Biomimetic all-weather dual-mode cooling film for passive heat dissipation

Biomimetic all-weather dual-mode cooling film for passive heat dissipation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Biomimetic all-weather dual-mode cooling film for passive heat dissipation Zhen Li, Jinqiu Yang, Xiangdong Zeng, Zhengfeng Xiong, Jingjia Li, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7497849/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract Passive radiative cooling technology offers a zero-carbon comfort solution for maintaining comfortable ambient temperatures. However, single-mode passive radiative cooling is significantly weakened by the shielding effect of high-humidity environments. Inspired by the thermoregulatory mechanisms of plant leaves, we designed a dendritic structure amino-functionalized cellulose (ACE) for passive heat dissipation. ACE provides abundant amino groups and Schiff base sites, which not only enhance interactions with water molecules through hydrogen bonding but also facilitate solar radiation absorption via the stretching vibrations of the imine bonds (-C = N-). Leveraging these properties, an ACE@PVA dual-mode cooling film was fabricated using self-assembly technology. Despite its ultrathin profile (80 µm), the film achieves a hygroscopic capacity exceeding 3.32 ± 0.36 g/g and a solar reflectivity of 43.6 ± 2.1%. Under outdoor conditions, the film demonstrated excellent passive cooling performance, achieving subambient cooling of 4.7°C to 13.7°C during daytime and 4.3°C at night. This ultrathin, dual-mode cooling film is well suited for dynamic seasonal and weather variations, offering significant potential for mitigating the energy crisis and reducing greenhouse gas emissions. Evaporation refrigeration Radiation refrigeration Moisture and thermal management Functionalized-cellulose Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction As global warming worsens, the demand for cooling continues to rise (Wang et al. 2025 ; Liang et al. 2023 ; Dong et al. 2023 ). Although conventional vapor- compression refrigeration systems offer significant cooling efficiency, they consume approximately 17% of global electricity and emit substantial greenhouse gases, further exacerbating environmental pressures (Falchetta et al. 2024 ; Ahn et al. 2018 ). Consequently, developing eco-friendly, sustainable refrigeration technologies powered by renewable energy has attracted widespread attention (Gao & Chen 2023 ; Cui et al. 2024 ). Passive radiative cooling (PRC) is a promising alternative that dissipates heat to outer space (~ 3 K) through the atmospheric transparency window (8–13 µm), theoretically enabling peak cooling powers exceeding 160 W/m² (Raman et al. 2014 ). To advance PRC toward practical applications, research efforts focus on two key strategies: optimizing material formats (e.g., films (Meng et al. 2024 ), coatings (Han et al. 2024 ), textiles (Pan et al. 2022), aerogels (Chen et al. 2024 )) and refining nano/microstructural designs (e.g., multilayer stacks (Pan et al. 2025 ), metamaterials (Cai et al. 2024 ), porous structures (Huang et al. 2023 ), randomized particle distributions(Xue et al. 2020 )). As a representative example under this research strategy, the dual-mode film material reported by Shi et al ( 2023 ) achieves solar reflectivity and infrared emissivity of 96.7% and 96.1%, respectively, enabling daytime sub-ambient cooling of 9.8°C with a theoretical cooling power of 107.5 W/m². However, PRC is frequently constrained by environmental conditions. For instance, when relative humidity (RH) ≥ 60%, PRC performance drops sharply as water vapor absorption in the critical infrared band exceeds 85%, reducing cooling efficiency by over 70% (Wang et al. 2021 ). Worse still, annual average RH levels are high across much of the globe, significantly limiting the broad applicability of PRC technology (Li et al. 2025 ). To address these limitations, Ye et al. developed an adhesive hydrogel coating employing radiative-coupled evaporative cooling (REC) (Ye et al. 2025 ). Applied to a 3D W-shaped substrate, this system exhibited exceptional passive cooling performance, reducing temperatures by 11.4°C below ambient under 400 W/m² solar irradiance. By combining material design (hBN-epoxy-LiCl composite) and structural innovation (3D W-shaped substrate), the coating delivers an efficient, sustainable passive cooling solution for outdoor equipment in high-temperature environments, through simultaneous and synergistic cooling via radiation, evaporation, and convection. Nevertheless, PRC still struggles to adapt to dynamic seasonal and weather variations. Herein, dendritic structure of amino-functionalized cellulose (ACE) was designed and synthesized as a functional unit for a dual-mode cooling film. Inspired by the thermoregulatory mechanisms of plant leaves, an ACE@PVA dual-mode cooling film was fabricated via self-assembly technology (Fig. 1 a). Because ACE provides abundant amino groups and Schiff-base alkaline sites, it not only enhances hydrogen bonding with water molecules, imparting excellent moisture absorption, but also absorbs solar radiation through the imine bond (-C = N-) stretching vibration. Leveraging these properties, the ACE@PVA film serves as a dual-mode cooling system combining radiative and evaporative cooling (Fig. 1 b). It achieves water capture capacity exceeding 3.32 ± 0.36 g/g from ambient air and a solar reflectivity of 43.6 ± 2.1%, despite its ultrathin profile (80 µm). Under outdoor conditions, the film demonstrated excellent passive heat dissipation, achieving daytime sub-ambient cooling of 4.7 to 13.7°C and nighttime cooling of 4.3°C below ambient. This work establishes a feasible strategy for synergistic all-weather passive cooling. Results and discussion After PEI-modifiled, white cellulose powder (Fig. S1 a) change to yellow ACE powder (Fig. 2 a), mainly due to introduced amino group are prone to form chromophores, leading to yellowing (Li et al. 2024 ). On the other hand, it also enhance interactions with water molecules through hydrogen bonding, demonstrating water-soluble properties (Fig. 2 b). At the microstructural level, dramatic difference with cellulose(Fig. S1 b), ACE shows dendritic structure (Fig. 2 c), which will enhances water delivery efficiency like capillary action. FT-IR spectrum validated the reaction of PEI-modified cellulose as shown in Fig. 2 d. Three new peaks at 1656, 1579 and 1430 cm − 1 , corresponding to N-H bend vibrations, C = N and C-N stretch vibrations, respectively, indicate that PEI was successfully grafted onto cellulose (Ma et al. 2024 ). Moreover, the characteristic peak at 3349 cm − 1 in cellulose offset to 3417 cm − 1 in the ACE, which is associated with the overlap of O-H and N-H stretch vibrations (Collom et al. 2024 ). Figure 2 e shows the diagrammatic sketch of Molecular structure before and after PEI-modifiled cellulose. For controlled hygroscopicity evaluation, a series of identically sized PVA films and ACE@PVA films with varying ACE content were prepared. The experimental setup (Fig. 3 a) employed two identical electronic balances to continuously monitor mass changes during humidity exposure. Ambient humidity was precisely controlled using a humidifier (Fig. 3 b). Results demonstrate that the hygroscopic capacity of the ACE@PVA films increases with ACE content. This enhancement stems from the amino groups (-NH₂) on ACE, which strengthen interactions with water molecules via hydrogen bonding. Specifically, the lone electron pair on the nitrogen atom facilitates hydrogen bond formation with water, significantly improving moisture absorption (Kim et al. 2021 ). At 6 wt% ACE content, the film achieves a maximum hygroscopic capacity of 3.32 g/g—representing a 249% increase over pure PVA film. However, ACE content exceeding 6 wt% leads to over-saturation, likely causing ACE aggregation, crystallization, and structural defects that markedly diminish moisture absorption performance. Furthermore, increasing film thickness from 0.08 mm to 0.21 mm reduced water uptake by 38.5% (Fig. 3 c). This decline is attributed to densified internal film structure impeding water molecule diffusion. Consequently, the ACE@PVA film with 6 wt% ACE content and 0.08 mm thickness was identified as optimal. The hygroscopic performance of this optimal film was then evaluated under controlled RH levels ranging from 45% to 90% (Fig. 3 d). Results confirm effective moisture capture across this broad humidity range, indicating potential for evaporative cooling in diverse, dynamic atmospheric conditions. This functionality arises from the amino-functionalized groups on the cellulose molecular chain acting as molecular-level water capture sites through hydrogen bonding (Fig. 3 e). For verification photothermal synergy and cooling performance, using UV-vis-NIR spectrophotometer to measure the reflectivity and transmittance of ACE@PVA films in the solar spectrum. With ACE content increase, the ACE@PVA films exhibit significant shielding effects against ultraviolet (Fig. 4 a), visible light (Fig. 4 b), and infrared radiation (Fig. 4 c). It’s due to the schiff alkali absorbs UV through its subamine bond (-C = N-) in its conjugated skeleton, converting light energy into thermal (Xue et al. 2024 ). And, ACE aggregation and crystallization make the chromophores formed leads to a decrease in light transmittance (Xu et al. 2021 ). In addition, N-H bend vibrations, C = N and C-N stretch vibrations absorbed infrared radiation energy, which is consistent with the results of FT-IR spectroscopy. It is noteworthy that the ACE@PVA film has a thickness of merely 80 µm has a total solar energy blocking rate of 43.5% (Fig. 4 d). In summary, ACE@PVA film integrates both radiative and evaporative cooling functionalities, has a huge potential in the fields of automotive glass, building coatings, humidity-permeable cooling clothing, etc. To verify the heat dissipation performance of the film under real-world conditions, an outdoor experiment was conducted (Fig. 5 a at daytime and Fig. 5 d at nighttime). Four PT-100 thermocouple monitors and humidity detection probe be used to record real-time temperature changes for both indoor and outdoor environments (Fig. S2). Besides the designed ACE@PVA film, a pure PVA film served as a reference to isolate the effects of thermal convection. During daytime testing, the ACE@PVA film exhibited an average temperature of 37.5°C, representing reductions of 2.6°C and 13.7°C relative to the PVA reference and ambient surface temperature, respectively (Fig. 5 b). It can be found that evaporation cooling played a major role compared with radiative cooling for heat dissipation, due to the condition of initial moisture absorption saturation. Under prolonged solar exposure, the ACE@PVA sample averaged 46.5°C, maintaining temperature reductions of 1.2°C and 4.7°C compared to the PVA film and ambient surface (Fig. 5 c). In this high-irradiance regime, radiative cooling dominated due to near-complete evaporation of environmental moisture. In the night time, the average temperature of the ACE@PVA sample was 31°C, corresponding to reductions of 1.2°C and 4.3°C versus the PVA film and ambient surface(Fig. 5 e). This behavior is explained by increasing nocturnal humidity and diminished solar radiation, which enhanced moisture capture and reactivated evaporation cooling. Throughout testing, ACE@PVA consistently maintained lower temperatures than both controls. (Fig. 5 f). Crucially, the ACE component facilitated atmospheric moisture capture via ACE-water interactions, ensuring sustained evaporative cooling during daytime operation. These results demonstrate that ACE@PVA enables all-weather passive cooling through synergistic evaporation and radiative mechanisms. Unlike conventional radiative materials, ACE@PVA dynamically shifts its dominant cooling mode in response to environmental conditions—akin to plant thermoregulation. Specifically, radiative cooling prevails under high solar irradiance and low humidity, while evaporation cooling dominates under low irradiance and high humidity (Fig. 6 ). This all-weather passive heat dissipation by coupling radiative cooling with evaporation cooling, avoiding the heat dissipation performance drops sharply of conventional radiative materials at high humidity environment. Conclusion Inspired by the thermoregulatory mechanisms of plant leaves, we engineered a dendritic amino-functionalized cellulose (ACE) structure for passive heat dissipation. ACE exhibited exceptional hygroscopicity and solar energy dissipation capabilities, owing to its abundant amino groups and schiff base sites. These functional groups not only enhance water molecule interactions through hydrogen bonding but also facilitate solar radiation absorption via the stretching vibrations of imine bonds (-C = N-). Leveraging these properties, we integrated ACE into PVA through self-assembly to form an ultrathin ACE@PVA film that synergistically combines radiative and evaporative cooling functionalities. Unlike conventional radiative cooling materials, ACE@PVA achieves all-weather passive cooling through dynamic coupling of radiative and evaporative mechanisms. This work provides a facile, eco-friendly, and sustainable biomimetic strategy for advanced outdoor thermal management applications. Experimental section Materials: Microcrystalline cellulose (Mw = 20,000) with an average size of 25 µm and density of 0.600 g/cm 3 was bought from Arkema Investment Co. Ltd. NaOH, urea and absolute ethyl alcohol was obtained from Shanghai Macklin Biochemical Co., Ltd. ANPEL laboratory technologies (shanghai) Inc provided hydrochloric acid solution (HCl). Sodium periodate and polyethyleneimine (PEI, Mw = 600, 99%) was purchased from Aladdin Co., Ltd. All other chemicals were used as received without further purification. Preparation of amino-functionalized cellulose: ACE was prepared via the PEI modified cellulose. Briefly, Microcrystalline cellulose was dissolved in Alkaline urea solution (1.75 M NaOH and 2 M urea mixed solution) in a glass beaker, followed by stirring for 30 min. Subsequently, 1 M HCl was dissolved in 200 mL Cellulose solution to react for 12 h at 25°C under stirring;2 g of Sodium periodate powder was slowly added to the above solution react for 3 h at 60°C under stirring༛In succession, 2 g of PEI add the reaction solution drop by drop into the flask, react for 3 h at 60°C under stirring, the ACE sediment was was repeatedly washed and centrifuged at 3500 rpm until pH = 7, and then collected after 5 min of centrifugation at 3500 rpm. Preparation of ACE@PVA film: ACE powder and PVA were added into a flask and stirred at 80°C for 2 h to form a ACE@PVA solution with a solute weight percentage of 0%, 2%, 3%, 4%, 5%, and 6%, and was denoted as ACE(0%), ACE(2%), ACE(3%), ACE(4%), ACE(5%), and ACE(6%), respectively. Pour the above solution into Petri dishes in separate amounts of 5g, 10g, and 15g respectively. A series of ACE@PVA films with different thicknesses and ACE contents can be obtained by using the casting method. Structural characterization: The microstructure of ACE was photographed using a Zeiss EVO-10 scanning electron microscope (5kV) and scanned electron microscope (SEM) images. Chemical Crosslinking Reaction: The reaction of PEI-modified cellulose was demonstrated using Fourier Transform Infrared Spectroscopy (FTIR, Nicolet 5700, Thermo, USA). Moisture Absorption Test: The water content can be obtained by: water wt.(%) = (W t -W 0 )/W t ×100%, where W t is the saturated water content mass, W 0 is the current water content mass. Spectral Reflectance Testing: UV-vis-NIR reflectivity (ρ) and transmissivity (τ) were measured using a UV-vis-NIR spectrometer (Lambda 1050+, PerkinELmer) accompanied by an integrating sphere attachment, and UV-vis-NIR absorptivity (α) was calculated using equation α = 1 − ρ − τ. Thermal Protection Test: The sample temperature was measured using a Temperature Cruiser (GK4500, GuoKe). Cooling performance characterization: Water Capture Tests: The sample was placed within a constant temperature and humidity chamber (HWS-80B) to control Temperature and Humidity. The mass change of the sample was measured by an electronic balance at each period. After each experiment, the sample's mass was restored to its initial value before the next experiment. Indoor experiments were conducted in a laboratory. Heat dissipation tests: Two 15×10 cm 2 cavity was dug out on top side of 20×20×15 cm 3 house model, which covered with ACE@PVA film. Identically, Prepare another house model of the same size, which covered with PVA film as control group. A PT-100 type thermocouple fixed on the inner of house model to detect real-time temperature fluctuations. The edge of the sample was sealed with an adhesive tape to ensure the tightness of the sample on the cavity. Additionally, outdoor temperature and humidity was recorded using a digital hygrometer-thermometer (M6052B, PEAKMETER). All the heat dissipation tests were performed outdoors at Zhejiang University of Water Resources and Electric Power, Hangzhou city, China (east longitude: 119°45′; northern latitude: 34°15′). Declarations Acknowledgements Special thanks to Prof. Xiuping Su from key laboratory of functional fibers and intelligent textiles. The authors would like to thank Mrs Zhuchang Qiao for the linguistic revision. We are furthermore grateful to Mr. Frank from for his constructive advice on the evaluation of the human thermal management. Funding declaration This work was financially supported by the Nanxu Scholars Program for Young Scholars of ZJWEU (RC2023021208); Technology Planning Project of Shaoxing (2024A13003), and Scientific research foundation of Zhejiang University of Water Resources and Electric Power (JBGS2025013). Authors contributions Corresponding author: Zhen Li Zhen Li: Writing-original draft, Conceptualization, Project Funding acquisition. Jinqiu Yang: Methodology. Xiangdong Zeng: Investigation. Zhengfeng Xiong: Soft ware. Jingjia Li:Investigation. Xiuping Su: Formal analysis. Yadng Li: Figures. Feng Liu: Investigation. All authors reviewed the manuscript. Data availability The data that support the findings of this study are available from the corresponding author upon reasonable request. Competing interests The authors declare no competing interests. Consent for publication The authors agreed to publish this article. References Ahn H, Rim DH, Freihaut JD (2018) Performance assessment of hybrid chiller systems for combined cooling, heating and power production. APPL ENERG 1(1):501–512. Cai CY, Wu XD, Cheng FL, Ding CX, Wei ZC, Wang X, Fu Y (2024) Cellulose metamaterials with hetero-profiled topology via structure rearrangement during ball milling for daytime radiative cooling. ADV FUNCT MATER 34:2405903. 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Supplementary Files SupportingInformation.docx Supporting information The optical photograph and microstructural of cellulose powder. (Figure S1) The distribution of the corresponding temperature detection probe and humidity detection probe in house model for testing the heat dissipation performance. (Figure S2) Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 03 Oct, 2025 Editor assigned by journal 03 Oct, 2025 Submission checks completed at journal 13 Sep, 2025 First submitted to journal 30 Aug, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7497849","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":524468400,"identity":"7c64c990-d1d0-4382-a0ea-731943a70e73","order_by":0,"name":"Zhen Li","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA00lEQVRIiWNgGAWjYBACPmYGNiBVw2Pf3nzgwIcfRGhhg2g5JmfAcyzx4MweYrSAEQOzsYFEjvFhDjZitLCzP3vwcQdb4naeMx8OM/AwyPOLHSDosHTDmWdkEne29244XGDBYDhzdgJBLcekedvYEhvOnN1weAYPQ4LBbYJaGNuk/7YxJzbcyHlwmIeNKC3MbNKMbUDv38hhIFYLG5tkb9sxOcmeYwbAQJYg7Bd+/uPPJH621fDwszc//vDhh408vzQBLehAgjTlo2AUjIJRMAqwAwD6LkFk09HPbwAAAABJRU5ErkJggg==","orcid":"","institution":"Zhejiang University of Water Resources and Electric Power","correspondingAuthor":true,"prefix":"","firstName":"Zhen","middleName":"","lastName":"Li","suffix":""},{"id":524468401,"identity":"2a20f848-5f14-4f80-8e39-09cc69a7a15d","order_by":1,"name":"Jinqiu Yang","email":"","orcid":"","institution":"Zhejiang University of Water Resources and Electric Power","correspondingAuthor":false,"prefix":"","firstName":"Jinqiu","middleName":"","lastName":"Yang","suffix":""},{"id":524468402,"identity":"d60b19bf-ead8-4766-9c1f-9a67c82723de","order_by":2,"name":"Xiangdong Zeng","email":"","orcid":"","institution":"Zhejiang University of Water Resources and Electric Power","correspondingAuthor":false,"prefix":"","firstName":"Xiangdong","middleName":"","lastName":"Zeng","suffix":""},{"id":524468403,"identity":"5c6ecefa-0299-475c-892c-11592a262f35","order_by":3,"name":"Zhengfeng Xiong","email":"","orcid":"","institution":"Zhejiang University of Water Resources and Electric Power","correspondingAuthor":false,"prefix":"","firstName":"Zhengfeng","middleName":"","lastName":"Xiong","suffix":""},{"id":524468404,"identity":"6b48b543-3712-4dff-9eed-e5882a12040c","order_by":4,"name":"Jingjia Li","email":"","orcid":"","institution":"Zhejiang University of Water Resources and Electric Power","correspondingAuthor":false,"prefix":"","firstName":"Jingjia","middleName":"","lastName":"Li","suffix":""},{"id":524468405,"identity":"dbc300d6-58cd-4435-8f98-f9aac703e584","order_by":5,"name":"Xiuping Su","email":"","orcid":"","institution":"Shaoxing University","correspondingAuthor":false,"prefix":"","firstName":"Xiuping","middleName":"","lastName":"Su","suffix":""},{"id":524468406,"identity":"a1d3cb7c-5f26-4193-b095-75f25c8fa680","order_by":6,"name":"Yadong Li","email":"","orcid":"","institution":"Zhejiang University of Water Resources and Electric Power","correspondingAuthor":false,"prefix":"","firstName":"Yadong","middleName":"","lastName":"Li","suffix":""},{"id":524468407,"identity":"a7ec1125-3066-4cbb-ae98-056325b25165","order_by":7,"name":"Feng Liu","email":"","orcid":"","institution":"Zhejiang University of Water Resources and Electric Power","correspondingAuthor":false,"prefix":"","firstName":"Feng","middleName":"","lastName":"Liu","suffix":""}],"badges":[],"createdAt":"2025-08-31 01:53:05","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7497849/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7497849/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":95222185,"identity":"39a2ab04-43b9-49f0-937f-e19a9e68a81f","added_by":"auto","created_at":"2025-11-05 16:20:15","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":286399,"visible":true,"origin":"","legend":"\u003cp\u003e(a) ACE@PVA flowchart of preparation of the membrane; (b) ACE@PVA diagram of membrane regulation mechanism of ambient temperature.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-7497849/v1/f18486e73d74c235d6d72c3e.png"},{"id":95050836,"identity":"474f32fa-ae46-47dd-8ea2-b0443795d87c","added_by":"auto","created_at":"2025-11-03 18:21:14","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1129045,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Photograph of ACE powder; (b) photographs of water-soluble ACE; (c) scanning electroscopes image of ACE; (d) FT-IR diagram of CE and ACE; (e) Diagrammatic sketch of molecular structure before and after amino-functionalized cellulose.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-7497849/v1/d88561284cdd1a2cd75cbecb.png"},{"id":95222349,"identity":"889623f7-a42e-4d78-bb48-58c97e41fd64","added_by":"auto","created_at":"2025-11-05 16:20:31","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":237693,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Diagram of an experimental device for hygroscopicity test; The time-moisture absorption curve of ACE@PVA film: Different ACE content (b); Different humidity conditions (c); Different thickness (d); (e) ACE@PVA film moisture absorption mechanism diagram.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-7497849/v1/a9070031af1a1923a2949bff.png"},{"id":95050838,"identity":"995395a5-d576-4b95-9b90-0d53cce6eeec","added_by":"auto","created_at":"2025-11-03 18:21:14","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":393931,"visible":true,"origin":"","legend":"\u003cp\u003e(a) UV-blocking rate; (b) Visible light transmission; (c) 940 nm infrared interference rate; and (d) total solar spectral interference rate of ACE@PVA film with different content of ACE.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-7497849/v1/26b0eb8f187f6f1a3bc8dfc8.png"},{"id":95224042,"identity":"d9f3b815-2848-44cb-98f9-1134396352f8","added_by":"auto","created_at":"2025-11-05 16:23:14","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1092896,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Heat dissipation test in the daytime; (b) and (c) ACE@PVA heat dissipation change curve at 10:00-11:00 noon (outdoor temperature 51.2 °C, humidity 35%); (d) Heat dissipation test in the nighttime; (e) and (f) ACE@PVA heat dissipation change curve at 18:30-19:30 p.m. (outdoor temperature: 35.3 °C, humidity 60%).\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-7497849/v1/eee8d08c755af42a94ade628.png"},{"id":95222647,"identity":"8502e840-71f4-4cde-9879-1b36855bbfa5","added_by":"auto","created_at":"2025-11-05 16:20:55","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":425245,"visible":true,"origin":"","legend":"\u003cp\u003eHeat dissipation mechanism diagram of ACE@PVA film.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-7497849/v1/39b9c024381bd7ae0be991e5.png"},{"id":95229813,"identity":"9eb7b5fe-b92f-4729-a414-35afbb51c72a","added_by":"auto","created_at":"2025-11-05 16:36:29","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3784650,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7497849/v1/abe6fb4c-655d-440b-972a-7004a8b66222.pdf"},{"id":95050841,"identity":"c1e15b87-1034-4c87-8d85-c7585e283a11","added_by":"auto","created_at":"2025-11-03 18:21:14","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":828840,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSupporting information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe optical photograph and microstructural of cellulose powder. (Figure S1)\u003c/p\u003e\n\u003cp\u003eThe distribution of the corresponding temperature detection probe and humidity detection probe in house model for testing the heat dissipation performance. (Figure S2)\u003c/p\u003e","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-7497849/v1/4430858614b266dda5819dcc.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Biomimetic all-weather dual-mode cooling film for passive heat dissipation","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAs global warming worsens, the demand for cooling continues to rise (Wang et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Liang et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Dong et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Although conventional vapor- compression refrigeration systems offer significant cooling efficiency, they consume approximately 17% of global electricity and emit substantial greenhouse gases, further exacerbating environmental pressures (Falchetta et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Ahn et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Consequently, developing eco-friendly, sustainable refrigeration technologies powered by renewable energy has attracted widespread attention (Gao \u0026amp; Chen \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Cui et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Passive radiative cooling (PRC) is a promising alternative that dissipates heat to outer space (~\u0026thinsp;3 K) through the atmospheric transparency window (8\u0026ndash;13 \u0026micro;m), theoretically enabling peak cooling powers exceeding 160 W/m\u0026sup2; (Raman et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). To advance PRC toward practical applications, research efforts focus on two key strategies: optimizing material formats (e.g., films (Meng et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), coatings (Han et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), textiles (Pan et al. 2022), aerogels (Chen et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2024\u003c/span\u003e)) and refining nano/microstructural designs (e.g., multilayer stacks (Pan et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2025\u003c/span\u003e), metamaterials (Cai et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), porous structures (Huang et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), randomized particle distributions(Xue et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e)). As a representative example under this research strategy, the dual-mode film material reported by Shi et al (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) achieves solar reflectivity and infrared emissivity of 96.7% and 96.1%, respectively, enabling daytime sub-ambient cooling of 9.8\u0026deg;C with a theoretical cooling power of 107.5 W/m\u0026sup2;.\u003c/p\u003e\u003cp\u003eHowever, PRC is frequently constrained by environmental conditions. For instance, when relative humidity (RH)\u0026thinsp;\u0026ge;\u0026thinsp;60%, PRC performance drops sharply as water vapor absorption in the critical infrared band exceeds 85%, reducing cooling efficiency by over 70% (Wang et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Worse still, annual average RH levels are high across much of the globe, significantly limiting the broad applicability of PRC technology (Li et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). To address these limitations, Ye et al. developed an adhesive hydrogel coating employing radiative-coupled evaporative cooling (REC) (Ye et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Applied to a 3D W-shaped substrate, this system exhibited exceptional passive cooling performance, reducing temperatures by 11.4\u0026deg;C below ambient under 400 W/m\u0026sup2; solar irradiance. By combining material design (hBN-epoxy-LiCl composite) and structural innovation (3D W-shaped substrate), the coating delivers an efficient, sustainable passive cooling solution for outdoor equipment in high-temperature environments, through simultaneous and synergistic cooling via radiation, evaporation, and convection. Nevertheless, PRC still struggles to adapt to dynamic seasonal and weather variations.\u003c/p\u003e\u003cp\u003eHerein, dendritic structure of amino-functionalized cellulose (ACE) was designed and synthesized as a functional unit for a dual-mode cooling film. Inspired by the thermoregulatory mechanisms of plant leaves, an ACE@PVA dual-mode cooling film was fabricated via self-assembly technology (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). Because ACE provides abundant amino groups and Schiff-base alkaline sites, it not only enhances hydrogen bonding with water molecules, imparting excellent moisture absorption, but also absorbs solar radiation through the imine bond (-C\u0026thinsp;=\u0026thinsp;N-) stretching vibration. Leveraging these properties, the ACE@PVA film serves as a dual-mode cooling system combining radiative and evaporative cooling (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). It achieves water capture capacity exceeding 3.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.36 g/g from ambient air and a solar reflectivity of 43.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.1%, despite its ultrathin profile (80 \u0026micro;m). Under outdoor conditions, the film demonstrated excellent passive heat dissipation, achieving daytime sub-ambient cooling of 4.7 to 13.7\u0026deg;C and nighttime cooling of 4.3\u0026deg;C below ambient. This work establishes a feasible strategy for synergistic all-weather passive cooling.\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cp\u003eAfter PEI-modifiled, white cellulose powder (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003ea) change to yellow ACE powder (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea), mainly due to introduced amino group are prone to form chromophores, leading to yellowing (Li et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). On the other hand, it also enhance interactions with water molecules through hydrogen bonding, demonstrating water-soluble properties (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). At the microstructural level, dramatic difference with cellulose(Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003eb), ACE shows dendritic structure (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec), which will enhances water delivery efficiency like capillary action. FT-IR spectrum validated the reaction of PEI-modified cellulose as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed. Three new peaks at 1656, 1579 and 1430 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, corresponding to N-H bend vibrations, C\u0026thinsp;=\u0026thinsp;N and C-N stretch vibrations, respectively, indicate that PEI was successfully grafted onto cellulose (Ma et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Moreover, the characteristic peak at 3349 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in cellulose offset to 3417 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the ACE, which is associated with the overlap of O-H and N-H stretch vibrations (Collom et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee shows the diagrammatic sketch of Molecular structure before and after PEI-modifiled cellulose.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFor controlled hygroscopicity evaluation, a series of identically sized PVA films and ACE@PVA films with varying ACE content were prepared. The experimental setup (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea) employed two identical electronic balances to continuously monitor mass changes during humidity exposure. Ambient humidity was precisely controlled using a humidifier (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). Results demonstrate that the hygroscopic capacity of the ACE@PVA films increases with ACE content. This enhancement stems from the amino groups (-NH₂) on ACE, which strengthen interactions with water molecules via hydrogen bonding. Specifically, the lone electron pair on the nitrogen atom facilitates hydrogen bond formation with water, significantly improving moisture absorption (Kim et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). At 6 wt% ACE content, the film achieves a maximum hygroscopic capacity of 3.32 g/g\u0026mdash;representing a 249% increase over pure PVA film. However, ACE content exceeding 6 wt% leads to over-saturation, likely causing ACE aggregation, crystallization, and structural defects that markedly diminish moisture absorption performance. Furthermore, increasing film thickness from 0.08 mm to 0.21 mm reduced water uptake by 38.5% (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). This decline is attributed to densified internal film structure impeding water molecule diffusion. Consequently, the ACE@PVA film with 6 wt% ACE content and 0.08 mm thickness was identified as optimal. The hygroscopic performance of this optimal film was then evaluated under controlled RH levels ranging from 45% to 90% (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). Results confirm effective moisture capture across this broad humidity range, indicating potential for evaporative cooling in diverse, dynamic atmospheric conditions. This functionality arises from the amino-functionalized groups on the cellulose molecular chain acting as molecular-level water capture sites through hydrogen bonding (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFor verification photothermal synergy and cooling performance, using UV-vis-NIR spectrophotometer to measure the reflectivity and transmittance of ACE@PVA films in the solar spectrum. With ACE content increase, the ACE@PVA films exhibit significant shielding effects against ultraviolet (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea), visible light (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb), and infrared radiation (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec). It\u0026rsquo;s due to the schiff alkali absorbs UV through its subamine bond (-C\u0026thinsp;=\u0026thinsp;N-) in its conjugated skeleton, converting light energy into thermal (Xue et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). And, ACE aggregation and crystallization make the chromophores formed leads to a decrease in light transmittance (Xu et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In addition, N-H bend vibrations, C\u0026thinsp;=\u0026thinsp;N and C-N stretch vibrations absorbed infrared radiation energy, which is consistent with the results of FT-IR spectroscopy. It is noteworthy that the ACE@PVA film has a thickness of merely 80 \u0026micro;m has a total solar energy blocking rate of 43.5% (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed). In summary, ACE@PVA film integrates both radiative and evaporative cooling functionalities, has a huge potential in the fields of automotive glass, building coatings, humidity-permeable cooling clothing, etc.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eTo verify the heat dissipation performance of the film under real-world conditions, an outdoor experiment was conducted (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea at daytime and Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed at nighttime). Four PT-100 thermocouple monitors and humidity detection probe be used to record real-time temperature changes for both indoor and outdoor environments (Fig. S2). Besides the designed ACE@PVA film, a pure PVA film served as a reference to isolate the effects of thermal convection. During daytime testing, the ACE@PVA film exhibited an average temperature of 37.5\u0026deg;C, representing reductions of 2.6\u0026deg;C and 13.7\u0026deg;C relative to the PVA reference and ambient surface temperature, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb). It can be found that evaporation cooling played a major role compared with \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eradiative\u003c/span\u003e cooling for heat dissipation, due to the condition of initial moisture absorption saturation. Under prolonged solar exposure, the ACE@PVA sample averaged 46.5\u0026deg;C, maintaining temperature reductions of 1.2\u0026deg;C and 4.7\u0026deg;C compared to the PVA film and ambient surface (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec). In this high-irradiance regime, radiative cooling dominated due to near-complete evaporation of environmental moisture. In the night time, the average temperature of the ACE@PVA sample was 31\u0026deg;C, corresponding to reductions of 1.2\u0026deg;C and 4.3\u0026deg;C versus the PVA film and ambient surface(Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee). This behavior is explained by increasing nocturnal humidity and diminished solar radiation, which enhanced moisture capture and reactivated evaporation cooling. Throughout testing, ACE@PVA consistently maintained lower temperatures than both controls. (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef). Crucially, the ACE component facilitated atmospheric moisture capture via ACE-water interactions, ensuring sustained evaporative cooling during daytime operation.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThese results demonstrate that ACE@PVA enables all-weather passive cooling through synergistic evaporation and radiative mechanisms. Unlike conventional radiative materials, ACE@PVA dynamically shifts its dominant cooling mode in response to environmental conditions\u0026mdash;akin to plant thermoregulation. Specifically, radiative cooling prevails under high solar irradiance and low humidity, while evaporation cooling dominates under low irradiance and high humidity (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). This all-weather passive heat dissipation by coupling radiative cooling with evaporation cooling, avoiding the heat dissipation performance drops sharply of conventional radiative materials at high humidity environment.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eInspired by the thermoregulatory mechanisms of plant leaves, we engineered a dendritic amino-functionalized cellulose (ACE) structure for passive heat dissipation. ACE exhibited exceptional hygroscopicity and solar energy dissipation capabilities, owing to its abundant amino groups and schiff base sites. These functional groups not only enhance water molecule interactions through hydrogen bonding but also facilitate solar radiation absorption via the stretching vibrations of imine bonds (-C\u0026thinsp;=\u0026thinsp;N-). Leveraging these properties, we integrated ACE into PVA through self-assembly to form an ultrathin ACE@PVA film that synergistically combines radiative and evaporative cooling functionalities. Unlike conventional radiative cooling materials, ACE@PVA achieves all-weather passive cooling through dynamic coupling of radiative and evaporative mechanisms. This work provides a facile, eco-friendly, and sustainable biomimetic strategy for advanced outdoor thermal management applications.\u003c/p\u003e"},{"header":"Experimental section","content":"\u003cp\u003eMaterials: Microcrystalline cellulose (Mw\u0026thinsp;=\u0026thinsp;20,000) with an average size of 25 \u0026micro;m and density of 0.600 g/cm\u003csup\u003e3\u003c/sup\u003e was bought from Arkema Investment Co. Ltd. NaOH, urea and absolute ethyl alcohol was obtained from Shanghai Macklin Biochemical Co., Ltd. ANPEL laboratory technologies (shanghai) Inc provided hydrochloric acid solution (HCl). Sodium periodate and polyethyleneimine (PEI, Mw\u0026thinsp;=\u0026thinsp;600, 99%) was purchased from Aladdin Co., Ltd. All other chemicals were used as received without further purification.\u003c/p\u003e\u003cp\u003ePreparation of amino-functionalized cellulose: ACE was prepared via the PEI modified cellulose. Briefly, Microcrystalline cellulose was dissolved in Alkaline urea solution (1.75 M NaOH and 2 M urea mixed solution) in a glass beaker, followed by stirring for 30 min. Subsequently, 1 M HCl was dissolved in 200 mL Cellulose solution to react for 12 h at 25\u0026deg;C under stirring;2 g of Sodium periodate powder was slowly added to the above solution react for 3 h at 60\u0026deg;C under stirring༛In succession, 2 g of PEI add the reaction solution drop by drop into the flask, react for 3 h at 60\u0026deg;C under stirring, the ACE sediment was was repeatedly washed and centrifuged at 3500 rpm until pH\u0026thinsp;=\u0026thinsp;7, and then collected after 5 min of centrifugation at 3500 rpm.\u003c/p\u003e\u003cp\u003ePreparation of ACE@PVA film: ACE powder and PVA were added into a flask and stirred at 80\u0026deg;C for 2 h to form a ACE@PVA solution with a solute weight percentage of 0%, 2%, 3%, 4%, 5%, and 6%, and was denoted as ACE(0%), ACE(2%), ACE(3%), ACE(4%), ACE(5%), and ACE(6%), respectively. Pour the above solution into Petri dishes in separate amounts of 5g, 10g, and 15g respectively. A series of ACE@PVA films with different thicknesses and ACE contents can be obtained by using the casting method.\u003c/p\u003e\u003cp\u003eStructural characterization: The microstructure of ACE was photographed using a Zeiss EVO-10 scanning electron microscope (5kV) and scanned electron microscope (SEM) images. Chemical Crosslinking Reaction: The reaction of PEI-modified cellulose was demonstrated using Fourier Transform Infrared Spectroscopy (FTIR, Nicolet 5700, Thermo, USA). Moisture Absorption Test: The water content can be obtained by: water wt.(%) = (W\u003csub\u003et\u003c/sub\u003e-W\u003csub\u003e0\u003c/sub\u003e)/W\u003csub\u003et\u003c/sub\u003e \u0026times;100%, where W\u003csub\u003et\u003c/sub\u003e is the saturated water content mass, W\u003csub\u003e0\u003c/sub\u003e is the current water content mass. Spectral Reflectance Testing: UV-vis-NIR reflectivity (ρ) and transmissivity (τ) were measured using a UV-vis-NIR spectrometer (Lambda 1050+, PerkinELmer) accompanied by an integrating sphere attachment, and UV-vis-NIR absorptivity (α) was calculated using equation α\u0026thinsp;=\u0026thinsp;1\u0026thinsp;\u0026minus;\u0026thinsp;ρ\u0026thinsp;\u0026minus;\u0026thinsp;τ. Thermal Protection Test: The sample temperature was measured using a Temperature Cruiser (GK4500, GuoKe).\u003c/p\u003e\u003cp\u003eCooling performance characterization: Water Capture Tests: The sample was placed within a constant temperature and humidity chamber (HWS-80B) to control Temperature and Humidity. The mass change of the sample was measured by an electronic balance at each period. After each experiment, the sample's mass was restored to its initial value before the next experiment. Indoor experiments were conducted in a laboratory.\u003c/p\u003e\u003cp\u003eHeat dissipation tests: Two 15\u0026times;10 cm\u003csup\u003e2\u003c/sup\u003e cavity was dug out on top side of 20\u0026times;20\u0026times;15 cm\u003csup\u003e3\u003c/sup\u003e house model, which covered with ACE@PVA film. Identically, Prepare another house model of the same size, which covered with PVA film as control group. A PT-100 type thermocouple fixed on the inner of house model to detect real-time temperature fluctuations. The edge of the sample was sealed with an adhesive tape to ensure the tightness of the sample on the cavity. Additionally, outdoor temperature and humidity was recorded using a digital hygrometer-thermometer (M6052B, PEAKMETER). All the heat dissipation tests were performed outdoors at Zhejiang University of Water Resources and Electric Power, Hangzhou city, China (east longitude: 119\u0026deg;45\u0026prime;; northern latitude: 34\u0026deg;15\u0026prime;).\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSpecial thanks to Prof. Xiuping Su from key laboratory of functional fibers and intelligent textiles. The authors would like to thank Mrs Zhuchang Qiao for the linguistic revision. We are furthermore grateful to Mr. Frank from for his constructive advice on the evaluation of the human thermal management.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was financially supported by the Nanxu Scholars Program for Young Scholars of ZJWEU\u0026nbsp;(RC2023021208); Technology Planning Project of Shaoxing (2024A13003), and Scientific research foundation of\u0026nbsp;Zhejiang University of Water Resources and Electric Power\u0026nbsp;(JBGS2025013).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCorresponding author: Zhen Li\u003c/p\u003e\n\u003cp\u003eZhen Li: Writing-original draft, Conceptualization, Project Funding acquisition. Jinqiu Yang: Methodology. Xiangdong Zeng: Investigation. Zhengfeng Xiong: Soft ware. Jingjia Li:Investigation. Xiuping Su: Formal analysis. Yadng Li: Figures. Feng Liu: Investigation.\u0026nbsp;All authors reviewed the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e The data that support the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e The authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e The authors agreed to publish this article.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAhn H, Rim DH, Freihaut JD (2018) Performance assessment of hybrid chiller systems for combined cooling, heating and power production. 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SMALL 21(17):2412221.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"cellulose","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"cels","sideBox":"Learn more about [Cellulose](https://www.springer.com/journal/10570)","snPcode":"10570","submissionUrl":"https://submission.nature.com/new-submission/10570/3","title":"Cellulose","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Evaporation refrigeration, Radiation refrigeration, Moisture and thermal management, Functionalized-cellulose","lastPublishedDoi":"10.21203/rs.3.rs-7497849/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7497849/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePassive radiative cooling technology offers a zero-carbon comfort solution for maintaining comfortable ambient temperatures. However, single-mode passive radiative cooling is significantly weakened by the shielding effect of high-humidity environments. Inspired by the thermoregulatory mechanisms of plant leaves, we designed a dendritic structure amino-functionalized cellulose (ACE) for passive heat dissipation. ACE provides abundant amino groups and Schiff base sites, which not only enhance interactions with water molecules through hydrogen bonding but also facilitate solar radiation absorption via the stretching vibrations of the imine bonds (-C\u0026thinsp;=\u0026thinsp;N-). Leveraging these properties, an ACE@PVA dual-mode cooling film was fabricated using self-assembly technology. Despite its ultrathin profile (80 \u0026micro;m), the film achieves a hygroscopic capacity exceeding 3.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.36 g/g and a solar reflectivity of 43.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.1%. Under outdoor conditions, the film demonstrated excellent passive cooling performance, achieving subambient cooling of 4.7\u0026deg;C to 13.7\u0026deg;C during daytime and 4.3\u0026deg;C at night. This ultrathin, dual-mode cooling film is well suited for dynamic seasonal and weather variations, offering significant potential for mitigating the energy crisis and reducing greenhouse gas emissions.\u003c/p\u003e","manuscriptTitle":"Biomimetic all-weather dual-mode cooling film for passive heat dissipation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-03 18:21:09","doi":"10.21203/rs.3.rs-7497849/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-10-03T23:35:38+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-10-03T23:12:08+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-09-13T13:47:29+00:00","index":"","fulltext":""},{"type":"submitted","content":"Cellulose","date":"2025-08-31T01:39:47+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"cellulose","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"cels","sideBox":"Learn more about [Cellulose](https://www.springer.com/journal/10570)","snPcode":"10570","submissionUrl":"https://submission.nature.com/new-submission/10570/3","title":"Cellulose","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"95d51e10-d5bd-4495-93ca-4efa867ddc31","owner":[],"postedDate":"November 3rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-12-07T14:23:10+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-03 18:21:09","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7497849","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7497849","identity":"rs-7497849","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}