsule for solar thermal energy storage. Therefore, microencapsulation technology can not only prevent leakage of organic phase change materials, but also allow the prepared organic phase change material microcapsules to be combined with fibers, coatings, plastics, adhesives, and other substrates as functional materials to prepare composite materials with wide applications in energy-saving buildings, smart fabrics, solar thermal collectors, human medicine, and aerospace. However, the preparation process of multifunctional composite films based on phase change microcapsules using existing technologies is complex. For example, CN107383734A discloses a carbon nanotube-modified PAN phase change material microcapsule composite film, the preparation method of which requires six preparation processes and involves a high-temperature reaction environment.Furthermore, the interaction between phase change microcapsules and the polymer matrix in multifunctional composite films prepared by existing technologies is relatively weak, which may lead to slippage or detachment during application, thus seriously affecting their stability. In addition, existing composite films also suffer from defects such as low solar energy capture efficiency, poor mechanical properties, low flexibility, and limited functionality. Summary of the Invention

[0003] This invention addresses the shortcomings of existing microcapsule composite films of phase change materials, such as complex preparation methods, low solar energy capture efficiency, poor mechanical properties, low flexibility, and limited functionality. It provides a flexible composite phase change film (PGAMF) capable of storing solar energy. This flexible composite phase change film utilizes highly thermally conductive composite phase change microcapsule materials as energy conversion materials, exhibiting excellent performance in efficient solar energy capture, rapid energy transfer, and thermal energy storage. Furthermore, its good flexibility allows it to meet the application requirements of various scenarios.

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

[0005] A flexible composite phase change membrane capable of storing solar energy comprises an upper membrane, an intermediate membrane, and a lower membrane.

[0006] The materials constituting the upper and lower membranes include polyvinyl alcohol and graphene nanosheets, and

[0007] The materials constituting the intermediate layer membrane include polyvinyl alcohol, graphene nanosheets, and phase change microcapsules.

[0008] In another preferred embodiment, the thickness of the intermediate layer film is 60–100 μm, and the thickness of the upper layer film and the upper layer film is 1–3 μm.

[0009] In another preferred embodiment, the upper, middle and lower layers of the flexible composite phase change membrane are formed from the same liquid material, wherein the molecular weight of the polyvinyl alcohol in the liquid material is 50,000 to 70,000.

[0010] In another preferred embodiment, the graphene nanosheets in the liquid have a diameter of 0.2–2 μm, more preferably 0.5–1 μm.

[0011] In another preferred embodiment, the mass ratio of polyvinyl alcohol, graphene nanosheets and phase change microcapsules in the liquid is 1:0.01-0.10:0.12-0.80.

[0012] In another preferred embodiment, the phase change microcapsule uses an aminated multi-walled carbon nanotube-modified styrene-divinylbenzene copolymer composite material as the shell material and n-octadecane as the energy storage core material.

[0013] The present invention also provides a method for preparing the above-mentioned flexible composite phase change film capable of storing solar energy, the method comprising the following steps:

[0014] (1) Preparation of phase change microcapsules;

[0015] (2) Add polyvinyl alcohol granules to water and stir until completely dissolved;

[0016] (3) Graphene nanosheets and phase change microcapsules were added sequentially to a polyvinyl alcohol aqueous solution, stirred for 1 to 3 hours, and then sonicated for 2 to 5 hours to obtain a stable mixture.

[0017] (4) Transfer the mixture to a glass petri dish, spread it out naturally, and dry it at 0-40℃ for 24-48 hours to obtain a phase change composite membrane.

[0018] In another preferred embodiment, the method for preparing phase change microcapsules includes the following steps:

[0019] (1-a) Stir and mix n-octadecane phase change thermal storage material, styrene (SM), divinylbenzene (DVB), and water;

[0020] (1-b) Add the surfactant to the mixture from step (1) and continue stirring to obtain a stable and uniform oil-in-water emulsion;

[0021] (1-c) Aminated multi-walled carbon nanotubes and an initiator were added to the above oil-in-water emulsion. The reaction system was heated to 60-100°C and maintained for 3-7 hours. The product was filtered and repeatedly washed with deionized water at 65-85°C to obtain phase change microcapsules.

[0022] In another preferred embodiment, in step (1-a), the mass ratio of n-octadecane, styrene, divinylbenzene and water is 1:0.40-0.49:0.10-0.01:15-16.

[0023] In another preferred embodiment, in step (1-a), the mixing temperature is 30-60°C, the mixing speed is 600-1000 r / min, and the mixing time is 0.5-2 hours.

[0024] In another preferred embodiment, the surfactant is selected from sodium dodecylbenzenesulfonate, and the amount added is 2.5 to 3 wt% of the weight of deionized water in the aqueous phase.

[0025] In another preferred embodiment, in step (1-c), the initiator is selected from azobisisobutyronitrile (AIBN), azobisisoheptanenitrile, dimethyl azobisisobutyrate, or a combination thereof, and is used in an amount of 10 to 20 wt% of the total weight of styrene and divinylbenzene.

[0026] In another preferred embodiment, in step (1-c), the amount of aminated multi-walled carbon nanotubes is 0.05 to 2.0 wt% of the total weight of styrene, divinylbenzene, and n-octadecane.

[0027] In another preferred embodiment, in step (2), the weight-to-volume ratio of polyvinyl alcohol particles to water is 60–90 mg / mL.

[0028] In another preferred embodiment, in step (3), the stirring time is 2.5 to 3 hours and the ultrasonic treatment time is 3 to 4 hours.

[0029] The present invention also provides the use of the above-mentioned flexible composite phase change film that can utilize solar energy for heat storage in the preparation of wearable thermal insulation materials or heat therapy materials.

[0030] The present invention also provides a wearable thermal insulation material comprising the above-mentioned flexible composite phase change membrane that can utilize solar energy for heat storage.

[0031] The present invention also provides a heat therapy material comprising the above-mentioned flexible composite phase change membrane capable of storing heat using solar energy. Attached Figure Description

[0032] Figure 1 Figure (a) shows the preparation process of phase change microcapsules (AMPCM), and Figure (b) shows the preparation process of flexible composite phase change membrane (PGAMF) that can utilize solar energy for thermal storage by adding polyvinyl alcohol aqueous solution and graphene nanosheets after obtaining phase change microcapsules.

[0033] Figure 2 Figure (a) shows a schematic diagram of the sandwich structure of a flexible composite phase change membrane that can utilize solar energy for thermal storage, and Figure (b) shows a diagram demonstrating the flexibility of a specific flexible composite phase change membrane that can utilize solar energy for thermal storage.

[0034] Figure 3 The image shows a SEM image of the phase change microcapsules filled inside a flexible composite phase change membrane that can utilize solar energy for thermal storage. The instrument used was an S-4800 manufactured by Hitachi, Japan. The phase change microcapsule samples were sputtered with gold and tested under an accelerating voltage of 10kV.

[0035] Figure 4Images (a), (a'), (d), and (d') are SEM images of the surface and cross-section of the PVA / GO composite film (Example 2), respectively. Images (b), (b'), (g), and (g') are SEM images of the surface and cross-section of the PGAMF-5 composite film (Example 5), respectively. Images (c) and (c') are SEM images of the cross-section of the PVA / GO composite film (Example 1), respectively. Images (e), (e'), (f), and (f') are SEM images of the cross-sections of the PGAMF-1 and PGAMF-3 composite films (Examples 3 and 4), respectively.

[0036] Figure 5 The figures show the DSC curves of the PVA film, PVA / GO composite film, PGAMF-1, PGAMF-3 and PGAMF-5 composite film prepared in this invention (the heating and cooling rate was controlled at 5℃ / min during the test, the temperature range was 15-45℃, and the instrument used was a Diamond DSC differential scanning calorimeter manufactured by PerkinElmer Instruments Ltd.).

[0037] Figure 6 Figure (a) shows the DSC phase transition enthalpy of PVA film, PVA / GO composite film, PGAMF-1, PGAMF-3 and PGAMF-5 composite phase change film, and Figure (b) shows the phase transition temperature of PGAMF-1, PGAMF-3 and PGAMF-5 composite phase change film.

[0038] Figure 7 The thermal conductivity of PVA film, PVA / GO composite film, PGAMF-1, PGAMF-3 and PGAMF-5 composite phase change film is displayed (using a TCM, C-Therm thermal conductivity meter manufactured by C-Therm Technologies Ltd., Canada).

[0039] Figure 8 Figure (a) shows the DSC curves of the PGAMF-5 phase change composite membrane prepared by the present invention during 500 thermal cycles with 50 thermal cycles as the interval, and Figure (b) shows the phase change enthalpy and phase change temperature of the phase change composite membrane.

[0040] Figure 9 The thermogravimetric analysis (TGA) curves of AMPCM membrane, PVA membrane, PVA / GO composite membrane and PGAMF-5 composite membrane are shown (the TGA testing instrument used was model STA-449C).

[0041] Figure 10 Figure (a) shows the temperature change over time at the center point of the membrane prepared in different embodiments obtained by photothermal cycling test, and Figure (b) shows the photothermal curve of the membrane obtained in Example 5 during 300 photothermal cycles at intervals of 150 cycles.

[0042] Figure 11 This is the testing apparatus used for the photothermal cycling test in this invention. The apparatus is a solar simulator (CEL-NP2000-2A) that simulates sunlight in the wavelength range of 320-2500nm to test the solar energy-thermal conversion performance of the prepared composite thin film. The manufacturer-specified operating parameters of the solar simulator are 50W radiation output, of which the ultraviolet output (<390nm) is 2.6W and the infrared output (>770nm) is 28.8W. The radiant density of the simulated sunlight is measured by a solar power meter (CEL-FZ-A). Detailed Implementation

[0043] In response to the shortcomings of existing technologies, the inventors of this application, through in-depth research, unexpectedly discovered that a liquid containing polyvinyl alcohol (PVA), graphene nanosheets (GO), and phase change microcapsules (AMPCM) can be naturally spread and flattened after stirring and ultrasonic treatment for a specific time to form a flexible composite phase change film with a sandwich structure. The upper and lower layers of the film contain polyvinyl alcohol and graphene nanosheets, and the middle layer contains polyvinyl alcohol, graphene nanosheets, and phase change microcapsules. Furthermore, it was unexpectedly discovered that this flexible composite phase change film not only efficiently converts solar energy into thermal energy but also possesses excellent flexibility.

[0044] The present invention provides a flexible composite phase change membrane capable of storing solar energy, comprising an upper membrane, an intermediate membrane, and a lower membrane.

[0045] The materials constituting the upper and lower membranes include polyvinyl alcohol and graphene nanosheets, and the materials constituting the intermediate membrane include polyvinyl alcohol, graphene nanosheets, and phase change microcapsules.

[0046] In the flexible composite phase change membrane of the present invention, polyvinyl alcohol serves as both a binder and a matrix material for the composite membrane. The polyvinyl alcohol used in this invention has a molecular weight of 50,000 to 70,000, and preferably a number-average molecular weight of 61,000.

[0047] In the flexible composite phase change film of the present invention, the role of graphene nanosheets is to enhance the photothermal conversion capability of the composite film. The preferred diameter of the graphene nanosheets used in the present invention is 0.2–2 μm.

[0048] In the flexible composite phase change membrane of the present invention, the phase change microcapsules serve to impart latent heat storage functionality to the composite phase change membrane. The phase change microcapsules used in this invention are commercially available or can be prepared according to the methods disclosed herein.

[0049] In a specific example of the present invention, the thermal conductivity of the phase change microcapsules used in the present invention is 0.20-0.30 W / (m·K), and the phase change enthalpy is 90-110 J / g.

[0050] In another preferred embodiment, the phase change microcapsule uses an aminated multi-walled carbon nanotube-modified styrene-divinylbenzene copolymer composite material as the shell material and n-octadecane as the energy storage core material.

[0051] Preparation method of phase change microcapsules

[0052] The preparation method includes the following steps: (1-a) mixing n-octadecane, styrene (SM), and divinylbenzene (DVB) with water; (1-b) adding a surfactant to the mixture in step (1) and continuing to stir to obtain a stable and uniform oil-in-water emulsion; (1-c) adding aminated multi-walled carbon nanotubes and an initiator to the above oil-in-water emulsion, heating the reaction system to 60-100°C and maintaining it for 3-7 hours, filtering the product and washing it repeatedly with deionized water at 65-85°C to obtain phase change microcapsules.

[0053] In step (1-a), the mass ratio of n-octadecane, styrene, divinylbenzene, and water can be used according to conventional amounts in the art. Preferably, it is 1:0.40-0.50:0.10-0.01:15-20. In step (1-a), preferably, the mixing temperature is 30-60°C, the stirring speed is 600-1000 r / min, and the stirring time is 0.5-2 hours. The purpose of stirring is to form a homogeneous and stable oil-in-water emulsion system. In step (1-b), the amount of surfactant used is conventional in the art, preferably 2-10 wt% of the deionized water content in the aqueous phase. In step (1-c), the initiator includes, but is not limited to, AIBN (azobisisobutyronitrile, dimethyl azobisisobutyrate), and its amount is 10-20 wt% of the combined content of styrene and divinylbenzene. In step (1-c), the amount of aminated multi-walled carbon nanotubes used is 0.05 to 2.00 wt% of the combined content of styrene, divinylbenzene, and n-octadecane.

[0054] Preparation method of flexible composite phase change membrane that can utilize solar energy for thermal storage

[0055] The preparation method includes the following steps: (1) preparing phase change microcapsules; (2) adding polyvinyl alcohol particles to water and stirring until completely dissolved, adding graphene nanosheets to water and stirring to disperse evenly; (3) adding the graphene nanosheet aqueous dispersion and phase change microcapsules to the polyvinyl alcohol aqueous solution in sequence, stirring for 1 to 3 hours, and then sonicating for 2 to 5 hours to obtain a stable mixture; (4) transferring the mixture to a glass petri dish, spreading it naturally, and drying it naturally at 0 to 40°C for 24 to 48 hours to obtain a flexible composite phase change film.

[0056] In step (1), the phase change microcapsules can be prepared according to existing techniques or according to the method described above in this invention. In step (2), preferably, the weight-to-volume ratio of polyvinyl alcohol particles to water is 60-90 mg / mL. When preparing the polyvinyl alcohol aqueous solution, water at 80-95°C is used. The obtained polyvinyl alcohol aqueous solution is used as a matrix to uniformly disperse the phase change microcapsules and graphene nanosheets. In step (3), the stirring time is more preferably 2.5-3 hours, and the ultrasonic treatment time is more preferably 2.5-3 hours.

[0057] Under the viscous effect of the polyvinyl alcohol / graphene (PVA / GO) solution, the phase change microcapsules can be suspended in the PVA / GO solution. During the natural cooling process to form a composite phase change film, PVA plays a binding role, which allows the phase change microcapsules to be embedded in the PVA / GO matrix and distributed in the middle of the film. The upper and lower layers of the composite phase change film are composed of PVA / GO, thus forming a film with a sandwich structure. Figure 4 Figures (e)(e'), (f)(f'), and (g)(g') confirm that the prepared PVA / GO / AMPCM composite membrane has the above-mentioned sandwich structure.

[0058] In the description of this invention, water refers to deionized water or distilled water.

[0059] This invention employs a suspension polymerization method to prepare phase change microcapsules (AMPCMs) with n-octadecane phase change material as the energy storage core and aminated multi-walled carbon nanotubes (ACNTs)-modified styrene-divinylbenzene copolymer (SDB) as the composite shell. By spreading a PVA / GO / AMPCM mixture on a plate and air-drying it at room temperature, a series of PGAMF composite films exhibiting a sandwich structure were obtained. The middle layer is a composite material of polyvinyl alcohol (PVA) / graphene nanosheets (GO) / phase change microcapsules (AMPCM), while the upper and lower layers are the same PVA / GO mixture. This invention prepares PGAMF composite films by naturally drying a PVA / GO / AMPCM suspension in a petri dish. Due to the viscosity of PVA in the suspension during the static process, the AMPCM microcapsules are fixed in the middle of the composite phase change film, such as... Figure 2The structural schematic shown in (a) illustrates this. Because the AMPCM microcapsules are fixed in the middle layer of the sandwich structure, they will not slip or detach during the use of the composite phase change membrane. The PGAMF composite film possesses dual functions of heat storage and photothermal conversion. Under the bonding effect of PVA, the prepared PGAMF composite film exhibits excellent flexibility. For the PGAMF composite film, AMPCM provides excellent heat storage performance, while the spatial synergy between GO and ACNTs on the AMPCM microcapsule surface provides excellent solar-thermal conversion and heat transfer performance. This solar-driven wearable composite film can provide heat to the human body in cold outdoor areas, showing broad application prospects in the field of human thermal therapy.

[0060] In the description of this invention, "natural drying" means placing the product in an environment for natural drying without any additional heating or other means to accelerate the drying process.

[0061] Compared with the prior art, the present invention has the following advantages:

[0062] (1) The flexible composite phase change film of the present invention, which can utilize solar energy for thermal storage, utilizes the heat storage performance of its internal high-heat-storage phase change microcapsules and the light absorption and photothermal conversion performance of GO nanosheets doped in a PVA matrix to convert solar energy into thermal energy and store the thermal energy. The present invention solves the defect of existing phase change films based on phase change microcapsules, which have a single function and only have the function of phase change energy storage (e.g., CN113099697A).

[0063] (2) The flexible composite phase change membrane for solar energy storage provided by this invention is simple to prepare and has strong practical applicability. Existing phase change composite thin films have complex preparation processes, and the reaction conditions involve high-temperature environments (e.g., CN107383734B). In addition, this invention solves to some extent the problems of low solar energy capture efficiency and low thermal energy conversion rate of existing composite membranes. By utilizing the heat absorption and release properties of phase change materials during phase change, it solves the problems of energy dispersion, instability, and difficulty in collection of solar energy in nature, achieving multifunctionality and thus broadening its application scenarios.

[0064] (3) The bonding effect of PVA gives the composite phase change film good mechanical properties and flexibility, which can be repeatedly recycled and has good thermal stability and durability.

[0065] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions, and unless otherwise stated, percentages and parts are weight percentages and weight parts.

[0066] The aminated multi-walled carbon nanotubes used in the following examples have a length of 5–30 μm, a diameter of ~2 nm, and a purity of 95 wt%. They were purchased from Shanghai Titan Technology Co., Ltd., and the internal code for this product is 041045724.

[0067] The PVA used in the following examples has a molecular weight of 61,000 and was purchased from Shanghai Titan Technology Co., Ltd. The internal code for this product is 013679955.

[0068] Example 1

[0069] Preparation of PVA membrane

[0070] The preparation method is as follows: 1.5g of PVA particles are added to 20mL of deionized water at 90℃ and stirred for 3 hours until completely dissolved. The mixture is then transferred to a 7cm diameter glass petri dish, spread out naturally, and dried at 25℃ for 48 hours to obtain a PVA film.

[0071] Scanning electron micrographs of the cross-section of the prepared PVA film are shown below. Figure 4 As shown in figures (c) and (c'), the cross-section is smooth, flat, and dense. The thermal conductivity of pure PVA is 0.190 ± 0.002 W / (m·K), as... Figure 7 As shown. No thermal degradation occurred below 100℃. Figure 9 DSC test results show that pure PVA film does not undergo phase change at 15–45℃ and does not have the function of latent heat storage.

[0072] Testing of photothermal conversion efficiency:

[0073] Place a 50mm diameter pure PVA film in an insulated box, such as... Figure 11 As shown, when a pure PVA film is irradiated with simulated sunlight, the power density of the simulated sunlight is measured to be 50 mW / cm². 2 That is, 0.5 solar masses. The surface temperature of the sample was recorded using an infrared thermal imager (FLIR One), and the resulting curve is shown in the figure. Figure 10 As shown in Figure (a), the temperature of the pure PVA film after 78 seconds of solar radiation was 25.4°C (the ambient temperature during the test was 5.0-7.0°C to simulate the temperature environment of a cold region). Therefore, the pure PVA film in Example 1 exhibited poor photothermal performance.

[0074] Example 2

[0075] Preparation of PVA / GO composite membrane:

[0076] The preparation method is as follows: 1.5g of PVA particles were added to 20mL of deionized water at 90℃ and stirred for 3 hours until completely dissolved. Then, 0.075g of graphene nanosheets were added to the above mixture and stirred continuously for 0.5 hours, followed by sonication for 3 hours until the graphene nanosheets were completely dispersed in the solution. After that, the mixture was transferred to a glass petri dish with a diameter of 7cm, spread naturally, and dried naturally at 25℃ for 48 hours to obtain a PVA / GO membrane.

[0077] Scanning electron micrographs of the surface and cross-section of the PVA / GO composite membrane (PGF membrane) are shown below. Figure 4 Figures (a), (a'), (d), and (d') show the PVA / GO film. These figures demonstrate that the PVA / GO film surface is smooth and flat, with GO nanosheets distributed throughout its cross-section and surface. Furthermore, the PVA / GO film is dense and pore-free internally. The thermal conductivity of the PGF film is 1.126 ± 0.004 W / (m·K). Figure 7 As shown. No thermal degradation occurred below 100°C (see, Figure 9 DSC test results show that the PVA / GO film did not undergo a phase transition at 15–45°C and does not have the function of latent heat storage.

[0078] Testing of photothermal conversion efficiency:

[0079] Place a 50mm diameter PVA / GO film in an insulated box, such as Figure 11 As shown. When a pure PVA / GO composite film was irradiated with simulated sunlight, the power density of the simulated sunlight was measured to be 50 mW / cm². 2 That is, 0.5 solar masses. The surface temperature of the sample was recorded using an infrared thermal imager (FLIR One), and the resulting curve is shown in the figure. Figure 10 As shown in Figure (a), this PVA / GO composite film exhibits superior photothermal response compared to the PVA film in Example 1, with a simulated solar radiation time of 58 s from 15.0 °C to 50.0 °C. This is because GO nanosheets with excellent light absorption properties and high photothermal conversion efficiency are introduced into the PVA / GO composite film.

[0080] Example 3

[0081] Preparation of phase change microcapsules

[0082] The preparation method includes the following steps:

[0083] (1) Add n-octadecane phase change thermal storage material, styrene (SM) and divinylbenzene (DVB) to a three-necked flask containing deionized water and mix at 45°C. Stir the mixture at 8000 r / min for one hour. The mass ratio of n-octadecane, SM, DVB and water is 1:0.45:0.06:18.

[0084] (2) Sodium dodecylbenzenesulfonate (SDBS) surfactant was added to the mixed solution and stirring was continued to obtain a stable and homogeneous oil-in-water emulsion. The mass fraction of SDBS surfactant added was 2.6 wt% of the deionized water content in the aqueous phase.

[0085] (3) Aminated multi-walled carbon nanotubes (ACNT) and initiator azobisisobutyronitrile (AIBN) were added to the above reaction emulsion. The mass fraction of ACNT added was 1.0 wt.% of the total content of styrene, divinylbenzene and n-octadecane, and the mass fraction of initiator AIBN added was 7.5 wt% of the total content of styrene and divinylbenzene.

[0086] (4) Heat the reaction system to 80-90℃ and maintain it for 3-7 hours. Filter the product and wash it repeatedly with deionized water at 65-85℃ to obtain AMPCM microcapsules.

[0087] Preparation of PVA / GO / AMPCM phase change composite film

[0088] The preparation method includes the following steps:

[0089] 1.5 g of PVA particles were added to 20 mL of deionized water at 90 °C and stirred for 3 hours until completely dissolved. Then, 0.075 g of graphene nanosheets and 0.19 g of phase change microcapsules were added to the mixture and stirred for 0.5 hours. After sonication for 3 hours, the mixture was transferred to a 7 cm diameter glass petri dish, spread naturally, and dried at 25 °C for 48 hours to obtain a PVA / GO / AMPCM membrane.

[0090] The phase change composite membrane prepared in this embodiment is named PGAMF-1, wherein the mass fraction of added AMPCM is 10.6% of the total weight of the composite membrane (i.e., PGAMF-1).

[0091] The microstructure of AMPCM microcapsules was characterized using SEM, such as... Figure 3 As shown in the figure, the AMPCM microcapsules are regularly spherical, defect-free, and have densely distributed ACNTs on their surface. The dense SDB shell provides encapsulation protection for the n-octadecane core, preventing leakage and flow in the molten state. Figure 7 As shown, the thermal conductivity of the AMPCM microcapsules is 0.284 ± 0.002 W / (m·K), and no thermal degradation occurs below 100 °C (see, Figure 9 DSC test results show that the melting enthalpy and crystallization enthalpy of AMPCM microcapsules can reach 119.1±0.9 and 112.2±0.8 J / g, respectively, and their melting temperature and crystallization temperature are 31.7±0.3 and 24.9±0.3℃, respectively.

[0092] Cross-sectional micrographs of the PGAMF-1 composite film, such as Figure 4 Figures (e) and (e') show the structure of the PGAMF-1 composite membrane. The figures reveal a sandwich structure, and the introduction of AMPCM creates some porosity within the membrane. The introduction of AMPCM inevitably leads to a decrease in the thermal conductivity of the composite membrane. The thermal conductivity of the PGAMF-1 composite membrane is 0.765 ± 0.003 W / (m·K). Figure 7 As shown. Figure 6 As shown in (a), DSC test results indicate that the PGAMF-1 membrane underwent a phase transition between 15 and 45 °C, demonstrating a certain latent heat storage function. The melting enthalpy and crystallization enthalpy of the PGAMF-1 composite membrane are 12.3 ± 0.3 and 10.9 ± 0.3 J / g, respectively. Figure 6 As shown in (b), the melting temperature and crystallization temperature of the PGAMF-1 composite film are 28.5 and 25.3 °C, respectively.

[0093] Testing of photothermal conversion efficiency:

[0094] Place a 50mm diameter PGAMF-1 composite film in an insulated box, such as Figure 11 As shown. The PGAMF-1 composite film was irradiated with simulated sunlight, and the power density of the simulated sunlight was measured to be 50 mW / cm². 2 That is, 0.5 solar masses. The surface temperature of the sample was recorded using an infrared thermal imager (FLIR One), and the resulting curve is shown in the figure. Figure 10 As shown in Figure (a), compared to PF and PGF films, the PGAMF-1 film exhibits superior photothermal response, with a simulated solar radiation time of 42 s from 15.0 °C to 50.0 °C. Furthermore, an isothermal thermal storage plateau appears in the range of 25–29 °C. This is because the PGAMF-1 composite film incorporates AMPCM microcapsules with high thermal storage performance and microcapsules with excellent photothermal conversion performance.

[0095] Example 4

[0096] Preparation of PVA / GO / AMPCM phase change composite film

[0097] The preparation method includes the following steps:

[0098] 1.5 g of PVA particles were added to 20 mL of deionized water at 90 °C and stirred for 3 hours until completely dissolved. Then, 0.075 g of graphene nanosheets and 0.56 g of phase change microcapsules (prepared according to Example 3) were added to the above mixture and stirred continuously for 0.5 hours, sonicated for 3 hours, and then transferred to a glass petri dish with a diameter of 7 cm, spread naturally, and dried naturally at 25 °C for 48 hours to obtain a PVA / GO / AMPCM membrane.

[0099] The phase change composite membrane prepared in this embodiment is named PGAMF-3, wherein the mass fraction of added AMPCM is 26.3%.

[0100] Cross-sectional microscopic images of the PGAMF-3 composite film, such as Figure 4 The figure (f)(f') shows that the PGAMF-3 composite membrane exhibits a sandwich structure, and the introduction of AMPCM creates pores within the membrane. As the AMPCM content increases, the thermal conductivity of the composite membrane gradually decreases. The thermal conductivity of the PGAMF-3 composite membrane is 0.426 ± 0.002 W / (m·K). Figure 7 As shown. Figure 6 As shown in (a), DSC test results indicate that the PGAMF-3 membrane underwent a phase transition between 15 and 45 °C, demonstrating a certain latent heat storage function. The melting enthalpy and crystallization enthalpy of the PGAMF-3 composite membrane are 32.3 ± 0.5 J / g and 29.3 ± 0.4 J / g, respectively. Figure 6 As shown in (b), the melting temperature and crystallization temperature of the PGAMF-3 composite film are 28.9 and 25.0 °C, respectively.

[0101] Testing of photothermal conversion efficiency:

[0102] Place a 50mm diameter PGAMF-3 composite film in the insulation box, such as Figure 11 As shown, when a pure PVA film is irradiated with simulated sunlight, the power density of the simulated sunlight is measured to be 50 mW / cm². 2 That is, 0.5 solar masses. The surface temperature of the sample was recorded using an infrared thermal imager (FLIR One), and the resulting curve is shown in the figure. Figure 10 As shown in Figure (a), compared to PF and PGF membranes, the PGAMF-3 membrane exhibits superior photothermal response, with a simulated solar radiation time of 53 s from 15.0 °C to 50.0 °C. This is somewhat slower than the PGAMF-1 composite membrane in reaching 50 °C, because the AMPCM content in the PGAMF-3 composite membrane is higher than that in the PGAMF-1 composite membrane. Therefore, the PGAMF-3 composite membrane requires a longer time to store the heat energy converted from photothermal energy within the AMPCM. Furthermore, a longer isothermal thermal storage plateau with a phase transition time compared to the PGAMF-1 composite membrane was observed in the 25-29 °C range. During this stage, the high-thermal-storage-performance AMPCM microcapsules in the PGAMF-3 composite membrane underwent a solid-liquid transition.

[0103] Example 5

[0104] Preparation of PVA / GO / AMPCM phase change composite film

[0105] The preparation method includes the following steps:

[0106] 1.5 g of PVA particles were added to 20 mL of deionized water at 90 °C and stirred for 3 hours until completely dissolved. Then, 0.075 g of graphene nanosheets and 0.75 g of phase change microcapsules (prepared according to Example 3) were added to the above mixture and stirred continuously for 0.5 hours, sonicated for 3 hours, and then transferred to a glass petri dish with a diameter of 7 cm, spread naturally, and dried naturally at 25 °C for 48 hours to obtain a PVA / GO / AMPCM membrane.

[0107] The phase change composite membrane prepared in this embodiment is named PGAMF-5. The mass fraction of AMPCM added is 32.3%.

[0108] The PGAMF-5 composite membrane exhibits excellent flexibility, showing no damage or breakage after 1000 folds. Figure 2 As shown. Cross-sectional microscopic image of the PGAMF-5 composite membrane, as shown. Figure 4 As shown in Figures (g) and (g'), the PGAMF-5 composite membrane exhibits a sandwich structure. Figure 7 As shown, the rate of decrease in thermal conductivity of the PGAMF-5 composite film is significantly reduced, and the thermal conductivity of the PGAMF-5 composite film is 0.390 ± 0.003 W / (m·K). Figure 6 As shown in Figure (a), DSC test results indicate that the PGAMF-5 membrane underwent a phase transition between 15 and 45 °C, demonstrating a certain latent heat storage function. The melting enthalpy and crystallization enthalpy of the PGAMF-5 composite membrane are 45.5 ± 0.7 and 43.3 ± 0.7 J / g, respectively. Figure 6 As shown in Figure (b), the melting temperature and crystallization temperature of the PGAMF-5 composite film are 29.2 and 24.8 °C, respectively. The PGAMF-5 composite film did not undergo thermal degradation below 100 °C. Figure 9 In addition, such as Figure 8 As shown, after 500 cycles, the phase transition enthalpy and phase transition temperature of the PGAMF-5 composite membrane decreased by no more than 0.7%, demonstrating excellent thermal reliability and thermal stability.

[0109] Testing of photothermal conversion efficiency:

[0110] Place a 50mm diameter PGAMF-5 composite film in the insulation box, such as Figure 11 As shown, when a pure PVA film is irradiated with simulated sunlight, the power density of the simulated sunlight is measured to be 50 mW / cm². 2 That is, 0.5 solar masses. The surface temperature of the sample was recorded using an infrared thermal imager (FLIR One), and the resulting curve is shown in the figure. Figure 10As shown in Figure (a), the PGAMF-5 membrane exhibits excellent photothermal response, with a simulated solar radiation time of 78 s from 15.0 °C to 50.0 °C. This is somewhat slower than the PGAMF-1 and PGAMF-3 composite membranes when reaching 50 °C. This is because the PGAMF-5 composite membrane has the highest AMPCM content, thus requiring a longer time to store the heat energy converted from photothermal energy within the AMPCM. A longer isothermal heat storage plateau with a phase change time compared to the PGAMF-1 and PGAMF-3 composite membranes was observed in the 25–29 °C range. During this stage, the high-heat-storage-performance AMPCM microcapsules in the PGAMF-5 composite membrane underwent a solid-liquid transition. Furthermore, the curves of the PGAMF-5 composite membrane after 150 and 300 cycles showed high consistency with the initial photothermal curves, as shown in Figure (a). Figure 10 As shown in Figure (b). The above results indicate that the PGAMF-5 composite membrane can be reused for a long period of time and has certain application value.

[0111] When sunlight (30mW / cm) 2 When sunlight shines on a fiber fabric coated with a PGAMF-5 composite film, the temperature of the area with the PGAMF-5 composite film increases by 14.0°C, reaching 38.4°C, compared to the temperature of ordinary fiber fabric (24.4°C). Therefore, wearing fiber fabric coated with a PGAMF-5 composite film in cold outdoor areas can provide excellent warmth. Furthermore, due to its high photosensitivity, the PGAMF-5 composite film can be used for heat therapy. When sunlight (50mW / cm²) is applied... 2 When the PGAMF-5 composite film used for hand heat therapy is irradiated, the surface temperature of the PGAMF-5 composite film reaches 52.1℃, which is within the temperature range of human body heat energy (50.0-60.0℃). Therefore, the prepared PGAMF film has great application value in human body insulation and heat therapy in cold regions.

[0112] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A flexible composite phase change membrane capable of storing heat using solar energy, characterized in that, The flexible composite phase change membrane capable of storing solar energy comprises an upper membrane, a middle membrane, and a lower membrane. The materials constituting the upper and lower membranes include polyvinyl alcohol and graphene nanosheets, and The materials constituting the intermediate layer membrane include polyvinyl alcohol, graphene nanosheets, and phase change microcapsules; The upper, middle, and lower layers of the flexible composite phase change membrane are formed by allowing the same liquid to stand. The molecular weight of the polyvinyl alcohol in the liquid is 50,000 to 70,000. The graphene nanosheets in the liquid have a diameter of 0.2~2 μm; The mass ratio of polyvinyl alcohol, graphene nanosheets, and phase change microcapsules in the liquid is 1:0.01~0.10:0.12-0.80; The preparation method of a flexible composite phase change membrane that can utilize solar energy for thermal storage includes the following steps: (1) Provide phase change microcapsules; (2) Add polyvinyl alcohol particles to water and stir until completely dissolved to obtain a polyvinyl alcohol aqueous solution; (3) Add graphene nanosheets and phase change microcapsules to polyvinyl alcohol aqueous solution in sequence, stir for 1 to 3 hours, and then sonicate for 2 to 5 hours to obtain a stable mixture; (4) Transfer the mixture to a glass petri dish, spread it out naturally, and dry it at 0 ~ 40 ℃ for 24 ~ 48 hours to obtain a phase change composite membrane.

2. The flexible composite phase change membrane capable of storing solar energy according to claim 1, characterized in that, The thickness of the intermediate layer film is 60~100 μm. The thickness of the upper membrane and the upper membrane are 1~3 μm respectively.

3. The flexible composite phase change membrane capable of storing solar energy according to claim 1, characterized in that, The phase change microcapsules use styrene-divinylbenzene copolymer composite material modified with aminated multi-walled carbon nanotubes as the shell material and n-octadecane as the energy storage core material.

4. The method for preparing the flexible composite phase change film capable of solar energy storage according to any one of claims 1 to 3, characterized in that, The preparation method includes the following steps: (1) Provide phase change microcapsules; (2) Add polyvinyl alcohol particles to water and stir until completely dissolved to obtain a polyvinyl alcohol aqueous solution; (3) Add graphene nanosheets and phase change microcapsules to polyvinyl alcohol aqueous solution in sequence, stir for 1 to 3 hours, and then sonicate for 2 to 5 hours to obtain a stable mixture; (4) Transfer the mixture to a glass petri dish, spread it out naturally, and dry it at 0 ~ 40 ℃ for 24 ~ 48 hours to obtain a phase change composite membrane.

5. The preparation method according to claim 4, characterized in that, The preparation method of phase change microcapsules includes the following steps: (1-a) Stir together n-octadecane, styrene, and divinylbenzene with water; (1-b) Add the surfactant to the mixture of step (1-a) and continue stirring to obtain a stable and uniform oil-in-water emulsion; (1-c) Aminated multi-walled carbon nanotubes and an initiator were added to the above oil-in-water emulsion. The reaction system was heated to 60-100 °C and maintained for 3-7 hours. The product was filtered and repeatedly washed with deionized water at 65-85 °C to obtain phase change microcapsules.

6. The preparation method according to claim 5, characterized in that, In step (1-a), the mass ratio of n-octadecane, styrene, divinylbenzene, and water is 1:0.40~0.5:0.10~0.01:15-20, and / or In step (1-a), the mixing temperature is 30~60 ℃, the mixing speed is 600~1000 r / min, the mixing time is 0.5~2 hours, and / or In step (1-b), the surfactant is selected from sodium dodecylbenzenesulfonate, and its addition amount is 2-10 wt% of the deionized water content in the aqueous phase. In step (1-c), the initiator is selected from azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, or a combination thereof, and its amount is 10-20 wt% of the total weight of styrene and divinylbenzene. In step (1-c), the amount of aminated multi-walled carbon nanotubes used is 0.05 to 2.0 wt% of the total weight of styrene, divinylbenzene and n-octadecane.

7. The preparation method according to claim 4 or 5, characterized in that, In step (2), the weight-to-volume ratio of polyvinyl alcohol to water in the polyvinyl alcohol aqueous solution is 60~90 mg / mL; In step (3), the stirring time is 2.5 to 3 hours and the ultrasonic treatment time is 3 to 4 hours.

8. Use of the flexible composite phase change membrane capable of storing solar energy as described in any one of claims 1 to 3 in the preparation of wearable thermal insulation materials or heat therapy materials.

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