Janus fiber membrane with switchable thermal management function and method of making the same

Abstract

The application provides a Janus fiber membrane with switchable thermal management function and a preparation method thereof, the fiber membrane comprises a hydrophilic radiation cooling layer and a hydrophobic radiation heating layer, and the two layers are directly compounded by an electrospinning process to form a fiber membrane with structural integration and firm interface bonding; the radiation cooling layer is composed of hydrophilic cellulose acetate and aluminum oxide nanoparticles, aiming to realize high solar reflectivity and high mid-infrared emissivity, and the radiation heating layer is composed of hydrophobic cellulose acetate and coated with a Mxene coating, the material has excellent solar absorption and low mid-infrared emission characteristics, so as to realize thermal regulation in a double-band full-scene mode. The application solves the environmental adaptability problem caused by single-band regulation, realizes full-scene and double-band collaborative thermal management, solves the problem of separation of thermal management and moisture management functions, realizes collaborative regulation of heat and moisture, and improves comfort and cooling efficiency.

Description

Technical Field

[0001] This invention belongs to the field of functional textiles, and in particular relates to a Janus fiber membrane with switchable thermal management function and its preparation method. Background Technology

[0002] Traditional HVAC systems consume enormous amounts of energy, while wearable devices based on electric heating or liquid cooling suffer from problems such as reliance on external power sources, bulky size, and poor wearing comfort. Therefore, passive radiative thermal management technology, which requires no external energy input, has become a research hotspot. Its basic principle lies in controlling the spectral characteristics of textiles in the solar spectrum (0.25-2.5μm) and the mid-infrared atmospheric window (8-13μm): in "radiative cooling" mode, the fabric should have high solar reflectivity and high-mid-infrared emissivity to radiate human body heat to the cold outer space; in "radiative heating" mode, the fabric should have high solar absorptivity and low mid-infrared emissivity to absorb sunlight and suppress heat loss from the human body. To adapt to dynamically changing environments, ideal thermal management textiles need the ability to switch between these two modes as needed.

[0003] Currently, textiles achieving dual-mode switching with spectral control mainly follow three technical paths: temperature response, humidity response, and mechanical flipping. Temperature-responsive technologies (such as thermochromic materials) have limited control over the mid-infrared band; humidity-responsive technologies (such as structures based on humidity-sensitive fibers) lack effective control over the solar radiation band, and their performance is severely constrained by environmental humidity. In contrast, achieving mode switching through the physical flipping of Janus structure fabrics with different optical properties on both sides (i.e., mechanical flipping) is considered an intuitive and reliable strategy. However, existing mechanical flipping textiles have significant technical drawbacks: firstly, spectral control is incomplete, making true all-scenario applicability difficult. Existing technologies (including temperature-responsive, humidity-responsive, and most mechanical flipping technologies) often focus only on controlling a single band. Temperature-responsive technologies primarily alter the absorption / reflection of the solar radiation band, with weak control over the mid-infrared; humidity-responsive technologies primarily control mid-infrared emissivity, ineffective for the solar radiation band, thus limiting their application scenarios. Therefore, the lack of coordinated and independent optimization capabilities for both solar and mid-infrared wavelengths is a key bottleneck preventing current technologies from meeting the thermal management needs of all-weather, multi-environment (indoor / outdoor, sunny / cloudy) conditions. Secondly, the technology is functionally limited, neglecting the coordinated management of thermal comfort in actual wearable devices. Most existing research equates thermal management with simple spectral control, severely ignoring the crucial physiological factor of sweat production during actual activities. This leads to two problems: first, poor comfort, as the materials lack proactive sweat management capabilities, resulting in stuffiness, stickiness, and other discomfort due to sweat accumulation; second, suboptimal performance, failing to actively combine and synergistically enhance the efficient "evaporative cooling" heat dissipation pathway with "radiative cooling," thus wasting the potential to further improve cooling efficiency and comfort through natural mechanisms.

[0004] Therefore, the urgent technical problem to be solved in the existing technology is: how to develop a smart textile that can achieve efficient and reliable switching between solar / mid-infrared dual-band coordinated thermal management and integrate active sweat management functions, so as to provide users with an adaptive and highly comfortable thermal and humidity experience in complex and ever-changing environments. Summary of the Invention

[0005] In view of this, the present invention aims to propose a Janus fiber membrane with switchable thermal management function and its preparation method. This Janus fiber membrane is structurally designed through double-layer electrospinning, integrating dual-band thermal switching and unidirectional moisture-wicking functions. A simple mechanical flipping method is used as its stable and reliable mode switching mechanism. The radiative cooling layer is composed of hydrophilic cellulose acetate and alumina nanoparticles, designed to achieve high solar reflectivity and high-mid-infrared emissivity. The radiative heating layer is composed of hydrophobic cellulose acetate and coated with an Mxene coating. This material has excellent solar absorption and low-mid-infrared emissivity, thereby achieving dual-band, all-scenario thermal regulation. By controlling the thickness and wetting gradient of the two layers, a self-driven unidirectional moisture-wicking channel from the hydrophobic side to the hydrophilic side is established. When the fabric is in cooling mode, sweat can be pumped to the outside and evaporated, utilizing the latent heat of vaporization to enhance the cooling effect and improve the thermal and moisture comfort of the fabric. This invention solves the environmental adaptability problem caused by single-band control, and realizes thermal management with dual-band coordination in all scenarios; it also solves the problem of separation of thermal management and humidity management functions, and realizes coordinated thermal and humidity control to improve comfort and cooling efficiency.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows: A Janus fiber membrane with switchable thermal management function comprises a hydrophilic radiative cooling layer and a hydrophobic radiative heating layer. The two layers are directly composited via electrospinning to form a structurally integrated fiber membrane with a strong interfacial bond. The radiative cooling layer is formed by electrospinning hydrophilic cellulose acetate and alumina nanoparticles dispersed therein, with the alumina nanoparticles added at an amount of 1-7 wt% relative to the hydrophilic cellulose acetate. The radiative heating layer is formed by electrospinning hydrophobic cellulose acetate into a nanofiber substrate, upon which MXene is then sprayed to form an MXene coating. The MXene coating has a sprayed areal density of 0.2-1.1 mg / cm³. 2 .

[0007] Hydrophilic cellulose acetate forms the fiber backbone, and the inherent vibrations of its molecular bonds are the basis for achieving the high infrared emissivity of the lower radiation-cooling layer, as well as the hydrophilicity of the fiber membrane forming the lower radiation-cooling layer. Compared with other polymers, hydrophilic cellulose acetate is mainly derived from natural cellulose, giving it the advantages of being environmentally friendly and biodegradable.

[0008] Al2O3 nanoparticles are uniformly dispersed in hydrophilic cellulose acetate. Their main function is to improve the mid-infrared emissivity of the fiber membrane at around 13μm. At the same time, they can efficiently scatter and reflect sunlight, thereby reducing solar radiation absorption and achieving a significant daytime radiative cooling effect.

[0009] Furthermore, Al2O3 and the hydrophilic cellulose acetate matrix form a spectral complementarity effect based on different physical mechanisms, which is the key to achieving high emissivity across the entire atmospheric window (8-13μm).

[0010] Al₂O₃, as a polar ceramic material, emits infrared light through phonon resonances caused by lattice vibrations, exhibiting a broad, continuous emission spectrum. In contrast, hydrophilic cellulose acetate, as a polymer, emits infrared light through the characteristic vibrational absorption of functional groups such as CO and C=O in its molecular chain, resulting in a discrete, sharp-peaked emission spectrum. Combining these two materials allows the broad, continuous emission of Al₂O₃ to superimpose with the discrete, sharp-peaked emission of cellulose acetate. The former provides background emission, while the latter fills in gaps, thus achieving full-spectrum continuous coverage of the 8-13 μm atmospheric window. This spectral complementarity effect, based on a dual mechanism of "lattice phonons + molecular vibrations," is unattainable through other methods.

[0011] Hydrophobic cellulose acetate forms the fibrous framework of the upper radiant heating layer, and its hydrophobic properties are key to achieving unidirectional moisture wicking. Its low surface energy effectively prevents liquid water from spreading on the skin side, allowing it to be pumped away by the capillary force of the hydrophilic layer.

[0012] The MXene coating uniformly adheres MXene as a functional coating to the surface of the hydrophobic radiative heating layer. It exhibits excellent light absorption performance across the solar spectrum while maintaining low emissivity in the mid-infrared band. This combination of properties enables it to efficiently absorb solar radiation and convert it into heat energy, while suppressing heat loss due to its own thermal radiation, thereby enhancing its radiative heating efficiency.

[0013] Furthermore, based on the seemingly contradictory spectral selectivity requirements of "high solar absorption + low infrared emission" proposed in this invention for the heating layer, MXene is one of the very few intrinsic materials that can simultaneously meet both requirements: on the one hand, thanks to its localized surface plasmon resonance effect, MXene has excellent photothermal absorption capabilities within the solar spectrum; on the other hand, its intrinsic infrared emissivity can be as low as 14.5%, far lower than that of carbon materials. Moreover, MXene possesses excellent solution processability, allowing it to be uniformly loaded onto the surface of hydrophobic cellulose acetate through spraying. Its surface functional groups form hydrogen bonds with the hydrophobic cellulose acetate molecular chains, ensuring that the coating remains firmly attached after repeated mechanical tumbling and washing, without sacrificing the fabric's flexibility. Therefore, this invention chose MXene based on a comprehensive consideration of its unique spectral selectivity and process adaptability.

[0014] Preferably, the amount of alumina nanoparticles added relative to hydrophilic cellulose acetate is 3-5 wt%; more preferably, the amount of alumina nanoparticles added relative to hydrophilic cellulose acetate is 5 wt%.

[0015] Preferably, the sprayed surface density of the MXene coating is 0.8-1.1 mg / cm³. 2 More preferably, the sprayed surface density of the MXene coating is 0.8 mg / cm³. 2 .

[0016] Furthermore, the thickness of the radiative cooling layer is 260±10μm, and the thickness of the radiative heating layer is 100±10μm.

[0017] In cooling mode, the radiative cooling layer faces directly towards the sky, undertaking the dual tasks of "reflecting sunlight" and "emitting infrared radiation." It requires sufficient optical thickness to ensure multiple scattering of incident light between the fibers and Al2O3 particles, achieving a solar reflectivity of over 96%. Simultaneously, as a hydrophilic layer, it needs sufficient porosity to provide capillary action to pump sweat out and promote evaporation. In cooling mode, the radiative heating layer is located on the inner side and does not directly participate in radiative heat dissipation, thus allowing it to be made thinner. A thinner hydrophobic layer also facilitates the directional transport of sweat from the hydrophobic side to the hydrophilic side.

[0018] If the thickness of the radiant cooling layer or the radiant heating layer deviates from the specified range, it will affect the performance of the fiber membrane.

[0019] For the radiative cooling layer: If the thickness is less than 250μm (e.g., 200μm), when the radiative cooling layer faces the sky, the insufficient thickness results in a short optical path, reduced emissivity and solar reflectivity, and a significantly weakened cooling effect. Furthermore, the reduced pore volume leads to insufficient sweat storage capacity, making it prone to backflow when sweating is heavy, thus affecting wearing comfort.

[0020] If the thickness is greater than 270μm (e.g., 300μm): the solar reflectivity tends to saturate (increase by no more than 0.5%), but the overall thermal resistance of the fabric increases significantly, hindering heat conduction from the skin to the outside, thus weakening the radiative heat dissipation effect; at the same time, breathability decreases, and the feeling of stuffiness increases when wearing it; the increased material usage leads to higher costs.

[0021] For the radiant heating layer: If the thickness is less than 90μm (e.g., 50μm): the hydrophobic layer is too thin and is easily penetrated by sweat when used in reverse, which damages the hydrophobic barrier and causes the one-way moisture-wicking function to fail.

[0022] If the thickness is greater than 110μm (e.g., 150μm): an excessively thick hydrophobic layer will hinder the unidirectional transport of sweat from the hydrophobic side to the hydrophilic side, resulting in a weakening of the capillary pressure driving force and a decrease in directional moisture wicking performance.

[0023] Furthermore, the particle size of the alumina nanoparticles is 50±10 nm.

[0024] Furthermore, the pore size of the hydrophilic radiation cooling layer is smaller than that of the hydrophobic radiation heating layer. The fiber diameter of the radiation cooling layer is between 200-500 nm, while the fiber diameter of the radiation heating layer is between 500-800 nm.

[0025] Furthermore, in the preparation of the radiation cooling layer, 40 wt% of the hydrophilic agent TF-629B was added relative to the amount of hydrophilic cellulose acetate added.

[0026] The hydrophilic agent further enhances the hydrophilicity of the fiber surface, causing the lower radiative cooling layer to change from a hydrophilic to a superhydrophilic state, forming a strong hydrophilic-hydrophobic contrast with the upper radiative heating layer, providing the main driving force for the directional transport of water from the hydrophobic side to the hydrophilic side.

[0027] The present invention also provides a method for preparing a Janus fiber membrane with switchable thermal management function as described above, the method comprising the following steps: S1. Alumina nanoparticles are added to a mixed solvent of acetone and N,N-dimethylacetamide and ultrasonically dispersed. Hydrophilic cellulose acetate and hydrophilic agent TF-629B are then added to the resulting mixed solution and stirred until dissolved to form a stable spinning precursor solution A. S2. The obtained spinning precursor solution A is loaded into an electrospinning device for spinning to form a radiation cooling layer. S3. Dissolve hydrophobic cellulose acetate in a mixed solvent of acetone and N,N-dimethylacetamide, and stir until dissolved to form a stable spinning precursor solution B; S4. Electrospinning the spinning precursor solution B directly onto the already formed radiation cooling layer to form a radiation heating layer. S5. Mix the MXene dispersion with anhydrous ethanol, and then spray it evenly onto the surface of the radiant heating layer using a spray gun to form an MXene coating. S6. Vacuum dry the obtained Janus fiber membrane to completely remove residual solvent.

[0028] Furthermore, in S1, the volume ratio of acetone to N,N-dimethylacetamide is 1:1, and the mixture is ultrasonically dispersed for 30-60 min. The mass percentage of the added hydrophilic cellulose acetate is 20 wt%, and the mixture is stirred continuously at 40-60℃ and 400-600 rpm. In S2, the spinning parameters are: voltage 18kV, receiving distance 15cm, feed speed 0.8mL / h, and ambient humidity 30-50%.

[0029] The use of an 18kV spinning voltage on the hydrophilic side is based on the following comprehensive considerations: (1) For electrospinning of hydrophilic cellulose acetate system, good fiber formation effect can usually be obtained in the voltage range of 15-25kV. 18kV is in the middle of this range and is a conventional parameter that can be tried first when no special problems are encountered. Moreover, experimental verification has shown that the hydrophilic side fiber is uniform, smooth, and free of beading or breakage defects under this voltage, which directly proves the effectiveness of this parameter.

[0030] (2) Matching with solvent system and solution concentration: The hydrophilic spinning precursor solution contains hydrophilic cellulose acetate, Al2O3 particles and hydrophilic agent TF-629B. The solution concentration and viscosity are relatively high. The high viscosity solution requires a high voltage to overcome the surface tension and form a stable jet. Experiments have verified that 18kV can match the solution system well and ensure the stability of the spinning process.

[0031] Furthermore, in S3, the volume ratio of acetone to N,N-dimethylacetamide is 1:1, the mass percentage of added hydrophobic cellulose acetate is 10wt%, and the mixture is stirred at 40-60℃ and 400-600rpm. In S4, the spinning parameters are: voltage 15kV, receiving distance 15cm, feed speed 1mL / h, and ambient humidity 30-50%.

[0032] Furthermore, in S5, the concentration of the MXene dispersion is 5 mg / mL, and the volume ratio of the MXene dispersion to anhydrous ethanol is 1:1; it is sprayed on a hot plate at 60°C using a spray gun.

[0033] Furthermore, in S6, the vacuum drying temperature is 60°C.

[0034] Compared with existing technologies, the Janus fiber membrane with switchable thermal management function and its preparation method described in this invention have the following advantages: (1) The Janus fiber membrane with switchable thermal management function described in this invention achieves the synergistic enhancement of multiple functions such as radiative cooling, radiative heating and unidirectional moisture conduction by precisely controlling the key structural parameters of the fiber membrane, such as the thickness of each layer and the fiber diameter. The parameters do not act independently, but are interrelated and jointly determine the comprehensive performance of the fiber membrane.

[0035] (2) The total thickness and the thickness of each layer of the Janus fiber membrane with switchable thermal management function described in this invention are the core structural parameters affecting its thermal and humidity management performance. The thickness of the radiative cooling layer is 260±10μm, and the thickness of the radiative heating layer is 100±10μm. This specific thickness ratio is set based on the following synergistic mechanism: Optimization of unidirectional moisture wicking performance: In radiative cooling mode, the hydrophilic radiative cooling layer faces the external environment, while the hydrophobic radiative heating layer is close to the skin. In this mode, its high solar reflectivity and high infrared emissivity dominate, achieving cooling. Simultaneously, the thicker hydrophilic radiative cooling layer (260±10μm) provides ample porous network and water-holding capacity, forming a strong capillary action zone. This not only efficiently "pumps" sweat from the skin side but also prevents "backflow" caused by rapid saturation due to excessive absorption. Meanwhile, the thinner hydrophobic radiative heating layer (100±10μm), while maintaining its structural integrity and photothermal function, serves as the initial contact interface with the skin. Its limited thickness minimizes the diffusion resistance of sweat transport from the skin surface to the underlying hydrophilic interface, ensuring rapid initiation of sweat transfer. This "thick hydrophilic - thin hydrophobic" combination constructs an ideal moisture transport path from high drive (lower layer) to low resistance (upper layer), which is key to achieving efficient and stable unidirectional moisture wicking performance. Sweat produced by the skin is pumped from the hydrophobic skin side to the hydrophilic side by capillary force under unidirectional moisture wicking and evaporates. This evaporation process can further enhance cooling efficiency and achieve synergistic management of heat and humidity.

[0036] Support for Thermal Management Functions: This thickness configuration also supports switchable thermal management. In radiant heating mode, the MXene-functionalized hydrophobic radiant heating layer faces the external environment, while the hydrophilic radiant cooling layer is close to the skin. The high solar absorption and low mid-infrared emissivity of the MXene coating enable effective radiant heating. The outward-facing hydrophobic surface provides self-cleaning capabilities, preventing the adhesion of external water droplets or contaminants and helping to maintain surface cleanliness and long-term stability of heating performance. The sufficiently thick hydrophilic radiant cooling layer ensures adequate material volume to support the high solar reflectivity and high infrared emissivity required for radiant cooling. The relatively thin, functionalized radiant heating layer ensures that the MXene coating effectively absorbs sunlight and achieves a rapid thermal response, while avoiding excessive heat conduction to the skin or accumulation within the material due to excessive thickness, which could affect the efficiency of the heating mode and user comfort.

[0037] (3) This invention intelligently couples passive radiative heat management with active perspiration management by constructing a self-driven unidirectional moisture-wicking channel from the hydrophobic side to the hydrophilic side. In cooling mode, this function can quickly wick away skin sweat to the outer layer for evaporation. The resulting latent heat of vaporization cooling effect synergistically enhances the overall cooling efficiency with the radiative cooling effect. At the same time, active perspiration management ensures that the skin surface remains dry, fundamentally solving the problem of traditional thermal management textiles neglecting the comfort of dampness and heat, and achieving a balance between thermal and dampness comfort.

[0038] (4) This invention provides an active, reliable, and user-friendly thermal management control method. Compared to passively responsive materials that rely on environmental stimuli, this invention gives users complete control over the thermal management mode by simply flipping the device, allowing them to actively and instantly switch modes. This human-controlled switching mechanism is not only fast and reliable, but also eliminates the problem of traditional smart textiles "failing" due to fixed response thresholds or unsuitable environmental conditions, greatly improving the user experience and functional practicality.

[0039] (5) This invention demonstrates good scalability and application potential. Based on mature electrospinning and spraying processes, and using low-cost basic materials, this invention has good prospects for large-scale production. The obtained fiber membrane structure is flexible and can be adapted to various applications such as clothing and tents, providing a practical material solution for developing next-generation high-performance adaptive thermal management products. Attached Figure Description

[0040] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The solar emissivity of the hydrophilic side radiative cooling layer under different alumina nanoparticle addition amounts in Example 1 of the present invention; Figure 2 The mid-infrared reflectance of the hydrophilic side radiative cooling layer under different alumina nanoparticle addition amounts in Example 1 of the present invention. Figure 3 The solar emissivity of the hydrophobic side radiative heating layer under different MXene coating amounts in Example 2 of the present invention; Figure 4 The mid-infrared reflectivity of the hydrophobic side radiative heating layer under different MXene coating amounts in Embodiment 2 of the present invention; Figure 5 Diagram of outdoor testing equipment; Figure 6 Real-time temperature curve for product M3; Figure 7 The image captured by a high-speed camera as water droplets wet both sides of the fiber membrane; Figure 8 This is a comparison of the actual application effects of the sample and commercially available cotton fabrics. Figure 9 Electron micrographs of the radiation-heated layers obtained under different spinning voltages: (a) +10kV, sample B1; (b) +15kV, sample B2; (c) +20kV, sample B3. Figure 10 This is a diagram showing the fiber diameter distribution on the hydrophobic side. Figure 11 This is a diagram showing the diameter distribution of the hydrophilic fiber side. Detailed Implementation

[0041] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0042] In this document, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0043] In this document, when values ​​are described as ranges, it should be understood that such disclosure includes disclosure of all possible subranges within that range, as well as the specific numerical values ​​falling within that range, regardless of whether the specific numerical value or specific subrange is explicitly specified.

[0044] In this article, the terms "multiple" or "more than" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0045] In this document, the terms "preferred" and "more preferred" are used only to describe implementation methods or embodiments with better effects, and should be understood as not constituting a limitation on the scope of protection of this invention.

[0046] In this document, terms such as "further" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0047] In this article, the term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0048] In this document, the term "about" means + / - 10% of a specified value, preferably + / - 5%, and more preferably + / - 1%.

[0049] In this article, the terms “include,” “including,” “have,” “contain,” etc., are all open-ended terms, meaning that they include but are not limited to.

[0050] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0051] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0052] Unidirectional moisture conduction: a functional property of a fabric or film that allows liquid water or water vapor to be rapidly transferred primarily in a single direction (from one side to the other), while restricting or preventing reverse transfer. In this application, this function is achieved by constructing a continuous wettability gradient from a hydrophobic layer to a hydrophilic layer.

[0053] Radiation cooling: a passive cooling technology that works by using materials with high solar reflectivity (reflecting most of the sunlight in the 0.3-2.5µm band) and high atmospheric window infrared emissivity (efficiently radiating heat into the cold outer space in the 8-13µm band) to achieve a cooling effect below ambient temperature.

[0054] Radiation heating: a passive heating technology that works by using materials with high solar absorptivity (efficiently absorbing sunlight in the 0.3-2.5µm band) and low infrared emissivity (suppressing its own thermal radiation loss) to convert absorbed solar energy into heat energy, thereby achieving a heating effect higher than the ambient temperature.

[0055] Atmospheric windows refer to the low absorption rate of specific wavelengths of electromagnetic radiation (mainly infrared radiation) in the Earth's atmosphere, allowing this radiation to pass relatively freely through the atmosphere into outer space. In the field of passive radiative cooling, this specifically refers to the 8-13µm wavelength range, which is the main channel for surface objects to radiate heat into space.

[0056] The hydrophobic cellulose acetate was purchased from Maclean Company in China, and the hydrophilic cellulose acetate was purchased from Aladdin Company in China.

[0057] This invention proposes a Janus fiber membrane with switchable thermal management function, comprising a hydrophilic radiative cooling layer and a hydrophobic radiative heating layer. The two layers are directly composited through an electrospinning process to form a structurally integrated fiber membrane with a strong interfacial bond. The radiative cooling layer is made by electrospinning hydrophilic cellulose acetate and alumina nanoparticles dispersed therein, with the alumina nanoparticles added at an amount of 1-7 wt% relative to the hydrophilic cellulose acetate. The radiative heating layer is made by electrospinning hydrophobic cellulose acetate into a nanofiber substrate, and then spraying MXene onto the nanofiber substrate to form an MXene coating with a sprayed areal density of 0.2-1.1 mg / cm³. 2The thickness of the radiation-cooling layer is 260±10 μm, and the thickness of the radiation-heating layer is 100±10 μm. The particle size of the alumina nanoparticles is 50±10 nm. The pore size of the hydrophilic radiation-cooling layer is smaller than that of the hydrophobic radiation-heating layer. The fiber diameter of the radiation-cooling layer is between 200-500 nm, and the fiber diameter of the radiation-heating layer is between 500-800 nm. A hydrophilic agent, TF-629B, was also added at 40 wt% relative to the amount of hydrophilic cellulose acetate added during the preparation of the radiation-cooling layer.

[0058] Example 1: Study on different amounts of alumina nanoparticles added This embodiment aims to investigate the effect of different amounts of alumina (Al2O3) nanoparticles on the optical properties of fiber membranes and determine the optimal range of addition amounts.

[0059] Preparation method: S1. According to Table 1, alumina nanoparticles were added to a mixed solvent of 16g ​​acetone:N,N-dimethylacetamide DMAc (v:v) = 1:1 and ultrasonically dispersed for 1h. Then, 4g of hydrophilic cellulose acetate and 1.6g of hydrophilic agent TF-629B (40wt% relative to the mass of hydrophilic cellulose acetate) were added to the resulting mixed solution. The solution was stirred at 60℃ and 500rpm until dissolved, forming a stable spinning precursor solution A. The amount of hydrophilic cellulose acetate = hydrophilic cellulose acetate / (hydrophilic cellulose acetate + acetone + N,N-dimethylacetamide) = 20wt%.

[0060] S2. The obtained spinning precursor solution A is loaded into an electrospinning apparatus for spinning. Under the conditions of +18kV voltage, receiving distance 15cm, flow rate 0.8mL / h and ambient humidity 40%, electrospinning forms a radiation cooling layer with a thickness of about 260μm on the roller receiver.

[0061] S3. Weigh 1.0 g of hydrophobic cellulose acetate and dissolve it in a mixed solvent of 9 g acetone:DMAc (v:v) = 1:1. Stir magnetically at 60°C and 500 rpm until completely dissolved to form a stable spinning precursor solution B. The amount of hydrophobic cellulose acetate used = hydrophobic cellulose acetate / (hydrophobic cellulose acetate + acetone + N,N-dimethylacetamide) = 10 wt%.

[0062] S4. Without damaging the radiation cooling layer film, using the spinning precursor solution B, electrospinning is performed directly on the formed radiation cooling layer to form a radiation heating layer with a thickness of about 100 μm under the conditions of voltage +15 kV, receiving distance 15 cm, flow rate 1 mL / h and ambient humidity 40%.

[0063] S5. Mix a 5 mg / mL MXene dispersion with anhydrous ethanol at a 1:1 ratio, and then uniformly spray the mixture onto the surface of the radiant heating layer using a spray gun on a hot plate at 60°C to form an MXene coating. The surface density of the coating is 0.8 mg / cm³. 2 .

[0064] S6. Place the sprayed composite fiber membrane in a vacuum drying oven and dry it at 60°C for 2 hours to obtain the final product.

[0065] Table 1. Al2O3 addition amount in different groups

[0066] The solar reflectance (250-2500 nm) of the hydrophilic side radiative cooling layer of products A1-A4 was measured using a UV-Vis-NIR spectrophotometer, and the emissivity in the mid-infrared band was measured using a Fourier transform infrared spectrometer. The results are as follows: Figure 1 and Figure 2 As shown.

[0067] from Figures 1-2 It can be seen that as the amount of Al2O3 nanoparticles added increases, the mid-infrared emissivity at 13μm gradually increases. The emissivity in this band is not much different between 5wt% and 7wt% additions. The solar reflectivity increases with the amount of Al2O3 nanoparticles added, but the reflectivity is the lowest at 7wt%. Therefore, the effect is better when the amount of Al2O3 nanoparticles added is 3-5%, and the optimal addition amount is 5wt%.

[0068] Example 2: Study on the optimization of MXene spraying amount This embodiment aims to investigate the effect of different MXene coating amounts on the optical properties of fiber membranes and determine the optimal coating amount.

[0069] Preparation method: S1. Add 0.2g of alumina nanoparticles to a mixed solvent of 16g ​​acetone:N,N-dimethylacetamide DMAc (v:v)=1:1 and ultrasonically disperse for 1h. Then add 4g of hydrophilic cellulose acetate and 1.6g of hydrophilic agent TF-629B (40wt% relative to the mass of hydrophilic cellulose acetate) to the resulting mixed solution. Stir at 60℃ and 500rpm until dissolved to form a stable spinning precursor solution A.

[0070] S2. The obtained spinning precursor solution A is loaded into an electrospinning apparatus for spinning. Under the conditions of +18kV voltage, receiving distance 15cm, flow rate 0.8mL / h and ambient humidity 40%, electrospinning forms a radiation cooling layer with a thickness of about 260μm on the roller receiver.

[0071] S3. Weigh 1.0g of hydrophobic cellulose acetate and dissolve it in a mixed solvent of 9g acetone:DMAc (v:v)=1:1. Stir magnetically at 60℃ and 500rpm until completely dissolved to form a stable spinning precursor solution B.

[0072] S4. Without damaging the radiation cooling layer film, using the spinning precursor solution B, electrospinning is performed directly on the formed radiation cooling layer to form a radiation heating layer with a thickness of about 100 μm under the conditions of voltage +15 kV, receiving distance 15 cm, flow rate 1 mL / h and ambient humidity 40%.

[0073] S5. Add MXene (Ti3C2T) at a concentration of 5 mg / mL. x The dispersion was mixed with anhydrous ethanol at a ratio of 1:1 and then uniformly sprayed onto the surface of the radiant heating layer on a hot plate at 60°C using a spray gun to form an MXene coating. The surface density of the sprayed coating is shown in Table 2.

[0074] S6. Place the sprayed composite fiber membrane in a vacuum drying oven and dry it at 60°C for 2 hours to obtain the final product.

[0075] Table 2. Spraying surface density of different MXene coatings

[0076] The solar reflectance (250-2500 nm) of the hydrophobic side radiative heating layer of products M1-M4 was measured using a UV-Vis-NIR spectrophotometer, and the emissivity in the mid-infrared band was measured using a Fourier transform infrared spectrometer. The results are as follows: Figure 3 and Figure 4 As shown.

[0077] from Figure 3 It can be seen that as the coating density increases, the mid-infrared emissivity gradually decreases, until the coating amount reaches 0.8 mg / cm³. 2 The emissivity has reached its limit, and further increasing the coating density cannot reduce it any further. From Figure 4 It can be seen that in the ultraviolet-visible region (0.25-0.75 μm), the solar reflectivity gradually decreases with increasing coating density. Therefore, when the coating amount reaches 0.8 mg / cm³, the solar reflectivity decreases. 2 The solar reflectivity is relatively low, and the mid-infrared emissivity reaches its limit. Increasing the coating density does not significantly change the coating's appearance. Therefore, the coating density should be between 0.8 and 1.1 mg / cm³. 2 For better results, the optimal spraying amount is 0.8 mg / cm³. 2 .

[0078] 1. Heating and cooling mode tests Product M3 was used as a sample for performance testing. Figure 5 The apparatus shown was used to test the outdoor thermal management performance of samples. Different samples were used to simulate skin: bare skin without a sample, M3 sample heating mode, M3 sample cooling mode, black polyester, and white polyester. Thermocouples were attached to the simulated skin surface to record the temperature between the textile and the skin in real time. The test lasted for 4 hours. The interior of the testing device was filled with foam to achieve efficient passive insulation; the exterior of the device was wrapped with highly reflective aluminum foil to effectively reflect broadband solar radiation and reduce the temperature rise of the outer shell; the top window of the device was covered with a layer of polyethylene (PE) film, which, by utilizing its high transmittance to the infrared band and its ability to block air convection, effectively suppressed convective heat loss from the sample surface while allowing radiative cooling.

[0079] The cooling mode has the hydrophilic radiative cooling layer facing outwards, and the heating mode has the radiative heating layer facing outwards.

[0080] Test results are as follows Figure 6 As shown, the solar irradiance at noon is approximately 600 W / m². 2 (11:00-13:00), the ambient temperature was approximately 18.5℃. When the sample was in heating mode, the temperature of the simulated skin covered was approximately 14.2℃ higher than that of bare skin and approximately 11.5℃ higher than that of skin covered with black polyester. When the sample was in cooling mode, the temperature of the simulated skin covered was approximately 1.4℃ lower than that of bare skin and approximately 2℃ lower than that of skin covered with black polyester.

[0081] As can be seen, the Janus fiber membrane with switchable thermal management function prepared by the present invention can achieve heating and cooling by simple mechanical flipping.

[0082] 2. One-way moisture conduction performance test A high-speed camera was used to record images of water droplets wetting both sides of the fiber membrane. For example... Figure 7 As shown, when a water droplet (10 μL) comes into contact with the hydrophilic radiative cooling layer, the droplet collapses rapidly, resulting in a decrease in the contact angle, and the diffusion rate gradually decreases until it is completely absorbed. However, when a water droplet (10 μL) comes into contact with the hydrophobic radiative heating layer, it stays there for a long time and slowly seeps down until it is completely absorbed, confirming the wetting difference between the hydrophilic and hydrophobic sides.

[0083] The effectiveness in practical applications has also been verified, such as Figure 8 As shown, when the sample covers the skin, the simulated sweat can be effectively wicked away, keeping the skin dry. In contrast, commercially available cotton fabric, lacking this water-wicking ability, leaves a large amount of simulated sweat on the skin, reducing wearing comfort.

[0084] In summary, this demonstrates that the Janus fiber membrane can achieve active heating by flipping to select the high-absorption surface, or radiative cooling by selecting the high-reflectivity, high-emissivity surface; the low-infrared-emissivity surface can effectively suppress heat loss from the human body to maintain warmth, while the high-emissivity surface can promote heat dissipation. This broad adaptability to environmental conditions and the ability to independently optimize both bands achieve true all-weather personal thermal comfort.

[0085] Comparative Example 1 This comparative example aims to investigate the effect of different spinning voltages on the diameter of the hydrophobic fiber, in order to determine the optimal spinning voltage that can ensure smooth fiber formation on the hydrophobic side and create a diameter difference with the hydrophilic side, thereby ensuring unidirectional moisture-wicking function.

[0086] 1. Preparation method Steps S1-S3 are the same as in Example 2.

[0087] S4. Without damaging the radiation cooling layer, using the spinning precursor solution B, and setting the spinning voltage to +10kV, +15kV, and +20kV (corresponding to samples B1, B2, and B3), electrospinning is performed directly on the formed radiation cooling layer under the conditions of a receiving distance of 15cm, a flow rate of 1mL / h, and an ambient humidity of 40%, to form a radiation heating layer with a thickness of approximately 100μm.

[0088] S5. Mix MXene dispersion with anhydrous ethanol at a volume ratio of 1:1, and spray the mixture evenly onto the surface of the radiant heating layer using a spray gun on a 60°C hot plate. The spray density is 0.8 mg / cm³. 2 This forms an MXene coating.

[0089] S6. Place the sprayed composite fiber membrane in a vacuum drying oven and dry it at 60°C for 2 hours to obtain the final product.

[0090] 2. Results and Analysis The fiber morphology of samples B1, B2, and B3 was observed using scanning electron microscopy, and the diameter distribution of the hydrophobic fibers was statistically analyzed. The results are as follows: Figure 9 As shown.

[0091] When the spinning voltage is 10kV (sample B1), the electric field force is insufficient to effectively stretch the spinning jet, resulting in a noticeable beaded structure on the fiber membrane surface and poor fiber forming quality. Figure 9 (a)

[0092] When the spinning voltage is increased to 15kV (sample B2), the electric field force is moderate, the spinning jet is fully stretched, the fiber diameter is uniform and the surface is smooth, no beading defects are generated, and the forming quality is optimal. Figure 9 (b)

[0093] When the spinning voltage was further increased to 20kV (sample B3), the electric field was too strong, the jet stretching rate was too high, and the polymer chains in the solution were not sufficiently entangled, making it impossible to maintain stability under high-speed stretching. This resulted in uneven fiber thickness, flattening, and breakage. Figure 9 (c)

[0094] Based on the above results, 15kV was determined to be the optimal spinning voltage for the hydrophobic side. Furthermore, this invention employs a spinning voltage of 18kV on the hydrophilic side. The difference in fiber diameter resulting from the voltage difference between the hydrophilic and hydrophobic sides achieves unidirectional moisture-wicking functionality.

[0095] At this voltage, the diameter distribution of the hydrophobic fiber is as follows: Figure 10 As shown (500-800nm), the diameter distribution of the hydrophilic side fibers is as follows. Figure 11 As shown (200-500nm). There is a significant difference in fiber diameter on both sides. This asymmetric fiber structure helps to form a capillary force gradient, thereby ensuring that the fiber membrane has unidirectional moisture-wicking function.

[0096] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A Janus fiber membrane with switchable thermal management function, characterized in that: The membrane comprises a hydrophilic radiative cooling layer and a hydrophobic radiative heating layer, which are directly composited through electrospinning to form a structurally integrated fiber membrane with a strong interfacial bond. The radiative cooling layer is made by electrospinning hydrophilic cellulose acetate and alumina nanoparticles dispersed therein, with the alumina nanoparticles added at a ratio of 3-5 wt% to the hydrophilic cellulose acetate. The radiative heating layer is made by electrospinning hydrophobic cellulose acetate into a nanofiber substrate, and then spraying MXene onto the nanofiber substrate to form an MXene coating with a sprayed areal density of 0.8-1.1 mg / cm³. 2 ; The thickness of the radiation cooling layer is 260±10μm, and the thickness of the radiation heating layer is 100±10μm. The pore size of the hydrophilic radiation cooling layer is smaller than that of the hydrophobic radiation heating layer. The fiber diameter of the radiation cooling layer is between 200-500nm, and the fiber diameter of the radiation heating layer is between 500-800nm.

2. The Janus fiber membrane with switchable thermal management function according to claim 1, characterized in that: The particle size of the alumina nanoparticles is 50±10 nm.

3. The Janus fiber membrane with switchable thermal management function according to claim 1, characterized in that: In addition to the addition of 40 wt% of hydrophilic agent TF-629B relative to the amount of hydrophilic cellulose acetate, the radiation cooling layer was also prepared.

4. A method for preparing a Janus fiber membrane with switchable thermal management function as described in any one of claims 1-3, characterized in that: The method includes the following steps: S1. Alumina nanoparticles are added to a mixed solvent of acetone and N,N-dimethylacetamide and ultrasonically dispersed. Hydrophilic cellulose acetate and hydrophilic agent TF-629B are then added to the resulting mixed solution and stirred until dissolved to form a stable spinning precursor solution A. S2. The obtained spinning precursor solution A is loaded into an electrospinning device for spinning to form a radiation cooling layer. S3. Dissolve hydrophobic cellulose acetate in a mixed solvent of acetone and N,N-dimethylacetamide, and stir until dissolved to form a stable spinning precursor solution B; S4. Electrospinning the spinning precursor solution B directly onto the already formed radiation cooling layer to form a radiation heating layer. S5. Mix the MXene dispersion with anhydrous ethanol, and then spray it evenly onto the surface of the radiant heating layer to form an MXene coating. S6. Vacuum dry the obtained Janus fiber membrane to completely remove residual solvent.

5. The method for preparing a Janus fiber membrane with switchable thermal management function according to claim 4, characterized in that: In S1, the volume ratio of acetone to N,N-dimethylacetamide is 1:1, and the mixture is ultrasonically dispersed for 30-60 min. The mass percentage of hydrophilic cellulose acetate added is 20 wt%, and the mixture is stirred continuously at 40-60℃ and 400-600 rpm. In S2, the spinning parameters are: voltage 18kV, receiving distance 15cm, feed speed 0.8mL / h, and ambient humidity 30-50%.

6. The method for preparing a Janus fiber membrane with switchable thermal management function according to claim 4, characterized in that: In S3, the volume ratio of acetone to N,N-dimethylacetamide is 1:1, the mass percentage of hydrophobic cellulose acetate added is 10wt%, and the mixture is stirred at 40-60℃ and 400-600rpm. In S4, the spinning parameters are: voltage 15kV, receiving distance 15cm, feed speed 1mL / h, and ambient humidity 30-50%.

7. The method for preparing a Janus fiber membrane with switchable thermal management function according to claim 4, characterized in that: In S5, the concentration of MXene dispersion is 5 mg / mL, and the volume ratio of MXene dispersion to anhydrous ethanol is 1:1; it is sprayed on a hot plate at 60°C using a spray gun.

8. The method for preparing a Janus fiber membrane with switchable thermal management function according to claim 4, characterized in that: In S6, the vacuum drying temperature is 60℃.

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