A coaxial electrospun radiation phase change cooling fiber membrane and its preparation method

Abstract

This invention belongs to the field of cooling fiber membrane technology, and particularly relates to a coaxial electrospun radiation phase change cooling fiber membrane and its preparation method. The shell spinning solution is prepared by adding poly(vinylidene fluoride-co-hexafluoropropylene) to a mixed solvent of N,N-dimethylformamide and acetone, heating and stirring at 45-60°C for 6 hours to obtain a homogeneous solution, and then allowing the homogeneous solution to stand at room temperature for 6 hours to eliminate bubbles. The core spinning solution is prepared by adding n-octadecane to chloroform, stirring for 30 minutes, and then storing at 35°C. Electrospinning is performed using an electrospinning device and a 22G / 17G coaxial needle. The shell and core spinning solutions are transferred to syringes and connected to the corresponding parts of the coaxial needle. Electrospinning parameters are adjusted to perform electrospinning, resulting in a coaxial electrospun radiation phase change cooling fiber membrane with a wrinkled structure. The weight-average molecular weight (Mw) of the poly(vinylidene fluoride-co-hexafluoropropylene) is 455,000, and the number-average molecular weight (Mn) is 110,000.

Description

Technical Field

[0001] This invention belongs to the field of cooling fiber membrane technology, and particularly relates to a coaxial electrospun radiation phase change cooling fiber membrane and its preparation method. Background Technology

[0002] With the continuous increase in demand for miniaturization of electronic devices, building energy conservation, and personal thermal management, efficient passive cooling technology has become a key direction for solving the energy consumption problem of traditional cooling solutions. Traditional active cooling methods rely on external energy input, which is not only energy-intensive but also limited by the application scenarios. Radiation cooling technology, on the other hand, can achieve energy-free cooling by radiating infrared energy into outer space, showing outstanding potential in the field of low-energy cooling. However, single radiation cooling materials lack effective heat buffering capacity under strong daytime sunlight or fluctuating ambient temperatures, making it difficult to maintain a stable cooling effect. Therefore, combining radiation cooling function with phase change heat storage characteristics has become an important research approach to improve the environmental adaptability of cooling materials.

[0003] Current technologies for radiation-induced phase change cooling fiber membranes still have significant limitations: most approaches employ simple blending or unstructured composites of phase change materials with polymer matrices, which can easily lead to leakage of the phase change materials during long-term use, resulting in decreased cooling performance and insufficient durability. Furthermore, the microstructure of the fiber membrane surface is difficult to control, making it impossible to further enhance solar reflectivity through surface morphology optimization, thus hindering improvements in cooling efficiency. In addition, some preparation processes are cumbersome and require stringent parameter control, increasing production costs and hindering large-scale production, failing to meet the dual requirements of stable cooling material performance and ease of preparation in practical applications. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned technical problems by providing a coaxial electrospun radiation phase change cooling fiber membrane and its preparation method.

[0005] In view of this, the present invention provides a method for preparing a coaxial electrospun radiation phase change cooling fiber membrane, comprising the following steps:

[0006] Step 1: Prepare the shell spinning solution:

[0007] Poly(vinylidene fluoride-co-hexafluoropropylene) was added to a mixed solvent of N,N-dimethylformamide and acetone, and heated and stirred at 45 to 60°C for 6 hours to obtain a homogeneous solution. The homogeneous solution was then allowed to stand at room temperature for 6 hours to eliminate bubbles and was ready for use.

[0008] Step 2: Prepare the core spinning solution:

[0009] Add n-octadecane to chloroform, stir for 30 minutes, and store at 35°C for later use;

[0010] Step 3: Coaxial electrospinning:

[0011] Electrospinning equipment and 22G / 17G coaxial needles were used to transfer the shell and core spinning solutions into syringes and fix them to the injection pump. The syringe containing the shell spinning solution was connected to the outer needle of the coaxial needle, and the syringe containing the core spinning solution was connected to the inner needle of the coaxial needle. Electrospinning parameters were adjusted to perform electrospinning and obtain a coaxial electrospinned radiation phase change cooling fiber membrane with a pleated structure.

[0012] The poly(vinylidene fluoride-co-hexafluoropropylene) has a weight-average molecular weight Mw of 455,000 and a number-average molecular weight Mn of 110,000.

[0013] The electrospinning parameters include: temperature of 36±2℃, humidity of 45 to 50%, positive spinning voltage of 14.5±2kV, negative voltage of -3 to -1kV, receiving distance of 20cm, shell advancing speed of 0.2mm / min, and core advancing speed of 0.01-0.04mm / min.

[0014] Preferably, the mass ratio of N,N-dimethylformamide to acetone is 7:3, 5:5, or 3:7.

[0015] Preferably, the solid content of the obtained shell spinning solution is 20%.

[0016] Preferably, the type of the folded structure is achieved by adjusting the mass ratio of N,N-dimethylformamide and acetone: when the mass ratio of N,N-dimethylformamide to acetone is 7:3, honeycomb-like folds are formed;

[0017] When the mass ratio of N,N-dimethylformamide to acetone is 5:5 or 3:7, parallel ridge valleys are formed.

[0018] Preferably, the height of the pleated structure and the surface roughness of the fiber membrane are achieved by adjusting the core layer advance speed: the lower the core layer advance speed, the flatter the fiber membrane surface and the smaller the pleat amplitude;

[0019] The higher the core layer advance speed, the longer the fold wavelength and the greater the amplitude, and the clearer the fold texture.

[0020] Preferably, the electrospinning parameters are any combination of the following:

[0021] The spinning positive voltage is 16kV, the negative voltage is -3kV, and the core layer advance speed is 0.01mm / min;

[0022] The spinning positive voltage is 14.5kV, the negative voltage is -2kV, and the core layer advance speed is 0.02mm / min;

[0023] The spinning positive voltage is 16.5kV, the negative voltage is -2kV, and the core layer advance speed is 0.03mm / min;

[0024] The spinning positive voltage is 14.3kV, the negative voltage is -2kV, and the core layer advance speed is 0.04mm / min;

[0025] The spinning positive voltage is 16kV, the negative voltage is -1.5kV, and the core layer advance speed is 0.01mm / min;

[0026] The spinning positive voltage is 14kV, the negative voltage is -1.7kV, and the core layer advance speed is 0.02mm / min;

[0027] The spinning positive voltage is 14kV, the negative voltage is -1.8kV, and the core layer advance speed is 0.03mm / min;

[0028] The spinning positive voltage is 16.5kV, the negative voltage is -1.9kV, and the core layer advance speed is 0.04mm / min;

[0029] The spinning positive voltage is 12.5kV, the negative voltage is -1.6kV, and the core layer advance speed is 0.01mm / min;

[0030] The spinning positive voltage is 13.5kV, the negative voltage is -1.5kV, and the core layer advance speed is 0.02mm / min;

[0031] The spinning positive voltage is 13.6kV, the negative voltage is -1.5kV, and the core layer advance speed is 0.03mm / min;

[0032] The spinning positive voltage is 13.5kV, the negative voltage is -2.5kV, and the core layer advance speed is 0.04mm / min.

[0033] The coaxial electrospun radiation phase change cooling fiber membrane has micro-nano-scale fiber diameter and pore structure, and maintains high emission characteristics in the atmospheric window. During outdoor daytime testing, the average temperature drop is about 7.6℃, the peak temperature difference can reach 12.4℃, the enthalpy value is 122J / g after 50 thermal cycles, and there is no n-octadecane leakage.

[0034] Preferably, the solar reflectivity of the fiber membrane is improved through multiple diffuse reflections and angle randomization of the pleated structure, and is higher than that of a fiber membrane with a smooth surface spun using a coreless spinning solution.

[0035] Preferably, the fiber membrane has a heat-insulating effect on the environment at night and has a phase change plateau characteristic for high-temperature buffering.

[0036] The beneficial effects of this invention are:

[0037] The coaxial electrospun radiation phase change cooling fiber membrane prepared by this invention can enhance solar reflectivity through multiple diffuse reflections under strong daytime sunlight, thanks to its micro-nano pores and surface wrinkled structure. It can also form a high-temperature buffer platform by utilizing the phase change properties of n-octadecane, effectively suppressing sudden temperature rises. The measured average temperature drop reached 7.6℃, with a peak temperature difference of up to 12.4℃. At night, it can exert a heat preservation effect to avoid excessive heat dissipation. After 50 thermal cycles, the enthalpy value still remains at 122J / g. The encapsulation effect of the coaxial structure solves the problem of easy leakage of phase change materials in traditional composite membranes, significantly improving the durability of the material.

[0038] Using a simple coaxial electrospinning process as its core, honeycomb or parallel ridge-like folds can be precisely prepared by adjusting the mass ratio of N,N-dimethylformamide to acetone in the shell layer. Combined with the adjustment of the core layer's advancing speed, the fold height and surface roughness can be flexibly changed, achieving customized microstructures without the need for complex equipment. The entire process is simple to operate and the parameters are easy to control, which reduces production costs and can stably produce fiber membranes with uniform performance. It can be widely adapted to various scenarios such as thermal management of electronic equipment, building energy conservation, and personal protection, effectively making up for the shortcomings of traditional cooling materials, such as cumbersome processes and limited performance. Attached Figure Description

[0039] Figure 1 The images show physical photos and optical micrographs of the radiation-phase change cooling fiber membranes of Examples 1-12.

[0040] Figure 2 This is a snapshot of the system trajectory from a molecular dynamics simulation.

[0041] Figure 3 The reflectance spectra of the fiber membranes in Examples 4, 8, 12 and Comparative Example 1 were measured using a UV-Vis-NIR spectrophotometer equipped with an integrating sphere.

[0042] Figure 4 Infrared emission spectra of fiber membranes in Examples 4, 8, 12 and Comparative Example 1 were measured using a Fourier transform infrared spectrometer equipped with a gold integrating sphere.

[0043] Figure 5 The reflectance spectra of the fiber membranes in Examples 1, 2, 3, and 4 were measured using a UV-Vis-NIR spectrophotometer equipped with an integrating sphere.

[0044] Figure 6 The reflectance spectra of the fiber membranes in Examples 5, 6, 7, and 8 were measured using a UV-Vis-NIR spectrophotometer equipped with an integrating sphere.

[0045] Figure 7 The reflectance spectra of the fiber membranes in Examples 9, 10, 11, and 12 were measured using a UV-Vis-NIR spectrophotometer equipped with an integrating sphere.

[0046] Figure 8 Infrared thermal images of cotton fabric, Comparative Example 1, and Example 4 during constant temperature heating.

[0047] Figure 9 This is a graph showing the real-time temperature change of the lower surface of the fabrics used in Example 4, Comparative Example 1, and pure cotton fabrics in a daytime outdoor environment.

[0048] Figure 10 This is a graph showing the real-time temperature change of the lower surface of the fabrics used in Example 4, Comparative Example 1, and pure cotton fabrics in a nighttime outdoor environment.

[0049] Figure 11 This is a transmission electron microscope image of Example 4.

[0050] Figure 12 The image shows the DSC curves for Example 4 at a heating / cooling rate of 10°C / min.

[0051] Figure 13 These are photos of the appearance of Examples 1, 2, 3, and 4 before and after 30 hours of continuous heating.

[0052] Figure 14 The curves show the residual mass rates of Examples 1, 2, 3, and 4 after 30 hours of continuous heating.

[0053] Figure 15 Examples 5, 6, 7, and 8 are photographs of their appearance before and after 30 hours of continuous heating.

[0054] Figure 16 The curves show the residual mass rates of Examples 5, 6, 7, and 8 after 30 hours of continuous heating.

[0055] Figure 17 These are photos of the appearance of Examples 9, 10, 11, and 12 before and after 30 hours of continuous heating.

[0056] Figure 18 The curves show the residual mass rates of Examples 9, 10, 11, and 12 after 30 hours of continuous heating.

[0057] Figure 19 This is an infrared thermal image of the clothing surface covered in Example 4. Detailed Implementation

[0058] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0059] It should be noted that all directional and positional terms used in this invention, such as "up," "down," "left," "right," "front," "back," "vertical," "horizontal," "inner," "outer," "top," "lower," "lateral," "longitudinal," and "center," are only used to explain the relative positional relationships and connections between components in a specific state (as shown in the accompanying drawings). They are merely for the convenience of describing the invention and do not require the invention to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. Furthermore, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0060] In the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0061] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0062] The raw materials used in this invention include: poly(vinylidene fluoride-co-hexafluoropropylene), n-octadecane, N,N-dimethylformamide, acetone, and chloroform.

[0063] The poly(vinylidene fluoride-co-hexafluoropropylene) described in this invention has a Mw of 455,000 and a Mn of 110,000.

[0064] A method for preparing a coaxial electrospun radiation-cooled fiber membrane includes the following steps: The shell spinning solution is prepared by adding poly(vinylidene fluoride-co-hexafluoropropylene) to a mixed solvent of N,N-dimethylformamide and acetone, heating and stirring at 45-60°C for 6 hours to obtain a homogeneous solution. The mixed solution obtained in the above steps is then allowed to stand at room temperature for 6 hours to eliminate bubbles and is ready for use. The core spinning solution is prepared by adding n-octadecane to chloroform, stirring for 30 minutes, and then storing at 35°C for use. The shell and core spinning solutions are transferred separately to syringes and fixed to an injection pump. The syringe containing the shell spinning solution is connected to the outer needle of a coaxial needle, and the syringe containing the core spinning solution is connected to the inner needle of a coaxial needle. Electrospinning is performed using an electrospinning device and a 22G / 17G coaxial needle. The electrospinning parameters are adjusted to obtain the phase change-radiation-cooled fiber membrane.

[0065] To further clarify, the mass ratio of N,N-dimethylformamide to acetone is 7:3, 5:5, and 3:7.

[0066] To further clarify, the solid content of the shell spinning solution is 20%.

[0067] To further explain, the specific parameters for electrospinning are as follows: temperature 36±2 ℃, humidity 45 to 50%, positive spinning voltage 14.5±2kV, negative voltage -3 to -1kV, receiving distance 20cm, shell layer advance speed 0.2mm / min, and core layer advance speed 0.01-0.04mm / min.

[0068] In this invention, the core layer TCM and the shell layer mixed solvent exhibit a significant asymmetry in evaporation rates. After deposition, the TCM continuously and rapidly disperses, causing strong dispersive adsorption / localized plasticization of the PVDF-HFP segments. This leads to in-plane shrinkage stress accumulation and out-of-plane buckling instability in the fiber network, forming macroscopic wrinkles. By controlling the ratio of the shell layer mixed solvent, a compliant, honeycomb-like wrinkle network with predominantly two-dimensional buckling can be formed; or anisotropy can be enhanced to form wrinkles with parallel ridges and valleys. Changing the core layer flow rate can also alter the wrinkle height and the surface roughness of the fiber membrane. This preparation method is simple, easy to implement, and readily controllable.

[0069] The present invention will be further described below with reference to specific embodiments.

[0070] Example 1: Poly(vinylidene fluoride-co-hexafluoropropylene) was added to a mixed solvent of N,N-dimethylformamide and acetone, and stirred at 55°C for 6 hours to obtain a shell spinning solution with a solid content of 20%, which was then allowed to stand at room temperature for 6 hours. The mass ratio of N,N-dimethylformamide to acetone was 7:3. Octadecylene was added to chloroform, and after stirring for 30 minutes, a uniformly mixed core spinning solution was obtained and stored at 35°C. Electrospinning equipment and a 22G / 17G coaxial needle were used for spinning. The spinning solutions for the shell layer and the core layer were transferred to syringes and fixed to an injection pump. The syringe containing the shell layer spinning solution was connected to the outer needle of the coaxial needle, and the syringe containing the core layer spinning solution was connected to the inner needle of the coaxial needle. The spinning temperature was set to 36±2℃, the humidity to 45 to 50%, the positive spinning voltage to 16kV, the negative spinning voltage to -3kV, the receiving distance to 20cm, the shell layer advance speed to 0.2mm / min, and the core layer advance speed to 0.01mm / min.

[0071] Example 2: The core spinning speed was adjusted to 0.02 mm / min, the positive spinning voltage was 14.5 kV, and the negative spinning voltage was -2 kV to obtain the corresponding radiation-phase change cooling fiber membrane. Other conditions were the same as in Example 1.

[0072] Example 3: The core spinning speed was adjusted to 0.03 mm / min, the positive spinning voltage was 16.5 kV, and the negative spinning voltage was -2 kV to obtain the corresponding radiation-phase change cooling fiber membrane. Other conditions were the same as in Example 1.

[0073] Example 4: The core spinning speed was adjusted to 0.04 mm / min, the positive spinning voltage was 14.3 kV, and the negative spinning voltage was -2 kV to obtain the corresponding radiation-phase change cooling fiber membrane. Other conditions were the same as in Example 1.

[0074] Example 5: Poly(vinylidene fluoride-co-hexafluoropropylene) was added to a mixed solvent of N,N-dimethylformamide and acetone, and stirred at 55°C for 6 hours to obtain a shell spinning solution with a solid content of 20%, which was then allowed to stand at room temperature for 6 hours. The mass ratio of N,N-dimethylformamide to acetone was 5:5. Octadecylene was added to chloroform, and after stirring for 30 minutes, a uniformly mixed core spinning solution was obtained and stored at 35°C. Electrospinning equipment and a 22G / 17G coaxial needle were used for spinning. The shell and core spinning solutions were transferred to syringes and fixed to an injection pump. The syringe containing the shell spinning solution was connected to the outer needle of the coaxial needle, and the syringe containing the core spinning solution was connected to the inner needle of the coaxial needle. The spinning temperature was set to 36±2℃, the humidity to 45 to 50%, the positive spinning voltage to 16kV, the negative voltage to -1.5kV, the receiving distance to 20cm, the shell advancing speed to 0.2mm / min, and the core advancing speed to 0.01mm / min.

[0075] Example 6: The core spinning speed was adjusted to 0.02 mm / min, the positive spinning voltage was 14 kV, and the negative spinning voltage was -1.7 kV to obtain the corresponding radiation-phase change cooling fiber membrane. Other conditions were the same as in Example 5.

[0076] Example 7: The core spinning speed was adjusted to 0.03 mm / min, the positive spinning voltage was 14 kV, and the negative spinning voltage was -1.8 kV to obtain the corresponding radiation-phase change cooling fiber membrane. Other conditions were the same as in Example 5.

[0077] Example 8: The core spinning speed was adjusted to 0.04 mm / min, the positive spinning voltage was 16.5 kV, and the negative spinning voltage was -1.9 kV to obtain the corresponding radiation-phase change cooling fiber membrane. Other conditions were the same as in Example 5.

[0078] Example 9: Poly(vinylidene fluoride-co-hexafluoropropylene) was added to a mixed solvent of N,N-dimethylformamide and acetone, and stirred at 55°C for 6 hours to obtain a shell spinning solution with a solid content of 20%, which was then allowed to stand at room temperature for 6 hours. The mass ratio of N,N-dimethylformamide to acetone was 3:7. Octadecylene was added to chloroform, and after stirring for 30 minutes, a uniformly mixed core spinning solution was obtained and stored at 35°C. Electrospinning equipment and 22G / 17G coaxial needles were used for spinning. The shell and core spinning solutions were transferred to syringes and fixed to the injection pump. The syringe containing the shell spinning solution was connected to the outer needle of the coaxial needle, and the syringe containing the core spinning solution was connected to the inner needle of the coaxial needle. The spinning temperature was set to 36±2℃, the humidity to 45 to 50%, the positive spinning voltage to 12.5kV, the negative voltage to -1.6kV, the receiving distance to 20cm, the shell advancing speed to 0.2mm / min, and the core advancing speed to 0.01mm / min.

[0079] Example 10: The core spinning speed was adjusted to 0.02 mm / min, the positive spinning voltage was 13.5 kV, and the negative spinning voltage was -1.5 kV to obtain the corresponding radiation-phase change cooling fiber membrane. Other conditions were the same as in Example 9.

[0080] Example 11: The core spinning speed was adjusted to 0.03 mm / min, the positive spinning voltage was 13.6 kV, and the negative spinning voltage was -1.5 kV to obtain the corresponding radiation-phase change cooling fiber membrane. Other conditions were the same as in Example 9.

[0081] Example 12: The core spinning speed was adjusted to 0.04 mm / min, the positive spinning voltage was 13.5 kV, and the negative spinning voltage was -2.5 kV to obtain the corresponding radiation-phase change cooling fiber membrane. Other conditions were the same as in Example 9.

[0082] Comparative Example 1: Poly(vinylidene fluoride-co-hexafluoropropylene) was added to a mixed solvent of N,N-dimethylformamide and acetone, and stirred at 55°C for 6 hours to obtain a shell spinning solution with a solid content of 20%, which was then allowed to stand at room temperature for 6 hours. The mass ratio of N,N-dimethylformamide to acetone was 3:7. Electrospinning was performed using an electrospinning device and a 22G / 17G coaxial needle. The shell spinning solution was transferred to a syringe and fixed to an injection pump. The syringe containing the shell spinning solution was connected to the outer needle of the coaxial needle, and an empty syringe was fixed to the injection pump and connected to the inner needle of the coaxial needle. The spinning temperature was set to 36±2°C, the humidity to 45-50%, the positive spinning voltage to 12.5kV, the negative voltage to -1.6kV, the receiving distance to 20cm, the shell advance speed to 0.2mm / min, and no spinning solution was injected into the core layer.

[0083] Appendix Figure 1 Examples 1-12 are shown in physical images and optical micrographs. The final pattern of the folds can be altered by changing the ratio of the shell-mixing solvent. During flight, the jet forms initial fibers and deposits on the receiver due to the rapid evaporation of acetone. When the DMF content is high, the shell evaporates slowly, curing is slow, the inter-fiber welds are strong, the network is softer, and stress can be transmitted in all directions, forming a uniform polygonal pattern. Increasing the acetone content leads to faster shell evaporation and curing. The fibers become more independent, and the network becomes more rigid. Rapid evaporation may result in a faster curing rate along the fiber axis, making it easier for stress to be released along the fiber direction, forming parallel ridges and valleys. Changing the spinning speed of the core layer can alter the amplitude of the folds. At low core speeds, the surface is basically flat or has only fine ripples, occasionally with short-wavelength, low-amplitude fine wrinkles; as the core speed increases, the wavelength gradually becomes longer, the amplitude increases, and the fold patterns gradually become clearer. Molecular dynamics simulations were used to demonstrate the interaction energies between DMF, acetone, and chloroform and PVDF-HFP at the shell-core interface. Figure 2 The image shows a snapshot of the system trajectory from molecular dynamics simulations. Table 1 shows the interaction energies. In the shell solvent, acetone has weak interactions with the polymer, leading to rapid solidification, while DMF has strong interactions, which is beneficial for forming a homogeneous solution. The interaction between chloroform and PVDF-HFP is dominated by strong van der Waals forces, indicating that chloroform strongly adsorbs onto PVDF-HFP through dispersion / induction forces, causing chain segment relaxation and localized plasticization. Due to its strong interaction with the polymer, volatilization generates strong localized stress. The faster the core velocity, the greater the amount of core layer per unit time (i.e., the more chloroform), resulting in a larger and more continuous area of ​​plasticized region, stronger synergistic contraction force, and increasingly clear wrinkle patterns.

[0084] Appendix Figure 3 and attached Figure 4The solar reflectance and infrared emissivity spectra of Examples 4, 8, 12, and Comparative Example 1 are shown. The surface wrinkled structures of Examples 4, 8, and 12 can improve solar reflectance through multiple diffuse reflections and angle randomization in geometric optics. Furthermore, the electrospun fiber membranes have micro- and nano-scale fiber diameters and pore sizes, and their synergistic design results in greater gain. Comparative Example 1, due to its smooth surface, has low scattering efficiency and thus lower solar reflectance. The wrinkled structure does not affect the material's high emissivity characteristics at atmospheric windows. (Appendix) Figure 5 The reflectance spectra of Examples 1-4 are attached. Figure 6 The reflectance spectra of Examples 5-8 are attached. Figure 7 The reflectance spectra of Examples 9-12 and the average reflectance data of Examples 1-12 in Table 2 show that, with the same shell solvent ratio, the faster the core layer speed, the higher the reflectance. This is because a higher core layer makes the surface wrinkles of the fiber membrane more obvious.

[0085] A polytetrafluoroethylene (PTFE) plate was placed on a 50°C constant-temperature heating platform. After the surface temperature of the PTFE plate reached 45°C, cotton fabric, Comparative Example 1, and Example 4 were placed on it. An infrared thermal imager was used to take pictures every two seconds to monitor the temperature rise of the samples. (Appendix) Figure 8 Infrared thermal images of cotton fabric, Comparative Example 1, and Example 4 during isothermal heating. The cotton fabric turned red rapidly in 8 seconds, while Comparative Example 1 did not turn red after one minute. Due to the presence of the phase change material, Example 4 exhibited a significantly lower surface temperature and a slower heating rate in the initial stage of heating.

[0086] Appendix Figure 9 and attached Figure 10 The cooling performance of Example 4 and Comparative Example 1 was tested outdoors during daytime and nighttime. The test setup consisted of four 12x12x5cm cavities made on the surface of a 30x30x30cm polystyrene foam box. Thermocouples were placed in the center of each cavity and fixed to test the lower surface temperature of the sample, with the sample tightly covering the thermocouples. One cavity was left empty to hold only the thermocouple probe and not cover the sample to test the ambient temperature. Aluminum foil was used to wrap the surface of the foam box, except for the cavities, to reduce heating of the test setup by sunlight. An infrared-transparent polyethylene film was used to cover the top of the setup to isolate it from heat convection and conduction from the surrounding environment. During the daytime outdoor test, a phase change plateau was observed initially, with the material temperature remaining constant, demonstrating high-temperature buffering performance. The average daytime temperature drop was approximately 7.6℃, with a peak temperature difference of 12.4℃. At night, the sample (Comparative Example 1) exhibited a heat-preserving effect compared to single-radiative cooling.

[0087] Appendix Figure 11 The TEM image for Example 4 shows that the shell successfully encapsulates the phase change material within the core layer, and the material is uniformly distributed at the center without any offset. (See attached image.) Figure 12The DSC curve for Example 4 shows almost no loss of enthalpy (122 J / g) after 50 cycles, indicating the durability and leak-proof properties of the prepared coaxial structure. To demonstrate its long-lasting effect, Examples 1-12 were continuously heated in a 50°C forced-air oven for 30 hours. Figure 13-18 As can be seen, the fiber membrane showed no obvious damage, and there were no traces of phase change material leakage on the filter paper surface. The remaining mass after heating was all above 98%. The solid n-octadecane, which was not sealed in the core layer, completely liquefied after heating for less than 5 seconds.

[0088] Apply Example 4 to the surface of the garment, attach... Figure 19 Infrared thermal imaging showed that its temperature was lower than that of everyday clothing, demonstrating its practical value in summer outdoor activities.

[0089] Table 1;

[0090] Van der Waals interactions (kJ / mol) Coulomb interaction (kJ / mol) Total interaction energy (kJ / mol) DMF -4.03 -1.58 -5.61 acetone -1.55 -0.67 -2.22 chloroform -10.54 -0.08 -10.46

[0091] Table 2;

[0092] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Example 11 Example 12 Comparative Example 1 Reflectivity % 92.1 93.2 94.3 97.2 90.3 91.7 92.7 95.1 92.3 92.8 94.0 95.6 86.5

[0093] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A method for preparing a coaxial electrospun radiation phase change cooled fiber membrane, characterized in that: Includes the following steps: Step 1: Preparation of shell spinning solution: Add poly(vinylidene fluoride-co-hexafluoropropylene) to a mixed solvent of N,N-dimethylformamide and acetone, heat and stir at 45 to 60°C for 6 hours to obtain a homogeneous solution, and let the homogeneous solution stand at room temperature for 6 hours to eliminate bubbles and set aside. Step 2: Prepare the core spinning solution: Add n-octadecane to chloroform, stir for 30 minutes, and store at 35°C for later use; Step 3: Coaxial electrospinning: Using electrospinning equipment and 22G / 17G coaxial needles, the shell and core spinning solutions are transferred to syringes and fixed to the injection pump. The syringe containing the shell spinning solution is connected to the outer needle of the coaxial needle, and the syringe containing the core spinning solution is connected to the inner needle of the coaxial needle. Electrospinning was performed by adjusting the electrospinning parameters to obtain a coaxial electrospinned radiation phase change cooling fiber membrane with a pleated structure. The poly(vinylidene fluoride-co-hexafluoropropylene) has a weight-average molecular weight Mw of 455,000 and a number-average molecular weight Mn of 110,000. The electrospinning parameters include: temperature of 36±2℃, humidity of 45 to 50%, positive spinning voltage of 14.5±2kV, negative voltage of -3 to -1kV, receiving distance of 20cm, shell spinning solution propulsion speed of 0.2mm / min, and core spinning solution propulsion speed of 0.01-0.04mm / min. The mass ratio of N,N-dimethylformamide to acetone is 7:3, 5:5 or 3:7; The solid content of the resulting shell spinning solution was 20%. The type of the folded structure is achieved by adjusting the mass ratio of N,N-dimethylformamide and acetone: when the mass ratio of N,N-dimethylformamide to acetone is 7:3, honeycomb-like folds are formed. When the mass ratio of N,N-dimethylformamide to acetone is 5:5 or 3:7, parallel ridge valleys are formed. The height of the pleated structure and the surface roughness of the fiber membrane are achieved by adjusting the core layer propulsion speed: the lower the core layer propulsion speed, the flatter the fiber membrane surface and the smaller the pleat amplitude. The higher the core layer advance speed, the longer the fold wavelength and the greater the amplitude, and the clearer the fold texture.

2. The method for preparing a coaxial electrospun radiation phase change cooled fiber membrane according to claim 1, characterized in that: The electrospinning parameters are any combination of the following: The spinning positive voltage is 16kV, the negative voltage is -3kV, and the core layer advance speed is 0.01mm / min; The spinning positive voltage is 14.5kV, the negative voltage is -2kV, and the core layer advance speed is 0.02mm / min; The spinning positive voltage is 16.5kV, the negative voltage is -2kV, and the core layer advance speed is 0.03mm / min; The spinning positive voltage is 14.3kV, the negative voltage is -2kV, and the core layer advance speed is 0.04mm / min; The spinning positive voltage is 16kV, the negative voltage is -1.5kV, and the core layer advance speed is 0.01mm / min; The spinning positive voltage is 14kV, the negative voltage is -1.7kV, and the core layer advance speed is 0.02mm / min; The spinning positive voltage is 14kV, the negative voltage is -1.8kV, and the core layer advance speed is 0.03mm / min; The spinning positive voltage is 16.5kV, the negative voltage is -1.9kV, and the core layer advance speed is 0.04mm / min; The spinning positive voltage is 12.5kV, the negative voltage is -1.6kV, and the core layer advance speed is 0.01mm / min; The spinning positive voltage is 13.5kV, the negative voltage is -1.5kV, and the core layer advance speed is 0.02mm / min; The spinning positive voltage is 13.6kV, the negative voltage is -1.5kV, and the core layer advance speed is 0.03mm / min; The spinning positive voltage is 13.5kV, the negative voltage is -2.5kV, and the core layer advance speed is 0.04mm / min.

3. A coaxial electrospun radiation phase change cooling fiber membrane, comprising the method for preparing a coaxial electrospun radiation phase change cooling fiber membrane according to any one of claims 1-2, characterized in that: The fiber membrane has micro- and nano-scale fiber diameters and pore structures, and maintains high emission characteristics in the atmospheric window. During outdoor daytime testing, the average temperature drop is 7.6℃, the peak temperature difference can reach 12.4℃, the enthalpy value is 122J / g after 50 thermal cycles, and there is no n-octadecane leakage.

4. The coaxial electrospun radiation phase change cooling fiber membrane according to claim 3, characterized in that: The solar reflectivity of the fiber membrane is enhanced by multiple diffuse reflections and angle randomization of the pleated structure, and is higher than that of a fiber membrane with a smooth surface spun in a coreless spinning solution.

5. The coaxial electrospun radiation phase change cooling fiber membrane according to claim 4, characterized in that: The fiber membrane has a heat-insulating effect on the environment at night and has a phase change plateau characteristic for high-temperature buffering.

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